SU1741092A1 - Method of determining volumetric activity of aerosols of alpha-emitting radionuclides - Google Patents

Abstract

The invention relates to methods for determining the volumetric activity of aerosols of alpha-emitting radionuclides in the air. The method includes measuring the energy spectra obtained from a reference source, sequentially closed by layers of dust-equivalent material. After removing the spectra, the parameters of the log-normal distribution f (E,) (geometric mean fi and standard geometric deviation a), as close as possible to this spectrum in the energy range of the detected particles, are calculated, and the values of the sensitivity of the apparatus p and the lower measurement threshold (EMIN) are calculated. Then, in the measuring equipment, the lower threshold of measurement is established, a sample of a certain volume is sampled on the filter, the energy spectrum of the alpha radiation of the aspirated filter is taken. The parameters of a log-normal distribution, as close as possible to the real spectrum, are calculated, and the volumetric activity of aerosols (q) is calculated, table 2. (Ls

Description

The invention relates to nuclear physics, in particular, to methods of radiation monitoring of air when contaminated with radioactive aerosols.

The purpose of the invention is to improve the measurement accuracy.

The proposed method is based on the analysis and formalization of the spectrum of the alpha radiation of an aspirated filter. It was established experimentally that the distribution of alpha particles recorded by a proportional detector (energy spectrum) with high probability (99.9%) follows a logarithmically normal law (when the spectrum is radially reflected about the Y axis and shifted to O ), and the integral of the log-normal distribution over the entire energy range (from 0 to co) is proportional to the activity of the aspirated filter.

The method includes measuring, using a pulse analyzer, the energy spectra obtained from a reference source, which is sequentially closed by layers (from 0 to n) of the dust-equivalent material. After the removal of the spectra, the parameters of the log-normal distribution (geometric mean / and standard geometrical deviation of st), as close as possible to this spec- trum, are calculated.

H)

N3

rub in the energy range of the detected particles, calculate the sensitivity of the apparatus p and the lower threshold of measurement Emin by the formulas

oo

Jf1 (E.rr $ dE

(D

 P / (J,

(2)

oo

where / f1 (E, a, / T) dE is the area under the logo's curve

normal distribution with parameters as close as possible to the real spectrum;

And - passport value of the activity of the reference source;

T is the spectrum acquisition time.

Then, in the measuring equipment, the lower threshold of measurement is established, which ensures the specified accuracy of measurement: the activity of the reference source. The sample of the investigated air of a certain volume is sampled to the filter. The energy spectrum of the alpha radiation of the aspirated filter is taken. Calculate the lognormal distribution parameters as close as possible to the real spectrum.

The volumetric activity of aerosols q is calculated according to the expression

oo

q /f(E.O/3)dEAVp

(3)

covered with layers of polyethylene terephthalate film with a thickness of 3 10.5 microns.

The parameters of the calculated distributions are presented in columns 3 and 4 of table 1. °°

The results of the calculation of / f1 (E, 7, /) dE with

the volume of the lognormal distribution parameters obtained are presented in columns 5

and 6 tabl, 1. The sensitivity at registration of radioactive aerosols is 0.18 and remains constant up to a thickness of 1.4 mg / cm. This value is used to determine the volumetric activity by

formula (3).

The EMSHG threshold, calculated by the formula (2), corresponds to 14.5 channels, which is equal to 1 MeV. This value is constant for any thickness of the absorber.

After establishing the values of Emin and

f selected plutonium aerosols - 239 with a volume of 7 m3 and volumetric activity

about

840 Bq.m in the detection unit on the filter tape with different dust

samples.

Table 2 (columns 3 and 4) shows the volumetric activities of plutonium aerosols calculated by the proposed method and method without taking into account the absorber.

The errors of both methods, given in columns 5 and 6, were calculated by the formula

  & $$

100.

(four)

where V is the volume of the selected sample;

p is the sensitivity determined in accordance with formula (1) when setting the lower measurement threshold at a level determined by expression (2),

Example. The proposed method was determined by the volumetric activity of plutonium -239 model aerosols obtained using a special generator. A measuring unit BDAS-OZP, built on the basis of a DKD-P-2.5p semiconductor detector and an LFS-2 filtering tape, was used as measuring equipment; AI-1024 pulse analyzer connected by a V 24 bus to a Robotron 1715 PC.

Using a pulse analyzer, energy spectra were taken from an exemplary source of discharge with Ri-238 nuclide from the OSAI set, sequentially

As can be seen from the tables, the accuracy of the proposed method is higher than that of the known method.

Claims (1)

Invention Formula A method for determining the volumetric activity of aerosols of alpha-emitting radionuclides, including sampling a specific volume on a filter, measuring the activity of a filter, and calculating the volumetric activity of aerosols, which in order to increase the accuracy of measurements, measure the alpha radiation For each measurement, the parameters of lognormal distributions, f (/ 9, o), as close as possible to the measured spectra, where / J is the geometric mean and a is the standard quadratic deviation, and the sensitivity of the pk apparatus with radioactive aerosols, then set the lower measurement threshold equal to, measure the spectrum of the filter’s alpha radiation, calculate the parameters of the log-normal distribution as close as possible to this spectrum and calculate aerosol activity q according to the expression with q / f (E, ovS) dE / TVp, where T is the spectrum acquisition time; V is the sample volume; E - enzrgip alpha particles. Spreadsheets table 2