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To review general concepts of radiation health.
The new sources of radiant energy range from large-scale applications of nuclear energy, especially for electric-power generation, through lasers and microwave technology in industry, to the use of radionuclides and x rays in the healing arts, the rapidly increasing use of microwaves by the communications industry, and in electronic equipment in the home. Scientific knowledge and protection against this radiation is still at a very early stage. The extensive use of x-ray and other devices based on radiant energy has added appreciable exposure loads to large numbers of patients. The rapidly expanding use of ionizing and nonionizing radiation for weapons manufacture, power development, industrial uses, communications and other purposes introduces to the air, water and land a pollutant awesome in its potentials and implications. Merely the problem of safe disposal of the large amounts of radioactive wastes is beginning to appear overwhelming. Added to this are the dangers of leakage from stored materials of radioactivity transmitted to cooling waters and the problem of thermal pollution of streams and lakes possibly eventually of even the ocean itself.
0f the total radiation exposure to which people in the United States are subject, 45% is from natural sources, such as from minerals and from the sky (cosmic), 55% is from man-made sources, most of which (45% of the total) is from medical equipment. Industrial and occupational sources account for 7% of the total, and television screens, luminous clock-watch dials and fallout plus fission testing account for 1% each. It is important to remember that radiation cannot be directly detected by the senses and that the effects of radiation are irreversible. There is no immunity against radiation; parts of the body escaping damage from one exposure do not have an increased tolerance for future exposures.
Radioactive substances emit radiation in several forms. Some, like alpha and beta radiation are particles of matter. Others - gamma rays and x rays are pure energy and possess no mass. Gamma rays and x rays are identical in their physical properties and biological effects. The only difference is that gamma rays are natural products of radioactive atoms while x rays are produced in man-made machines. Particulate radiation does not penetrate body tissue as deeply as gamma or x rays. It mainly damages the skin and surface organs, although it can harm the surfaces of internal organs if it is inhaled or ingested. Gamma and x rays penetrate more deeply into the body and can do their damage throughout any internal organs that are exposed. Ionizing radiation gradually uses up its energy as it collides with the atoms of the material through which it travels. The material -- for example, living tissue -- absorbs the energy, mainly through the ionization of its atoms. It is this transfer of energy that can cause tissue damage and adverse health effects. The damage can be done by external radiation, such as gamma rays from an atomic bomb explosion, or internally, for example, from drinking milk contaminated with radioactive iodine that is giving off beta particles. In addition to these, there are other types of radiation:
Deuteron
Electron
Infrared
Laser
Microwave
Neutrino
Positron
Proton
Radar
Ultraviolet
The protection of injury to living matter by ionizing radiation is the result of the transfer of large amounts of energy indiscriminately to individual molecules in the region through which the radiation passes. These large energy transfers causes disruptions of the molecular structure, and when the molecules affected are essential for the normal functioning of a cell, the cell in turn suffers injury or dies. Thus, the imparting of energy by ionizing radiation to living matter may be characterized in general as a harmful process, and the greater the energy imparted, the greater is the injury produced. The most drastic chemical effect that can be produced on a molecule by energy transfer is to completely remove an electron, that is to ionize the molecule.
The effects produced by ionizing particles depend not only on the amount of energy imparted to the body but the location and extent of the region of the body exposed and the time interval over which the energy is imparted. These and other factors must be taken into account in specifying maximum exposure levels.
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These results reflect the inadequate protection used in the past and do not reflect present-day life expectancies of people occupationally exposed to radiation.
Various biological effects of radiation are summarized in Table 2 below:
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Radiation can cause a cell to divide prematurely, too late, or not at all. Further, the new cells might be altered such that they have an abnormal growth rate, are unable to reproduce, or may reproduce at an abnormal rate.
Different cells are susceptible are susceptible to the effects of radiation in varying degrees. The time of cell division, its nourishment and its metabolic rate can greatly influence the ability of the cell to withstand exposures. The following list of cells of the human body is given in relative order of sensitivity to radiation. The first cells listed are more susceptible than the next, and so on.
