SU467666A1 - Method for determining neutron energy - Google Patents

Description

The invention relates to methods for determining the energy of neutrons and can be used when working with sources of monoenergy neutrons (for example, on accelerators in narrow beams).

A known multi-sphere method for determining neutron spectra, which, in particular, can be used to determine the neutron energy. Polyethylene spheres with diameters 50.8; 76.2 N 203.2 mm are alternately mounted on the fiber in such a way that the Zil crystal is located in the center of the sphere. Registration of neutrons with an energy greater than heat is achieved by slowing them down in ethylene. In the field of monoenergetic neutrons, a different speed of light is observed for each sphere. The resulting ratios of counting rates allowed; Using the graph, we can determine the neutron energy after preliminary calibration of the spheres.

In a series of experiments, it is necessary to determine the neutron energy in a narrow beam. For this purpose, the multi-sphere method is unsuitable, since the replacement of spheres of different diameters changes the solid angle (measurement geometry), which leads to a change in the energy interval (for example, neutrons are formed in the solid tritium target of the nuclear accelerator T (p, n) He .

In order to reduce the influence of changes in the geometry of measurements and increase the accuracy of determining the energy of intermediate and fast neutrons, a detector of slow and fast neutrons is used as a detector, with the help of which measurements are made: one without moderator, the second with moderator.

The method of drying is as follows.

In a narrow beam of monoenergetic neutrons, the counting rate of a scintillator detector, which consists of a scintillator, a photomultiplier tube (FEI-13. FEI-52) and an electroinducer device, which amplifies and discriminates pulses and their count, is measured. Then, the counting rate of the sensor with a polyethylene retarder is measured, which includes the same scintillator and a zion detector, with the retarder and scintillator diameters being the same, which leaves the measurement geometry virtually unchanged. In both cases, the counting rates are measured by the relative counting rates of the monitor. Then, the ratio of counting rates, -. Using the graph, the neutron energy is determined.

The proposed removal of energy from the neutrons can be done in another way. Continuous monitoring of the value

energy is carried out using a scintillation detector and a moderator with a moderator instead of a monitor. Both devices are positioned symmetrically with respect to the direction of the accelerated particles at the same distance from the target.

FIG. Figure 1 shows the sensitivity curves (relative counting rates) versus neutron energy for various variants of scintillators and moderators; in fig. 2 - counting rate ratios

- depending on neutron energy Еп1

Curve 1 is obtained when the diameter of the scintillator is 40 mm, thickness 2.5 mm, without moderator; curve 2 - the diameter of the scintillator is equal to 70 mm, thickness 2.5 mm, without delay. In both cases, the grain size of the light composition T-1 does not exceed 300 microns, the distribution density of the grains in organic glass is such that the magnitude is of the order of 0.1 (where l is the boron number in 1 b is the boron interaction for thermal neutrons; / - thickness of the scintillator). Curve 3 is obtained when the diameter of the scintillator is 70 mm, thickness 3 mm, without moderator. In this case, the grain size is 1000 microns, nS of the order of 1. Curves 4, 5, and 6 are obtained with the first version of the scintillator (curve 1), but with different retardants: curve 4 — diameter of a polyethylene cylinder 40 mm, height 20 mm; curve 5 - diameter 40 mm, height 35 mm; curve 6 - diameter 70 mm, height 35 mm. Curve 7 was obtained with the second version of the scintillator (curve 2): retarder diameter 70 mm, thickness 35 mm. Curve 8 was obtained with the third variant of a scintiller (curve 3): retarder diameter 70 mm, thickness 20 mm. FIG. 2 shows the counting rate ratios -

depending on the neutron energy Ep. Curve I is determined from the data shown in FIG. 1 curves 1 and 4; curve II - curves 1 and 5; curve 1P - curves 1 and 6; curve IV - curves 2 and 7; curve V - curves 3 and 8.

Curve I (Fig. 2) allows neutron energies in the range of 250 keV and above to be determined. The magnitudes of the ratios for the two values of the energy of monoenergetic neutrons are more different from each other in magnitude than in other cases. Assuming that the measurement accuracy of the ratio

 f jQo / g jj is the same in the measured dia

In terms of energy, the uncertainty in the TF obtained from curve I (Fig. 2) lies within ± 5–8%, worsening with increasing neutron energy. Curves II, P1, IV and V can be used when it is necessary to increase the sensitivity. For example, curve V allows one to determine energies only above 500 keV, but with much

greater sensitivity, and the uncertainty in the value of "at 1 MeV is reduced to ± 5-6%, if the accuracy of the measurement of the value of the ratio is 11 ± 10%. I

Reducing the boron content in the scintillator of slow and fast neutrons leads to the expansion of the range of energy in which ;. rum is possible to determine the energy of neutrons, but this decreases the sensitivity

sensor with retarder.

Claims (1)

Invention Formula A method for determining neutron energy, which consists in transmitting a peitron beam alternately through retarders with different thicknesses and registering slow neutrons with a detector, characterized in that, in order to reduce the influence of changes in the measurement geometry and increase due to this accuracy of neutron energy determination; a detector of slow and fast neutrons is used as a detector, with which two measurements are made: one without a moderator, the second with a moderator. T, OEP, e & T, OEg,. PZK 10EP, peV 0.5-1, OEP, er