FIELD OF INVENTION

The invention relates to the field of simultaneous detection of sources of gamma and neutron radiation and can be used in various industries and in medicine, particularly as a part of the detectors used for radiation monitoring, for example to prevent unauthorized relocation of nuclear and radioactive materials, as well as to control sources of radioactivity.

DESCRIPTION OF THE RELATED ART

The operation of modem detectors of gamma and neutron radiation is based on the use of scintillators - substances that have the ability to emit light during the absorption of ionizing radiation (gamma quanta, electrons, alpha particles, etc.). As a rule, the number of photons being emitted for a given type of radiation is approximately proportional to the amount of energy absorbed, which makes it possible to obtain energy spectra of radiation. In a scintillation detector, the light emitted during scintillation is collected by a photodetector; then it is converted into a pulse of current, amplified and recorded by some registration system. The scintillator can be organic (crystals, plastics or liquids) or non-organic (such as crystals or glasses). Gaseous scintillators are also used. Known gamma radiation and neutron radiation detectors usually comprise a sensor and an electronic signal-processing unit.

There is a known detector of ionizing radiation, neutrons and gamma quanta, comprising a sensor and an electronic signal-processing unit, equipped with a circuit of time- selection of scintillation pulses, wherein slow and fast neutrons are detected against a concomitant gamma radiation with a help of three scintillators that are connected both in parallel and in series. The detector comprises: an external neutron scintillator sensitive to fast neutrons that is made of a plastic-based hydrogen-containing substance (CH)n or of stilbene; a Nal(Tl) scintillator that is sensitive to gamma radiation, placed inside the well of the external scintillator; an internal glass scintillator sensitive to thermal neutrons, and a photomultiplier - all placed in the same enclosure. The electronic signal-processing unit additionally includes a spectrometric scintillation analyzer that analyzes scintillation pulses produced by the Nal(Tl) scintillation crystal. The thickness of the external scintillator made from a hydrogen-containing substance is chosen sufficient to slow down the fast neutrons passing through it to thermal-level energies. The internal scintillator that is sensitive to thermal neutrons is made of cerium-activated lithium silicate glass containing the *Li isotope in the amount of up to 10 ²² cm ^'3 , that should be enough to effectively detect thermal neutrons [1],

The drawback of this detector is its insufficient reliability in operation due to the difficulty of providing proper optical coupling of three scintillators that are connected both in parallel and in series, as well as its high cost.

There is another known scintillation detector of neutron radiation and gamma radiation. Its sensor comprises: an external neutron scintillator made of a hydrogen-containing substance based on (CH)„ plastic or stilbene, which is sensitive to fast neutrons; an internal NaI(Tl) scintillator, which is sensitive to gamma radiation, placed inside the well of the external scintillator. The detector comprises also a photomultiplier and an electronic signal-processing unit, which includes a temporal selection circuit and a spectrometric scintillation pulse analyzer - all placed in the same enclosure. Additionally, the sensor includes two sleeves made of boron- containing material for providing the (n, a, g) reaction, wherein the first sleeve houses the external organic scintillator, and the second sleeve, placed inside the well of the external scintillator, houses the container of the internal NaI(Tl) scintillator. The boron-containing material for sleeves is one of boron nitride or boron carbide, wherein the thickness of boron- containing material sleeves is chosen sufficient for complete absorption of thermal neutrons f2].

The drawbacks of this detector are large dimensions, high power consumption, a large number of signal processing channels, which leads to an increase in signal processing time, as well as considerable production cost.

Closest to the claimed (prototype) is a radiation detector that can detect both gamma and neutron radiation, comprising the element sensitive to radiation, comprising the first scintillator sensitive to gamma radiation, and the second scintillator sensitive to neutrons; and photo sensor, wherein one scintillator is connected to the photo sensor directly, while the other scintillator is connected to the photo sensor via a wavelength-shifting material. The first scintillator is made of a lanthanum halide-based material. The second scintillator emits light in the range of 300-500 nm. The second scintillator structure prevents it from exciting the first scintillator as well as from being excited by the first scintillator. A wavelength-shifting material contains wavelength-shifting fibers [3],

The drawbacks of this solution are the large dimensions of the detector, high power consumption and its considerable cost.

At present, there is an increasing need for practical high-resolution detectors of gamma and neutron radiation. Tt is also desirable that such type of device be portable or compact. SUMMARY OF THE INVENTION

The technical problem solved by the invention is to create a portable gamma and neutron radiation detection unit that is resistant to mechanical and the magnetic impacts, which allows solving the problems described above.

This problem is solved by a gamma and neutron radiation detection unit, in which there is a sensor comprising:

an external neutron-sensitive scintillator, which is made of a material with a low effective atomic number containing an element with a high neutron interaction cross section to form charged particles by means of reactions;

a gamma-sensitive internal scintillator, optically-coupled to an external scintillator, which is made of a material with a high effective atomic number;

a photodetector, which allows simultaneous registration of optical signals from said scintillator and convert the signals into electrical pulses of various shapes.

