RU984324C - Device for recording density of directed neutron radiation flux - Google Patents

Description

The invention relates to the registration of neutron flux density, and more specifically to the registration of higher neutron flux densities. Most effectively, the invention can be used for 5 measurements of the time dependence of the neutron radiation flux density of nuclear reactors (NR).

A direct charge detector (DPS) is known. The principle of operation of the DPS is based on the transfer of a charge of particles resulting from the decay of radiator substances activated by neutrons into a signal electrode .. .-.,. A significant disadvantage of the DPS is 15 time resolution due to the decay rate of the activated substance of the radiator, d% e1 juice, the signal from) is emitted11 radiation field of the NR with a dose ratio of 20 from) radiation and neutron fluence 2.5x x10 ° r.cm Hl .

A neutron registration device is also known, comprising an aluminum collector and a hydrogen-containing 25 radiator with a conductive shielding of a material with a low atomic number, separated by a vacuum gap.

The device operates on the principle of transferring the charge of recoil protons arising in the field of neutron radiation in the radiator material to the collector. ,

A disadvantage of the known construction is that upon irradiation a hydrogen-containing substance; decomposing, fumes the vacuum gap. As a result, the device must be constantly evacuated.

The closest in technical essence to the proposed device is a device for detecting the flux density of directional neutron radiation, comprising a collector enclosed in a metal housing, separated from the housing 5 by two dielectric layers, one of which is made of a hydrogen-containing material, and the other of hydrogen atom free material.

The detector consists of a housing and collector made in the form of metal plates separated by two layers of dielectric, moreover, the housing and collector are made of low atomic metal (for example, aluminum), one 55 layer of the dielectric is made of hydrogen-containing material (for example, polyethylene), and the other from a material that does not contain hydrogen atoms (for example.

fluoroplastic) with an effective atomic number not exceeding the atomic number of the body material and the collector.

The detector operates on the principle of transfer of recoil protons in a hydrogen-containing dielectric.

A significant drawback of the D & P design is the accumulation of a volume charge in a hydrogen-containing insulator near the interface with a non-hydrogen-containing substance, resulting in the transfer of recoil protons, and in the entire volume / dielectric (due to a weakening of the neutron flux into the scattering material).

A volume charge distributed inside a hydrogen-containing dielectric creates an electric field, which, along with the high radiation conductivity of dielectrics, leads to the absorption of the volume charge, i.e. to the occurrence of a dielectric conduction current. Conductivity current, combined with the current of recoil protons, leads to an error in the measurement of the current of recoil protons in the collector circuit; a. The magnitude of the conductance current depends on the preliminary fluence and quanta (i.e., on the magnitude of the electric field inside the dielectric that is created at a given moment in time) and on the dose rate, cos; the substance of the scatterer at a given instant in time (i.e., from the instantaneous value of the dielectric conductivity

Indeed, assuming that the radiation conductivity Op is constant over the Volume of the hydrogen-containing diffuser, the equation for the charge plane in the hydrogen-containing diffuser has

view

fTp (t) EL-L

q (x, t) p (x, t).

(1)

Keo

gder (x, t) is the rate of formation of a volume charge in a hydrogen-containing dielectric:

G is the dielectric constant of a hydrogen-containing dielectric.

Solution of equation 1 for neutron flux density

0.

(t)

