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Physics for Scientists and Engineers, 6e
Chapter 44 - Nuclear Structure
Consider the following three nuclei: 12C, 13N, 14O.
These nuclei have the same
1
1.
number of protons
2.
number of neutrons
3.
number of nucleons
2
3
4
5
33%
1
33%
2
33%
3
The value of N = A – Z is the same for all
three nuclei.
Consider the following three nuclei: 12N, 13N, 14N.
These nuclei have the same
1
1.
number of protons
2.
number of neutrons
3.
number of nucleons
2
3
4
5
33%
1
33%
2
33%
3
The value of Z is the same for all three nuclei
because they are all nuclei of nitrogen.
Consider the following three nuclei: 14C, 14N, 14O.
These nuclei have the same
1
1.
number of protons
2.
number of neutrons
3.
number of nucleons
2
3
4
5
33%
1
33%
2
33%
3
The value of A is the same for all three
nuclei, as seen by the unchanging presuperscript.
On your birthday, you measure the activity of a
sample of 210Bi, which has a half-life of 5.01 days.
The activity you measure is 1.000 μCi. What is the
activity of this sample on your next birthday?
1
1.
1.000 μCi
2.
0
3.
~ 0.2 μCi
4.
~ 0.01 μCi
5.
~ 10–22 μCi
2
3
20% 20% 20% 20% 20%
4
5
1
2
3
4
5
A year of 365 days is equivalent to 365 d/5.01 d ≈
73 half-lives. Thus, the activity will be reduced after
one year to approximately (1/2)73 (1.000 μCi) ~ 10–
22 μCi.
Suppose you have a pure radioactive material with
a half-life of T1/2. You begin with N0 undecayed
nuclei of the material at t = 0. At 1/2t = T1/2, how
many of the nuclei have decayed?
1
1.
1/4N0
2.
1/2N0
3.
3/4N0
4.
0.707N0
5.
0.293N0
2
3
4
20% 20% 20% 20% 20%
5
1
2
3
4
5
The time we are interested in is half of a half-life.
Thus, the number of remaining nuclei is
(1/2)1/2N0 = N0 / √2 = 0.707N0. The number of
nuclei that have decayed is N0 – 0.707N0 =
0.293N0.
Which of the following is the correct daughter
nucleus associated with the alpha decay of
?
1.
2.
33%
33%
33%
3.
1
2
3
4
5
1
2
3
In alpha decay, the atomic number decreases
by two and the atomic mass number
decreases by four.
Which of the following is the correct daughter
nucleus associated with the beta decay of
?
1.
2.
33%
33%
33%
3.
1
2
3
4
5
1
2
3
In e– decay, the atomic number increases by
one and the atomic mass number stays fixed.
None of the choices is consistent with e+
decay, so we assume that the decay must be
by e–.
Which of the following do you expect not to vary
substantially mong different isotopes of an element?
1
1.
atomic mass number
2.
nuclear spin magnetic
moment
3.
chemical properties
2
3
4
5
33%
1
33%
2
33%
3
Isotopes of a given element correspond to
nuclei with different numbers of neutrons.
This results in different atomic mass numbers
of the nucleus—and different magnetic
moments, because the neutron, despite being
uncharged, has a magnetic moment. The
chemical behavior, however, is governed by
the electrons. All isotopes of a given element
have the same number of electrons and,
therefore, the same chemical behavior.