The photodetector is connected to the signal-processing unit, while the external scintillator is made in the form of a coating or a film deposited on the entire external surface of the internal scintillator except for the area adjacent to the input window of the photodetector, which is made in the form of a solid-state silicon photomultiplier. The signal-processing unit contains a preamplifier, which allows generating signals with amplitude necessary for the operation of the associated pulse shape analyzer, designed to separate signals from external and internal scintillators by means of pulse shape discrimination method and associated with a spectrometric amplifier, which allows you to separately form signals from internal scintillator.

In an exemplary embodiment, the internal scintillator is made of CeFj, or BGO, or

The external scintillator is made of one of a composite, a non- organic, or an organic material. In an exemplary embodiment of the present invention, the composite material is or the non-organic material is one of LiI:Eu, LiIxNa(l-x):Eu, LiCaAlF6:(Eu, Na), and the organic material is stilbene.

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS

Figure l illustrates the claimed invention by a schematic depiction of the inventive gamma and neutron radiation detection unit. DESCR1PTI0N OF THE PREFERRED EMBODIMENTS

The gamma and neutron radiation detection unit comprises a sensor that includes an external scintillator 1, sensitive to neutron radiation, and an optically associated with it internal scintillator 2 sensitive to gamma radiation. It also comprises a photodetector 3, which provides simultaneous registering of optical signals from an external scintillator I and internal scintillator 2 and converting them into electrical pulses of various shapes and a signal-processing unit 4. The external scintillator 1 is made of a material with a low effective atomic number containing an element with a high cross section for interaction with neutrons, which acts as a converter of neutron radiation into charged particles by means of (n-p), (h-a), (n- ³ H) reactions. The internal scintillator 2 is made of a material with a high effective atomic number. The external scintillator 1 is placed over outer surface of the inner scintillator 2 as a coating or film covering the entire surface, except for the area adjacent to the input window of the photodetector 3, which is a solid- state silicon photomultiplier. The signal-processing unit comprises a preamplifier 5, a spectrometric pulse shaper/amplifier 6 and a pulse shape analyzer 7. The preamplifier 5 generates a signal with amplitude that is necessary to function of the spectrometric pulse shaper/ amplifier 6 and a pulse shape analyzer 7. The pulse shape analyzer 7 separates the signals produced by the external scintillator 1 from those produced by the internal scintillator 2. The spectrometric pulse shaper/amplifier 6 generates signals from the internal scintillator 2, which is sensitive to gamma radiation, while neutron and gamma radiation signals are separated using a pulse shape discrimination method.

The claimed gamma radiation and neutron radiation detector is designed to operate in mixed gamma-and-neutron fields. Gamma-radiation is detected by the internal scintillator 2 that is made of materials that ensure effective enough detection of gamma-quanta while keeping the neutron flux to a minimum. At the same time, the internal scintillator 2 has scintillation kinetics significantly faster than the scintillation decay time of the external scintillator 1 that detects neutron radiation. The external scintillator 1 provides effective enough detection of neutrons while keeping the absorption of gamma quanta to a minimum. Separation of gamma radiation from neutron radiation by the shapes of their corresponding pulses is made possible due to a significant difference in the scintillation decay times of the external scintillator 1 and the internal scintillator 2. Optical signals produced by the external scintillator 1 and the internal scintillator 2 are recorded by a solid-state silicon photomultiplier 3 and converted by it into electrical pulses of various shapes. The preamplifier 5 generates the amplitude of the signal necessary for the function of the spectrometric pulse shaper/amplifier 6 and pulse shape analyzer 7. The pulse shape analyzer 7 separates the signals produced by the external scintillator 1 from those produced by the internal scintillator 2, using a significant difference in the shape of the corresponding pulses. The spectrometric pulse shaper/amplifier 6 generates signals from the internal scintillator 2, which is sensitive to gamma radiation.

When the mixed gamma-neutron radiation effect on the unit, neutrons are largely absorbed by an external scintillator 1. Due to a smaller neutron cross section of the internal scintillator 2, the neutron flux has insignificant interaction with the internal scintillator 2. Gamma radiation penetrates through the external scintillator I almost without interacting with it, mainly because the external scintillator lis thin, and absorbed by the internal scintillator 2.

INDUSTRIAL APPLICABILITY

The advantage of the unit according to the present invention with respect to the selected prototype is a significant increase in the neutron sensitivity of the proposed unit due to the use of an external scintillator over the entire surface of the internal scintillator except, with for the input window of the photodetector. The use of a solid-state silicon photomultiplier as a photodetector makes it possible to make the gamma radiation and neutron radiation detector - and, effectively, the detector itself - smaller in size, reducing its power consumption and cost, and increasing its resistance to mechanical and magnetic impacts.

References:

1. Patent of the Russian Federation No. 214371 1, published on 12/27/1999.

2. Patent of the Russian Federation No. 2189057, published on 09/10/2002.

3. Patent of the Russian Federation No. 2411543, published on 02/10/2011.