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Chapter III
Sources and Effects of Radiation

Biological Effects of Radiation

Living organisms are a collection of complex systems of many symbiotic parts arranged and packaged in a manner to allow maintenance of their internal environment and self-reproduction. The basic units are composed of cells. Cells of similar origin and structure are further grouped to form tissues. The four main groups of tissues are: muscle, nerve, connective and epithelial. Associated cells and tissues form organs which, taken collectively, function to create and control the necessary internal conditions suitable for life.

A great diversity exists among the different kinds of cells found in the body. Many have a brief lifespan, undergoing division (a process called mitosis) in a period of hours, while others (such as nerve cells) do not divide at all after birth. Mitosis represents there production of the chromosome, on which the genes containing all the genetic information necessary for cell function resides. Any alteration of the genetic information carried by the genes, or of the processes associated with mitosis can result in either a permanent change in the nature of the cell (mutation), or in the cell's death. When a cellular component is damaged by any agent (chemicals, radiation, excessive heat, etc.), a multitude of measurable effects can result. The changes may initially be restricted to a single or a few types of cells. In time, whole organs or organ systems may be affected due to the absence of a required function that upsets the equilibrium or control of the whole interrelated system. Gross physiological or morphological changes may result from an initial damage to a sufficient number of many kinds of cells. The type of cell damage will depend upon what the specific agent is that the cell is exposed to, and the amount of damage will be related to how much of the agent reaches that particular kind of cell. Biological effects from radiation are produced as a result of the transfer of energy from the radiation to the cells through ionization and excitation as described in the next section.

Radiosensitivity of Cells

Radiation passing through living cells causes ionization or excitation of atoms and molecules contained in the cell. This is the same process that occurs in any material, as described in Chapter I, Part 5. Since most of the human body is water, water molecules are a likely target for being hit by photons or charged particles. The reaction which occurs when this happens is an ionization to form a positive ion and an electron:



and the H₂O⁺ is rapidly hydrated to form:

     H2O+ + H2O --> H30+ OH.

Here the OH^. is a "free radical", a species that contains an unpaired orbital electron, and is highly reactive chemically. The free electron will also react with a water molecule (after it slows down from bumping into other molecules) to yield another free radical, this time hydrogen:

e- + H2O --> OH- + H.

The overall reaction is thus:

with the products separated by a considerable distance so that immediate back reactions to form water are not favored. Such radicals can combine with each other and with dissolved oxygen to give a variety of potent oxidizing agents such as hydrogen peroxide, superoxide, molecular oxygen and the perhydroxy radical.

Both the initial radicals and these products can migrate to biologically important molecules (like DNA - the structural material of genes) and cause bond breakage and/or oxidation of attached groups. In this way, energy of the radiation is transferred to biologically significant molecules, changing their structure. This mode of energy-transfer is known as the Indirect Effect and can account for an appreciable fraction of damage. Note that the presence of oxygen can magnify this pathway due to additional radical formation.

In addition to the indirect effect, radiation may itself cause ionization in DNA or other biological molecules. The energy of ionization is far greater than the bond energy in organic molecules, thus causing bond breakage. The amount of this Direct Effect occurring depends on the number of a particular type of molecule in the cells, and its size. The larger a molecule is, the better target it makes. Since DNA is the largest molecule in the cell as well as the site of all the genetic information, its response has a central role in the mediation of radiation effects. Depending on how it is damaged, different results will occur. If the damage results in a strand break in its backbone (breaking the molecule in half), subsequent mitoses may fail resulting in cellular death. If the break is in one of its side groups (bases), it will then transmit different genetic data during subsequent division resulting in some kind of a mutation. Both direct and indirect effects contribute to the overall number of such damaging events to the DNA and will vary for individual cell types.

The radiosensitivity of a particular cell depends on a number of factors. An early observation of this difference is reflected in the "Law of Bergonie and Tribondeau" which states "the radiosensitivity of a tissue is directly proportional to the reproductive activity and inversely proportional to the degree of differentiation". Tissues consisting of rapidly dividing stem cells (like blood or sperm cell precursors) are quite sensitive to radiation whereas cells that do not divide or only rarely divide (like nerve or muscle cells) are considerably more resistant. From microscopic examination, cells appear to get stuck in the division process and never successfully complete it after radiation exposure, which is consistent with the "Law" above. Other factors involved include metabolic rate, state of nourishment, oxygen level and presence of particular enzymes within the cell. The latter are most likely involved with the repair of some of the radiation damage.

