SU1538716A1 - Method of measuring fluence of neutrons - Google Patents

Description

(46) 06/15/92.Bul. 22

(21) 4400304/25

(22) 31.03.N8

(72) V.N. Andreev and A.V. Davydov

(53) 539.1.07.8108Я.8)

(.56) D. Yuz. Neutron studies on nuclear boilers. - M. Foreign literature, 1954, p. 107.

D. Yuz. Neutron studies on nuclear boilers. - M .: Foreign literature, 1954, p. 10J-108.

(54) METHOD FOR MEASURING NEUTRON FLUENCE

(57) The invention relates to neutron measurements and can be used with prolonged exposures, for example, in the manufacture of radioactive isotopes. The purpose of the invention is to determine the value of the measured fluence, independent of the nature of the change in the magnitude of this fluence or its interruption during the measurement, with a significant simplification of measurements, reducing the radiation hazard to the operator. In the method, a sample with a known number of nuclei and a neutron absorption cross section is irradiated and its mass increment is determined, which is a measure of the neutron fluence.

The invention relates to nuclear FISTIKL, or more specifically, to the physics of slow neutrons and can be used in long-term experiments with neutrons, requiring the determination of the time-averaged neutron flux acting on the object of study, or the total number of neutrons, interact over a long time with the object of study.

The aim of the invention is to determine the neutron fluence, independent of the nature of changes in the fluence or its interruptions during the time of its summation, with a significant simplification and measurement procedure, reducing the radiation hazard for the operator and ensuring unlimited storage of physical radiation stored in the irradiated sample. .

Substance and Mon are explained below by mgs. As a result of neutron absorption, the core mass changes by:

E „„

& m

EU +

E +

gap -

(one)

(L

Here mn is the neutron mass, Ec is the neutron binding energy in the nucleus formed after its absorption, Ep is the energy carried away during beta decay of this core, Ey is the energy of gamma rays emitted by the daughter core after beta decay, c is the speed of light in a vacuum. It will be understood that line (1) refers to the mass difference between the final stable core formed after all the decay processes associated with neutron absorption and the original core. If after neutron capture a chain of radioactive transformations follows, then the values of E p and Ef have, respectively, the meaning of the total energy loss during all beta decays and all processes of gamma radiation. Obviously

SP

with

00

with&

In each particular case, it is possible to determine the accuracy of the Hggcom about fvm from mn (this is not very small - about 1%), in r; The op-decay schemes are practically well studied,

If a sample containing a substance capable of absorbing neutrons with a SG absorption section, sang, placed and 1 streaming from a premium t 1 iH HipoHon tutus tjf (t) / cm2 "s, then the number of units of time, mm Hmm IK itronoi will be equal to n (O - ),

2)

evil poch premir irradiation t oka

W. I AM p.tllHMM

N

JntMrit - A6) Kt) (3),

rnt, - flux-not neutrons over time

The null during the irradiation time of the sample increased by DM. Then the number of absorbed neutrons can be

determined by formula:

Ij

LI

& ch

(BUT)

I-1 (3) h (j) follows

F Y

(five)

Lo D p

Let us estimate BOTrfoAFijTo value Aga for a similar experience. As the material of the irradiated sample, we take a substance with a sufficiently large and well-known neutron absorption cross section, for example, gold — 147, which in natural conditions represents a SO-irpcent isotope. The thermal neutron absorption cross section for it is 100 barn. If 1 g of gold is irradiated over a period of time by a day, a neutron flux with a density of 5x10 J n / cm. c, then the weight gain will be approximately

ii

-S9

DM - -PAR umt -5-10

x 1.67. 0, about., 26-10

year

Yui.1o-P

If the sample is weighed before and after irradiation on an analytical balance with an accuracy of 1 mg, then the accuracy of determining the mass increment obtained will be 3,.)%. It is likely that one can achieve greater accuracy by using a larger mass or a larger neutron absorption cross section.

ten

five

,

20

T.

.

25

thirty

35

40

45

P

50

55

The experimental procedure for irradiating a sample is somewhat complicated by the fact that under the action of an intense flux of neutrons and hard gamma quanta produced during neutron capture, surface exchange of the gases dissolved in the material and the substances of the sample and its surrounding parts is possible. Such an exchange can lead to a distortion of the sample mass increment, due only to the absorption of neutrons. To avoid this, the sample must be placed in a double ampoule of a substance that weakly absorbs neutrons. The sample is in the internal ampoule. Both ampoules before soldering together with the sample are degassing by heating and pumping. First, the internal ampoule is sealed, after h "; its first weigh. Then it is placed in the second vial, which is also sealed under pumping. The exchange of atoms between the sample and the intra-, early vial does not cause a change in their total mass. The outer ampoule is made similar in size to the inner ampoule. With the same materials and sizes of both ampoules, the exchange of atoms between them does not change the mass of the internal ampoule. The experience has shown that when irradiated in a thermal neutron flux of two quartz ampoules inserted one into another, the mass gain of the internal ampoule can be made smaller than 0.1 mg. Since the second weighing of the internal ampoule with the sample can be performed after an arbitrarily long time after the end of the irradiation, it is possible to almost completely eliminate the radiation hazard when handling the sample.

Claims (1)

Invention Formula A method of measuring neutron fluence based on neutron irradiation of a sample with a known neutron absorption cross section of a given spectrum, characterized in that, in order to determine the value of the measured fluence, independent of the nature of the change in the magnitude of this fluence or its interruption during the measurement time and simplify the measurement process , reducing radiation hazard to the operator and 5ШН716. 6 To ensure an unlimited period of time, the mass increment of the physical information storage sample, the internal ampoule, which is fixed in the irradiated sample, a measure of the number of neutrons absorbed, is placed in a double ampoule. from which, according to the known cross section of the substance that is transparent to neutron absorption of neutrons and the number of absorber, it is irradiated in the sample under study in a sample by a neutron bombardment, after which the determination of neutrons.