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Pedestrian Portal for Detection of Radioactivity

#0928


Transportable Pedestrian Portal Monitor with Low False Alarm Rate for Detection of the Radioactive Sources and Special Nuclear Materials and their Location

Tech Area / Field

  • ENV-MIN/Monitoring and Instrumentation/Environment

Status
8 Project completed

Registration date
23.03.1997

Completion date
27.05.2003

Senior Project Manager
Bugaev D V

Leading Institute
NIIIT (Pulse Techniques), Russia, Moscow

Collaborators

  • Lawrence Livermore National Laboratory, USA, CA, Livermore

Project summary

It should be noted that the level of technical instrumentation of enterprises and industrial projects dealing with fissile materials must be higher to prevent the unauthorized removal of fissile materials. Much attention is paid to the development of the equipment for radiation posts by both state institutions and private companies.

Equipment used for radiation posts may be pided into three main groups by their function:


- Pedestrian Portal Monitors;
- Vehicle Portal Monitors;
- Hand-Held Instruments to control pedestrians and transportation facilities.

If a law-breaker carries (or drives) a radioactive material through the radiation post, the portal generates sound and light alarm signals. Portals presented on the market may generate one false alarm signal for 1000 controlled pedestrians (transportation facilities). Therefore, the security service must locate the radioactive material by means of a hand-held monitor before the detention of the law-breaker. Documenting is not carried out in the case of the detention.

Operation of the radiation monitor may also caused by medical or common isotopes, for example, a luminous dial.

For carrying the radioactive material through the pedestrian portal, the lawbreaker may use a metallic container. The container absorbs radiation of the material placed inside it. Therefore, except for the radiation monitor, a metal detector should be installed at the checkpoint.

Structurally, pedestrian portals are stationary equipment with a weight as high as 200-400 kg, that complicates the use of portals as transportable equipment for arrangement of special check points with the purpose of the VIP security during the official meetings, or for the work of the special groups watching removal of the radioactive materials.

At the present time, a wide range of pedestrian portal monitors is commercially produced. The study of the comparison features of pedestrian portal monitors and the consumer requirements allow us to make a conclusion that the improvement in Portal characteristics may be achieved by:


1) the decrease in the false alarm rate, that is important for portal monitors working in the places with a lot of pedestrians (customs, big enterprises dealing with radioactive materials, etc.);
2) the increase in the detection probability;
3) the identification of the radionuclides, that allows us to exclude the false alarm of Portal Monitor from common and medical isotopes (e.g., luminous dial, etc.) and to detect the radioactive radiation from the protection container, where the radioactive material is hidden;
4) the indication of the zone where the law breaker has hidden the radioactive material;
5) documenting during the detention;
6) the decrease in the Portal weight, that is important for Portal Monitor transportation and for execution of routine activities to arrange the makeshift check-points.

Project Purpose

In the proposed Project we plan to develop the Pedestrian Portal satisfying the aforesaid requirements. For this, we should:


1) carry out the investigations;
2) elaborate the electronic circuits, software, complete design plans;
3) produce the experimental model of Pedestrian Portal Monitors that makes it possible to detect radioactive and fissile materials with the following features:

type of detectable radiation

gamma-ray

detection sensitivity of highly enriched uranium (HEU) against a background of 20 nR/hr

1 g

detection probability

more than 0.999

false alarm rate

less than 10-6

work modes: pass through Portal at V = 5 km/hr

sound and light alarm, location of radioactive sources;

detention for control radionuclide identification; documenting of the detention results

control time 10s

Radiation portal proposed for the development will combine the functions of detection, location, identification and documenting. Its weight will be less than 25kg.

Pedestrian portal of category III SPM-904 produced by company ISA, USA costs » $35,000. The hand-held monitor JHH-31 produced by company CANBERRA, USA costs $7,800. Time required for control is more than one minute. Documenting and identification are not conducted.

At the commercial production the cost of the Portal Monitor we propose to develop in our Project would not exceed US $ 20,000.

Technical Approach and Expected Results

The purpose in hand is achieved by:


1) selecting the mathematical model for data processing which is different from the models previously used in this field of research;
2) using four Nal (TI)-Csl (TI) phoswich detectors as a sensitive element;
3) including a Notebook computer in the data processing unit that will make it possible to print out data for documenting;
4) making the Portal as modular units which are easy to install at the demountable lightened rack.

Operation principle of the Portal proposed to the development is as follows.

