Biomedical Engineering Reference
In-Depth Information
In reviewing the available CT systems, it is important to compare them not only in tech-
nical terms but against what one considers to be an ideal scanner. The ultimate objective of
computerized tomography is to provide accurate diagnostic information that significantly
improves patient care. In the ideal case, a CT scanner would provide an unambiguous diag-
nosis, thereby eliminating the necessity for further tests. Since financial considerations are
also important and CT scanners require a high capital outlay and have considerable main-
tenance costs, the ideal system should process a large patient load quickly, providing high
“patient throughput.” A good scanner, therefore, must satisfy two major criteria: it must
provide good diagnostic information and it must permit high patient throughput.
15.5 EXERCISES
1.
Represent the decay process discussed in Example Problem 14.2 in symbolic form.
2.
Compute the energy liberated when
238
238.050786) decays to
234
92
U (amu
¼
90
Th (amu
¼
emission.
3.
Carbon 14,
1
6
C is a radioactive isotope of carbon that has a half-life of 5,730 years. If an initial
sample contained 1,000
14
C nuclei, how many would still be around after 22,920 years?
4.
A 50-g sample of carbon is taken from the pelvis bone of a skeleton and is found to have a
14
C
decay rate of 200 decays/min
232.038054) via
a
It is known that carbon from a living organism has a decay rate
of 15 decays/min X g and that
14
C has a half-life of 5,730 years
.
10
9
min. Find the age
¼
3.01
of the skeleton.
5.
The half-life of a radioactive sample is 30 min. If you start with a sample containing 3
10
16
nuclei, how many of these nuclei remain after 10 min?
6.
Find the energy liberated in the beta decay of
1
6
Cto
1
7
N.
7.
How long will it take for a sample of polonium of half-life 140 days to decay to one-tenth its
original strength?
8.
Suppose that you start with 10
3
g of a pure radioactive substance and 2 h later determine
that only 0.25
10
3
g of the substance remains. What is the half-life of this substance?
9.
The half-life of an isotope of phosphorus is 14 days. If a sample contains 3
10
16
such nuclei,
determine its activity.
10.
How many radioactive atoms are present in a sample that has an activity of 0.2
m
Ci and a
half-life of 8.1 days?
11.
A freshly prepared sample of a certain radioactive isotope has an activity of 10 mCi. After 4 h,
the activity is 8 mCi.
(a)
Find the decay constant and half-life of the isotope.
(b)
How many atoms of the isotope were contained in the freshly prepared sample?
(c)
What is the sample's activity 30 h after it is prepared?
12.
Tritium has a half-life of 12.33 years. What percentage of the nuclei in a tritium sample will
decay in 5 years?
13.
For the following process
2
10
Ne
13
!
23
11
Ne
12
þ
e
þ
v
, what is the maximum kinetic energy of the
emitted electrons?
14.
The half-life of
235
U is 7.04
10
8
years. A sample of rock that solidified with the earth 4.55
10
9
years ago contains N atoms of
235
U. How many
235
U atoms did the same rock have when it
solidified?
Continued
