# Isotope Half Lives

Updated 2009-03-12 00:09

## Half-Lives of Commonly Used Radioisotopes

IsotopeHalf-Life
3H12.26 years
14C5730 years
22Na2.62 years
32P14.28 days
35S87.9 days
42K12.36 hours
45Ca163 days
59Fe45.6 days
125I60.2 days
203Hg46.9 days

Reference: p.385 of of Lubert Stryer's "Biochemistry" 3rd Edition, 1988, W. H. Freeman, New York (ISBN=0-7167-1843-X).

IsotopeHalf-LifeArea of Body Studied
131I8.1 daysThyroid
59Fe45.1 daysRed Blood Cells
99Mo67 hoursMetabolism
32P14.3 daysEyes, Liver, Tumors
51Cr27.8 daysRed Blood Cells
87Sr2.8 hoursBones
99Tc6.0 hoursHeart, Bones, Liver, Lungs
133Xe5.3 daysLungs
24Na14.8 hoursCirculatory System

Reference: Ch.21 of "Chemistry" by Stephen S. Zumdahl, 1986, D. C. Heath and Company (ISBN=0-669-04529-2).

## Half-Life Problems

In the following, the equation M(t)=M0 2-t/t1/2 holds.
M0 is the initial mass of a radioactive sample,
M(t) is the mass of the sample a time t later, and
t1/2 is the half-life for radioactive decay of the sample.

____ of M0 remains at time t if the half-life is t1/2M0 2-t/t1/2
M of ____ remains at time t if the half-life is t1/2M 2t/t1/2
M of M0 remains at time ____ if the half-life is t1/2t1/2 ln(M0/M)/ln(2)
M of M0 remains at time t if the half-life is ____t ln(2)/ln(M0/M)
____ of 800g remains at 6 hours if the half-life is 2 hours100g
____ of 400g remains at 4 hours if the half-life is 4 hours200g
20g of ____ remains at 5 hours if the half-life is 2.5 hours80g
10g of ____ remains at 5 hours if the half-life is 1 hour320g
125g of 500g remains at ____ if the half-life is 2 hours4 hours
10g of 640g remains at ____ if the half-life is 0.25 hour1.5 hours
100g of 800g remains at 9 hours if the half-life is ____3 hours
2g of 32g remains at 8 hours if the half-life is ____2 hours

## General Nuclear Reactions

The information in all of the following sections comes from

Ch.21 of "Chemistry" by Stephen S. Zumdahl, 1986,
D. C. Heath and Company (ISBN=0-669-04529-2).

X in AZX is the ____symbol for a particular element
Z in AZX is the ____atomic number
Z in AZX is the ____number of protons in a nucleus
A in AZX is the ____mass number
A in AZX is the ____sum of protons and neutrons in a nucleus
A-Z in AZX is the ____number of neutrons in a nucleus
Each of 126C, 136C, and 146C is an ____ of Cisotope
0-1e is a ____beta particle or β particle
0-1e is an ____electron
01e is a ____positron
42He is an ____alpha particle or α particle
42He is a ____helium nucleus
00γ is a ____gamma ray or γ ray
10n is a ____neutron
11H is a ____proton
1-1H is an ____anti-proton
126Ccarbon-12
136Ccarbon-13
146Ccarbon-14
23892Uuranium-238
Unstable nuclides with A-Z >> Z have too many neutrons and decay via spontaneous ____ productionbeta particle or β particle
Unstable nuclides with A-Z << Z have too many protons and decay via spontaneous ____ productionpositron

## Stability of Nuclei

All nuclides with 84 or more protons are ____ with respect to radioactive decayunstable
Light nuclides are ___ when Z equals A-Z, that is, when the neutron/proton ratio is 1stable
For heavy nuclides to be ____, the neutron/proton ratio must be larger than 1, and this ratio rises with Zstable
A nuclide with an odd number of protons tends to be more ____ than one with an even number of protonsunstable
A nuclide with an odd number of neutrons tends to be more ____ than one with an even number of neutronsunstable
Nuclides with a magic number (2, 8, 20, 28, 50, 82, or 126) of protons or neutrons are especially ____stable

## Miscellaneous Nuclear Reactions

For this chart and the ones that follow, in each reaction, make sure that all the superscripts on the left side of the arrow give the same total as all the superscripts on the right side. Also make sure that all the subscripts on the left side of the arrow give the same total as all the subscripts on the right side.

