Radioactive isotopes emit radiation as they decay over time. There are three main types of radiation: alpha, beta, and gamma. Alpha radiation occurs when an atom emits an alpha particle, which is a helium nucleus, changing the emitting atom into a new element. Beta radiation occurs when a neutron converts to a proton, emitting an electron and creating an ion. Gamma radiation is high energy electromagnetic radiation emitted during alpha and beta decay. Radioactive isotopes will continue decaying until they reach a stable form, and their half-life can be used to determine the age of samples by estimating their original quantity.

1. Radioactive Isotopes

2. Radioactive isotopes are isotopes that degrade overtime and
emit radiation in the form of particles.
There are three types of radiation.

5. Alpha decay occurs when an atom’s nucleus is ‘too big’ so a
He+2 (2n+2p) is released. This is an alpha particle.
Due to the loss of protons, a new element is formed. The
atomic mass decreases by 4amu (2 proton + 2 neutron).

6. Alpha radiation is the least dangerous in terms of exposure.
They can be stopped by skin & clothes, but can be dangerous
when inhaled (Radon gas).

7. Beta decay occurs when an electron is emitted (a beta particle)
and when a neutron is converted into a proton. This results in
an ion.
Due to the gain of a proton, a new element is formed
(transmutation). The atomic mass remains the same.

8. Gamma radiation is the energy emitted when an isotope
releases alpha/beta particles. The energy has very small
wavelengths and a large frequency.

11. Review Questions
1. If C-14 undergoes beta decay, what will the daughter
element be?
2. If C-14 undergoes alpha decay, what will the daughter
element be?
3. Write the equations if the following underwent alpha
decay:
Pb-210 Th-235 Pu-240
4. Write the equations if the following underwent beta
decay:
Pt-196 Fe-58 Pd-108

12. Radioactive isotopes will continue to degrade until they
become stable atoms.
Many isotopes degrade at a known rate and so can be used to
deduce the age of samples (rocks, fossils, etc.)

13. An isotope’s half-life is the amount of time it takes for half of
that isotope to degrade.
At every half-life
interval, approximately
50% of the remaining
isotopes will have
degraded into another
element.
By estimating, how
many isotopes there
were in the beginning,
we can ‘age’ objects.

15. Practice Questions
1. If the half-life of an isotope is 24 hours and we started with
4g, how much will be left after 1 day? 2 days?
2. The half-life of Carbon is 5730 ± 40 years. If 10% of the
isotope is left, how old is the organic material?
** How would you set this up to solve it?

16. 100% 500g
50%
25%
12.5%
6.25
3.125
1.56
0.78
Half Life
If the half life is 15
years, roughly how long
will it take to reduce
the original quantity to
~32.0g