Environmental Engineering Reference
In-Depth Information
The spectrometric installation comprises three detection units (DUs), a pulse ampliier, one inte-
gral and one differential discriminators, a switching unit with three inputs, two count rate meters, a
conversion device, a stable-amplitude generator, and a power pack.
The samples' activity measurements by means of the alpha-spectrometric method are carried
out with two DUs; the irst one includes a semiconductor detector with a working area of 2 cm
2
whereas the second one is a scintillation detector consisting of a 63 * 0.35 mm CsI(Tl) crystal and
a spectrometric photoelectron ampliier type FEU-82. The irst DU is suitable for measuring under
atmospheric pressure, an atmospheric rareied down to ∼0.7 Pa, and at different distances between
the detector and ilter. The alpha particles' registration eficiency can attain 0.7 for a resolution of
∼150 keV with respect to
238
Pu.
The second DU comprises a collimator with a 2 mm aperture diameter and height, thus making it
possible to record only the alpha particles which leave the ilter almost perpendicularly to the detec-
tor. Its registration eficiency is substantially lower than that of the irst DU and amounts to 0.10 for
a resolution of ∼250 keV with respect to RaC'. Both DUs are suitable for measuring either by means
of the alpha-spectrometric or counting method. The discriminator levels are set in the irst DU by
means of spectrometric alpha source (RSAS) with
226
Ra radionuclides.
The activity of the samples with respect to beta radiation is measured with DU based on a halo-
gen counter type SBT-11. The registration eficiency of the radionuclide
90
Sr +
90
Y beta particles
amounts to 0.22.
The instrument for measuring the VA of the vapors
131
I is simultaneously a beta and gamma
radiator and consists of two DUs, a conversion device, and a power pack. One of the DUs, made on
the basis of a 40 * 40 mm NaI(Tl) monocrystal and a type FEU-82 photomultiplier, is intended for
recording gamma count; the second DU, based on a halogen counter type SBT-11, is intended for
recording beta particles. The recording eficiency of gamma-quants amounts to 0.25, and of beta
particles to 0.18. Measurements are made by means of the counting method.
For computing the VA from the number of recorded pulses N the following formulae are used:
For counting method
N
=
ευηθ
q
For the alpha-spectrometric method of Radon decay products
N
a
( , )
θ
ευη
t
C
1
q
=
a
[
]
C
2
N
( ,
θ
t
)
−
C N
( ,
θ
t
)
−
C N
( ,
θ
t
)
c
2
3
c
2
4
a
2
q
=
b
ευη
[
]
C N
( ,
θ
t
)
−
C N
( ,
θ
t
)
+
C N
( ,
θ
t
)
5
c
1
6
c
2
7
a
1
q
=
c
ευη
where θ is the pumping through the ilter. The GERA-5 installation is intended for generating and
investigating the disperse composition of aerosols virtually in the entire range of their particle
dimensions that is, for reproducing the “aerosol-particle dimension scale” (Kravchenko and Ruzer,
1978) which includes the highly dispersed aerosols with particle sizes smaller than 0.1 μm, the
medium-dispersed aerosols with particle sizes of ∼0.1-1, and coarsely dispersed aerosols with par-
ticle sizes exceeding 1 μm.
Search WWH ::
Custom Search