RU133944U1 - RADIATION MONITOR - Google Patents

Abstract

A radiation monitor containing detectors based on gas meters placed in a neutron moderator, and containing a high-voltage power supply for the detectors, a pulse amplifier, a discriminator and an analog-to-digital converter, a power supply and control unit connected to them with a low-voltage power supply for electronic circuits, an electronic signal processing system , light and sound alarms, characterized in that the detection units are installed in the zone of minimum sensitivity of the radiation monitor and contain at least at least one counter based on isotope B, covered by neutron moderators, from polyethylene plates on the front and back sides, while the thickness of the moderator on the front side is 2-3 cm, and the thickness of the moderator on the back side is more than 4 cm.

Description

The utility model relates to the field of radiation monitoring, to the control of unauthorized movement of nuclear materials and radioactive substances.

Known radiation monitor type SPM-904 manufactured by TSA Systems ltd, containing a two-rack portal located in the portal blocks of detection of γ-radiation and neutrons based on organic plastic scintillators, each of which contains a node for high-voltage power detectors, pulse amplifier, discriminator and analog-to-digital a converter, a power and control unit connected to them, comprising a low-voltage power unit of electronic circuits, an electronic signal processing system, a light and sound signal unit lizings. Catalog of TSA Systems ltd. Longmont, СО 80502, 1995. Analogue. The monitor has a large detection threshold, large overall dimensions, large mass, and high cost.

Known radiation monitor designed to record radioactive emissions when moving through it nuclear materials and radiation-hazardous substances. The monitor contains a block for detecting neutron radiation from slow neutron counters made on the basis of ³ He, a block for detecting gamma radiation, sensors for detecting an object, as well as a remote unit with a control panel with a microcomputer, a siren and an actuator, as well as a modem for transmitting information about the results of detection. Pedestrian radiation monitor of gamma-neutron radiation KSAR1U.031-DOZOR, Federal State Unitary Enterprise STC "Nuclear Physics Research". Advertising brochure. Prototype.

The disadvantage of the prototype is the large threshold for the detection of neutron radiation materials experiencing spontaneous fission, a large background count of neutrons, a high supply voltage of neutron detectors, the high cost of ³ non-counters and their shortage.

The objective of the utility model is to eliminate these shortcomings and increase the efficiency of the device, reduce the detection threshold of the monitor, increase reliability.

The technical result of the utility model is to reduce the detection threshold of the monitor, increasing reliability.

The technical result is achieved in that in a radiation monitor containing detectors based on gas meters placed in a neutron moderator and containing a high-voltage power circuit of the detectors, a pulse amplifier, a discriminator and an analog-to-digital converter, a power supply and control unit connected to them with a low-voltage electronic power supply unit circuits, electronic signal processing system, light and sound signaling, detection units are installed in the zone of minimal sensitivity of radiation monitors ora and contain at least one counter based on isotope B, covered moderated neutrons from polyethylene plates on the front and back side, wherein the thickness of the retarder on the front side 2-3 cm, and the thickness of the retarder at the rear side of a 4 cm.

The essence of the utility model is illustrated in figures 1-3.

Figure 1 schematically shows a radiation monitor, where:

1 - detection blocks with a size of 400 × 200 × 50 mm ³ ; 2 - counter based on the ^{10 V} isotope; 3 and 3 _a - neutron moderators; in the form of polyethylene plates with a thickness of 20 and 40 mm, located on the front and back sides of the detection units 1; 4 - node electronic circuits; 5 - high voltage power; 6 - pulse amplifier; 7 - discriminator with analog-to-digital Converter; 8 - power supply and control unit; 9 - low voltage power supply of electronic circuits; 10 - electronic signal processing system; 11 - microprocessor device with light and sound alarm.

Figure 2 presents a block diagram of the communication of the constituent parts of a radiation monitor, in the process of its operation on the example of one detection unit, where: 1 - detection unit; 2 - counter based on the ^{10 V} isotope; 4 - node electronic circuits; 5 - high voltage power; 6 - pulse amplifier; 7 - discriminator with analog-to-digital Converter; 8 - power supply and control unit; 9 - low voltage power supply of electronic circuits; 10 - electronic signal processing system; 11 - microprocessor device with light and sound alarm.

3 is a neutron count as a function of the thickness of the retarder 3 and the counter 3 _and 2 on the basis of the isotope, ¹⁰ disposed on the front side (dashed line) and back (solid line).

The radiation monitor works as follows:

Turn on the monitor and monitor the device in automatic mode. Switch the monitor to the operating mode, in which the current background neutron radiation is measured.

