4.1 Radioactivity and types of radiation

In certain types of radioactive nuclei that have too many neutrons, a neutron may be converted into a proton, an electron and another particle called a neutrino. The high energy electrons that are released in this way are the $\beta$ - particles. This process can occur for an isolated neutron.

In $\beta$ + decay, energy is used to convert a proton into a neutron(n), a positron (e+) and a neutrino ( $\nu$ e):

So, unlike $\beta$ -, $\beta$ + decay cannot occur in isolation, because it requires energy, the mass of the neutron being greater than the mass of the proton. $\beta$ + decay can only happen inside nuclei when the value of the binding energy of the mother nucleus is less than that of the daughter nucleus. The difference between these energies goes into the reaction ofconverting a proton into a neutron, a positron and a neutrino and into the kinetic energy of these particles.

The diagram below shows what happens during $\mathrm{\beta -}$ decay:

During beta decay, the number of neutrons in the atom decreases by one, and the number of protons increases by one. Since the number of protons before and after the decay is different, the atom has changed into a different element. In [link] , Hydrogen has become Helium. The beta decay of the Hydrogen-3 atom can be represented as follows:

${}_1^3\mathrm{H}{\to }_2^3\mathrm{He}+\beta \mathrm{particle}+\overline{\nu }$

Gamma ( $\gamma$ ) rays and gamma decay

When particles inside the nucleus collide during radioactive decay, energy is released. This energy can leave the nucleus in the form of waves of electromagnetic energy called gamma rays. Gamma radiation is part of the electromagnetic spectrum, just like visible light. However, unlike visible light, humans cannot see gamma rays because they are at a much higher frequency and a higher energy. Gamma radiation has no mass or charge. This type of radiation is able to penetrate most common substances, including metals. Only substance with high atomic masses (like lead) and high densities (like concrete or granite) are effective at absorbing gamma rays.

Gamma decay occurs if the nucleus is at a very high energy state. Since gamma rays are part of the electromagnetic spectrum, they can be thought of as waves or particles. Therefore in gamma decay, we can think of a ray or a particle (called a photon) being released. The atomic number and atomic mass remain unchanged.

[link] summarises and compares the three types of radioactive decay that have been discussed.

Discussion : radiation

In groups of 3-4, discuss the following questions:

• Which of the three types of radiation is most dangerous to living creatures (including humans!)
• What can happen to people if they are exposed to high levels of radiation?
• What can be done to protect yourself from radiation (Hint: Think of what the radiologist does when you go for an X-ray)?

Radiation and radioactive elements

1. There are two main forces inside an atomic nucleus:
   1. Name these two forces.
   2. Explain why atoms that contain a greater number of nucleons are more likely to be radioactive.
2. The isotope ${}_{95}^{241}$ Am undergoes radioactive decay and loses three alpha particles.
   1. Write the chemical formula of the element that is produced as a result of the decay.
   2. How many nucleons does this element contain?
3. Complete the following equation: ${}_{82}^{210}Pb\to$ (alpha decay)
4. Radium-228 decays by emitting a beta particle. Write an equation for this decay process.
5. Describe how gamma decay differs from alpha and beta decay.