The Three Types of Radiation

There are three types of radiation: alpha (α), beta (β) and gamma (γ) radiation, which all have different properties due to their structure. Radiation is emitted from radioactive isotopes (isotopes are different versions of the same element with the same number of protons but a different number of neutrons, so they have the same atomic number but a different atomic mass). These properties make each type of radiation useful for specific purposes.

Alpha Radiation:

Alpha radiation consists of alpha particles that have been released from radioactive isotopes as they decay. Each alpha particle is made up of two protons and two neutrons, giving the particle an overall relative mass of four and a relative charge of 2+. This is the same as the nuclei of helium atoms.

Alpha radiation is the most ionising out of the three types. This means that it will react easily in order to gain a neutral charge as alpha particles have a strong positive charge. Additionally, it travels the least distance in air because it’s highly ionising.  Alpha particles are the least penetrative as well compared to beta and gamma radiation due to its large mass, making them harder to go through materials. In fact, alpha radiation can be stopped by paper because it’s not very penetrative. It is also the slowest out of all the radiation types due to its mass; it has a speed of about 1/10 of the speed of light.

One of the main uses of alpha radiation is in smoke detectors. The radioactive isotope (usually amercium-241) is positioned in front of a radiation sensor which is a few centimetres away from the radioactive source. The alarm remains silent as long as the alpha particles hit the sensor. If smoke enters the detector, the alpha particles ionise the smoke particles and no longer hit the sensor, triggering the alarm. Alpha radiation is more useful here because it will detect the presence of smoke quicker as it is the most ionising compared to beta and gamma radiation.

Beta Radiation:

When a neutron in a radioactive isotope’s nucleus breaks down into a proton and electron, that electron is emitted from the nucleus. That electron is a beta particle. As beta particles are essentially electrons, they have a relative mass of 1/2000 and a relative charge of 1-.

Beta radiation is less ionising than alpha radiation as it has a weaker charge compared to alpha radiation. This also means that it travels a longer distance in air because beta particles don’t ionise as easily. Beta particles are more penetrating than alpha particles as they have a much lower mass; they can be stopped by thick aluminium. Beta radiation is also much faster than alpha radiation as it has a speed of approximately 9/10 of the speed of light.

One of the main uses of beta radiation is to measure the thickness of thin materials such as paper. The beta particles pass through the material and reach a detector which is connected to a computer that controls the rollers. A signal is sent to the rollers to move apart if too much radiation is detected, meaning that the material is too thin and needs to be thicker and, to move closer together if far less radioactive particles are detected, meaning that the material is too thick and needs to be thinner. Beta radiation is more useful here because it can be used to detect slight changes in the thickness of the material easily. Alpha radiation is the least penetrative and so would be blocked by the material and gamma radiation is too penetrative and so can’t be used to detect minor changes.

Gamma Radiation:

Unlike Beta and alpha radiation, gamma radiation is an electromagnetic wave. Therefore, gamma radiation has no charge or mass.

Gamma radiation is the least ionising out of the three types of radiation because it has no charge. Gamma radiation is also the fastest as it travels at the speed of light, which is 3 x10⁸ m/s approximately. Gamma radiation also travels the furthest in air because it doesn’t ionise easily; in fact, it knocks into atoms due to its fast speed. Gamma radiation is the most penetrative due to the fact that it has no mass and so can easily go through materials; it can only be stopped by thick lead which is why isotopes that emit gamma radiation are stored in lead-lined boxes.

Gamma radiation is useful for medical tracers to detect any internal damage to the body of a patient. The patient receives the radioactive source in the form of an injection or orally. The isotope is given time to work its way around the patient’s body to allow the area that has been affected to show up on a scan of the patient.  Gamma radiation is used because it’s the least ionising, meaning that it wouldn’t ionise and affect body cells preventing problems for the patient such as cell mutation and organ damage. Gamma radiation is also highly penetrative so it can also leave the patient’s body safely too.