ANSI N42.41-2007

2022-06-19 来源：易榕旅网

American National Standard

Minimum Performance Criteria forActive Interrogation Systems Usedfor Homeland Security

N42.41Accredited by the American National Standards Institute

Sponsored by the

National Committee on Radiation Instrumentation, N42

IEEE

3 Park Avenue

New York, NY 10016-5997, USA15 February 2008

ANSI N42.41-2007

American National Standard

Minimum Performance Criteria for

Active Interrogation Systems Used for Homeland Security

Sponsor

National Committee on Radiation Instrumentation, N42

Accredited by the

American National Standards Institute

Secretariat

Institute of Electrical and Electronics Engineers, Inc.

Approved 29 October 2007

American National Standards Institute

Abstract: The performance criteria for active interrogation systems in homeland security applications are described in this standard. These systems are intended for non-intrusive inspection of closed containers, vehicles, and packages of a wide range of types and sizes. In these systems, the contents of an inspection zone are irradiated with penetrating ionizing radiation to determine the presence of a hidden substance-of-interest by the analysis of stimulated secondary radiations or nuclear-resonance absorption spectra that are indicative of the chemical and/or nuclidic composition of the substance-of-interest.

Keywords: active interrogation, baggage, cargo, chemical warfare agents, detection, explosives, gamma-rays, high-energy x-rays, homeland security, identification, neutrons, SNM, special nuclear materials, weapons of mass destruction, WMD

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Introduction

This introduction is not part of ANSI N42.41-2007, American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security.

This standard is the responsibility of the Accredited American Standards Committee on Radiation Instrumentation, N42. The standard was approved by the N42 letter ballot of March–April 2007.

Notice to users

Errata

Errata, if any, for this and all other standards can be accessed at the following URL: http:// standards.ieee.org/reading/ieee/updates/errata/index.html. Users are encouraged to check this URL for errata periodically.

Interpretations

Current interpretations can be accessed at the following URL: http://standards.ieee.org/reading/ieee/interp/ index.html. Patents

Attention is called to the possibility that implementation of this standard may require use of subject matter covered by patent rights. By publication of this standard, no position is taken with respect to the existence or validity of any patent rights in connection therewith. The IEEE shall not be responsible for identifying patents or patent applications for which a license may be required to implement an IEEE standard or for conducting inquiries into the legal validity or scope of those patents that are brought to its attention.

Participants

At the time it approved this standard, the Accredited Standards Committee on Radiation Instrumentation, N42, had the following membership:

Morgan Cox, Chair

Louis Costrell, Deputy Chair William Ash, Administrative Secretary

Organization Represented...................................................................................................Name of Representative

Bartlett Services ………………………………………………………...………….…………………Morgan Cox Canberra ……………………………………………………………………………………………Markku Koskelo Chew, M.H …………………………………………………………………...….…………………….Jack M. Selby Commerce Dept, U.S. NIST ………………………………………………………..………..Michael P. Unterweger ..............................................................................................................................................................Louis Costrell (Alt.) Consultant ..................................................................................................................................................Frank X. Masse Department of Homeland Security …………………………..………………………………………….Peter Shebell Entergy-ANO ……………………………………………..…………………………………………...Ron Schwartz Health Physics Society ………………………………………………….……………………………….Sandy Perle IEEE ..............................................................................................................................................................Louis Costrell ...............................................................................................................................................................Julian Forster (Alt.) .........................................................................................................................................................Anthony Spurgin (Alt.) ...............................................................................................................................................Michael P. Unterweger (Alt.) International Medcom …………………………………..…………………………………………………Don Sythe Lawrence Berkeley National Lab ……………………….…………………………………………Edward J. Lampo Lawrence Livermore National Lab ………………………..…………………………………………...Gary Johnson NASA, GSFC ……………………………………………..………………………………….Sachidananda R. Babu Nuclear Regulatory Commission ………………………………………………………..……………..Cynthia Jones Nuclear Stds Unlimited ……………………………………………………..………………………Al N. Tschaeche ORNL ……………………………………………………………………………..………………Peter J. Chiaro, Jr. ………………………………………………………………..………………………………...Charles Britton (Alt.) ORTEC ………………………………………………………………..…………………………..Ronald M. Keyser Pacific NW Labs ………………………………………………………..…………………………...Richard Kouzes Swinth Associates …………………………………………………..…………………………….Kenneth L. Swinth U.S. Army …………………………………………………………..………………………………Edward Groeber Members-At-Large ……………………………………………………………….…………………....Ernesto Corte ……………………………………………………………………………………………….....Joseph C. McDonald …………………………………………………………………………………………………….…..Paul L. Phelps …………………………………………………………………………………………………….….Joseph Stencel …………………………………………………………………………………………………….…..Lee J. Wagner

At the time this standard was completed, Subcommittee N42.HSI had the following membership:

Morgan Cox, Co-Chair

Michael P. Unterweger, Co-Chair

Paul Bailey

Peter J. Chiaro, Jr. David Gilliam Mark D. Hoover

Cynthia G. Jones Ronald Keyser Richard Kouzes

Joseph C. McDonald

Leticia Pibida Brian Rees Peter Shebell David Trombino

At the time this standard was completed, the ANSI N42.41 Working Group had the following membership:

David M. Gilliam, NIST, Chair and Project leader William Bertozzi …………..…………………………………………………………MIT, Passport Systems David Chichester …………………………………………………………………………………………SNL Ed Franco …………………………………………………………..Rapiscan Systems (formerly ARACOR) Tsahi Gozani ………………………………………………..………………………Rapiscan Systems/HEIC Siraj M. Khan ………………………………………………………..Customs and Border Protection/DNDO James L. Jones …………………………………………………………………………………………….INL Steve Korbly ………………………………………………………………………………..Passport Systems Robert Ledoux ……………………………………………………………………………...Passport Systems David F. R. Mildner ……………………………………………………………………………………..NIST Thomas L. Moore ………………………………………………………………………………………LLNL Calvin E. Moss …………………………………………………………………………………………LANL Frank H. Ruddy ………………………………………………………………………………...Westinghouse Dennis R. Slaughter …………………………………………………………………………………….LLNL George Vourvopoulos …………………………………………………………………………………...SAIC

