SU1508747A1 - Method of activation analysis - Google Patents

Abstract

The invention relates to methods for nuclear-physical methods of analyzing a substance and can be used to determine the content of elements transformed into positron emitters in metals, alloys, composite materials and other substances. The whole invention is to reduce the error in the analysis of samples with high absorption. The sample under investigation and the standard are irradiated with a flux of penetrating radiation, after which, in a coincidence mode, the intensity of the flux of annihilation quanta and the flux of cascade quanta 5 emitted by a radionuclide, formed from the matrix material. The cascade transition in the decay scheme of the said radionuclide is chosen based on the following conditions: | fv - 0.25 / L, /, 7l, 4 / L, where L is the maximum sample size, f /. Mi p. - linear absorption coefficients of gamma quanta in the matrix for the annihilation line, soft and hard components of the cascade transition, respectively. The mass of the element to be determined is found by the relative method from the ratio M of of np j t-- S 4r (М „p- 2.„ „- (kvs-2-" to "in the MPR Mpl - the mass of the determined impurity in the sample and the reference , respectively, q "c is the number of counts in the peaks corresponding to the annihilation and cascade line e for the sample, for the reference" - "and for the reference - Exactly r (L SP о 00

Description

The proposed method relates to methods of nuclear-physical analysis methods and can be used to determine the content of elements transformed under the action of penetrating radiation into positron emitters in metals, alloys, composite materials, products of chemical industry,

as well as agricultural products and other substances.

The aim of the invention is to reduce the uncontrolled error in the analysis of samples with high absorption capacity. .

The invention is explained in the Appendix Vl4 by calculating a simple analysis model, which shows that

315

The proposed method allows to take into account

self-absorption effect, which reduces the analysis error.

A rod of length L irradiated in a stream of penetrating radiation is placed between two gamma-radiation detectors, the detectors being moved close to the ends of the sample and

the areas of the ends and the detectors coincide. The c-detector signals are fed to a coincidence circuit, which controls the recording of the energy spectrum of one of the detectors.

Matches will be recorded only in the event that the quanta move along the axis of the sample, the problem is one-dimensional and can be solved analytically.

The sum of the peak annihilation radiation

np-fn sS e

-the-x-x)

dx, (1)

KM

ETC

and 1 - (M.-HI) L +

+ e

.-Il

..(five)

provided that

The dependence on the sample size is contained in the last two terms of the expression in square brackets, these terms can be neglected when

e i 1

(6)

provided that

To obtain a specific estimate of the limits within which the parameters of the cascade must be chosen (p and f), it is necessary to set the characteristic error of the analysis. As such, a value of 25% is chosen,

In this case, relations (6) can be specified:

0,2,5

If / rKi -f; -.

, s.

(7)

“-De at„ p N

Yes

 braid

- e

where p, hi

Based on the relations (t) and (2)

impurity concentration; “With a given error of 25% of the estimated linear coefficient, to make it more rigid, the EU- absorption of the annihil of the cy- real sample under the on-nq quanta in the matter of L means its maximum size,

it will be understood that the limitations obtained above will be satisfied with a margin.

The proposed method for gamma-gamma coincidence activation analysis using an internal standard is carried out as follows. The test sample (AI) is irradiated with the control

to

al matrix; S is the sample area.

The sum of the peak cascade transition-K, x

35

dx, (2) - linear absorption coefficients of the soft and rigid components of the cascade in the matrix. From (1) and (2) it follows

sample (KO), Determine that the score on the annihilation peak is

AND ABOUT

KO and IO, J, X

km

(MI-MI) L

R

(3)

where М „p is the mass of the element to be determined in the sample.

KMn, D - (PrHi) -Ljx

xCl ..

(four)

(H, Ml is used here)

to

sample (KO), Determine, “n account at the annihilation peak, respectively

square

AND ABOUT

KO and IO, J, X

score at the peak corresponding to the soft cascade line. The mass of the element being determined is found from the ratio

0

M

yo pr

M

to"

etc

V

-Q

-IO-cce

Kh.

v

f- he

(eight)

The choice of a cascade transition, adopted as an internal standard, in accordance with conditions (7) ensures with at least 25% accuracy that the result is independent of the shape and size of the sample.

An example of the method. A sample of tungsten tested for fluorine content, together with a control sample, was irradiated on a neutron 2

the generator

ten

ten

by the flow

F

n / s for. 60 min

T ,,, 1,8 h).

Conditions (7) are made for

The measurements were carried out for Tj, jn "60 min. Time for inspection, mini, for test specimen

The standard was adopted by a cascade of gamma transitions in tungsten with parameters E, 0.134 MeV, E 0.552 MeV (T, 23.9 h). The absorption coefficients for gamma rays are 1 34.7 1 / cm and 2.32 1 / cm. For annihilation lines, p 2.55 1 / cm. The characteristic size of the CO L 0.8 cm. (Analytical isotope - fluorine-18 with a half-life

For IO L 0.5 cm.

KO,

so for IO. Mass KO 33.4 g. Mass IO 110.7 g. Measurement results:

KO BUT Bill in peak

0.511 MeV 627 343 Error 7% 12% Score at the peak

0.134 MeV 1332 457 Error 4% 8%

The control sample contains 0.34 mg of fluorine (8% error). The fluorine content in the EUT is found by the formula (8)

m, 0.34 "||| i ||| 0.543 mg.

ftp

457

Thus, the relative content of fluoride in AI is 4.0–10 wt.% (Error less than 20%),.

Claims (1)

Invention Formula The method of activation analysis based on irradiation five 0 A sample of a flux of penetrating radiation with a subsequent meager measurement of induced activity by registering annihilation quanta in the coincidence mode and comparing the result obtained with the activity of the standard, characterized in that the flux of cascade quanta emitted by a radionuclide is formed from the matrix material, and the corresponding cascade transition in the decay scheme is mentioned PA-th dionukl1scha selected based on the following conditions; L n 25 - where L -, HI maximum sample size} 2 linear absorption coefficients of gamma quanta in the matrix for the ankigilation line, soft and hard components of the cascade transition, respectively, and the mass of the element being determined is found by the ratio off. .aK .G ok us  m t kMC impurity in the sample and reference, respectively; the number of counts at the peaks corresponding to the annihilation and cascade lines for the sample; the same for the standard.