SU448773A1 - Activation Assay Device - Google Patents

Description

one

The invention relates to the field of activation analysis and can be used in determining the concentrations of elements in powder samples.

A device for neutron activation analysis of powder samples is known, which contains a radioactive radiation detector, a container for the irradiated material and a photomultiplier (PMT) with a radio engineering circuit, fixing light flashes arising from detection or radiation. The powder sample is poured into the tank, activated with neutrons and the induced p or T radioactivity of the sample is measured with the help of the PMT detector and radio engineering circuit.

However, the known device has a low efficiency in registering and Y-radiation, and it is impossible to exclude the influence of the moving elements in it, which leads to significant difficulties in extracting the useful signal at the background level.

The purpose of the invention is to increase the sensitivity and selectivity of the activation analysis of powder samples.

The goal is achieved by the fact that, in the proposed device, the radiation detector is made in the form of two blocks, each of which consists of two cylindrical scintilla t-ores. One of the scintillators is preferentially sensitive to (-radiation of induced radioactivity, and the other to J-radiation. The capacity for the irradiated material is located between the scintillators that are primarily sensitive to fb radiation.

FIG. 1 depicts a detector

part of the proposed device, common

view; in fig. 2 shows the decay scheme

sixteen

.N

with a period

radioactive isotope, half-life of 7.35 seconds.

Claims (3)

The device consists of two blocks. Each block consists of two cylindrical scintillators. Scintillators 1 are sensitive to radiation of a radioactive isotope, Scintillators 2 to jb radiation. Between the blocks is placed a cylindrical container 3 for a powder sample. Above the unit is placed PMT 4, the device operates as follows. The powder sample irradiated by the neutron flux, located in capacitance 3, emits | b and -radiation. The decay of a radioactive isotope is often cascade: a jb-particle is emitted, and then after a period of less than 10 ° s, one or several / p-quanta are emitted. The scintillator 2 with high efficiency registers the fb radiation of the sample and practically does not register its emission. The scintillator 1 registers mainly the γ-radiation of the sample. Since the departure and jt-particles from the sample occurs almost simultaneously, the PMT 4 with the electronic circuit registers the total energy of the cascade fr and radiation lost in the detector units. This total energy significantly exceeds the average energy of P-radiation and the energy of y-quanta and is an additional specific characteristic of the radioactive core. In order to simplify the radio circuit and to allow registration of radiation using a single PMT, scintillators 1 and 2 must be made of substances with the same conversion efficiency. In order to equalize the light energy of the flash from scintillators 1 and 2, in a number of cases it is advisable to use filter suppressors between the photomultiplier and scin-gillor. The use of the proposed device allows for a number of elements to increase the sensitivity and selectivity of their determination. Calculations and preliminary testing in laboratory experimental installations show that it is advisable to use devices in determining lithium, beryllium, fluorine, silver, indium, and a whole number of other elements. Example. Determination of fluorine in powdered samples. FIG. 2 shows a diagram of the decay of a radioactive isotope. N with a half-life of 7.35 seconds resulting from the activation of fluorine by fast neutrons, p (i, eC) N®. An analysis of the pacnaf scheme shows that the maximum of the total energy of | b and -radiation is 10.3 MeV for the isotope of any decay scheme. Since the spectrum (5-radiation is white rather than linear and has a maximum at a certain average energy, the energy that can be detected by a nuclear radiation detector when it fully absorbs cascade | b and jp-radiation energy is N about 8 MeV. In known devices for neutron activation analysis, P or 2P -radiation of the sample is measured. The efficiency of detectors for p -radiation can be made very high. However, due to the influence of interfering isotopes A and M, it is necessary to measure p-radiation with more energy 3 MeV. Consideration of the N decay scheme taking into account the shape of the b spectra shows that no more than 10-15% is emitted per decay of N (b particles with energy more than 3 MeV. You can measure the y radiation of the N isotope with energy 2.3 MeV (the energy of the interfering -radiation of radioactive isotopes does not exceed this value.) The J4 isotope emits 76% of γ-quanta with energy exceeding this value. However, the efficiency of g-radiation detectors for γ-quanta of high energy is very small. Therefore, with the help of a known device, it is difficult to obtain a high sensitivity and selectivity analysis for fluorine. The proposed device makes it possible to record all acts of radioactive decay and, with a discrimination threshold of more than 4.6 MeV, it is possible to record up to 50-70% of N acts of decay in the absence of interfering radiation. The sensitivity of the analysis for fluorine increases by 3-10 times. The experimental design for determining fluorine has the following parameters: Internal block CmO mm 8Ох8О Detector j radiation Radiation scintillating plastic Detector p-radiation: Internal diameter mm 80 The external diameter mm100 The thickness of the sample container, plastic, mm0.5 The thickness of the cylindrical sample , mm5 External block Scintillating plastic Diameter mm40O Also a synthetic fiber is used as a light guide from the detector location to the PMT-49. Claim 1. Device for activation analysis of material samples containing a radiation detector, a capacitance for the irradiated material and a photomultiplier tube (PMT) with a radio engineering circuit, which is designed so as to increase the sensitivity and selectivity of the analysis By making it possible to measure the total energy and y-radiation emitted in the detector during each decay of a radioactive isotope, the radiation detector is made in the form of two blocks, each of which consists of cylindrical scintids ll tori, one predominantly sensitive to radiation Tf, another sensitive mainly to | b-radiation. Moreover, the capacity for the irradiated material located between scintillators sensitive to fb radiation. 2. The device according to claim 1, that is, in order to simplify the electronic circuit, the scintillators are made of a substance with the same conversion efficiency. 3. The device according to paragraphs. 1 and 2, about t l and the fact that between the scintillator sensitive mainly to In -radiation, and the PMT is placed absorber, reducing the intensity of the flash of light.