vii

Contents

1. Overview....................................................................................................................................................1 1.1 Scope...................................................................................................................................................1 1.2 Purpose................................................................................................................................................2 1.3 General considerations.........................................................................................................................2 2. Normative references..................................................................................................................................2 3. Definitions..................................................................................................................................................3 3.1 General................................................................................................................................................3 3.2 Definitions of particular relevance to N42.41......................................................................................5 3.3 Special word usage..............................................................................................................................6 4. General characteristics of active interrogation systems..............................................................................6 4.1 Inspection zone characteristics............................................................................................................6 4.2 Interrogating radiation type and physical principles............................................................................7 4.3 Physical configurations........................................................................................................................8 5. Performance requirements..........................................................................................................................8 5.1 Simulants.............................................................................................................................................8 5.2 Requirements for PD, PFA, and statistical confidence........................................................................9 5.3 Average allowed inspection times.....................................................................................................10 5.4 Simulated cargo loadings and simulant locations..............................................................................12 5.5 Specification of masses to be detected..............................................................................................13 6. Electromagnetic, mechanical, environmental, and radiation protection requirements.............................14 6.1 Ambient temperature.........................................................................................................................14 6.2 Relative humidity (RH).....................................................................................................................14 6.3 Radio frequency (RF)........................................................................................................................14 6.4 Radiated emissions............................................................................................................................14 6.5 Magnetic fields..................................................................................................................................15 6.6 AC line voltage operation..................................................................................................................15 6.7 Electrostatic discharge.......................................................................................................................15 6.8 Conducted disturbances induced by bursts and radio frequencies.....................................................15 6.9 Vibration and shock...........................................................................................................................15 6.10 Sealing.............................................................................................................................................15 6.11 Radiation protection........................................................................................................................16 7. Documentation.........................................................................................................................................17 7.1 Type test report..................................................................................................................................17 7.2 System description.............................................................................................................................17 7.3 Operation and maintenance manuals.................................................................................................17

viii

Annex A (informative) Simulants................................................................................................................18 A.1 C4 or Plastique military explosive....................................................................................................18 A.2 Ammonium nitrate plus fuel oil (ANFO) explosive.........................................................................19 A.3 Sarin nerve agent GB........................................................................................................................20 A.4 Mustard gas HD................................................................................................................................20 A.5 Low-enrichment uranium (LEU) with 19.5% 235U...........................................................................20 A.6 Tungsten carbide spherical shell.......................................................................................................20 Annex B (informative) Statistical considerations.........................................................................................21

American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

1. Overview

1.1 Scope

This standard specifies the operational and performance requirements for active interrogation systems for use in homeland security applications. These systems employ penetrating ionizing radiation (e.g., neutrons, high-energy x-rays, gamma-rays) to detect and identify hidden chemical, nuclear, and explosive agents by detection of stimulated secondary radiations or by nuclear resonance contrast, giving elemental and/or nuclidic identification of the composition of the substances-of-interest. These inspection systems may be designed for open inspection zones of various sizes or for various sizes of containers such as small packages, briefcases, suitcases, air cargo containers, passenger vehicles, two-axle trucks, intermodal cargo containers, semi-trailers/tractor rigs, or rail cars. The systems may be designed for operation in indoor, outdoor, or mobile facilities.

At the time of this writing, there are only a few commercially available active interrogation systems, and most of these are still in a stage of rapid development. None are yet deployed on a very broad scale, either domestically or internationally. The requirements of this standard provide a set of minimally acceptable performance criteria for preliminary screening of candidate systems for further consideration. Prior to deployment on a broad scale, more detailed and realistic testing beyond the scope of this standard should be carried out, with some test specifications outside of the public domain. Detectable amounts of substances in this standard may correspond to quantities that are larger or smaller than those of significance in particular circumstances. Successful completion of the tests described in this standard should not be construed as certification of an ability to successfully detect and identify all chemical, nuclear, and explosive agents in all possible cargos, nor as a certification that false positive rates in actual stream-of-commerce applications will be no larger than in these tests.

This standard does not consider radiographic imaging characteristics. However, if active interrogation features that provide chemical or nuclidic identification of substances are included in a system that is primarily intended for radiography, then the active interrogation features of the system may be tested and evaluated under this standard.

ANSI N42.41-2007

American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

1.2 Purpose

The purpose of this standard is to specify the minimum performance criteria for active interrogation systems to be considered for use in homeland security applications.

1.3 General considerations

1.3.1 Evaluation of active interrogation systems

Testing is to be conducted under a set of specified conditions to determine if an active interrogation system meets the requirements of this standard. Special applications, which could include a system’s operation under extreme or unusual conditions, shall require additional testing.

In contrast with x-ray and gamma-ray imaging systems for which clutter in the images is the limiting factor in recognition of substances- or items-of-interest, the limiting factors in active interrogation systems are usually attenuation of the interrogating radiation and attenuation of the secondary emissions from the concealed substances by other contents of the packages, vehicles, or cargo containers. The test conditions described in this standard are representative of the range of attenuation conditions pertaining to closed packages, vehicles, and cargo containers in the stream of commerce. Another significant factor in limiting the specificity of elemental or nuclidic identification in active interrogation is interference of resonance absorption or emission peaks from different substances. This factor is reduced if detectors with better energy resolution are employed, and this problem may often be avoided by analysis of other non-interfering peaks.

There is one kind of clutter that may also be a problem in active interrogation. If other substances with constituents similar to those of the substance-of-interest are present, but not spatially resolved, then the perceived stoichiometry may be distorted. 1.3.2 Meeting performance specifications

Obtaining and maintaining operating performance that meets or exceeds the specifications as stated in this standard depends upon proper installation and/or deployment of the systems, establishing appropriate operating parameters, providing security for the systems, maintaining calibration, implementing a suitable response testing and maintenance program, auditing compliance with quality requirements, and providing proper training for operating personnel.

2. Normative references

This standard shall be used in conjunction with the following publications. When the following standards are superseded by an approved revision, the revision shall apply.

ANSI N42.23-1996, American National Standard Measurement and Associated Instrument Quality Assurance for Radioassay Laboratories.1

FCC Rules, Code of Federal Regulations, Title 10, Part 20, Standards for Protection Against Radiation.2, 3

The ANSI N42 publications included in this clause are available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, Piscataway, NJ 08855-1331, USA (http://standards.ieee.org/). 2

CFR publications are available from the Superintendent of Documents, U.S. Government Printing Office, P.O. Box 37082, Washington, DC 20013-7082, USA (http://www.access.gpo.gov/). 3

See http://www.gpo.gov/nara/cfr/waisidx_01/10cfr20_01.html, 2007.

ANSI N42.41-2007

American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

FCC Rules, Code of Federal Regulations, Title 10, Part 50.2, Nuclear Regulatory Commission Definition of Low Enrichment Uranium (LEU).4

FCC Rules, Code of Federal Regulations, Title 21, Part 179: Irradiation in the Production, Processing and Handling of Food.5

FCC Rules, Code of Federal Regulations, Title 29, Part 1910, Occupational Safety and Health.6

Filliben, J. J. and Heckert, N. A., Guide to Available Mathematical Software, Inverse Binomial Function BINPPF Subroutine, NIST Statistical Engineering Division.7

IEC 61000-4 (all parts):2001, Electromagnetic Compatibility (EMC), Testing and Measurement Techniques.8

IEC 60068-2 (-1, -2, and other parts as appropriate):2007, Environmental testing—Part 2: Tests.

NCRP Statement No. 10, Dec. 2004, “Recent Applications of the NCRP Public Dose Limit for Ionizing Radiation.”9

3. Definitions

The following definitions have been developed at the request of the U.S. Department of Homeland Security (DHS) for systems used by DHS for interdiction and emergency response.

3.1 General

3.1.1 accuracy: The degree of agreement between the observed value and the conventionally true value of the quantity being measured.