Generally, from this list, those tissues and organs which are most sensitive to radiation can be determined. They include:
Chromosomes are threadlike structures that are contained in the nuclei of most human cells. Genes are components of the nuclei which align themselves along the chromosomes. These components determine hereditary characteristics of cells and the whole individual. Radiation can cause changes in genes, mutations in cells, or it can increase the normal mutation rate. Breaks in chromosomes can also occur. Mutations can result in life span reduction, sterilization, and even death.
There are three cancer-causing forms of radiation:
A direct effect would be cancer caused by exposure to a large dose of radiation. A boost effect would be cancer caused as a result of small exposure to radiation, spurring cancer agents. A remote effect would be cancer caused in one part of the body by radiation-induced cancer in an other part of the body.
Radiologists and others who work with radioactive materials have relatively large incidences of cancer. The biological effects of radiation can be devastating.
The settings and execution of guidelines for radiation protection are based upon underlying philosophy in which two factors are of prime importance .
- First is the assumption that radiation effects follow a linear, or non-threshold dose response relationship. I would like to point out that this is somewhat controversial but is followed since it is the more conservative hypothesis. According to the non-threshold relationship, therefore, implies that there is no radiation protection guideline, no matter how low, which can insure absolute safety to every individual in a large population receiving the guideline dosage.
The second major factor to consider is that radiation, like many other developments of modern life (such as the automobile), confers treatment both society and the individual along with its risk to health. Consideration of the extent of these benefits makes a certain degree of risk acceptable. Information accumulated on cause-effect relationships of radiation dose and biological danger is difficult to evaluate and controversies after consideration of some significant data. Remember that these are the occupational units. Currently it is recommended that the yearly radiation exposure of individuals in the general population (exclusive of natural backgrounds and the deliberate exposure of patients by dentists and doctors) should be one-tenth of the occupational levels. Thus, for whole-body exposure of individuals in the general population, the radiation dose should not exceed 0.5 rem per year.
There are several things that one can do to protect himself from radiation.
Distance is a very effective method of radiation protection. The reason for this is the inverse square law which states that radiation intensity from a point source varies inversely as the square of the distance from the source or
________
I2 = (R1)2 I2 = radiation at distance R2
Shielding is one of the most important methods for radiation protection. On passing through shielding materials, the radiation loses its energy by three methods: photoelectric effect, Compton effect, and pair production. The predominating mechanism depends upon the energy or the radiation and the absorbing materials. The photoelectric effect is most important at low energies, the Compton effect at intermediate energies, and pair production at high energies. The last cannot occur unless the incident radiation has more through an absorber, their decrease in number caused by the absorption processes is governed by the energy of the radiation, the specific absorber medium, and the thickness of the absorber medium transverses. The NCRP also puts tables and guides to determine required thicknesses of shielding materials. One can also employ leaded gloves, gonadal shields etc.
Obviously the less time spent in radiation areas the less the exposure
The amount of radiation energy absorbed per unit of mass in anything. When applied to man, it is the amount of radiation energy absorbed per unit mass by the body or by any portion of the body. The word exposure is frequently used instead of dose when it applies to man.
Radiation dose delivered per unit time. Frequently expressed in milli-Roentgen per hour (mR/hr), or millirems per hour (mrem/hr).
That quantity of a radioactive material disintegrating at the rate of 9.7 x 1010 atoms per second (not to be confused with dose measurements). Note: A five curie source of cesium 137 would not give you the same dose rate as a five curie cobalt 6O source because there is an energy difference.
Time required for a radioactive substance to lose 50% of its activity by decay. Each radionuclide has an unique half life.
A dose unit used in measuring exposure from X ray and gamma radiation only (83 ergs/gram air absorbed).
A dose unit used in measuring all types of radiation absorbed dose in any material (100 ergs/gram).
A unit used as a measure of the dose or exposure of any ionizing radiation to body tissue in terms of its estimated biological effect relative to a dose of one Roentgen or X-rays.
Values are established by the AEC. The concentrations of radioactive isotopes permissible in air or water.
The process or the result of any process by which a neutral atom or molecule acquires either a positive or a negative charge.
A factor by which absorbed doses (RAD) are to be multiplied to obtain the rem unit. RAD x OF - rem.
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