Describe the structure of the nucleus of the isotope
shown below.
Ac
This nucleus has 89 protons and 138
neutrons. The nucleus has 227 nucleons in
89 total.
To calculate the number of neutrons, subtract
the atomic
...
Describe the structure of the nucleus of the isotope
shown below.
Ac
This nucleus has 89 protons and 138
neutrons. The nucleus has 227 nucleons in
89 total.
To calculate the number of neutrons, subtract
the atomic number (smaller number) from the
mass number (bigger number).
2. Complete the decay equation, showing an isotope
decaying via alpha decay into an unknown element, X.
You are expected to know the properties (mass and atomic
number) of an alpha particle/helium nucleus. Once you’ve
filled those in, work backwards to balance the equation.
3. Complete the decay equation, showing an isotope
decaying via beta decay into an unknown element, X.
1
An easy mistake to make on beta decays is to see the -1 and
subtract it from the 15 on the left. Always check that the top
and bottom lines balance after you’ve put your answer in
Determine the half-life of a radioactive source which decreases from an activity of 160 Bq
to 20 Bq in 48 years.
160 (x 1/2 =) 80 (x 1/2 =) 40 (x 1/2 =) 20
Count the half-lives
3 half-lives = 48 years
1 half-life = 48/3 = 16 years
A flow chart method, like in the first line, can be used to figure out any half-life question.
5. Determine the fraction of a radioactive source which has decayed after 24 hours, if the
source has a half-life of 12 hours.
Number of half-lives = 24/12 = 2 half lives
100 % --12 hours--> 50% --12 hours--> 25%
25% remaining so fraction which has decayed = 100% - 25% = 75%
This sort of question may give you an initial mass (e.g. 200g) and ask you to work out how
much is remaining after a certain amount of time. Use the exact same method, but with
masses instead of percentages.
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