The task of any engineer
was to find a simple way to collaborate without the use of expensive spectrometric
equipment. Measurements of radon and thoron flux density with ground surfaces.
This method should work for a long time and reliably
at monitoring stations in difficult climatic conditions without the presence
of an operator. In our system, we use a measurement method with
the location of a measuring device (detector) operating in counting mode
inside the storage chamber.
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A simple solution to the problem
was made after
analysis of the growth curve of the pulse counting velocity from
alpha radiation generated by the decay of radon isotopes and their decay
products accumulated inside the storage chamber (Figure).
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You can see that the growth curve
alpha particle output from thoron and its products decay has a specific shape
and is determined by the physical properties of radionuclides, and
namely, the ratio of their half-lives. At a time equal to 6...7 minutes after
the start accumulation curve (alpha Tn) reaches saturation
(equilibrium state) and then practically no Changes. Increase in the yield
of alpha particles from radon and of its decay products (alpha Rn) has almost
linear shape.
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Analysis of these calculations (Figure)
showed that The separation of radon and thoron during their joint measurement
is possible by the shape of the growth curve of the velocity of counting
pulses from alpha radiation inside storage chamber. As a result, a simple
method was developed for joint measurement of the density of radon and thoron
fluxes from the soil surface, based on the registration of alpha radiation
of radon, thoron and their decay products accumulated inside the storage
chamber.
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Measuring the Pulse Count Rate in
a given method is produced by an alpha detector installed inside the storage
chamber, which works in counting mode. Separation of equipment signals from
radon and thoron is carried out according to the shape of the of the growth
curve of the pulse counting velocity by one of the of the following two options:
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1. Pulse counting speed is measured
within 40...60 minutes from the beginning of accumulation. Next, the accumulation
curve is processed are produced using appropriate algorithms that allow you
to extract a linear a section whose inclination angle is proportional to
the radon flux density qRn and the height of the pedestal on which the linear
section is raised, which corresponds to the equilibrium value The rate of
counting the pulses from thoron and its decay products is proportional to
the density of the thoron flux qTn from the ground surface.
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2. Make only two measurements of
counting speed
pulses, the first is at a moment in time
t1=6 min, after the start of accumulation, and the second in
time t2 from 40 to 60 min and then qRn and
qTn, Bk·m–2·s–1, are determined from the expressions.
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The choice of the first time of measurement
t1 is due to the fact that at the 6th minute (Fig.) the total counting speed
corresponds to the equilibrium (area
saturation) the value of the counting speed from the toron and
its alpha emitting decay products.
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The recommended minimum time of the
second measurement t2 is 40 minutes, which is determined by the volume of
statistics, since with less than
It is difficult to reliably determine the measurement time
Radon signal from the total signal. Limitation on the maximum time of the
second measurement
T2, equal to 60 min, is associated with the possibility of a violation of
the stationarity condition, i.e., a change in the flux of radon from the
Earth's surface, which will lead to a
increased uncertainty of the measurement result.
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Limitation on the distance of the
sensitive detector surface from the ground surface, equal to 10 cm, allows
you to get rid of the "background" that may be due to the registration of
alpha particles formed during the decay of radionuclides, contained in the
soil.
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Proposed Method for Density Measurement
radon and thoron flow from the soil surface along the alpha radiation is
simple and inexpensive, because it does not require the use of complex
spectrometric equipment, technical techniques and means for separating signals
from thor and radon. The method is reliable because:
1) it is not required to separate signals from radon, thoron and their decay
products by various technical means, the use of which leads to an increase
in the total error;
2) the statistics are increased due to the fact that the total speed of counting
pulses from radon, thoron and alpha emitting products of their decay, which
is about 4 to 5 times higher, than separately from radon or thoron.
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