Balancing nuclear equations is done by keeping the "sum of the nucleon numbers" and the "sum of the atomic numbers" the same on each side of the yield sign. Thus one may predict one of the reactants or products if all other substances are given.

The radiation types may be summarized as follows:

Radiation Type	Symbol
Alpha	42He
Beta	0-1e
Gamma	00g *
Positron	0+1e
Neutron	01n

* g = greek symbol gamma

Examples:
²³⁸₉₂U ---> ______ + ²³⁴₉₀Th

For the missing product:
the nucleon number = 4. (238-234)
the atomic number = 2. (92-90)
thus the radiation type is ⁴₂He.

¹⁴₆C ---> ______ + ⁰_-1e

For the missing product:
the nucleon number = 14. (14-0)
the atomic number = 7. (6-(-1))
thus the daughter isotope is ¹⁴₇N.

_______ ---> ¹⁵₇N + ⁰₊₁e

For the missing reactant:
the nucleon number = 15. (15+0)
the atomic number = 8. (7+1)
thus the parent isotope is ¹⁵₈O.

¹²¹₅₁Sb + ¹₁H ---> ______ + ¹₀n

For the missing product:
the nucleon numbers = 121. (121 + 1 - 1)
the atomic number = 52. (51 + 1 -0)
thus the isotope is ¹²¹₅₂Te

In half life tables:
time increases by half life, and grams, as well as counts per minute (CPM), drop in half for each successive half life. Time always starts at "0".

In a typical example:
If a radiosotope has a half life of 15 days and one currently has 200 grams of the isotope, and it has a counting rate of 1000 CPM (counts per minute), calculate how many grams of the radioisotope is left, and its counting rate, after 75 days.

Time	0	15	30	45	60	75
Grams	200	100	50	25	12.5	6.25
CPM	1000	500	250	125	62.5	31.25