READ: Types of Radiation

READ: Types of Radiation

Many nuclei are radioactive (unstable nucleus that can change by emitting particles). When aradioactive nucleus gives off radiation, the nucleus frequently changes the number of protons in the nucleus and changes the element in the process. In ordinary chemical reactions, atoms of one element never change into different elements. That is because in all other types of changes we have talked about only the electrons were changing. In these changes, the nucleus, which contains the protons which dictate which element an atom is, is changing. All nuclei with 84 or more protons are radioactive and elements with less than 84 protons have both stable and unstable isotopes. All of these elements can go through nuclear changes and turn into different elements.

Elements that have an unstable ratio of protons to neutrons in the nucleus of atoms tend to break down and release energy in the form of radiation. Oxygen isotopes all have 8 protons, but Oxygen 16 has 8 neutrons and Oxygen-17 has 9 neutrons. Oxygen-17 will be unstable, and release radiation. Carbon-12 and Carbon-14 are isotopes. Carbon-14 has more neutrons than Carbon-12 so is unstable.

In natural radioactive decay, three common emissions occur. When these emissions were originally observed, scientists were unable to identify them as some already known particle and so named them alpha particles (α), beta particles (β), and gamma rays (γ) using the first three letters of the Greek alphabet. Some later time, alpha particles were identified as helium-4 nuclei, beta particles were identified as electrons, and gamma rays as a form of electromagnetic radiation like x-rays except much higher in energy and even more dangerous to living systems. Both alpha and beta decay change the number of protons in an atom’s nucleus, thereby changing the atom to a different element. In alpha decay, the nucleus loses two protons. In beta decay, the nucleus gains a proton as a neutron becomes a proton. In gamma decay, no change in proton number occurs, so the atom does not become a different element.

Comparing only the three common types of ionizing radiation, alpha particles have the greatest mass. Alpha particles have approximately four times the mass of a proton or neutron and approximately 8,000 times the mass of a beta particle. Because of the large mass of the alpha particle, it has the highest ionizing power and the greatest ability to damage tissue. That same large size of alpha particles, however, makes them less able to penetrate matter. They collide with molecules very quickly when striking matter, add two electrons and become a harmless helium atom. Alpha particles have the least penetration power and can be stopped by a thick sheet of paper or even a layer of clothes. They are also stopped by the outer layer of dead skin on people. This may seem to remove the threat from alpha particles but only from external sources. The emitters can be inhaled or taken in with food or water and once the alpha emitter is inside you, you have no protection at all.

Beta particles are much smaller than alpha particles and therefore, have much less ionizing power (less ability to damage tissue), but their small size gives them much greater penetration power. Beta particles can be stopped by a one-quarter inch thick sheet of aluminum. Once again, however, the greatest danger occurs when the beta emitting source gets inside of you.

Gamma rays are not particles but a high energy form of electromagnetic radiation (like x-rays except more powerful). Gamma rays are energy that have no mass or charge. Gamma rays have tremendous penetration power and require several inches of dense material (like lead) to shield them. Gamma rays may pass all the way through a human body without striking anything. They are considered to have the least ionizing power and the greatest penetration power.

Summary

• Radioactive decay is the process in which unstable nuclei of radioactive atoms become stable by emitting charged particles and energy.
• There are three types of radioactive decay: alpha decay, beta decay, and gamma decay. Alpha and beta decay change one element into another. Gamma decay does not.
• Radioactive decay can damage living things. Alpha decay is the least damaging, and gamma decay is the most damaging.
• The most common emissions of radioactive elements were called alpha, beta, and gamma radiation.

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