Biomedical Engineering Reference
In-Depth Information
Fig. 6.9
Cell culture covered with Lucite and lead (Problems 21 and 22).
23.
Estimate the slowing-down time in water for positrons of
energy
(
a
) 100 keV
(
b
)1MeV.
24.
(
a
) Use the information from Problems 6 and 7 to calculate
the slowing-down rate of a 9.5-keV electron in CO
2
at STP.
(
b
) Estimate the stopping time for the electron.
25.
(
a
) Estimate the stopping time of a 9.5-keV electron in soft
tissue.
(
b
) Why is this time considerably shorter than the time in
Problem 24(b)?
26.
(
a
) Calculate the ratio of the slowing-down times of a 1-MeV
proton and a 1-MeV electron in water.
(
b
) Calculate the ratio for a 250-MeV proton and a 0.136-MeV
electron (
β
=
0.614
for both).
(
c
) Discuss physical reasons for the time difference in (a)
and (b).
27.
(
a
) Approximately how many secondary electrons are
produced when a 5-MeV electron stops in water?
(
b
) What is the average number of ions per cm (specific
ionization) along its track?
28.
For a 150-eV electron, the ordinate in Fig. 5.3 has an average
value of about 0.03 in the energy-loss interval between 19 eV
and 28 eV. What fraction of the collisions of 150-eV electrons in
water result in energy losses between 19 eV and 28 eV?
29.
(
) Use Fig. 6.8 to estimate the probability that a normally
incident, 740-keV electron will penetrate a water phantom to a
maximum depth between 1,500
µ
m and 2,000
µ
m.
a
