Biomedical Engineering Reference
In-Depth Information
7
Turner, J. E., “An Introduction to Mi-
crodosimetry,”
Rad. Prot. Management
9(3), 25-58 (1992).
Wide Web by simply searching “radiation dose
calculations”. Valuable links to diverse areas in
the profession of health physics are available.
Computer codes can be obtained and run on
personal computers (e.g., VARSKIN for as-
sessing beta and gamma skin dose from skin
and clothing contamination). A useful site is
www.doseinfo-radar.com.
Section 12.9 showed a sampling of approxi-
mate dose calculations that can be performed
by hand. A number of sophisticated compu-
tational systems can be found on the World
12.12
Problems
1. (a)
What is the average absorbed dose in a 40-cm
3
region of a
body organ (density
=
0.93 g cm
-3
)
that absorbs
3
10
5
MeV of energy from a radiation field?
×
(b)
If the energy is deposited by ionizing particles with an LET
of 10 keV
µ
m
-1
in water, what is the dose equivalent
according to Table 12.1?
(c)
Express the answers to (a) and (b) in both rads and rems as
well as Gy and Sv.
2.
A portion of the body receives 0.15 mGy from radiation with a
quality factor
Q
= 6
and 0.22 mGy from radiation with
Q
= 10
.
(a)
What is the total dose?
(b)
What is the total dose equivalent?
3.
A beam of X rays produces 4 esu of charge per second in 0.08 g
of air. What is the exposure rate in (a) mR s
-1
and (b) SI units?
4.
If all of the ion pairs are collected in the last example, what is
the current?
5.
A free-air ionization chamber operating under saturation
conditions has a sensitive volume of 12 cm
3
. Exposed to a beam
of X rays, it gives a reading of 5
10
-6
mA. The temperature is
18
◦
C and the pressure is 756 torr. What is the exposure rate?
×
6.
A free-air ionization chamber with a sensitive volume of
14 cm
3
is exposed to gamma rays. A reading of 10
-11
Ais
obtained under saturation conditions when the temperature is
20
◦
C and the pressure is 762 torr.
(a)
Calculate the exposure rate.
(b)
How would the exposure rate be affected if the temperature
dropped 2
◦
C?
(c)
Would the current change?
A current of 10
-14
A is produced in a free-air chamber
operating under saturation conditions. The sensitive volume,
in which electronic equilibrium exists, contains 0.022 g of air.
What is the exposure rate?
7.
