KEY
Practice Problems: Nuclear Chemistry
CHEM 1A
1. Write the equation for the nuclear reaction described in each of the following processes:
a. Americium-241 (241Am) undergoes alpha decay (inside a smoke detector)
Am 
Np +
He
b. Iodine-131 (131I) undergoes normal beta decay (used in therapy for hyperthyroidism)
I 
Xe +
–
e
c. Fluorine-18 (18F) undergoes positron emission (one of the radionuclides used in PET scans)
F 
O +
e
d. Technetium-99m (99mTc) undergoes gamma decay to form 99Tc (a diagnostic radioactive tracer
used to locate tumors, the “m” indicates a metastable excited nuclear state)
Tc 
Tc +

e. Chromium-51 (51Cr) undergoes electron capture (a diagnostic radioactive tracer used to study
blood)
Cr +
–
e 
V
2. Sulfur-35 (35S) is a naturally occurring radioactive isotope of sulfur that is produced in the upper
atmosphere. What type of radioactive decay would you expect for this isotope, and why?
Normal beta decay ( –). Based on the average atomic mass of sulfur from the periodic table,
the most abundant isotope of sulfur is 32S. 35S has three additional neutrons, and nuclides with
too many neutrons (above the belt of stability) undergo beta decay.
3. What type of radioactive decay would you expect for 238U, and why?
Alpha decay (). Uranium has 92 protons, therefore the nucleus is too large (>83 protons).
Large nuclei undergo a series of decays in which alpha decay allows the nucleus to become
smaller. Decay series also typically include some beta decays (to adjust the neutron/proton ratio),
and gamma decays (to relax from excited nuclear states that occur).
4. Match the type of emitted radiation to the minimum amount of shielding required to stop it:
A. alpha particle
C several lead bricks
____
B. beta particle
A paper
____
C. gamma ray
B thin piece of lead
____