3.1.2 adjust: To alter the reading of a system by means of a built-in variable (hardware or software) control.

3.1.3 alarm: An audible, visual, or other signal that alerts an operator to a condition requiring attention or response.

3.1.4 calibrate: To adjust and/or determine the response or reading of a device relative to a series of conventionally true values.

3.1.5 calibration: A set of operations that establishes, under specified conditions, the relationship between values indicated by a measuring instrument or measuring system, and the conventionally true values of the quantity or variable being measured.

See http://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-0002.html. See http://www.access.gpo.gov/nara/cfr/waisidx_00/21cfr179_00.html, 2007. 6

See http://www.access.gpo.gov/nara/cfr/waisidx_04/29cfr1910_04.html, 2007. 7

NIST publications are available from the National Institute of Standards and Technology (NIST), 100 Bureau Drive, Gaithersburg, MD 20899. http://www.itl.nist.gov/div898/software/datapac/homepage.htm. 8

IEC publications are available from the Sales Department of the International Electrotechnical Commission, Case Postale 131, 3 rue

de Varembé, CH-1211, Genève 20, Switzerland/Suisse (http://www.iec.ch/). IEC publications are also available in the United States from the Sales Department, American National Standards Institute, 11 West 42nd Street, 13th Floor, New York, NY 10036, USA (http://www.ansi.org). 9

NCRP documents are available from the National Council on Radiation Protection and Measurements, 7910 Woodmont Avenue, Suite 400, Bethesda, Maryland 20814-3095 (http://www.ncrp.com).

ANSI N42.41-2007

American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

3.1.6 conventionally true value (CTV): The commonly accepted best estimate of the value of that quantity. This and the associated uncertainty will preferably be determined by a national or transfer standard, or by a reference instrument that has been calibrated against a national or transfer standard, or by a measurement quality assurance (MQA) interaction with the National Institute of Standards and Technology (NIST), or an accredited calibration laboratory.

3.1.7 detection limits: The extreme of detection or identification for the substance-of-interest. The lower detection limit is the minimum statistically quantifiable system response or reading. The upper measurement limit (if any) is the maximum level at which the system responds correctly.

3.1.8 detector: A device or component designed to produce a quantifiable response to ionizing radiation normally measured electronically.

3.1.9 false alarm: An alarm not caused by detection of a non-negligible amount of a substance-of-interest or specified simulant. See also: negligible amount of substance-of-interest.

3.1.10 indication: A displayed signal from the system to the user conveying information such as detection of a substance-of-interest, system status, system malfunction, or other critical information.

3.1.11 interdiction: Stopping the illicit or inadvertent movement of explosives, chemical warfare agents, or nuclear materials that have been discovered as a result of active interrogation.

3.1.12 monitoring: The means provided to indicate continuously the state or condition of a system or assembly.

3.1.13 precision: The degree of agreement of repeated measurements of the same parameter.

3.1.14 range: All values lying between the lower detection limit and the upper measurement limit.

3.1.15 routine test: A test that applies to a complete system to ascertain compliance with specified criteria.

3.1.16 standard deviation: The positive square root of the variance.

3.1.17 test: A procedure whereby the system or component is evaluated.

3.1.18 type test: A test of one or more production systems taken to be representative of the model to show that it meets defined specifications.

3.1.19 uncertainty: The estimated bounds of the deviation from the conventionally true value, generally expressed as a percentage of the mean, ordinarily taken as the square root of the sum of the square of two components:

a) Type A uncertainties that are evaluated by statistical methods; and b) Type B uncertainties that are evaluated by other methods.

ANSI N42.41-2007

American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

3.2 Definitions of particular relevance to N42.41

3.2.1 active interrogation: A process in which the contents of an inspection zone are irradiated with penetrating ionizing radiation (e.g., neutrons or high-energy photons) to determine the presence of and chemical or nuclidic composition of a hidden substance-of-interest by the analysis of stimulated secondary radiation or by analysis of nuclear resonance contrast.

3.2.2 confidence level (CL): A measure of the reliability of the determination of the probability of detection (PD) or the probability of a false alarm (PFA). Higher values of the CL indicate greater reliability. Larger numbers of trial are required to establish a higher CL. The mathematical definitions in 3.2.3 and 3.2.4 are discussed more fully along with some examples and tables in Annex B.

3.2.3 confidence level (CL) for the probability of detection (PD): If m successes are found in a single set of n trials in a system obeying the binomial distribution law, then for any chosen value of PD, designated PDC, there is a corresponding number called the confidence level CL(m, n, PDC), which is equal to the probability that any such system with m successes in a single set of n trials will have a true PD value greater than or equal to that chosen value PDC.

3.2.4 confidence level (CL) for the probability of a false alarm (PFA): If j false-positive results are found in a single set of k trials in a system obeying the binomial distribution law, then for any chosen value of PFA, designated PFAC, there is a corresponding number called the confidence level CL(j, k, PFAC), which is equal to the probability that any such system with j success results in a single set of k trials.

3.2.5 fully compliant simulant: A benign substitute for a substance-of-interest, having the same elemental and nuclidic densities as the threat substance within ±10%.

3.2.6 negligible amount of a substance-of-interest: A very small quantity of the substance that is at least ten-thousand times smaller than the detectable mass criteria of Table 4, within the smallest resolved volume element of the inspection zone. (Since both a mass and volume are specified, a negligible density is also specified.)

3.2.7 normal cargo package: A package containing common substances such as sand, salt, sugar, graphite, plastics, water, lye, aluminum, steel, lead, and bismuth, or combinations of such substances. In the testing of active interrogation systems under this standard, normal cargo packages shall be configured to resemble packages of simulants of substances-of-interest as they appear radiographically (but not chemically or nuclidically). In particular, normal cargo packages shall not contain any isotope of uranium in more than a negligible amount as defined in 3.2.6.

3.2.8 open inspection zone: Active interrogation systems may be designed to operate with the inspection zone not enclosed by any sort of walls or tunnel. This arrangement is referred to as an open inspection zone.

3.2.9 partially compliant simulant: A benign substitute for a substance-of-interest, having the same elemental and nuclidic densities as the substance-of-interest within 10%, with exceptions as specified.

3.2.10 probability of detection/identification (PD): The probability that the operator will correctly report the detection and identification of a substance-of-interest when an active interrogation procedure has been carried out on an inspection zone and at least a specified minimum amount of the substance (e.g., Table 4) was actually present in the inspection zone during the interrogation period. Also called PTP, the probability of a “true positive” report.

3.2.11 probability of false alarm (PFA): The probability that the operator will incorrectly report the detection and identification of a substance-of-interest when an active interrogation procedure has been carried out on an inspection zone and at most a negligible amount of the identified substance was actually present during the interrogation period. Also called PFP, the probability of a “false positive” result.

ANSI N42.41-2007

American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

3.2.12 probability of a missed detection or false negative (PFN): The probability that the operator will fail to report the detection and identification of a substance-of-interest when an active interrogation procedure has been carried out on an inspection zone and at least a specified minimum amount of the substance (e.g., Table 4) was actually present in the inspection zone during the interrogation period.

