Introduction to Radiation: Definition of Terms

©Health Physics Society

Introduction to Radiation

• Objectives • To provide useful information about

radiation for interested individuals• To introduce basic concepts of radiation

and radioactivity• To improve understanding of radiation –

what it is and how it interacts

What Is Radiation?

• Radiation is energy in the form of waves or moving subatomic particles.

• A radionuclide is a radioactive element, man-made or from natural sources, with a specific atomic weight.

What Is Radioactivity?

• Radioactivity is the property of some atomic nuclei of spontaneously emitting gamma rays or subatomic particles (e.g., alpha and beta particles).

• Radioactive material is material that, by being present in a radiation environment, has become radioactive or is contaminated with radioactive materials (see radioactivity).

What Is Contamination?

• Contamination is the presence of radioactive material anywhere it is not wanted – most commonly by adhering, or sticking to surfaces.

• Decontamination is a process of removing the presence of radioactive materials from surfaces through cleaning and washing.

What Is Exposure?

• Exposure is the act of (1) being exposed to a radiation source or (2) being irradiated.

• Exposure rate is the amount of exposure or dose you are receiving per unit time (e.g., 1 mrem per hour).

• To irradiate is the act of exposing someone or something to radiation. Irradiated food means food that was exposed to radiation.

Contamination versus Exposure

• External Exposure –• Whole-body or partial-

body (no radiation hazard to emergency staff)

Contamination –• External radioactive

material: on the skin

• Internal radioactive material: inhaled, swallowed, absorbed through skin or wounds

ExternalExposure

InternalContamination

ExternalContamination

Chocolate Chip Cookies

• We can detect radioactivity…

• Are the cookies emitting radiation?

• Are the cookies radioactive?

• Are the cookies contaminated?

• Are the cookies being irradiated?

Chocolate Chip Cookies

• No, the cookies are not emitting radiation.

• No, the cookies are not radioactive.

• No, the cookies are not contaminated.

• Yes, the cookies are being irradiated – why?

Fiesta Ware

• The plate is glazed with uranium.

• The uranium has the chemical form U3O8.

• This form is called “yellowcake” because it is bright yellow in color.

• Firing the plate in a kiln turns the color to orange.

Contamination versus Exposure

• So, the cookies are exposed to the radiation emitted from the plate.

• The radioactivity in the plate does not come off so the cookie is not contaminated.

• Since the cookie is not contaminated, it is not radioactive.

What Is Half-Life?

• Radiological or physical half-life is the amount of time it takes for half of the radioactivity in a material to be gone or to decay. The half-life of a radionuclide can be fractions of a second or up to millions of years.

What Is Half-Life?

• Biological half-life refers to elimination of internal radioactivity by biological processes.

• Effective half-life is a combination of radioactive decay and biological elimination.

What Is Half-Life?

• As an example, the half-life of iodine-131 is eight days. Starting with 10 radioactivity units, after eight days there are five radioactivity units left. After eight more days (16 total), there are 2½ radioactivity units left, or a fourth of what we started with.

What Is Ionization?

• Ionization is the process by which a neutral atom (an atom with no charge) gains a positive or negative charge.

• The most common use of the word radiation refers to ionizing radiation. Ionizing radiation has enough energy to ionize atoms or molecules while nonionizing radiation does not.

Why Are Elements Radioactive?

• Unstable Nucleus• Has excess internal energy• Wants to return to ground

state (become stable)• Becomes stable by getting

rid of the energy• Gives off the energy as

ionizing radiation

Pictures are compliments of John W. Poston, Sr., PhD, and Paul Frame, PhD.