487
Chapter 30
Nuclear Energy and
Elementary Particles
Problem Solutions
30.6
At 40.0% efficiency, the useful energy obtained per fission event is
(
)
(
)
13
11
0.400 200 MeV event
1.60
10
JMeV
1.28
10
Jevent
event
E
−
−
=
×
=
×
The number of fission events required each day is then
(
)
(
)
9
4
24
11
1.00
10 Js
8.64
10 sd
6.75
10
eventsd
1.28
10
Jevent
event
t
N
E
−
×
×
⋅
=
=
=
×
×
P
Each fission event consumes one
235
U
atom. The mass of this number of
235
U
atoms is
(
)
(
)
(
)
24
27
6.75
10
eventsd
235.044u
1.66
10
kg u
2.63 kg d
atom
m
N m
−
=
⎡
⎤
=
×
×
=
⎣
⎦
In contrast, a coalburning steam plant producing the same electrical power uses more
than
6
6
10 kg d
×
of coal.
t 1800 miles)
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488
CHAPTER 30
30.8
The estimated
weight
of the naturally occurring uranium is
(
)
9
12
2000 lbs
1 N
1.0
10
tons
8.9
10
N
1 ton
0.2248 lbs
w
⎛
⎞
⎛
⎞
=
×
=
×
⎜
⎟
⎜
⎟
⎝
⎠
⎝
⎠
and its mass is
12
11
2
8.9
10
N
9.1
10
kg
9.80 m
s
w
m
g
×
=
=
=
×
The total number of uranium nuclei contained in this mass of uranium is
(
)
(
)
11
36
27
9.1
10
kg
2.3 10
average mass of uranium atom
238.03 u
1.66
10
kg u
total
m
N
−
×
=
=
=
×
×
Of this total, 0.720% is the fissionable
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 Spring '07
 Smith
 Physics, Energy, ev, 3. × 1022 event yr 07 s Q 2.

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