Anyone who has seen movies or watched TV has heard of radiation. However hollywood and reality seldom are one and the same. Lets take a closer look at what radiation really is.
Nuclear Radiation is emitted by certain isotopes as a means of releasing energy as they seek to reach a stable (non-radioactive) state. An isotope is each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei. This makes the element differ in relative atomic mass for each form, but not in chemical properties. So any isotope of an element will look, taste and smell alike, but some isotopes will emit radiation.
Some isotopes like Radioactive iodine (I131) emits two types of radiation as it decays toward stable state. Once this happens, it is no longer radioactive.
Beta particles are emitted as part of this decay. The easiest way to think of a beta particle is as a small projectile like a BB from a BB gun. One BB fired at low speed has little impact and won’t penetrate deeply. However, firing many BBs at low speed will cause damage, to a person, even if they don’t penetrate deeply.
The second radioactive component of I131 decay is a gamma photon. This is best thought of like an Xray. It is energy without any real mass. Because it has almost no mass, it is able to penetrate tissue much deeper. This is why you are instructed to keep a distance from other people, as the gamma radiation is exiting your body and can be “seen” by a device such as a geiger counter. Limited exposure to this gamma radiation is not considered harmful to others, since the amount of damage that it does is very limited. However, prolonged exposure by others is not recommended, since the effect is cumulative.
Every time you double the distance from the source of the radiation (the patient), the amount of exposure is reduced to 25%. While these numbers are completely arbitrary, for the sake of example, let’s say that a person is 5 feet from a treated patient and is getting 100 (units) of radiation from them. If that person moves to 10 feet away, they will now be receiving only 25 (units) of radiation. This is commonly known as the “inverse square law”.