Physical Agent Data Sheet (PADS)
Ionizing Radiation is the name given to a band of energy on the electromagnetic spectrum. X-rays and radioactive substances are examples of ionizing radiation.
In order to understand the difference between ionizing and nonionizing radiation it is necessary to review the structure of an atom.
All matter is made up of molecules which are chains of atoms hooked together in various combinations and shapes. An atom is the smallest unit of an element (like helium, oxygen or carbon) that still has all the properties of that element. Atoms are so small they cannot be seen with even the most powerful microscope.
All atoms are made up of three major subatomic particles: protons, neutrons, and electrons. Protons and neutrons make up the nucleus or center of the atom. Protons have a positive electric charge but neutrons have no electric charge. Electrons circle the nucleus and have a negative charge. In most atoms the negative charges of the electrons exactly balance the positive charges of the protons in the nucleus. If an atom has too many or too few electrons in orbit to balance the protons, the atom is called an ion.
The number of protons in the nucleus of an atom determines which element it is. An atom of helium has two protons and two neutrons. An atom of carbon has six protons and six neutrons. If the atom has too many or too few neutrons for the number of protons, the atom is unstable and is called an isotope. It will give off bursts of energy (radiation) in an attempt to become stable.
These bursts of energy or disintegrations may be in the form of alpha particles (two protons and two neutrons), beta particles (a negatively-charged electron), or gamma rays (an energy wave). If these charged particles or waves interact with another atom, they have enough energy to knock an electron out of its orbit, creating an ion. That is why this type of radiation is called ionizing radiation.
other forms of energy, like visible light, radiowaves, and infrared light, do not have enough power to knock electrons out of their orbits so they are called non-ionizing radiation.
Amounts of ionizing radiation can be expressed in several different units. A roentgen (R) is an amount of x-rays or gamma radiation which causes a specified amount of ionization among the atoms and molecules in a cubic centimeter of air. Another unit is the rad which applies to all ionizing radiation. It is a measure of the amount of energy absorbed from radiation in a specific volume of material.
A third unit which is more useful and used more commonly is the REM (Roentgen Equivalent Man). Measuring radiation in rems or millirems (one thousandth of a rem) allows direct comparison of the biological effects of different types of radiation.' Alpha particles, beta particles, and x-rays or gamma radiation, differ in their ability to cause damage in tissues due to their differences in ionizing and penetrating ability. Alpha particles are 20 times more damaging in tissue as the same amount of x-rays. Measuring radiation in rems takes this difference into account so that one rem of alpha radiation in tissues has the same effect as one rem of beta radiation or one rem of x-rays. A rem is a relatively large quantity of radiation so most human exposures are measured in millirems. An easy way to remember the difference between these units is that a roentgen is a measure of how much you are exposed to, the rad is how much you absorb, and the rem is how much damage it does.
All people receive ionizing radiation from naturally occurring sources. Depending on where you live, most people receive an exposure in the range of 100 - 200 millirems per year from cosmic radiation from outer space and from naturally occurring isotopes (excluding radon) in the ground, air, food, and water. Radon is estimated to add another 150 -200 millirems per year to our background.
Medical and dental uses of x-rays can also contribute to a person's yearly radiation exposure. A typical well conducted chest x-ray involves an exposure of 10 - 30 milliroentgens.
With the use of radioactive isotopes in industry and the increasing use of x-ray sources, ionizing radiation exposures may occur in a wide variety of occupations. The following examples show the diversity of occupations potentially exposed to ionizing radiation.
Aircraft workers Military personnel
Atomic energy plant workers Nurses
Biologists Oil well loggers
Cathode ray tube makers Ore assayers
Ceramic workers Pathologists
Chemists Petroleum refinery workers
Density testers Physicians
Dental assistants Physicists
Dentists Pipeline oil flow testers
Dermatologists Pipeline weld radiographers
Drug makers Plasma torch operators
Drug sterilizers Plastic technicians
Electron microscope makers Prospectors
Electron microscopists Radar tube makers
Electrostatic eliminator operators Radiologists
Embalmers Radium laboratory workers
Fire alarm makers Radium refinery workers
Food preservers Research workers
Food sterilizers Television tube makers
Gas mantle makers Thickness gauge operators
High voltage television repairmen Thorium-aluminum alloy workers
High voltage vacuum tube makers Thorium-magnesium alloy workers
High voltage vacuum tube users Thorium ore producers
Industrial fluoroscope operators Tile glaziers
Industrial radiographers Uranium dye workers
Inspectors using, and workers in Uranium mill workers
proximity to, sealed gamma ray Uranium miners sources
sources (cesium-137, cobalt-60, Veterinarians
and iridium-192) X-ray aides
Klystron tube operators X-ray diffraction apparatus operators
Liquid level gauge operators X-ray technicians
Luminous dial painters X-ray tube makers
Machinists, fabricated metal product
The health risks and effects of exposure to ionizing radiation are dependent on the type of radiation (alpha, beta, gamma or x-ray), the energy, the dose rate, the quantity, and the body part exposed.
