Answer Key
Chapter 19: Standard Review Worksheet
1. The net effect of beta production is to change a neutron to a proton. The net effect of
positron production is to change a proton to a neutron. Examples will vary, and some are
given in Section 19.1 of the text.
2. The Z is the atomic number (number of protons). A given element always has the same
atomic number. For example, carbon always has an atomic number of 6, regardless of the
isotope of carbon we are considering.
3.
A
Z X
4
A- 4
He +
2
Z-2 Y
A
Z X
0
A
e
+
-1
Z + 1Y
A
Z X
0
1e +
A
Z X
4.
0
+ -1 e
A
Z- 1 Y
A
Z-1 Y
a.
53
V
23
0
53
e
- 1 + 24 Cr
b.
244Cm
96
5.
a.
4
2
He
b.
4
2
He
4
240
He +
Pu
2
94
6.
a. Kr-81 (it has the longest half-life)
b. Kr-73 (it has the shortest half-life)
c. Kr-73:
24 h _
60 min
_ 60 s =
1h
1 min
86,400
=
27 s
86,400 s
3200 half-lives
Essentially no Kr-73 is left after 24 hours.
Kr-74:
24 h _ 60 min = 1440 min
1h
1440 mi
= 125
11.5 min
half-lives
Essentially no Kr-74 is left after 24 hours.
Kr-76:
24 h
= 1.7 half-lives, almost 2 half-lives
14.48 h
About _ (or 31 mg) Kr-76 is left after 24 hours.
Kr-81:
24 h _ 1 day _ 1 year = 2.7 _ 10–3 years
24 h
3
2.7 10 yr
2.1 105yr
365 day
= 1.3 _ 10-8 half lives
Essentially all 125 mg of the Kr-81 remains.
7. For a chain reaction to occur, sufficient neutrons must be produced and captured by other
nuclides to sustain a reaction. The critical mass is the amount of material needed to provide
these conditions.
8. In a breeder reactor, fissionable fuel material is produced as the reactor runs
(nonfissionable U-238 is changed to fissionable Pu-239).