NOTE—The probability of a “false negative” report is PFN = 1 - PTP.

3.2.13 probability of a true negative (PTN): The probability that the operator will correctly report no detection of a substance-of-interest when an active interrogation procedure has been carried out on an inspection zone and at most a negligible amount of any substance-of-interest was actually present during the interrogation period.

NOTE—The probability of a “true negative” report is PTN = 1 - PFP.

3.2.14 substance-of-interest: A special nuclear material, an explosive, or a chemical warfare agent that could cause significant injury to persons and/or damage to property.

3.3 Special word usage

The following word usage applies throughout this standard:

⎯ The word “shall” signifies a mandatory requirement (where appropriate, a qualifying statement is

included to indicate that there may be an allowable exception).

⎯ The word “should” signifies a recommended specification or method.

⎯ The word “may” signifies an acceptable method or an example of good practice.

4. General characteristics of active interrogation systems

4.1 Inspection zone characteristics

4.1.1 Dimensions

Inspection zones of various sizes are listed in Table 1. These sizes are chosen to be appropriate for various kinds of containers, packages, or vehicles, but they also are used to categorize open inspection zones of the same maximum dimensions, where the specifically named container is not present. 4.1.2 Fixed or scanned

Some active interrogation systems inspect a fixed zone, but most of the commercially available devices scan at least one of the dimensions of the inspection zone by moving the zone through a radiation beam, moving the beam over the zone, moving the entire system along one axis of the zone, or some combination of these.

ANSI N42.41-2007

American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

Table 1 —Container categories and inspection zone dimensions for active interrogationa

Container categorya

A B C D

Maximum dimensions of inspection zone: depth, height (meters)

0.3, 0.57 1.53, 1.56 2.0, 1.8 2.2, 2.2 2.6, 3.0 2.6, 3.0 2.6, 4.2

Inspection zone maximum length

length scanned (meters) 0.71 or scanned 1.60 or scanned 5.6 or scanned 7.6 or scanned 9.1 or scanned 12 or scanned 12 or scanned 26 or scanned 27.4 or scanned

Container type Small article, carry-on, suitcase

Airline cargo container

Automobile

2 axle vehicle ≤2 ton cargo

E Intermodal cargo container (≤30 ft)

F Intermodal cargo container (>30 ft)

G Truck (>30 ft)

H Tractor/semi-trailer 2.6, 4.2 I

aRail car 2.9, 5.0

For an open inspection zone there is no container, but the maximum dimensions still apply.

4.2 Interrogating radiation type and physical principles

4.2.1 Fast neutron interrogation

Fast neutron interrogation may be steady-state or pulsed, with a mono-energetic or broad spectrum. The neutron source may be a radioactive nuclide such as 252Cf, or a neutron generator (accelerator). The secondary radiation phenomena by which chemical or nuclidic content in the inspection zone is analyzed may be characteristic gamma-rays from nuclear states exited by inelastic scattering, prompt gamma-rays from capture of moderated or thermalized neutrons, decay gamma-rays from neutron activation, prompt or delayed neutrons from induced fission, or prompt or delayed gamma-rays from induced fission. The induced-fission neutrons may cause additional fission chains, thus yielding more neutrons and gamma-rays, especially in kg masses with significant multiplication. Elemental and/or nuclidic identification may also be made by measurement of energy-dependent transmission of neutrons in the resonance absorption range. 4.2.2 Thermal neutron interrogation

Thermal neutrons are produced by thermalization of fast neutrons within the active interrogation system itself, usually employing a combination of inelastic scattering and elastic scattering processes. The secondary radiations by which chemical or nuclidic content in the inspection zone is analyzed may be prompt gamma-rays from capture of thermalized neutrons, decay gamma-rays from activation by thermalized neutrons, prompt or delayed neutrons from induced fission, or prompt or delayed gamma-rays from induced fission. As with fast neutron interrogation, the induced-fission neutrons may cause additional fission chains, thus yielding more neutrons and gamma-rays, especially in kg masses with significant multiplication.

4.2.3 High-energy photon interrogation

High-energy x-ray sources or accelerator-produced mono-energetic gamma-rays may be used for elemental or nuclidic analysis by nuclear-resonance fluorescence emission or nuclear-resonance absorption. In

ANSI N42.41-2007

American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

addition, prompt or delayed neutrons from induced fission, or prompt or delayed gamma-rays from induced fission may be used as an indicator of fissionable material. As with fast and thermal neutron interrogation, the induced-fission neutrons may cause additional fission chains, thus yielding more neutrons and gamma-rays, especially in kg masses with significant multiplication.

4.3 Physical configurations

4.3.1 Portable systems

Some very compact systems may be carried in a few backpacks or cases. These systems may be required to satisfy extra criteria for weather tolerance and portable power supplies with which fixed indoor installations usually do not have to contend. 4.3.2 Mobile systems

Some mobile systems are operated from a slowly moving vehicle in scanning mode. Others may be moved to a desired location and then operate in a fixed position. These systems may operate in open geometry with source and detector co-located or may define a closed interrogation zone using an opposed detector and source configuration with one or the other on an attached boom arm, or separate gantry, away from the main body of the system. These systems may be required to satisfy extra requirements beyond those for fixed installations for weather tolerance and portable power supply capabilities. 4.3.3 Fixed installations

Some fixed installations have an enclosed inspection chamber in which one object at a time, or a small number of objects at a time, is placed for inspection. Most systems, however, scan at least one dimension of the objects placed in their inspection zones, which allows long objects or multiple objects to be interrogated in series. Fixed installations, with one or more dimensions scanned, usually cannot permit a driver to enter the inspection zone because of radiation dose limitations; therefore, some form of conveyor system is required to move the container or vehicle through the inspection zone. If multiple scans are used, the conveyor system shall be able to reproduce positions very accurately.

5. Performance requirements

5.1 Simulants

Since the actual substances-of-interest may be extremely hazardous or require elaborate safeguards against diversion, and since the manufacturers of active interrogation systems need to be able to perform relevant tests of their own to optimize their systems’ performance, less hazardous simulants or simulants with fewer safeguarding requirements shall be employed in the testing and evaluation of these systems. This ensures that the U.S. DHS-related testing does not itself increase the risks of detonation, release of a dangerous agent, or improper diversion of sensitive materials.

Because nuclear interactions with ionizing radiation are employed in the detection and identification schemes, the ideal simulant for a substance-of-interest would have the same nuclidic densities and shapes as the actual substances- or items-of-interest. Since chemical and explosive agents are almost always produced from materials of natural isotopic abundances, these natural materials or normal commercially available materials (in the case of lithium) shall always be employed in the corresponding simulants. Each active interrogation system will be tested with up to six simulants as specified below. A given system will be tested only for simulants of substances-of-interest that the manufacturer claims to be able to detect and identify.