The following table gives a summary of how various cell, tissues, organs and organ systems are affected by radiation. The doses reported are for X or gamma rays only and represent a single, acute exposure.

Relative Radiosensitivity of Cells, Tissues and Organs

Type	Biological Response
Blood-forming Organs lymph nodes, thymus, spleen, bone marrow	Extremely Radiosensitive Exposures as low as 50 rad can affect the white cell population within 15 minutes. Red cell counts fall 2 to 3 weeks later. Results in a feeling of general weakness, anemia, and a lower resistance to infection.
Reproductive Organs female, male	Moderately Radiosensitive Exposures below 100 rad can reduce fertility. Temporary sterility can occur lasting 12 to 15 months following 200-300 rad. On the average, a larger exposure is needed to produce sterility in the male than in the female. Damage to the germ cells can lead to somatic and/or hereditary changes.
Digestive Organs small intestine, lower intestine, pharynx, esophagus	Radiosensitive Degenerative changes occur as soon as 30 minutes after exposure of 500-1000 rad. Initial effects are: impaired secretion of necessary fluids: cell breakdown results in failure of food and water absorption leading to infection and dehydration from diarrhea.
Vascular System arteries (lg & sm) capillaries, veins	Moderately Radiotesistant Sensitivity varies for the vascular system. Damage is great only in the 600-1500 rad range. This damage by radiation contributes to some of the heart, changes in other tissues.
Skin	Radioresistant Exposures between 500-1000 rad can produce skin changes. However, as little as 100 rad can cause cell death in the germinal layer.
Bone and Teeth	Some parts of bone can be damaged by 700-1500 rad. Regeneration can begin 2 to 6 weeks after exposure.
Respiratory System	Relatively Radioresistant Inflammation of the lungs can occur at 1000-2000 rad. Possible hemorrhaging due to changes produced in blood vessels.
Urinary System	Secondary effects can show up years after exposure in the 500-2000 rad range due to changes in blood vessels.
Muscle and Connective Tissues	Very Radioresistant Massive exposures (over 2000 rad) are needed to cause slight changes in these tissues.
Nervous Tissue	Extremely Radioresistant Massive exposures are required (over 3000 rad) to bring about morphological changes in these tissues.

The most radiation-sensitive state of any individual is during embryonic development. If irradiated at a time when a particular tissue or organ is being differentiated, exposures as small as 25-50 rad can lead to gross malformations. In humans, this corresponds to 2-6 weeks of gestation. This sensitivity is due to the presence of only a few cells at this stage which ultimately will give rise to a particular tissue or organ. If these are destroyed, other cells cannot replace them.

Acute Lethal Response

Lethal effects are observed in mammals within a period of 30 days from acute exposures in the few-hundred rad range. Acute exposure refers to a short time period of delivery of the radiation, generally within minutes. Expression of this response is known as the LD₅₀³⁰ or the dose which yields 50% lethality in an irradiated group of a particular species measured at 30 days. At doses appreciably below the LD₅₀³⁰, very little lethality occurs; whereas at doses appreciably above,100% lethality occurs.

Acute Lethal Responses
Species	RADS
guinea pig	175-409
dog	350
goat	350
man	350-450
mouse	550
rat	590-970
monkey	600
rabbit	800
fowl	1000
goldfish	2300

The ranges shown above represent an uncertainty only in the case of man, where precise experimental data does not exist. Other ranges represent a difference depending on the particular strain of the species used. The cause of death at the LD_50/30 is due to response of the blood forming organs (described previously). Death occurs when the radiation exposure has reduced the number of these cells surviving to a level below that necessary for life. Interestingly, at the tissue level, a given dose yields about the same observable damage in any species. Some species, however, are better able to cope with the damage and so survive.

When organisms are exposed at or above the acute LD_50/30 value, characteristic physiological responses are seen. These responses are known as "radiation sickness" and "acute radiation syndrome". The following tables illustrate the symptoms and their timing from various whole-body dosages.

