Gilson and Voss - Voss Associates

Radioactive Decay
Radioactive Decay
A
t
= Aoe -ët
A
o
= A
t
/ e -ët
t = ln(A
t
/ A
0) / -ë
half-life = -t x 0.693 / ln(A
t/A 0)
Where; A
t
is the activity at the end of time ‘t’
A
o
is the activity at the beginning
ë is 0.693 divided by the half-life
t is the decay time
Given:
32
10 mCi of P with a half-life of 14.3 days
Find: the activity remaining after 125 days
1. Determine the number of half-lives during the decay by
dividing 125 by 14.3 = 8.74
2. Locate 8.74 on the horizontal axis and move up to where
the radioactive decay line crosses 8.74, then horizontally
to the “Fraction of Activity Remaining” vertical axis, this
value is approximately 0.002.
3. Multiply the original activity, 10 mCi, by 0.002; the activity
remaining after 125 days is 0.02 mCi (20 ìCi).
Page 12
A
t
= Aoe -ët
A
o
= A
t
/ e -ët
t = ln(A
t
/ A
0) / -ë
half-life = -t x 0.693 / ln(A
t/A 0)
Where; A
t
is the activity at the end of time ‘t’
A
o
is the activity at the beginning
ë is 0.693 divided by the half-life
t is the decay time
Given:
32
10 mCi of P with a half-life of 14.3 days
Find: the activity remaining after 125 days
1. Determine the number of half-lives during the decay by
dividing 125 by 14.3 = 8.74
2. Locate 8.74 on the horizontal axis and move up to where
the radioactive decay line crosses 8.74, then horizontally
to the “Fraction of Activity Remaining” vertical axis, this
value is approximately 0.002.
3. Multiply the original activity, 10 mCi, by 0.002; the activity
remaining after 125 days is 0.02 mCi (20 ìCi).
Page 12
Radioactive Decay
Radioactive Decay
A
t
= Aoe -ët
A
o
= A
t
/ e -ët
t = ln(A
t
/ A
0) / -ë
half-life = -t x 0.693 / ln(A
t/A 0)
Where; A
t
is the activity at the end of time ‘t’
A
o
is the activity at the beginning
ë is 0.693 divided by the half-life
t is the decay time
Given:
32
10 mCi of P with a half-life of 14.3 days
Find: the activity remaining after 125 days
1. Determine the number of half-lives during the decay by
dividing 125 by 14.3 = 8.74
2. Locate 8.74 on the horizontal axis and move up to where
the radioactive decay line crosses 8.74, then horizontally
to the “Fraction of Activity Remaining” vertical axis, this
value is approximately 0.002
3. Multiply the original activity, 10 mCi, by 0.002; the activity
remaining after 125 days is 0.02 mCi (20 ìCi).
Page 12
A
t
= Aoe -ët
A
o
= A
t
/ e -ët
t = ln(A
t
/ A
0) / -ë
half-life = -t x 0.693 / ln(A
t/A 0)
Where; A
t
is the activity at the end of time ‘t’
A
o
is the activity at the beginning
ë is 0.693 divided by the half-life
t is the decay time
Given:
32
10 mCi of P with a half-life of 14.3 days
Find: the activity remaining after 125 days
1. Determine the number of half-lives during the decay by
dividing 125 by 14.3 = 8.74
2. Locate 8.74 on the horizontal axis and move up to where
the radioactive decay line crosses 8.74, then horizontally
to the “Fraction of Activity Remaining” vertical axis, this
value is approximately 0.002.
3. Multiply the original activity, 10 mCi, by 0.002; the activity
remaining after 125 days is 0.02 mCi (20 ìCi).
Page 12