Reactions marked with (*) below are exceptions to the above rules
because they convert energy into matter via E=mc2.

13153I -> 13154Xe + ____0-1e
2211Na -> 2210Ne + ____01e
0-1e + ____ -> 00γ01e
20180Hg + ____ -> 20179Au + 00γ0-1e
22789Ac -> 22790Th + ____0-1e
7333As + ____ -> 7332Ge0-1e
Excited State Nucleus ->
Ground State Nucleus + ____
00γ
116C -> 115B + ____01e
23793Np -> 23391Pa + ____42He
19579Au + ____ -> 19578Pt0-1e
3819K -> 3818Ar + ____01e
147N + ____ -> 178O + 11H42He
2713Al + ____ -> 3015P + 10n42He
10n -> 11H + ____0-1e
11H + 10n + lots of energy(*) ->
2 11H + 1-1H + ____
10n
4019K -> 4020Ca + ____0-1e
0-1e + ____ -> 2 00γ01e
21H + 31H -> 10n + ____42He

## Carbon-Dating

146C -> 147N + ____0-1e
147N + ____ -> 146C + 11H10n

## Nuclear Fission

10n + 23592U -> 14256Ba + 9136Kr + 3 ____10n
10n + 23592U -> 13752Te + 9740Zn + 2 ____10n

## Breeder Reactors

23892U + ____ -> 23992U10n
23992U -> 23993Np + ____0-1e
23993Np -> 23994Pu + ____0-1e

## Fusion in the Sun

11H + 11H -> 21H + ____01e
11H + 21H -> ____32He
32He + 32He -> 2 11H + ____42He
32He + 11H -> 42He + ____01e

## Carbon-Nitrogen Cycle in the Sun

126C + ____ -> 137N + 00γ11H
137N -> 136C + ____01e
11H + ____ -> 147N + 00γ136C
11H + ____ -> 158O + 00γ147N
158O -> 01e + ____157N
11H + 157N -> 42He + 00γ + ____126C
4 11H -> 2 01e + ____42He

## Syntheses of Transuranium Elements

23892U + ____ -> 23992U10n
23992U -> 23993Np + ____0-1e
23993Np -> 23994Pu + ____0-1e
23994Pu + 2 ____ -> 24194Pu10n
24194Pu -> 24195Am + ____0-1e
23994Pu + ____ -> 24296Cm + 10n42He
24296Cm + ____ -> 24598Cf + 10n42He
23892U + ____ -> 24698Cf + 4 10n126C
24998Cf + ____ -> 257104Rf + 4 10n126C
24998Cf + ____ -> 260105Ha + 4 10n157N
24998Cf + ____ -> 263106Unh + 4 10n188O

## 23892U Decay Series

23892U -> 23490Th + ____42He
23892U -> 23490Th + ____ + 2 00γ42He
23490Th -> 23491Pa + ____0-1e
23491Pa -> 23492U + ____ 0-1e
23492U -> 23090Th + ____ 42He
23090Th -> 22688Ra + ____ 42He
22688Ra -> 22286Rn + ____ 42He
22286Rn -> 21884Po + ____ 42He
21884Po -> 21482Pb + ____ 42He
21482Pb -> 21483Bi + ____ 0-1e
21483Bi -> 21484Po + ____ 0-1e
21484Po -> 21082Pb + ____ 42He
21082Pb -> 21083Bi + ____ 0-1e
21083Bi -> 21084Po + ____ 42He
21084Po -> 20682Pb + ____ 42He

Reference: Ch.21 of "Chemistry" by Stephen S. Zumdahl, 1986, D. C. Heath and Company (ISBN=0-669-04529-2).