Background gamma rays are detected by four detectors with scintillation crystals. Amplitude of output signal is proportional to the energy of detected gamma-quanta. We select regions in the energy spectrum where count rate is expected to exceed the background level (185 keV for U-235). In the selected region, the count rate of the background gamma-quanta is considered to be a random and stationary process. As informative files from each of the four detectors are statistically independent, their parameters are described by the following functions:


a) mean square of the background count rate for the measurement time selected (describes the process rate);
b) distribution density of the probability that the background count rate will be within a certain range at some instant of time (describes the process value at fixed points of the distribution);
c) autocorrelation function that defines the interdependence of the background count rate at a given instant of time on the background count rate at some other instant of time (describes the process behavior in time);

To describe the joint characteristics of four processes or some combination of four random processes, the following functions should be used:


a) joint density of probability distribution. It defines the probability that count rates from each of the detectors will simultaneously be within certain ranges of their values at some instant of time;
b) cross-correlation function of informative files describes the interdependence of the values of each file on the values of all other files.

The removal of radioactive and nuclear materials in the portal area will be identified as violation of the process stationary by examining the functions given above.

The application of the above-mentioned principles for data processing will allow us to increase the probability of the radioactive material detection, to decrease the probability of false alarm rate, and to point to the zone where the radioactive source may by concealed. For 1 g of U-235 with an activity of 6-104 g-quanta-s-1-g-1, the search zone may be a volume of 10-20 cm radius.

To identify radioactive material, an assembly of Csl (TI) and Nal (TI) inorganic crystals is used in the detectors. Presence of a thin beryllium-coated Csl (TI) crystal at the entrance window of the assembly permits detecting X-rays of the metal of which the container is made. Moreover, using a thin crystal, it is possible to detect gamma radiation of Pu-239 and Am-241 with 17 and 59.5 keV energies. Gamma radiation of radioactive materials carried through the Portal is detected with a Nal (TI) crystal. When a pedestrian stops for 10 s, he is examined and isotopes are identified.

Isotope composition of gamma-radiating materials will be taken into account, when the processing program is developed. Instrument memory retains a table with common isotopes (luminous dial, medical isotopes, etc.). If these isotopes are detected by the radiation portal, alarm signal will not be generated. Isotopes used to mark the objects, in which the special services are interested, may be included in the table.

Radiation monitoring data at the moment of the detention are documented using a personal computer.

Demountable and lightened construction of the Portal includes four detector blocks, two racks for fastening, and an electronic unit that permits connecting a Notebook personal computer. This construction makes it possible to use the Portal as transportable equipment for arrangement of special control posts. Design-basis weight of radiation portal is 25 kg.

After the implementation of our methods and detection technique, the characteristics of the Portal should allow it to be competitive on the world market.

Preliminary experiments have shown the validity of the methods we propose.

RIPT employees who have some experience in developing radiometry equipment and a number of published works will participate in the work on the Portal.

Purpose

Pedestrian Portal may be used at:


- enterprises of different types dealing with radioactive materials, since the Portal is easy to set to some gamma-radiating isotopes;
- customs, since the Portal can accomplish the examination function and document the detention and has a low false alarm rate;
- control posts arranged for solving special problems (plunder, removal of radioactive materials, etc.), since the Portal weighs 25 kg and is easy to transport and mount.

Potential role of foreign collaborators

The following institutions have a great experience in solving the problems of excluding the unauthorized removal of radioactive materials through check points: Los Alamos National Laboratory, USA; Center for International Threat Reduction, Oak Ridge, USA; Lockheed Martin Energy Systems, Oak Ridge, USA; United Kingdom's Atomic Energy Research Establishment Harwell; Herfurth GMBN, Hamburg, Germany; BEFIC, France; Sandia National Laboratory, USA.

Portal Monitors of the following companies are known on Russian market: TSA Systems, USA, CANBERRA, USA, Rados Technology GmbH, Finland.

In the context of project proposed we invite foreign Research Institutes and commercial companies to collaboration.

We suppose to discuss with collaborators:


1) algorithm of the Portal operation;
2) possible configuration of the Portal;
3) plan of the experiments;
4) methods for calibration;
5) program of testing under field conditions;
6) possibility of commercial production.

During the work on the Project, joint papers and co-authorship of technical approaches are possible. To carry out pilot usage, the experimental model of the Portal may be installed at interested enterprises to work out proposals for production of the commercial model.


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