Radioactive Isotopes

Radioactive isotopes are isotopes that degrade overtime and emit radiation in the form of particles.

There are three types of radiation.

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).

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).

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.

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

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-2404. Write the equations if the following

underwent betadecay:

Pt-196 Fe-58 Pd-108

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.)

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.

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?

100% 500g50%25%12.5%6.253.1251.560.78

Half Life

If the half life is 15 years, roughly how long

will it take to reduce the original quantity to

~32.0g