1355
Chapter 40
Nuclear Physics
Conceptual Problems
1
•
Determine the Concept
Two or more nuclides with the same atomic number Z but
different
N
and
A
numbers are called isotopes.
(
a
) Two other isotopes of
14
N are:
15
N,
16
N
(
b
) Two other isotopes of
56
Fe are:
54
Fe,
55
Fe
(
c
) Two other isotopes of
118
Sn are:
54
Fe,
55
Fe
2
•
Determine the Concept
The parent of that series,
237
Np, has a half-life of 2
×
10
6
y that is
much shorter than the age of the earth. There is no naturally occurring Np remaining on
earth.
3
•
Determine the Concept
Generally,
β
-decay leaves the daughter nucleus neutron rich,
i.e., above the line of stability. The daughter nucleus therefore tends to decay via
β
–
emission which converts a nuclear neutron to a proton.
*4
•
Determine the Concept
14
C is found on earth because it is constantly being formed by
cosmic rays in the upper atmosphere in the reaction
14
N + n
→
14
C +
1
H.
5
•
Determine the Concept
It would make the dating unreliable because the current
concentration of
14
C is not equal to that at some earlier time.
6
•
Determine the Concept
An element with such a high
Z
value would either fission
spontaneously or decay almost immediately by
α
emission
(see Figure 40-3).
7
•
Determine the Concept
The probability for neutron capture by the fissionable nucleus is
large only for slow (thermal) neutrons. The neutrons emitted in the fission process are fast
(high energy) neutrons and must be slowed to thermal neutrons before they are likely to be
captured by another fissionable nucleus.

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