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Phys320 – Spring 2004 (Baski)
Quiz #6:
Nuclear Physics
April 21, 2004
Name: ___SOLUTIONS
_____
Complete both of the following problems.
Show all of your work for full credit.
Problem 1:
Radioactivity
The counting rate from a radioactive source is initially 4 million decays per second, and it decreases to
500,000 s
–1
after 6 seconds. Find the
τ
and halflife of this source in seconds. Also, find the counting rate after
20 seconds has elapsed.
Solving for
τ
in the decay equation R = R
o
e
– t/
τ
gives:
( 29
( 29
1/2
6
5
6
11
6s
2.885
s
an
d
ln
2
(2.885)(0.693
)
2.0s
4
10
ln
ln
5
10
ex
p
(
4
1
0
)ex
p
20
s
2.885
s
3,90
3s
o
o
t
t
tt
R
R
R
R
ts
t

=
=
=
=
==
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 Spring '04
 Baski
 Physics, Work

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