1, t 0

in the initial condition q (xO) qo (x} has the form q (xt) 1 -exp (-tf / p / f: fo) to fo / Oo (x) fjp + qo (x) exp (-t OO / E fio). where Pb X is the charge distribution density in a hydrogen-containing insulator arising from proton transfer by a single neutron fluence. When a DDA with a thickness of a hydrogen-containing scatterer D is irradiated, the current I in the collector circuit, normalized to the unit surface area of the collector, is (-c) ( qo (x) dx exp (F OR / e o) The magnitude of the DDA signal l (t) turns out to be time-dependent with a constant time t and depends on the initial charge distribution over the volume of the dielectric. This either limits the range of the DDA measurements or causes a systematic error depending on the time.The aim of the invention is to expand the range and improve the accuracy of the measurements of the DDA. The goal is achieved by so far in a device containing a collector enclosed in a metal housing, separated from the housing by two dielectric layers, one of which is made of a hydrogen-containing material, and the other of a material that does not contain hydrogen atoms, the collector is made of a hydrogen-containing material with a thickness e less than the weighted average of the projection path of the recoil protons in the hydrogen-containing dielectric on the direction of propagation of neutrons is surrounded on all sides by the actuator conductive shielding film of a material having a low atomic number thickness not superior to that of the weighted average projection proton path length returns in the matter of the shielding film on the direction of propagation of neutrons. Such a design of the directed neutron radiation flux density detector provides an extension of the range and accuracy of measurements of the time dependence of the neutron flux density while maintaining a simple assembly and operation of the detector due to the screening of the influence of a significant part of the volume charge arising in a hydrogen-containing insulator near the interface with non-hydrogen-containing substance during the transfer of recoil protons in a hydrogen-containing dielectric, nl, the conductivity current in collector chain. The volume charge arising from a hydrogen-containing diffuser. located between the collector and the housing near the interface with the non-hydrogen-containing substance of the Kon / veKTOpa shielding film, the charge of recoil protons transferred from the hydrogen-containing collector material through the shielding film is largely compensated. In this case, the bulk charge of the hydrogen-containing material T of the collector during dissipation does not affect the conductivity current of the dielectric on the magnitude of the current of recoil protons in the collector circuit, since the conductive film surrounding the dielectric forms a short-circuited internal circuit. Fig. 1 shows the waveform of the DVR signal when the conductivity current of the polyethylene Dielectric exceeds the recoil proton current when recording the time dependence of the flux density, i.e. / Ob (x) - qo (x) 0. figure 2 is a General view of the detector. The density detector of the directional neutron radiation flux consists of a collector made in the form of a plate of hydrogen-containing material 1 (e.g. polyethylene) surrounded on all sides by a conductive shielding film of material 2 with a low atomic number (e.g. aluminum). The collector is separated from Method I of the Personal Body 3 by two dielectric layers, one of which is made of hydrogen-containing material 4, and the other is made of material 5. not containing hydrogen atoms (for example, fluoroplastic), with an effective atomic number not exceeding the atomic number of the case material and shielding film. The device operates as follows. When neutrons are irradiated from the side of a non-hydrogen-containing insulator, the charge proton charge is transferred in the direction of neutron propagation in the dielectric 4. The volume charge that arises in the dielectric 4 near the interface with the non-hydrogen-containing shielding film 2 due to the transfer of recoil protons from the material of the dielectric 4. recoil protons arising in the hydrogen-containing material 5 and transferred through a conductive shielding film 2, For better compensation, the thickness of the hydrogen / yusod 1 rzhaschego dielectric choose not less than the weighted average of the projection-d ishy spobodnogo path recoil protons in the hydrogen-containing dielectric on the direction of propagation of neutrons, and the thickness of the shielding conductive film 2 is not more sredneveveshennoy the projection path of the recoil protons in the material of the shielding film on the direction of propagation of neutrons. (For the distribution of neutrons by energies at the INR and substances of polyethylene and aluminum, thicknesses are 0.1-0i4 mmi 210 mm, respectively). The charge that has flowed in the collector circuit during the neutron fluence is mainly determined by the charge equal to the charge of dielectric 1 arising from the transfer of protons through the shielding film 2 to a non-hydrogen-containing dielectric 4. In this case, the conductivity current of dielectric 1, according to the law continuity of current, does not contribute to the charge flowing in the collector circuit. The thickness of the dielectric 4 is selected for reasons of the electric capacitance of the detector.

Claims (1)

The claims DEVICE FOR REGISTRATION OF DENSITY OF THE FLOW DIRECTIONAL NEUTRON RADIATION, containing a collector enclosed in a metal housing, separated from the housing by two layers of dielectric, one of which is made of a hydrogen-containing material, and the other of a material that does not contain hydrogen atoms, characterized in that, for the purpose range extension and measurement accuracy, collector made of a hydrogen-containing dielectric with a thickness of at least a weighted average projection of the path of protons 30 recoil in a given hydrogen-containing dielectric to the neutron propagation direction surrounded on all sides by a conductive shielding film of a material with a low atomic number thickness not exceeding the weighted average projection of the recoil proton path in the shielding film material on the neutron propagation direction. The proposed device for detecting the flux density of directional neutron radiation in comparison with the best samples of similar equipment allows expanding the measurement range, limited mainly by the neutron fluence by about 10 times, while maintaining a relatively simple detector manufacturing technology. The device also makes it possible to increase the accuracy of measurements of the time dependence of the neutron flux density. The implementation of the device for detecting the flux density of the directed neutron radiation in the described manner provides satisfactory accuracy of the detector readings near the active region of the INR in the time interval corresponding to 95% of the neutron fluence. (56) A.I. Abramov et al: Fundamentals of experimental methods of nuclear physics. M .: Atomizdat, 1977, p. 507. Copyright certificate of the USSR N 713293, class C 01T 3/00, 1979. Figure 1 g f / g