ANSI N42.41-2007

American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

There are, of course, many more substances- and items-of-interest to homeland security than are considered in this standard, many more types of explosives, chemical warfare agents, and nuclear weapons materials and configurations; however, a device that can detect and identify the specified simulants reliably can probably be configured to recognize most real agents of interest in these classes. Because the specified simulants are sometimes not very faithful representatives of the actual substances- or items-of-interest [particularly in the case of special nuclear materials (SNM) and nuclear weapons components], the active interrogation systems may have to be adjusted or configured differently for optimum performance in real stream-of-commerce applications. For example, it is recognized that in testing under this standard, it would be acceptable for a system to report detection based on indication of the isotope 238U only, whereas a deployed system should be capable of detection of either 238U or 235U.

Simulants for up to six of the substances-of-interest discussed in 5.1.1, 5.1.2, and 5.1.3 will be included in the testing, and recipes are provided for the simulants in Annex A. 5.1.1 Explosives

⎯ C4 or plastique military explosive

⎯ Ammonium nitrate plus fuel oil (ANFO) explosive 5.1.2 Chemical warfare agents

⎯ Sarin nerve agent ⎯ Mustard gas blister agent

5.1.3 Special nuclear materials and nuclear weapons components (LEU, WC shell)

⎯ Low-enrichment uranium (LEU) with 19.5% 235U ⎯ Tungsten carbide spherical shell

5.2 Requirements for PD, PFA, and statistical confidence

The main goals of the testing of each active interrogation system are to establish the PD, the PFA, and the average inspection time for up to six simulants of specified masses, packed within each of four representative types of surrounding cargo. The results will be reported separately for each combination of simulant type and surrounding cargo type. However, the conduct of the trials for all types of simulants under consideration will be intermingled.

Because very simplified cargo loading configurations are to be used (see 5.4), and because many active interrogation devices have some imaging capability, every test position will always contain either a simulant or a normal cargo package that resembles one of the simulant packages radiographically, but not chemically nor nuclidically. Normal cargo packages shall contain common substances such as sand, salt, sugar, graphite, plastics, water, soap, lye, lead, and bismuth, or combinations of such substances. Each normal cargo package shall be made as radiographically-similar as possible to one of the simulants under test, for the type or types of interrogating radiation emitted by the active interrogation system under test.

The number of trials required for a given simulant in a particular cargo type to establish a given PD level with 68% confidence is shown in Table B.1 in Annex B (see Filliben and Heckert). For example, to establish a PD ≥90% with a CL of 68%, a minimum of ten trials with a simulant of that type are required, with correct identification being achieved in all of the trials, if only the minimum number of trials (ten) were done. Table B.2 shows the number of trials required to establish a PFA ≤5% at the 68% confidence level. For each type of simulant and each of the four representative types of surrounding cargo, a minimum

ANSI N42.41-2007

American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

of twenty-two trials with a normal cargo package in one of the test positions is required, and the appropriate null response would have to be achieved in all twenty-two of these trials to establish a PFA of 5% or less, if only the minimum number of trials (twenty-two) were done. Note that if the active interrogation system under test does not have radiographic capability, then the PFA tests apply to all possible stimulant types at once; but if the system under test does have radiographic capability, then a given PFA test with a normal cargo package counts only for simulants that match that normal cargo package radiographically. In the latter case more tests would be required so that the PFA would be based on true elemental and/or nuclidic identifications rather than radiographic clues.

Except for a code number, all simulant packages and normal cargo packages will have identical external appearance. This uniform appearance is required, because the testing shall be done in a double blind manner, with neither the loading team nor the system operating team knowing what is in the packages. The loading and coding of the packages will be done by a planning and analysis team.

In 5.4, the possibility of multiple test regions within the longer scanned containers and vehicles (categories E–J, in Table 1) is discussed for the purpose of reducing the total number of vehicles and/or containers to be loaded and manipulated. 5.2.1 Requirement

A minimum of ten trials shall be carried out for each simulant to be tested, for each of the four simulated cargo loadings specified in 5.4 (i.e., a minimum of 4 x 10 = 40 trials altogether for each simulant). For each simulant, the amount of test substance shall be as indicated in Table 4. The simulant packages or normal cargo packages shall be located at test positions as specified in 5.4, within the inspection zone as indicated in Table 1. To receive the highest possible score in the report of the tests, a sufficient number of correct responses shall be obtained to establish a probability of detection and identification that exceeds 90% (at the 68% confidence level) and to establish a false positive rate of less than 5% (at the 68% confidence level) within the allowed average inspection times of Table 3.

The report of the testing will indicate roughly the degree to which the system tested satisfies the requirement stated above for each combination of cargo type and simulant separately. If the system under test is purported to be applicable to more than one category of inspection zone, then the tests should be carried out for the largest of these. For categories A–D, a container or vehicle filling the maximum dimensions for the inspection zone of that category will be used in the testing. The detailed criteria for the various performance ratings will be given in a separate document or documents, not in this standard. 5.2.2 Alternative test criteria

The vendor of an active interrogation system may request testing to establish a shorter-than-required average inspection time if that vendor wishes to have this advanced capability verified in a non-public report of the testing. On the other hand, a vendor may request testing with a longer average inspection time if that vendor concedes that his/her system cannot satisfy the normal criteria, but wants to have its limited capabilities verified in a non-public report of the testing. The public report of the testing will nevertheless indicate only results relative to the normal detection and identification criteria. Any other verified capabilities of systems are regarded as sensitive data, the public release of which could compromise homeland security if the systems were widely deployed.

5.3 Average allowed inspection times

Two different applications are considered separately: complete inspection of entire inspection zones and spot-checking of previously selected sub-zones that have been identified externally by some other means.

ANSI N42.41-2007

American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

5.3.1 Average allowed inspection times—full inspection zones

The sensitivities of almost all active interrogation systems are limited by counting statistics, so that some limit must be placed on inspection times to fairly compare competing systems. In actual service for screening stream-of-commerce loads, true positives will be rare events, so that the appropriate average of inspection times is the average over true negative loads (loads with only normal cargo packages). These must be true negative loads for all simulant types, although some may be scored falsely as positives by the system operating team. If inspection times are somewhat longer for loads scored correctly as positive for one of the simulants, this additional time is well justified for getting a definitive location and identification of the substance, whereas the exact location or identification of the substance might be ambiguous at a shorter inspection time. Allowed average inspection times for normal cargo loads are listed in Table 2. For loads with a simulant of a substance-of-interest present, the allowed average inspection time may be up to three times as long as the values in Table 2 and Table 3 below.

Table 2 —Average allowed inspection time for clearing the full inspection zone

containing only normal cargo packages

Container category

Allowed average inspection timea Container type

(seconds)

A Small article, carry-on, suitcase 90 B Airline cargo container 900

C Automobile 150 D 2 axle vehicle ≤2 ton 200 E Intermodal cargo container 300

(≤30 ft)

F Intermodal cargo container 600 (>30 ft)

H Truck (>30 ft) 600 G Tractor with semi-trailer 600 I Rail car 900 aIncludes all re-scans made to clear any initial scan alarms.

