Environmental Engineering Reference
In-Depth Information
considerable the potentialities of installations for measuring the aerosols, disperse composition
and electrical parameters.
The improved special state standard for the volumetric activity (VA) unit of radioactive aero-
sols incorporates generators type GERA-1 of artiicial aerosols; generators GERA-2 of natural
radioactive aerosols; generators GERA-3 of vapors
131
I; spectrometric equipment type GERA-4 for
measuring activity of alpha-, beta, and gamma-radiating aerosol samples; installation GERA-5 for
generating and measuring the disperse composition and counted concentration of inactive aerosols;
installation GERA-6 for generating and measuring the parameters of aeroions and electroaerosols.
The generators type GERA-1 are based on the method of bubbling pure air through a radioac-
tive solution of the appropriate radionuclide salt (
90
Sr +
90
Y) and
239
P producing beta radiation;
239
Pu
and
210
Po producing alpha radiation. The aerosols are formed in the following manner: under the
effect of surface tension the ilms of bubbles which are formed on the surface of the solution are
disintegrated into drops. These drops are subsequently dried at temperatures of 140°C-150°C
and converted into solid crystals. The artiicial radioactive aerosols with a solid disperse phase
thus obtained are diluted with pure air. The VA of artiicial radioactive aerosols can be varied by
changing the activity of the solution which is poured into the generation unit as well as the rate of
bubbling and pure air dilution. The generators have a high reproducibility of radioactive aerosol
VA in the range of (7 × 10
−2
-10
−3
) s
−1
m
−3
and a mean-square deviation (MSD) for measurement
results not exceeding 5 × 10
−2
.
The GERA-2 set comprises generators of the radon, thoron, and actinon daughter products. The
radon daughter generator is based on the method of accumulation these products in an enclosed
volume and it suitable for reproducing their VA in the range of (2 × 10
2
-4 × 10
5
) s
−1
m
−3
with a mea-
surement-results MSD not exceeding 5 × 10
−2
. Investigations of the generator's radon atmosphere
carried out by means of the GERA-6 installation have shown that the fraction of the RaA charged
aerosols amounts to 89% ± 8% for a radon daughter products VA of 259 Bq L
−1
and a median aerosol
particle radius of R
m
= 0.11 μm ± 15%.
The thoron and actinon daughter product generators are also based on the method of cumulat-
ing emanation daughter products in an enclosed volume. Since their half-lives are insuficient time
for penetrating from the bubblier to the atmosphere of the container, the bubblier is replaced by
solid unsealed sources with thin layers of a substance based on
227
Ac and
228
Th and possessing an
adequate emanation capacity. The basic raw material for obtaining the
227
Ac and
228
Th preparations
consisted of
226
Ra irradiated with neutrons which form from it the required preparations as a result
of the following reaction:
236
237
227
228
228
Ra
+
n
r
−
Ra
−
β
Ac nr
+
−
Ac
−
β
Th
The
227
Ac and
228
Th sources were prepared at the V.G. Khlopin Radium Institute and placed in 1 m
3
containers type 2BP2-OS.
The thoron and actinon daughter product generator's reproducibility expressed in MSD term
does not exceed 35%. This value is due to the small generator volume, but for practical cases it is
completely satisfactory.
The natural radioactive-aerosols' VA can be varied by means of diluting ilters. Aerosol samples
are obtained with spectrometric ilters types AFA-RSP-3 and AFA-RSP-10.
The Gera-3 generator of vaporous
131
I is based on the method of distilling by oxidizing KI potas-
sium dichromate solution. It possesses a high VA reproducibility in the range of (7 × 10
−4
-10
56
) s
−1
m
−3
with a measurement-result MSD not exceeding 5 × 10
−2
.
The Gera-4 spectrometric equipment for measuring the activity of aerosol samples includes a
spectrometric installation for measuring the activity of the disperse phase deposited on the ilter
and of artiicial and natural alpha-, and beta-radiating aerosols, and an instrument for measuring the
131
I activity in the sample by means of betas and gamma radiation.
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