What is radiation?
Radiation is a form of energy. In this situation, we are discussing ionizing radiation that may
cause damage to living tissue and is used in medicine and industry.
Radiation is either electromagnetic waves or particles. A prime example of electromagnetic radiation is X-ray and
Gamma radiation. For the particles, Alpha and Beta radiation are the most frequently encountered types. In some
cases, neutrons can also be particle radiation. Because of the nature of the radiation, different techniques are used
to stop the different types of radiations. Lead is good for x-rays and gamma rays, but thick paper stops alpha
particles. Beta radiation is most often stopped using a plastic, like Lucite or Plexiglas. Neutrons are stopped mostly
by using materials with lots of hydrogen, like water or concrete.
Natural background radiation and radioactivity occur naturally in our environment. For example, the radioactive
materials, radium and radon gas occur naturally in our soil, air, and water. All animals and plants contain small
amounts of naturally occurring radioactive materials. We are also exposed to cosmic radiation from the sun, space,
as well as radiation emitted from radioactive material in the bricks and concrete used in building our homes.
Other sources of radiation exposure are x-ray and nuclear medicine studies, certain consumer products like some
smoke detectors used in our homes to improve our safety. A mrem is a term used to quantify doses and the potential
effect of radiation has on the body.
Typical Radiation Doses
Source Dose Source Dose
Natural Radiation Medical
5-hr jet airplane ride 3 mrem Chest X-ray 8 mrem
Cosmic radiation 30 mrem CT scan 1000 mrem
Internal (own body) 40 mrem/year Dental x-ray 1 mrem
Consumer Products Occupational
Building materials 4 mrem/year Nuclear Power 450 mrem/year
Tobacco products 5,300 Scientist 25 mrem/year
mrem/year X-ray Technicians 120 mrem/year
(Amount a smoker’s lungs receive from 20 cigarettes per
The average American receives about 1 mrem per day from natural background and medical radiation. Some areas
of the country are more or less than that, based on radon concentrations, soil make up and elevation.
Average U.S. Background and Medical Radiation Total: 360 mrem/year
Internal 40 mrem
Soil 35 mrem
Are there limits for radiation exposure?
A person who works with radiation as part of their job can legally receive 5,000 mrem/year. A facility cannot expose
the general public to more than 100 mrem/year. On a tour of our facility, you will not receive any radiation exposure
Workers protect themselves from radiation using three main methods: Time, Distance and Shielding.
Whenever possible, we will reduce time we are exposed to a radiation field, increase our distance from source and
use shielding between the source and us. Shielding is dependent on the radiation itself, as shown below.
Radiation: Radiation cannot be seen, felt or heard. It Roentgen Equivalent Man (REM): The REM relates
comes in waveform, like light and in particulate form the RAD to the biological impact caused by different
(very small particles), like electrons. types of radiation. It is a term used to quantify does
and the potential effect a does of radiation has on the
Radioactive Material: Any material that contains body. In most cases the rem is that same value as
radioactive atoms. For example, when you get a the rad. A millirem (mrem) is 1/1,000th of a rem.
nuclear medicine scan, you are injected with
radioactive material. Curie (Ci): The curie is a unit to measure radioactivity
much as we would measure water in gallons, quarts,
Radiation Absorbed Dose (RAD): The RAD is a unit or ounces. The amount of radioactive material given
used to measure the amount of energy absorbed in to a patient is usually in millicuries (mCi). A mCi is
any material such as concrete, steel, bone, lead, and 1/1000th of a curie.
For more information on radiation, see the Radiation Information Network at
Examples of Applications of Radiation
Diagnostic X-rays (dental X-rays, CAT scans, mammograms, etc).
Therapeutic (Co-60, accelerators for cancer treatments).
Diagnostic nuclear medicine (liver function tests).
Therapeutic nuclear medicine (1-131 for thyroid cancer treatment).
Nuclear thermoelectric-powered heart pacemakers.
X-ray diffraction (study of molecular structure - e.g. DNA structure).
Isotopic tracers (e.g. C-14 to study photosynthesis).
Isotopic labeling (e.g. P-32 DNA electrophoresis)
Accelerators (nuclear structure, materials analysis).
Cathode ray tubes (TVs)
Luggage screening systems. (X-ray).
Sterilization (of medical materials & supplies).
Insect eradication (release of insects sterilized by irradiation).
Process control (density/Thickness gauges).
“Curing” of plastics.
Moisture content for soil
Industrial radiography (verification of welds & structures).
Ion implantation (semiconductor industry).
Electron beam applications (e.g. vacuum deposition)
Strategic defense (X-ray lasers, particle beams, etc.)
Nuclear Fission Reactors for electricity (~20% of US electricity).
Nuclear Fission Reactors on Navy ships and submarines.
Nuclear Fusion (future use).
Isotopic electric power sources (satellites, spacecraft).
Visiting labs that use radioactive materials or radioisotopes.
Important things to keep your eye out for:
1) How do people protect themselves from the radiation?
2) Why are they using the radioisotopes?
3) How is the radioisotopes controlled?
4) How are the labs that use radioisotopes posted (labeled)?
5) How are the radioisotopes labeled?
6) What other uses of radiation do you see?
How a Geiger counter (Geiger Mueller detector) works
Incident Ionizing Radiation
Anode + Voltage Source
The most common type of instrument is a gas filled radiation detector. This instrument works on the principle that
as radiation passes through air or a specific gas, ionization of the molecules in the air occur. Ionization means that
the radiation gives up some energy to the surrounding atoms, causing those atoms to loose their electrons. This
results in ionized atoms (positive charged) and free electrons (negative charge). When a high voltage is placed
between two areas of the gas filled space, the positive ions will be attracted to the negative side of the detector (the
cathode) and the free electrons will travel to the positive side (the anode). In a GM tube as shown above, the
voltage difference is high, so that the ions gain energy as they move towards the anode and cathode, causing more
ionization. The whole tube will ionize, causing a large amount of charge at one time. The charge is collected by
the anode and cathode as a pulse of current in the wires going to the detector. By placing a very sensitive
measuring device along that wire, the pulse measured and displayed as a count. The more radiation which enters
the chamber, the more count are seen by the instrument.