5.3.2 Average allowed inspection times—externally-specified sub-zones

If a particular active interrogation system is to be tested as a spot-check device, to inspect only previously selected sub-zones that have been identified externally by some other means, then somewhat shorter times are allowed for this kind of operation, as indicated in Table 3.

ANSI N42.41-2007

American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

Table 3 —Average allowed inspection time for clearing a single, externally-specified

sub-zonea containing only normal cargo packages

Allowed average inspection time (seconds)

A Small article, carry-on, suitcase 60 B Airline cargo container 300 C Automobile 80 D 2 axle vehicle ≤2 ton 90 E Intermodal cargo container 140

(≤30 ft)

F Intermodal cargo container 200 (>30 ft)

H Truck (>30 ft) 200 G Tractor with semi-trailer 200 I Rail car 300 aA specified sub-zone shall not be larger than one eighth of the full inspection zone in volume as indicated in Table 1. The greatest dimension of a sub-zone shall not be larger than one fourth of the greatest dimension of the full test zone for container categories A–G, and shall not be larger than one eighth of the greatest dimension of the full test zone for categories H and I. Container category

Container type 5.4 Simulated cargo loadings and simulant locations

The stream of commerce presents such an immense variety of cargo loadings that no testing program could ever guarantee that all cargo-loading possibilities have been tested. Nevertheless, some sort of simplified but fairly representative simulated loading choices would be much better than just testing with simulants in otherwise-empty containers or than always employing the most difficult kind of cargo for the type of active interrogation technology under test.

The testing under this standard will be done with four different simulated cargo loadings:

a) Test zone empty (air-filled except for the simulant and very light supports for the simulant

mass)

b) Test zone filled uniformly with newsprint at a specific gravity of 0.6 (+0%, −20%) c) Test zone filled uniformly with aluminum at a specific gravity of 0.4 (±10%) d) Test zone filled quasi-uniformly with steel at a specific gravity of 0.4 (±10%)

The steel loading is termed “quasi-uniform” because it is only uniform on a coarse scale, having rather large void spaces on a finer scale.

The three non-trivial loadings may be realized at reasonable cost from a) surplus newsprint, b) crushed aluminum cans, and c) cubes made of folded sheet steel. The module size should be chosen to be no larger than 0.33 m or 1/5 of the minimum inspection zone dimension, whichever is smaller. For small packages, alternating layers of honeycomb and metal sheet may be used for the aluminum and steel loads.

For large test zones (cargo containers, trucks, and rail cars), the simulant mass or normal cargo package would be positioned in the center of the cargo area as seen from above, and would be positioned randomly in one of three possible vertical positions a) at the vertical center of the load, b) roughly mid-way between the vertical center of the load and the top of the load, or c) roughly mid-way between the vertical center of the load and the bottom of the load. A simulant package or normal cargo package would only occupy one of the three possible vertical positions, while the other two are filled with the same simulated cargo material as the rest of the test zone.

ANSI N42.41-2007

American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

For test zones in categories A–B, the simulant will always be positioned at the geometrical center of the test zone. For test zones in categories C and D, the simulant will always be positioned at the geometric center of the largest cargo space of the vehicle.

If filling the test zone at the required specific gravity would result in a gross weight exceeding the normal limits for a given category of test zone (e.g., gross weight limit for a truck or cargo container), then the height of the simulated cargo load would be reduced to that which would match the gross weight limit.

Each normal cargo package will have a shape and radiographic density matching one of the simulant packages as closely as possible. However, the normal cargo substance would not closely match the elemental or nuclidic composition of any of the simulants.

For container categories E through I, more than one test position may be simultaneously employed within a single container or vehicle, with spacing along length of the major axis of the inspection zone, greater than or equal to 2 m. If so desired, different kinds of loading materials could fill the container or vehicle space along a span of 2 m or more surrounding these multiple test positions.

When multiple small test regions are employed along the scanned axis of the inspection zone, then the scanning time shall be recorded separately for each small test region, and an equivalent inspection time for a load with normal cargo packages throughout the entire inspection zone is derived by scaling up the total inspection time for each small test region by the ratio of the total inspection zone length to the length of the small test region.

5.5 Specification of masses to be detected

Table 4 gives the mass of substance-of-interest for each container category and type of substance. This mass will be in a single convex solid volume of normal density, except for the tungsten carbide mass, which will have the form of a spherical shell.

Table 4 —Amount of specified substance-of-interest in an active interrogation system test

Container category

Explosive mass

(kg)

Chemical warfare

agent mass (kg)

Fissionable material massa

(kg)

Weapon shell

massb (kg)

A 1 B 5 5 5 5 16 25 16 C 50 100 25 16 D 200 200 E 200 200 F 200 200 G 200 200 H 200 200 I 300 300 ab

25 25 25 25 25 16 16 16 16 16 25 16 LEU at 19.5% enrichment. Spherical shell of tungsten carbide, 14 cm O.D., 8 cm I.D., at a density of 13.7 g/cm3.

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American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

6. Electromagnetic, mechanical, environmental, and radiation protection requirements

6.1 Ambient temperature

Systems intended for operation only in controlled indoor environments with temperatures in the range of 10 °C to 40 °C may be excluded from the requirement in 6.1.1. 6.1.1 Requirement

The system shall be able to operate over an ambient temperature range from −30 °C to +55 °C.

6.2 Relative humidity (RH)

Systems intended for operation only in controlled indoor environments with RH in the range of 30% to 65% may be excluded from the requirement in 6.2.16.2.1 Requirement

The system shall be able to operate during and after exposure to relative humidity levels of 15% to 95%, non-condensing. There shall not be any observable effects from the exposure.

6.3 Radio frequency (RF)

6.3.1 Requirement

The system should not be affected by RF fields over the frequency range of 80 MHz to 2500 MHz at an intensity of 10 V/m.

6.4 Radiated emissions

6.4.1 Requirement

The emission limits when measured at 10 m from the system surface or boundary shall be less than that shown in the table below (FCC Class A Commercial/Industrial emission limits).

Emission frequency range

Field strength (MHz)

(microvolts/meter)

30–88 90 88–216 150 216–960 200 > 960 300

ANSI N42.41-2007

American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

6.5 Magnetic fields

6.5.1 Requirement

The system should be unaffected by a 3 A/m 60 Hz magnetic field.

6.6 AC line voltage operation

6.6.1 Requirement

For those systems capable of operating on 120/240 or 240/480 VAC, the requirement is: The system shall operate properly for AC lines with a supply voltage that is within ±10% of the nominal voltage and within ±5% of the nominal 50/60 Hz frequency.

6.7 Electrostatic discharge

6.7.1 Requirement

The system shall function properly after exposure to electrostatic discharges at intensities of up to 6 kV for contact (for 150 picofarads through 330 Ω) and 8 kV for air.

6.8 Conducted disturbances induced by bursts and radio frequencies

6.8.1 Requirement

The system should not be affected by RF interference that may be conducted into the system through an external conducting cable, up to 3V rms from 150 kHz to 80 MHz (see IEC 61000-4-3).

