Biomedical Engineering Reference
In-Depth Information
contained. For example, an infinitely long, water-reflected cylinder of aqueous so-
lution with a concentration of 75 g
235
U per liter is subcritical as long as its diameter
is less than 6.3 in. Without water reflection the limiting diameter is 8.7 in. When
using such “always safe” geometry, attention must be given to the possibility that
two or more subcritical units could become critical in close proximity.
9.12
Suggested Reading
1
Attix, F. H.,
Introduction to Radiolog-
ical Physics and Radiation Dosimetry
,
Wiley, New York, NY (1986). [Chapter
16 covers neutron interactions and
dosimetry.]
2
Bromley, D. A., “Neutrons in Science
and Technology,”
Physics Today
3
Cember, H.,
Introduction to Health
Physics
, 3rd ed., McGraw-Hill, New
York, NY (1996). [Neutron interac-
tions are described. Chapter 12 is on
criticality.]
4
Turner, J. E., Kher, R. K., Arora, D.,
Bisht, J. S., Neelavathi, V. N., and
Vora, R. B., “Quantum Mechanical
Calculation of Neutron Stopping
Power,”
Phys. Rev. B
(12),
30-39 (Dec. 1983). [This article de-
scribes various uses of the neutron as
a tool for basic physics research; for
industrial applications, such as min-
ing and food preservation; and for art
history.]
36
8
, 4057-4062
(1973).
9.13
Problems
Calculate the neutron energy from a
24
NaD
2
O source
(Table 9.3).
1.
2.
(a)
What is the maximum energy that a 4-MeV neutron can
transfer to a
10
B nucleus in an elastic collision?
(b)
Estimate the average energy transferred per collision.
3.
(a)
Estimate the average energy that a 2-MeV neutron transfers
to a deuteron in a single collision.
(b)
What is the maximum possible energy transfer?
4.
Make a rough estimate of the number of collisions that a
neutron of 2-MeV initial energy makes with deuterium in order
for its energy to be reduced to 1 eV.
5.
Repeat Problem 4 for a 4-MeV neutron in carbon.
6.
(a)
If a neutron starts with an energy of 1 MeV in a graphite
moderator, what is the minimum number of collisions it
must make with carbon nuclei in order to become
thermalized?
(b)
What is the minimum number of collisions if the
moderator is hydrogen?
