Biomedical Engineering Reference
In-Depth Information
They are fixed indefinitely in the polymer, and can be counted visually or with an
automatic reader. Dosimeter properties can be adjusted to meet different objectives
by varying the polymer and the detecting liquid. After reading, the bubbles can be
made to disappear by recompression through a screw-cap assembly on the unit,
thus restoring it to the unexposed state.
The bubble detector is a sensitive, passive neutron dosimeter. Although com-
monly manufactured to have about one bubble per mrem of fast-neutron dose
equivalent (Section 12.2), it has been produced with up to three orders of magni-
tude higher sensitivity. Its threshold neutron energy of about 100 keV is lower than
that of nuclear-track film. The tissue-equivalent dose response is flat from approx-
imately 200 keV to more than 15 MeV. It is isotropic and completely insensitive to
gamma radiation. A compound containing
6
Li and dispersed in the polymer can be
used to monitor thermal neutrons. Sets of bubble detectors, fabricated with differ-
ent neutron-energy thresholds, have been employed to obtain spectral information
for dosimetry.
10.8
Suggested Reading
The best sources of information in the diverse
and rapidly expanding field of radiation de-
tection and instrumentation are on the World
Wide Web. Detailed data can be found on
virtually any current or historic topic. The
following publications are suggested as sup-
plements to this chapter.
1
Frame, Paul W., “A History of Radi-
ation Detection Instrumentation,”
Health Phys.
88
, 613-637 (2005). [This
important publication appears in the
issue commemorating the 50th an-
niversary of the Health Physics So-
ciety. It provides a comprehensive,
in-depth review of the history of ra-
diation detection from early days
through modern technology. Exten-
sive bibliography. The numerous
photographs in the article are of in-
struments in Oak Ridge Associated
Universities' Historical Instrumenta-
tion Collection, which is managed
by Dr. Frame. The collection can
be accessed on-line at http://www.
orau.org/ptp/museumdirectory.htm.]
2
ICRU Report 31,
Average Energy Re-
quired to Produce an Ion Pair
,Inter-
national Commission on Radiation
Units and Measurements, Washing-
ton, DC (1979).
3
Knoll, Glenn F.,
Radiation Detection
and Measurement
,3rdEd.,Wiley,New
York (2000). [This authoritative text-
book covers many of the subjects of
this chapter in detail.]
4
Poston, John W., Sr., “External
Dosimetry and Personnel Monitor-
ing,”
Health Phys.
88
, 557-564 (2005).
[This review is another in the issue
commemorating the 50th anniver-
sary of the Health Physics Society.
Radiation detection is discussed with
emphasis on personnel dosimetry. Ac-
companying historical information is
included. Bibliography.]
10.9
Problems
1.
How many electrons are collected per second in an ionization
chamber when the current is
5
10
-14
A? What is the rate of
×
29.9
eV ip
-1
?
energy absorption if
W
=