6.9 Vibration and shock

This requirement applies to mobile and movable systems, and to systems subject to vibrations from moving vehicles or heavy machinery. 6.9.1 Requirement

The system shall perform its intended function without alarm when subjected to physical shock and impacts up to 1.0 g and vibration up to 0.5 g over a frequency range of 10 Hz to 150 Hz, as transmitted through air, structures, or the ground, or caused by passing or stationary vehicles. The physical condition and functionality of the system shall not be affected by the exposure.

6.10 Sealing

6.10.1 Requirement

The manufacturer shall state the precautions that have been taken to prevent the intrusion of moisture.

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American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

The enclosures shall be constructed for either indoor or outdoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment. For outdoor use, enclosures shall provide a degree of protection against falling dirt, rain, sleet, snow, windblown dust, splashing water, hose-directed water, and external formation of ice on the enclosure.

All components that are intended for outdoor use shall be exposed to a rain test of 3 mm/min for a minimum of 15 min (see IEC 60068-2-18). After exposure, an inspection shall determine seal success or failure.

In some installations there may be additional requirements to the enclosure such as corrosive resistance, and the manufacturer shall state on the type test report as to which standard the enclosures are built.

6.11 Radiation protection

6.11.1 Workers without dosimetry and members of the general public

Workers without monitored radiation dosimeters and passersby shall receive no more radiation dose than is allowable to the general public: 100 mrem (1 mSv) per year (see FCC Code of Federal Regulations Title 10, Part 20).

6.11.2 Workers with dosimetry

The system operation shall not require routine exposure of operators or other workers in excess of the exposures allowed in the Code of Federal Regulations 10 CFR 20 (see FCC Code of Federal Regulations Title 10, Part 20 and FCC Code of Federal Regulations Title 29, Part 1910). 6.11.3 Stowaways

The inadvertent exposure of stowaways shall not exceed the effective dose limits of 100 mrem (or 500 mrem, if necessary for national security objectives) as specified in references (see NCRP Statement No. 10 and FCC Code of Federal Regulations Title 10, Part 20).

6.11.4 Pre-screened inspection zones (stowaway protection exemption)

If a container or vehicle has been pre-screened by a radiography system that would expose any possible stowaway to no more than 100 mrem under any load conditions, and if this pre-screening is capable of detecting human occupancy with probability greater than or equal to 95%, and if that pre-screening shows no human occupancy, then the inspection of that vehicle or container by the active interrogation system may proceed without further regard to radiation protection limits, up to 20 rem. Other limits, such as those set by the Food and Drug Administration (FDA) for activation, may still apply (see FCC Code of Federal Regulations Title 21, Part 179). 6.11.5 Activation

Limits on induced radioactivity in FCC Code of Federal Regulations Title 21, Part 179 and FCC Code of Federal Regulations Title 10, Part 20 shall not be exceeded.

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American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

7. Documentation

7.1 Type test report

The manufacturer shall make available, at the request of the purchaser, the report on the type tests performed to the requirements of this standard. This public report of the testing will indicate roughly the degree to which the system tested satisfies the requirement for each combination of cargo type and simulant separately.

7.2 System description

The manufacturer shall provide the following information, as a minimum:

⎯ Contact information for the manufacturer including name, address, telephone number, fax number,

e-mail address

⎯ Type of system, types of substances or items that the system is designed to detect and identify ⎯ Overall system dimensions ⎯ Power requirements

⎯ Results of tests performed to this standard ⎯ Recommended operational parameters ⎯ Description of the evaluated system

⎯ Specification and classification of system enclosure

⎯ Presence of any hazardous substances or conditions that may require additional regulation

7.3 Operation and maintenance manuals

The manufacturer shall supply operation and maintenance manuals containing the following information to the user:

⎯ Operating instructions and restrictions

⎯ Troubleshooting guide

⎯ Description and protocol for communication methods of transmitting and receiving data ⎯ Preventive maintenance schedule ⎯ Calibration schedule

⎯ Description of any safety interlocks

ANSI N42.41-2007

American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

Annex A (informative) Simulants

A variety of simulant recipes for the six separate substances- or items-of-interest are considered, because some appear to be more like the real substance- or item-of-interest than others, depending on the types of interrogating radiations and detected radiations. The manufacturer may be given the choice of the more appropriate simulant for that manufacturer’s system, provided that a reasonable justification is given for the choice.

A.1 C4 or Plastique military explosive

C4: melamine, C3H6N6, sand, polyethylene, and graphite, representing 100 g of C4

Agent C4 Simulant Mass Mass

Element

(g) (g) material

Melamine 51.6 H 2.5 C 14.7 N 34.4

Sand 75.4 Si 35.2

O 40.2

Polyethylene 7.3 C 6.3 H 1.0

Graphite 0.9 C 0.9 Total 135.2

Example: To represent 200 kg of this explosive, 270.4 kg of this simulant would be required.

Another simulant for C4 is composed of melamine, C3H6N6, magnesium formate dihydrate, Mg(COOH)2·2H2O, magnesium oxide, MgO, and graphite, representing 100 g of C4.

Agent C4 Simulant Mass Mass

Element

(g) (g) material

Melamine 51.6 H 2.5 C 14.7 N 34.4

Magnesium 26.1 Mg 4.2

C 4.2 formate

dehydrate H 1.0

O 16.7

MgO 59.3 Mg 35.8

O 23.5

Graphite 3.0 C 3.0 Total 140.0

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American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

One more possible simulant for C4 is composed of melamine, C3H6N6, ammonium bicarbonate, (NH4) HCO3, and commercial grade lithium carbonate Li2CO3. This simulant would not be appropriate for thermal neutron interrogation because of heavy absorption in the lithium.

Agent

Simulant material

Mass (g)

Element

Mass (g)

C4 H 2.1 C 12.6 N 29.3

Ammonium 25 N 4.4

H 1.6 bicarbonate

C 3.8 O 15.2

Lithium 36 Li 6.7

C 5.9 carbonate

O 23.4

Total 105.0 Melamine 44 A.2 Ammonium nitrate plus fuel oil (ANFO) explosive

Because the high-density ammonium nitrate granules are not particularly hazardous until combined with a finely divided flammable powder or liquid, alternating layers of 1 mm thick high density polyethylene sheet and a 2 cm thickness of ammonium nitrate (NH4NO3) should make an acceptable simulant for ANFO.

Agent ANFO

Mass Mass Element

(g) (g) 93.6 H 4.7

C N 32.8 O 56.1

Polyethylene 6.4 H 0.9

C 5.5

Total 100.0 Simulant material Ammonium nitrate

However, at facilities that will not permit ammonium nitrate, an alternative simulant could be used. One possibility is a 50–50 mixture of melamine, C3H6N6, and table sugar, C12H22O11, for which the carbon and oxygen contents are very different from those in ANFO, but the hydrogen and nitrogen fractions are very close.

