activity 7 since it cant be opened
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chem_activity_7_rev.docxName: __________________________
ChemActivity #7
Radioactivity
Model 1: Types of Radioactivity
1. Alpha Decay – loss of a helium nucleus
2. Beta Decay – loss of a nuclear electron
3. Gamma Decay – emission of pure, high-energy electromagnetic radiation
4. Positron Emission – loss of a nuclear positron
Critical Thinking Questions:
1. In -decay, what changes in the mass number are observed? What changes in the atomic number are observed?
2. In -decay, what changes in the mass number are observed? What changes in the atomic number are observed?
3. In -decay, what changes in the mass number are observed? What changes in the atomic number are observed?
4. In positron emission, what changes in the mass number are observed? What changes in the atomic number are observed?
5. Make a checklist for solving radioactive decay equations:
Exercises:
1. Write a reaction for the -decay of:
2. Write a reaction for the -decay of:
3. Write a reaction for the -decay of:
4. Write a reaction for the positron emission of:
5. Complete the following reactions and name the type of radioactivity emitted:
Model 2: Half-Life
Half-life (t1/2) is the time for 50% (1/2) of the radiation to
decay.
1 t1/2 2 t1/2 3 t1/2 4 t1/2 5 t1/2
Amount Remaining
100% ----> 50% ---> 25% ---> 12.5% ---> 6.25% ----> 3.125%
Radioactive decay is a first-order process since it is only dependent on the amount of radioactive element present.
Rate = k[Radioisotope]
A = A0e-kt
k = 0.693/t1/2 or t1/2 = 0.693/k
Exercises:
1. If 30mCi of 99mTc is prepared at 4AM, how much is left at 1:30PM?
Steps in the Solution: a) Look up t1/2 of 99mTc.
b) What is the time interval, t?
c) How many half-lives passed?
d) Count down the half-lives from starting 30mCi:
e) Estimate the answer:
f) Use the first-order rate decay equation to more accurately calculate the
amount of radioactivity remaining:
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