Radioactive Aerosols - Aerosols: Measurement, Dosimetry, and Health Effects - page 405

TABLE 15.2
Human Body Spectrometer Measurements

Impulses per 100 s
Single Detection

Mode of Measurement

Dual Detection

Background (open door) 914 1540

Background (closed door) 427 843

Background (closed door) with a person 500 978

Person with a 226 Ra sample
590 Bq. — 1244

175.4 Bq. 557 1088

704 —

0.016 μ Ci.

TABLE 15.3
Relative Errors (%) in Human Body Spectrometer Measurements

Activity of 226 Ra One Detector Two Detectors

t b 10 min 100 s 10 min

t b + p + s 100 s 3 min 5 min 10 min 100 s 5 min 10 min

590 Bq 9.5 7.4 6.4 — 12 — —

175 Bq 46 36 30 24 57 15 12

t b , time of the background measurement; t b + p + s , time of the measurement of the
person + 226 Ra source + background.

The detector was a NaI(Tl) crystal and samples of 226 Ra containing RaCl 2 solution with activity
590 Bq (a) and 175.4 Bq (b) were placed in different positions in the chest of the phantom, and a
80 × 50 mm NaI(Tl) detection crystal and photomultiplier was placed on the back. The activity of
the sample (a) corresponded to approximately 0.75 of annual permissible concentration (APC) and
(b) 0.25 APC in air.
Tables 15.2 and 15.3 show the results of these measurements concerning the assessment of the
detection limit and the statistical errors with one and two detectors (minimal distance from the
sample to the detector was 23 cm). The results of these model experiments suggested that at the level
of concentration of radon progeny in the air of 0.75APC.

15.10.2.5 Phantom Measurements and Geometric Corrections
For calibration purpose in laboratory conditions a phantom of the human torso was used. The mea-
surements were made with a NaI(Tl) crystal with a window diameter of 77 mm, a lead shield and
cylindrical sample of 226 Ra activity of 3.9 × 10 −5 Ci size 160 × 16 mm placed in different positions in
the phantom.
Results of phantom measurements including positions of the sample and detector are shown in
Table 15.4. Measurements were provided by scintillation detector of NaI(Tl) with lead shield (diam-
eter of the window 77 mm).
For the ield measurements a more primitive phantom was used, that is, a long-sized vessel illed
with water size close to the size of lungs, in which the sources of 226 Ra were placed in different
positions.
The systematic errors associated with the contamination of the body and work clothes in real
working conditions, for example, the inluence of radon accumulated in the adipose tissue of the