Alpha particles, due to their relatively large size and mass, do not travel very far in air (a few centimeters) and cannot pass through skin or even a sheet of paper. Alpha radiation is only hazardous if inhaled or ingested. It is the most damaging to tissue, however if it is inhaled or ingested. Beta particles are more penetrating than alpha; a thin sheet of aluminum will stop beta radiation, but beta radiation is not as damaging to tissue.
X-rays (and gamma) are the most penetrating and least damaging to tissue. Their penetrating capability makes them useful for medical diagnoses.
Some body parts are more sensitive to damage from ionizing radiation than other body parts. The reproductive and blood-forming organs and the eyes are the most sensitive while the extremities such as arms, hands, and feet are less sensitive.
The quantity of ionizing radiation to which a person is exposed is the greatest factor in the risk and severity of a radiation-related injury. Information on the health effects of a single large dose of ionizing radiation is readily available from studies of the casualties and survivors of the atomic explosions in Hiroshima and Nagasaki, from studies of people exposed to radioactive fallout from the early atom bomb testing and from accidents involving ionizing radiation.
Table 1 briefly outlines the health effects of a single acute dose of whole body radiation.
less than 25 rems
No detectable effect
25 - 50 rems
Drop in white blood cell count, no serious injury
50 - 100 rems
Possible injury and sickness; no disability
100 - 200 rems
Acute radiation sickness (nausea, vomiting, diarrhea, weakness, shock, skin sores, hair loss); possible disability
200 - 400 rems
Acute radiation sickness; disability certain, possible death without treatment
400 - 500 rems
50% death rate without treatment
> 600 rems
100% death rate
Occupational exposure to ionizing radiation is usually limited to a small area of the body such as the hands resulting in reddening of the skin or dermititis. Whole body radiation and acute radiation sickness occurs very rarely in occupational settings.
The health effects of long term exposure to low levels of ionizing radiation are less easily studied and documented. The concern about possible health effects, cancer and genetic effects in particular, from low level radiation stems from the known health effects of high doses of radiation and the assumption that the degree of risk is directly related to the degree of exposure. It is assumed (not proven) for safety sake, that any exposure to radiation above natural background levels contributes to small increases in the risk of developing cancer. Reducing exposure to the lowest level possible will, therefore, reduce the risk to the lowest level possible.
The following emergency procedures were developed for medical facilities but can be generally applied to any workplace where radioactive substances are used.
Accidental spillage of radioactive material is rare, but cannot be prevented absolutely, and may occur in any laboratory, in any hall or passageway traversed by messengers transporting such material.
Except for a major accident to a shipping container or a serious spill in the hot laboratory, the amount of radioactive material involved in a spill will usually be small and the radiation from it will not constitute a serious hazard. The real danger is the spread of the contamination on shoes or other contaminated garments. The following is a general outline of the procedure to be followed in the event of a spill.
B. Loss of a Sealed Source
The following is a general outline of the procedure to be followed in the event of loss of a sealed source:
C. A Ruptured or Broken Sealed Source
D. A Major Calamity: Fire, Earthquake, A Massive Spill
Medical treatment of a person who has been accidentally over exposed to ionizing radiation will depend on the dose. Exposures less than 25 rems generally do not require treatment. The treatment will also depend on whether the source of the radiation is outside the body such as from x-ray equipment or a gamma emitter, or from inside the body such as when a radioactive dust is inhaled or ingested.
When the source of radiation is outside the body, and treatment is considered necessary, it is started after the entire radiation dose has been received. The dose cannot be lessened, therefore the objective of the treatment is to lessen the acute effects of radiation sickness, prevent secondary infections and provide transfusions to supplement weakened and damaged blood cells.
When the source of the radiation (the emitter) has been inhaled or swallowed, radiation exposure will continue and the goal of treatment is to reduce the quantity of the emitter in the body. This may be accomplished by speeding up the excretion of the emitter by chelation therapy. A chelating agent is a chemical which binds with Radioactive heavy metals enabling the body to excrete them faster. Chelation therapy is effective for internal emitters which are soluble in body fluids. Insoluble emitting substances which have been inhaled can be removed to some extent by bronchopulmonary lavage, a procedure which rinses out the lung's air sacs and airways.