Agent ANFO Simulant Mass Element

material (g)

Melamine 50.0 C H N

Table sugar 50.0 C H O

Total 100.0 Mass (g) 14.3 2.4 33.3 21.1 3.2 25.7

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American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

A.3 Sarin nerve agent GB

The recommended simulant contains red phosphorus, which is stable. The simulant is composed of 20% Teflon® (PTFE), 55.4% polyethylene (PE), and 24.6% red phosphorus.10

Simulant Mass Mass

Element

material (g) (g)

Sarin Polyethylene 55.4 C 47.5 H 7.9

aTeflon® 20.0 C 4.8 F 15.2

Red phosphorus 24.6 P 24.6 Total 100.0 aNo endorsement of any particular PTFE brand is implied by this product reference.

Agent

A.4 Mustard gas HD

The suggested stimulant is composed of 78% polyvinylchloride (PVC), 20% sulfur, and 2% polyethylene (PE).

Agent Mustard gas

Simulant Mass

Element

material (g)

PVC 78.5 H C Cl

Sulfur 20.1 S

Polyethylene 1.4 C H

Total 100.0 Mass (g) 3.8 30.1 44.6 20.1 1.2 0.2

A.5 Low-enrichment uranium (LEU) with 19.5% 235U

LEU can be obtained and stored with substantially less burdensome regulation and security requirements than those applicable to more highly enriched fissile materials. See FCC Code of Federal Regulations Title 10, Part 50.2.

A.6 Tungsten carbide spherical shell

Spherical shell of tungsten carbide, 14 cm O.D., 8 cm I.D., at a density of 13.7 g/cm3. (Tungsten carbide powder at a density of about 14 g/cm3 is similar to materials in some weapon assemblies.)

No endorsement of any particular PTFE brand is implied by this product reference.

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American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

Annex B (informative)

Statistical considerations

The probability of detection (PD) or probability of false alarm (PFA) of a detection system can only be determined accurately by a large number of trials. However, for a system whose correct and false responses follow the binomial distribution law in repeated sets of trials, there is a number called the confidence level (CL) that indicates what one could expect from a large number of trials, based on a single small set of trials.

The active interrogation systems to be evaluated by this standard are all assumed to behave according to the binomial distribution law. Only two outcomes are considered in each trial with a simulant present: the detection system either correctly reports a detection or something else (e.g., no detection or reports detection of the wrong agent). This is really just the very minimal assumption that a definite, fixed value of PD exists for the system during the period of testing. Otherwise, it is meaningless to perform tests to determine estimates of this quantity.

The limiting value of PD found in a very large number of trials is called the true value of PD. Consider the example in which one finds twenty-nine correct results in a single set of thirty trials. If the system under test obeys the binomial distribution law, then based on the result of twenty-nine of thirty correct responses in that one set of tests, one could make many different correct inferences such as:

the PD >0.95 with 46% confidence, the PD >0.90 with 83% confidence, or the PD >0.85 with 96% confidence. Two different ways to obtain the CL numbers will be given below.

Continuing the examples above, if a large number of different systems were tested, then in cases where twenty-nine correct results were found on a first set of thirty trials, it would be found by more exhaustive testing of each of these systems that the true value of PD would exceed 0.85 for 95% of the systems, it would exceed 0.90 for 83% of the systems, etc. So for any value of PD of interest, there is an associated percentage of systems for which the true value of PD would exceed that value of interest. This associated percentage of systems is called the confidence level.

Definition of the confidence level, CL: If m successes are found in a single set of n trials in a system obeying the binomial distribution law, then for any chosen value of PD, designated PDC, there is a corresponding number called the confidence level, CL(m, n, PDC), which is equal to the probability that any such system with m successes in a single set of n trials will have a true PD value greater than or equal to that chosen value PDC.

The CL value is given by [1 – BetaDist(PD, m+1, n+1-m)], where BetaDist is the standard cumulative beta distribution (as found in common spreadsheets). Table B.1 gives the inverse function m(CL, PD, n) for a CL of 68%. CL may also be found as the integral:

CL(m, n, PD) = (n+1) PD∫1 b(m: n, p) dp

where b(m: n, p) is the (non-cumulative) binomial distribution function, also known as the binomial mass distribution function.

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American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

For PFA: If j false-positive results are found in a single set of k trials in a system obeying the binomial distribution law, then for any chosen value of PFA, designated PFAC, there is a corresponding number called the confidence level, CL(j, k, PFAC), which is equal to the probability that any such system with j false results in a single set of k trials will have a true PFA value less than or equal to that chosen value PFAC. (In each of these trials no simulant is present, and a successful outcome would be for the detection system to report no detection.)

For PFA, the CL value is given by BetaDist(PFA, j+1, k+1-j). Table B.2 gives the inverse function j(CL, PFA, k) for a CL of 68%. CL may also be found as the integral:

CL(j, k, PFA) = (k+1) 0∫ PFA b(j: k, p) dp

Table B.1—Detection criteria for verifying a lower bound on the probability of detection,

with 68% confidence In a single set of n trials, the minimum number of successes m required to assure the indicated lower bound on the probability of detection PD.a

PD >0.50

PD >0.75

PD >0.80

PD >0.85

PD >0.90

PD >0.95

n = 9 6 8 9 9 ...b ... n = 10 6 9 10 10 10 ... n = 15 9 13 14 14 15 ... n = 20 12 17 18 19 20 ... n = 25 14 21 22 23 24 25 n = 30 17 24 26 27 29 30 aFor a single set of n trials, the detection probability is established as greater than the PD column heading value with at least 68% confidence, based on m or more successes. b

When the minimum required number of correct results is indicated as “...”, then the number of trials in that set is insufficient to verify (at the 68% confidence level) that the detection probability is greater than the PD column heading, even if the result of every trial in that set were correct.

NOTE—The values of m in this table may be obtained from inspection of a tabulation of CL(m, n, PDC) or from Filliben and Heckert's Guide to Available Mathematical Software, Inverse Binomial Function BINPPF Subroutine.

ANSI N42.41-2007

American National Standard Minimum Performance Criteria for Active Interrogation Systems Used for Homeland Security

Table B.2—Detection criteria for verifying upper bound on false positives

with 68% confidence

In a single set of k trials, the maximum permissible number j of false positives to assure the indicated upper bound on the probability of a false positive (PFA).a

PFA <0.10

PFA <0.075

PFA <0.05

PFA <0.025

k = 10 k = 15 k = 20 k = 21 k = 22 k = 23 k = 24 k = 25 k = 30 k = 40

a0 0 0 0 1 1 1 1 1 2

...b0 0 0 0 0 0 0 1 1

... ... ... ... ... 0 0 0 0 0 0

... ... ... ... ... ... ... ... ...

k = 50 3 2 1 0

For a single set of k trials, the probability of a false positive is established as less than the PFA column heading value with at least 68% confidence, based on no more than j false results. b

When the maximum number of permissible false positives is indicated as “...”, then the number of trials in that set is insufficient to verify (at the 68% confidence level) that the probability of a false positive is less than the PFA column heading, even if there were no false positives in the trials.

NOTE—The values of j in this table may be obtained from inspection of a tabulation of CL(j, k, PFAC) or from Filliben and Heckert's Guide to Available Mathematical Software, Inverse Binomial Function BINPPF Subroutine.

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ANSI N42.41-2007