Radioactive Aerosols of Chernobyl Accident - Aerosols: Measurement, Dosimetry, and Health Effects - page 492

6

Cs-137
Long-lived beta-activity
Pb-212
Pb-214

5

4

3

2

1

0

30.11 5.12 10.12 15.12

Data of sampling

20.12 25.12 30.12

FIGURE 18.12 AMAD of aerosol carriers of 137 Cs, long-lived beta-active nuclides, 212 Pb, and 214 Pb in room
207/5 of the “Shelter” in December 2000.

submicrometer particles with small amounts of even dry particles can be formed. It should be noted
that during welding work, sizes of radiocesium were AMAD = 1.02 μm.
Aerosols of radon and thoron daughters belong to condensation aerosols. They form due to
deposition of atoms of metals (Po, Pb, Bi) that arise during radioactive decay of gaseous mater-
nal substances on very small aerosol particles, called condensation nuclei. These aerosols can be
formed both inside the “Shelter” due to emanation of radon and thoron from building constructions
and from the free atmosphere. The AMAD values of such particles are in the range of 0.08-0.8 μm.
Important data were received on December 9 in room 207/5, when aerosol concentration was
the highest. Three methods were used: beta-radiation radiometry, gamma-spectrometry, and
beta-spectrometry. It was found that all radionuclides ( 90 Sr, 134 Cs, 137 Cs, 241 Am) were disposed on
the same particles with AMAD values near 1.5 μm. The ratio of 137 Cs/ 90 Sr was near 1.15 and was
practically equal to the data presented in Ref. [45] for average nuclear fuel of the fourth block at the
moment of the accident.
During the study of ejection from the “Shelter” from 1996 to 2000, a ive-cascade impactor of the
Institute of Biophysics (Russia) and an Andersen impactor PM-10 were used.
A majority of the measurements were provided for 137 Cs (22 samples) and 241 Am (16 samples). It
was found that the AMAD for aerosols of 137 Cs was 2.9 ± 1.5 μm, and for 241 Am it was 1.4 ± 0.4 μm.
No systematically measured AMAD values of aerosols of 90 Sr and 239 + 240 Pu were in the range
of 3.1-4.5 and 6.0-9.3 μm, respectively. It should be noted that these data are similar to the data
obtained by the MMF. Unfortunately, in Ref. [46] there were no comments on the substantial differ-
ence in the size of Pu and Am, which is a DP of 241 Pu.

18.9.6 r adioactive a erosol d isPersity in tHe “b yPass ”
s ysteM oF tHe “s Helter ” in 2002-2010
Over 300 samples taken on three-layer ilters at the “Bypass” system enabled us to determine the
size distribution of aerosols. It was established that the radioactive products of Chernobyl accident
had been leaving the “Shelter” on particles with AMAD > 1 μm and DPs of radon and thoron—on
submicron particles.