Safety Procedures and Control Measures
The specific aspects, equipment, and procedures of a workplace radiation safety program will depend on the nature of the source, the type of radiation emitted, and the circumstances of its use. only general concepts of protection and control can be covered in a data sheet of this scope. The National Council on Radiation Protection and Measurements (NCRP) offers recommendations for specific uses of radiation emitting substances and equipment. A list of publications available from NCRP and an order form are attached to this data sheet.
Restricted Access: Only authorized trained personnel, should be allowed in work areas where radiation emitting substances or equipment are used. Signs and warning notices using the standard radiation symbol must be posted.
Shielding: The selection of materials and designs for shielding will depend on the type of radiation, the use factor of the equipment, occupancy times, and workload.
Ventilation: Operations that routinely produce airborne contamination should utilize engineered containment and ventilation systems to prevent airborne releases. Appropriate respirators may be used but only when effective engineering controls are not feasible.
Radiation Monitoring: Radiation survey equipment appropriate for the type of radiation to be measured must be maintained and used to evaluate exposure conditions for employees. Working areas must be monitored at a frequency which will ensure safe working conditions. Individuals working in most industrial settings and many medical facilities must wear appropriate radiation monitoring devices to measure actual occupational exposures. Records of results for area and personal monitoring must be maintained.
Licensing and Registration: All by-product radioactive material and special nuclear material must be licensed by the Nuclear Regulatory Commission, and conditions of that license met by the user. Radioactive materials not under the jurisdiction of the Nuclear Regulatory commission and all x-ray sources must be registered with the Alaska Department of Health and Social Services. Use must meet requirements of the Alaska Radiation Protection Regulations, DH & SS, in addition to the Occupational Health and Environmental Control regulations of the Department of Labor. The NRC and the state may conduct inspections of licensees and registrants to ensure compliance.
Consultation: The Radiological Physicist with the Alaska Department of Health and Social Services is available for consultation on all radiation safety matters involving both ionizing and non-ionizing radiation sources. Write to Radiological Physicist, Alaska Department of Health and Social Services, PO Box H, Juneau, AK 99811-0613, or call (907) 465-3019.
Personal Protective Equipment
Respirators used for protection against airborne contamination should be approved by the National Institute of Occupational Safety and Health (NIOSH). If air-purifying respirators are used if only high efficiency (HEPA) cartridges approved for dusts, fumes, mists, and radionuclides or radon daughters (progeny) may be used. A good respirator program must include consideration of respirator type, fit, maintenance, testing, and training.
Protective clothing must be provided if the potential for skin or clothing contamination exists. Selection must be based on the nature of the contaminant (liquid or dry material) and the type of radiation emitted. Appropriate methods of laundering or disposal are also required. Contaminated clothing must not be taken home.
Permissible Exposure Limit
The Occupational Health and Environmental Control regulations of the Alaska Administrative Code (8AAC) in 04.0105(b) state:
(b) Exposure of individuals to radiation in restricted areas.
(1) Except as provided in 04.0105(b)(2), no employer shall possess,, use, or transfer sources of ionizing radiation in such a manner as to cause any individual in a restricted area to receive in any period of one calendar quarter from sources in the employer's possession or control a dose in excess of the limits specified in Table 1-18.
Whole body: Head and trunk; active
Hands and forearms; feet and ankles
Skin of whole body
(2) An employer may permit an individual in a restricted area to receive doses to the whole body greater that those permitted under 4.0105(b)(1) so long as:
(A) During any calendar quarter the dose to the whole body hall not exceed three rems; and
(B) The dose to the whole body, when added to the accumulated occupational dose to the whole body, shall not exceed five (N-18) rems, where "IN" equals the individual's age in years at his last birthday; and
(C) The employer maintains adequate past and current exposure records which show that the addition of such a dose will not cause the individual to exceed the amount authorized in 04.0105(b)(1). As used in 04.0105(b), "Dose to the whole body" shall be deemed to include any dose to the whole body, gonad, active bloodforming organs, head and trunk, or lens of the eye.
(3) No employer shall permit any employee who is under 18 years of age to receive in any period of one calendar quarter a dose in excess of ten percent of the limits specified in Table 1-18.
These regulations (OHEC 04.0105) also cover definitions, exposure to airborne radioactive material, precautionary measures and personal monitoring, caution signs, labels and symbols, evacuation warnings, instruction of personnel, waste disposal, notification of incidents, reports of overexposure, records and disclosure.