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
Natural Radiation
5-hr jet airplane ride
Cosmic radiation
Internal (own body)
3 mrem
30 mrem
40 mrem/year
Consumer Products
Building materials
Tobacco products
4 mrem/year
5,300 mrem/year
(Amount a smoker’s lungs receive from 20 cigarettes per
day)
Source
Dose
Medical
Chest X-ray
CT scan
Dental x-ray
8 mrem
1000 mrem
1 mrem
Occupational
Nuclear Power
Scientist
X-ray Technicians
450 mrem/year
25 mrem/year
120 mrem/year
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
Radon 200
mrem
Medical
55 mrem
Internal 40
mrem
Soil 35
mrem
Cosmic 30
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
above background.
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.
Glossary
Radiation: Radiation cannot be seen, felt or heard. It
comes in waveform, like light and in particulate form
(very small particles), like electrons.
Radioactive Material: Any material that contains
radioactive atoms. For example, when you get a
nuclear medicine scan, you are injected with
radioactive material.
Radiation Absorbed Dose (RAD): The RAD is a unit
used to measure the amount of energy absorbed in
any material such as concrete, steel, bone, lead, and
tissue.
Roentgen Equivalent Man (REM): The REM relates
the RAD to the biological impact caused by different
types of radiation. It is a term used to quantify does
and the potential effect a does of radiation has on the
body. In most cases the rem is that same value as
the rad. A millirem (mrem) is 1/1,000th of a rem.
Curie (Ci): The curie is a unit to measure radioactivity
much as we would measure water in gallons, quarts,
or ounces. The amount of radioactive material given
to a patient is usually in millicuries (mCi). A mCi is
1/1000th of a curie.
For more information on radiation, see the Radiation Information Network at
http://www.physics.isu.edu/radinf/index.html
Examples of Applications of Radiation
Medical:
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.
Blood irradiation
Research:
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).
Electron microscopes.
Consumer Products:
Cathode ray tubes (TVs)
Smoke detectors.
Emergency lighting.
Static eliminators.
Luggage screening systems. (X-ray).
Industrial:
Sterilization (of medical materials & supplies).
Insect eradication (release of insects sterilized by irradiation).
Food preservation.
Process control (density/Thickness gauges).
“Curing” of plastics.
Asphalt density
Moisture content for soil
Industrial radiography (verification of welds & structures).
Ion implantation (semiconductor industry).
Electron beam applications (e.g. vacuum deposition)
National Defense:
Nuclear weapons.
Strategic defense (X-ray lasers, particle beams, etc.)
Power:
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)
2)
3)
4)
5)
6)
How do people protect themselves from the radiation?
Why are they using the radioisotopes?
How is the radioisotopes controlled?
How are the labs that use radioisotopes posted (labeled)?
How are the radioisotopes labeled?
What other uses of radiation do you see?
How a Geiger counter (Geiger Mueller detector) works
GM Instrument
Incident Ionizing Radiation
Ne +Halogen
Cathode -
Gas
+
+
+
-
+
-
Anode +
-
Electrical
Current
Measuring
Device
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.