Biomedical Engineering Reference
In-Depth Information
What reactive species exist in pure water at times
>
10
-12
s after
irradiation?
2.
3.
Do all of the reactive species (Problem 2) interact with one
another?
Estimate how far an H
3
O
+
ion will diffuse, on the average, in
water in
5 × 10
-12
s.
4.
5.
Estimate the average time it takes for an OH radical to diffuse
400 Å in water.
6.
If an OH radical in water diffuses an average distance of 3.5 Å
in 10
-11
s, what is its diffusion constant?
Estimate how close an H
3
O
+
ion and a hydrated electron must
be to interact.
7.
8.
How far would a water molecule with thermal energy
(0.025 eV) travel in 10
-12
s in a vacuum?
9.
If a 20-keV electron stops in water and an average of 352
molecules of H
2
O
2
are produced, what is the
G
value for H
2
O
2
for electrons of this energy?
10.
If the
G
value for hydrated electrons produced by 20-keV
electrons is 1.13, how many of them are produced, on the
average, when a 20-keV electron stops in water?
30
eV ip
-1
11.
What is the
G
value for ionization in a gas if
W
=
(Section 10.1)?
12.
Use Table 13.3 to find the average number of OH radicals
produced by a 500-eV electron in water.
13.
For what physical reason is the
G
value for H
2
in Table 13.3
smaller for 20-keV electrons than for 1-keV electrons?
Why do the
G
values for the reactant species H
3
O
+
, OH, H,
and e
aq
decrease between 10
-12
sand10
-6
s? Are they constant
after 10
-6
s? Explain.
14.
15.
For 5-keV electrons, the
G
value for hydrated electrons is 8.4 at
10
-12
s and 0.89 at
2.8
10
-7
s. What fraction of the hydrated
electrons react during this period of time?
×
16.
(a)
Why are the yields for the reactive species in Table 13.4 for
protons greater than those for alpha particles of the same
speed?
(b)
Why are the relative yields of H
2
and H
2
O
2
smaller?
17.
A 50-cm
3
sample of water is given a dose of 50 mGy from
10-keV electrons. If the yield of H
2
O
2
is
G
1.81 per 100 eV,
how many molecules of H
2
O
2
are produced in the sample?
=
18.
Assume that the annual exposure of a person in the United
States to radon daughters is 0.2 WLM. Use the BEIR-IV
estimated lifetime risk of 350 excess cancer deaths per 10
6
person WLM to predict the annual number of such deaths in a
population of 250 million people.