In the case of the appearance of radioactive material in the area of the radiation monitor, neutrons enter the detection unit 1, pass the neutron moderator 3, where part of them slows down and enters the counter 2 based on the ^{10 V} isotope, causing a reaction with the formation of alpha particles and lithium isotope, not slowed down neutrons then pass to the moderator 3a, where they are slowed down and reflected back to the counter based on the ^{10 V} isotope, additionally forming alpha particles and lithium ions.

Alpha particles and lithium ions, ionizing the gas, ultimately give rise to voltage pulses, which are recorded. The number of voltage pulses is proportional to the number of formed alpha particles and bombarding neutrons.

In the boron counter reaction occurs:

,

,

α particles and ⁷ Li ions are formed. The ionization of the gas occurs, filling the internal volume of the gas meter 2 based on the ^{10 V} isotope, with the formation of electrons.

Electric pulses are fed to the input of amplifier 6, and after amplification, to a discriminator with an analog-to-digital converter 7, which, in accordance with a pre-set level, cuts off noise pulses of smaller amplitude and passes pulses of larger amplitude.

An analog-to-digital converter that converts pulses to digital form. The digital signal is sent via a communication line to the electronic signal processing system 10, where they are processed in digital form using the moving average algorithm.

The presence or absence of excess of the recorded radiation over the background level is recorded.

In case of inoperability of the monitor, the signal enters the front panel of the power supply and control unit 8.

, где z - коэффициент (квантиль нормального распределения), зависящий от принятой вероятности ложных срабатываний.When the monitor is operable, the registration threshold L is determined by the value of the background using the electronic signal processing system 10 as

, where z is the coefficient (quantile of the normal distribution), which depends on the accepted probability of false positives.

The monitor is put into an operating mode in which measurements are made continuously or only if there is an object of control and the resulting score is compared with the registration threshold L.

If the account exceeds the registration threshold, an alarm is issued through the microprocessor device 11 with light and sound alarms, the red photodiode is lit, and the buzzer on the power supply and control unit 8 is turned on.

If there is no excess over the registration threshold, then depending on the established operating parameters, they either update the background, taking into account previous measurements (dynamic mode of operation), or leave the background account unchanged (static mode of operation). Power supply of electronic circuits with a voltage of 24 V is carried out from the output of a low-voltage power supply unit of electronic circuits 9.

A decrease in the monitor detection threshold is achieved due to the lower background corresponding to the boron counter N _background , the location of the detection units 1 in the minimum sensitivity zone, which is determined experimentally based on the response of the radiation monitor to the radiation of a test source located in 10 cm increments over the entire volume of the controlled space, in lower point of the middle of the controlled volume. A retarder as defined thickness values located on the front side 3 and the back side of the counter 3 _and 2 on the basis of the isotope ^10.

With a moderator thickness of 3 to 3 cm, polyethylene is placed on the front side of the counter 2 based on a ^{10 V} isotope. A further increase in its thickness leads to a decrease in counting.

By arranging the retarder 3 _and on the rear side 2 of the counter ¹⁰ on the basis of the isotope ⁱⁿ the maximal observed growth account polyethylene to a thickness of 4 cm.

The increase in counting occurs further, but with a smaller gradient.

Thus, the thickness of the moderator 3 is 2-3 cm from the front of the counter 2 based on the ^{10 V} isotope and the thickness of the moderator 3 _{a of} counter 2 based on the ^{10 V} isotope over 4 cm from the back of the counter 2 based on the ^{10 V} isotope provides the maximum detector response 1, i.e., the minimum detection threshold. As the working thicknesses, their minimum optimal values were selected to ensure the minimum mass and dimensions of the detection unit 1 (2 and 4 cm, respectively).

Improving reliability is achieved due to the lower supply voltage of the detectors.

The table shows the comparative characteristics of the counters.

Table Counter type U _pit , kB Background, s ^-1 Detection threshold, g plutonium Monitor cost, rel. ³ He 1.25 0.19 90 1,5 ¹⁰ B 0.575 0.04 thirty one

Claims (1)

A radiation monitor containing detectors based on gas meters placed in a neutron moderator, and containing a high-voltage power supply for the detectors, a pulse amplifier, a discriminator and an analog-to-digital converter, a power supply and control unit connected to them with a low-voltage power supply for electronic circuits, an electronic signal processing system , light and sound alarms, characterized in that the detection units are installed in the zone of minimum sensitivity of the radiation monitor and contain at least at least one counter based on the ¹⁰ V isotope, covered by neutron moderators, from plastic plates on the front and back sides, while the thickness of the moderator on the front side is 2-3 cm, and the thickness of the moderator on the back side is more than 4 cm.

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