SU528012A1 - Device for determining nitrogen content - Google Patents

Abstract

A DEVICE FOR DETERMINATION, - NITROGEN CONTENT, consisting of an isotope • source of fast neutrons, a fast neutron moderator, detectors of capture gamma radiation and immobilized neutrons, single-channel and integral amplitude discriminators, characterized in that increase the sensitivity of the determination of nitrogen content, it is equipped with a fast neutron detector connected to an integral discriminator, the output of which is connected to the first input of the first circuit of the introduced ratio schemes, the second input of which nen yield integral discriminator connected to the output of the detector of slow neutrons, and a second input of the second ratio circuit, whose first input is connected to the output of the single-channel pulse-height analyzer, and the ratio circuit outputs connected to the inputs of the difference circuit inputted. (A

Description

Devices are known for determining the nitrogen content of materials such as nitrogenous fertilizers, grain, flour, and the fast neutron gamma method (radiative capture of slow neutrons).

The closest in technical essence to the proposed invention is a device containing a fast neutron moderator, a camera surrounding the test sample, an isotopic neutron source, gamma-radiation detectors, a pulse mixer, a single-channel ammunition analyzer, a slow neutron detector, an integral detector, and counters.

A disadvantage of this device is the determination of nitrogen content in controlled materials by recording the number of pulses from a single-channel amplitude analyzer, which extracts signals from a gamma ray detector, corresponding to energies of 9.810, 8 MeV, i.e. the region of the tamma-radiation spectrum, in which the main contribution is made by gamma-quanta of the radiation capture of slow neutrons by nitrogen nuclei (10.8 MeV), and by recording the flux of thermal neutrons in the control zone, without taking into account the influence of the contribution of fast neutrons, which create the main background in the selected areas of gamma radiation. The magnitude of the background changes. ns by changing the flux of fast neutrons at the location of the gamma-ray detector, which, in turn, depends on the hydrogen content in the controlled material. Thus, fluctuations in the background level during the transition from one analyzed sample to another result in errors in the determination of nitrogen content. Experimental verification showed that the ratio of the intensity of the background pulses of the gamma-ray detector to the intensity of the pulses from the output of the fast neutron detector n remains almost constant for controlled materials with different hydrogen contents, V JS. To const. while the flux of slow neutrons, for example, with decreasing flux of fast neutrons, decreases in comparison with it with greater speed, i.e. disproportionately. The purpose of the invention is to increase the sensitivity of the determination of nitrogen content. This is achieved by introducing into the detector a fast neutron device connected to an integral discriminator whose output is connected to the first input of the first ratio circuit, a second input of which is connected to the output of the integral discriminator connected to the output of the slow neutron detector, and the second input which is connected to the output of a single-channel amplitude analyzer, and the outputs of the ratio are connected to the inputs of the difference circuit. The drawing shows a block diagram of the proposed device. The device for determining the nitrogen content contains a fast neutron moderator from paraffin 1, surrounding chamber 2 with the sample under study, an isotopic source of 3 fast Neutrons, lead protection 4 of a gamma-ray detector 5 from a gamma-ray neutron source, a preselector 6, which separates pulses only from gamma quanta high energy, connected to the input of amplifiers l 7, amplitude 1st single-channel analyzer 8, separating the spectral region of the gamma radiation 9.8-10.8 MeV, detector 9 fast neutrons, connected by an output to the input Ate 10 connected to the input of an integral discriminator 11, which separates pulses corresponding to fast neutrons, a slow neutron detector 12 connected to an amplifier 13, which is connected in turn to an integrated discriminator 14. The output of the discriminator 14 is connected to the second input of the ratio 15 the first input of which is connected to the output of the discriminator 11 y and to the second input of the ratio circuit 16, the first input of which is connected to the output of the single-channel analyzer 8. The outputs of the ratio circuits 15 and 16 are differentially connected to the inputs Amplifier 17 (difference circuit), which subtracts the arrival of 1X to its signal inputs from one another, and shows the device 18 connected to the output of the differential amplifier 17. The device works in a similar way. The test sample is placed in chamber 2, where it is irradiated with a stream of neutrons. Gamma radiation is detected with a Nal (Te) scintillation detector, fast neutrons with a stilbene scintillation detector, and a pulse separation circuit from fast neutrons and gamma quanta. Slow neutrons are recorded with a boron counter. During the analysis, the value is measured proportional to the nitrogen content in the sample, where ni, n, np are the recorded gamma-radiation intensity, the flux of slow and fast neutrons, respectively ;, Kc / p. When the device operates, the pulses allocated in all channels arrive at the corresponding inputs of the ratio circuit. An analog value is removed from the output of the ratio circuit, namely, the voltage, the magnitude of which is proportional to the ratio of the pulse intensities input to the circuit inputs. Thus, the voltage at the output of the circuit 16 is proportional to the ratio ni / n, and at the output of the circuit 15 the ratio is, respectively. But since it is necessary to remove the voltage value K times smaller from the output of circuit 15, a resistive divider (variable resistance) is set at the output of circuit 15. At the same time, this divider serves to configure the device, i.e. choosing such a coefficient K so that 52 6 when the background changes (in the absence of azo-ta) at the outputs of circuits 15 and 16 from alternation, the voltages are equal. Thus, the magnitude of the voltage from the output of the differential amplifier can be used to judge the magnitude of the nitrogen content in the material being analyzed, which is accomplished by a corresponding graduation of the scale of the instrument

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Claims (2)

<claim-text> DEVICE FOR DETERMINATION - NITROGEN CONTENT, consisting of an isotopic source of fast neutrons, a fast neutron moderator, detectors of capture gamma radiation and </ claim-text> </ li> </ ul> 2 slow neutrons, single-channel and integral amplitude discriminators. characterized by the fact that, in order to increase the sensitivity of determining the nitrogen content, it is equipped with a fast neutron detector connected to an integral discriminator, the output of which is connected to the first input of the first circuit of the introduced relational schemes the output of the integral discriminator connected to the output of the slow neutron detector, and the second input of the second relational circuit, the first input of which is connected to the output single-channel pulse-height analyzer circuitry and outputs connected to inputs of attitude entered difference scheme.