Expected Effects of Acute
Whole-Body Radiation Doses

Acute Dose (rads)	Probable Effect
0 - 50	No obvious effect, except possibly minor blood changes.
80 - 120	Vomiting and nausea for about 1 day in 5 to 10 percent of exposed personnel. Fatigue but no serious disability.
130 - 170	Vomiting and nausea for about 1 day, followed by other symptoms of radiation sickness in about 25 percent of personnel. No deaths anticipated.
180 - 220	Vomiting and nausea for about 1 day followed by other symptoms of radiation sickness in about 50 percent of personnel. No deaths anticipated.
270 - 330	Vomiting and nausea in nearly all personnel on first day, followed by other symptoms of radiation sickness. About 20 percent deaths within 2 to 6 weeks after exposure; survivors convalescent for about 3 months.
400 - 500	Vomiting and nausea in all personnel on first day, followed by other symptoms of radiation sickness. About 50 percent deaths within 1 month; survivors convalescent for about 6 months.
550 - 750	Vomiting and nausea in all personnel within 4 hours from exposure, followed by other symptoms of radiation sickness. Up to 100 percent deaths; few survivors convalescent for about 6 months.
1000	Vomiting and nausea in all personnel within 1 to 2 hours. Probably no survivors from radiation sickness.
5000	Incapacitation almost immediately. All personnel will be fatalities within 1 week.

The Effects of Nuclear Weapons U.S. Government Printing Office, May 1957



Acute Radiation Syndromes

Response	Dose,rads	Synsrome
Hematopoietic Death	700 to 1000	Death in 10-21 days caused by blood changes resulting in infection or hemorrhaging.
Gastro-intestinal Death	1000 to 10000	Death in 4-7 days. Nausea, vomiting and diarrhea; food and water intake depressed. Death by severe morphological changes in gastrointestinal tract.
Central Nervous System Death	10000 to 100000	Death within 2 days. Minutes after exposure disorientation, incoordination and semi-consciousness develops. Coma and death occurs from central nervous system damage.
Molecular Death	over 100000	Immediate death. Death caused by inactivation of substances required for basic metabolic processes.

Chronic Exposure Response

If a given radiation exposure is delivered over a longer time period, the effect observed is less. Experiments utilizing the "split-dose" technique have shown that radiation damage is repaired by the organism as long as any single exposure is less than the LD_50/30. For example, if animals are given one-half of the LD_50/30 (called a "conditioning dose") followed some time later by another equal dose (called the "test dose") with sufficient separation of the two doses (say, a few weeks), the animals will survive. If no time elapses between them, death occurs within 30 days. Spreading the dose over weeks or months at a low rate reduces the effect appreciably. For the induction of mutations in mice, the mutation yield for chronic exposure is about half that for acute exposure. Many other responses appear to follow this reduction in effectiveness under chronic exposure conditions.

Late Effects of Radiation

Radiation, given either acutely or chronically, increases the incidence of a number of conditions observable from 5-20 years after the exposure was delivered. None of these responses are unique to radiation exposure, they occur with some normal incidence in the general population, but are increased in frequency in irradiated populations. The following have been shown to be associated with radiation:

Types of Late Effect

Carcinogenesis The reason for increases in certain forms of cancer by radiation (or other carcinogenic agents) is still speculative. Leukemia, skin, lung and bone cancers are radiogenic.

Tissue Effects Of most concern are cataracts and sterility. Cataracts develop slowly, but can stop or even regress. Sterility can be either permanent or temporary.

Hereditary Effects Since the time between generations is long, and controlled experimentation can only be performed in animals which may or may not represent the human response, the ultimate effect on us remains in question.

Lifespan Shortening Chronic exposure results in about a 7% lifespan shortening for every dose equivalent to the LD₅₀ received. A survivor of an acute LD₅₀ dose has a life expectancy reduced to 50% of an unirradiated control.

The above late effects can only be predicted for large populations. For an individual in an irradiated group, death cannot be identified as to its exact cause, either natural or from one of the many environmental agents capable of producing the same effect. No amount of experimentation is expected to yield any way to identify the precise agent which may be the cause of any of these effects when several are present. That is because each agent will contribute to the risk in proportion to its amount and effectiveness, as well as factors related to the genetic resistance or sensitivity of the individual exposed.

Comparison of Health Effects

Studies have compared the projected loss of life expectancy resulting from exposure to radiation with other health risks. Estimates are calculated by looking at large numbers of individuals, recording the age at which death occurs from apparent causes, and estimating the number of days of life lost as a result of these early deaths. The total number of days of life lost is then averaged over the total group observed.

Estimated Loss of Life Expectancy From Health Risks

                                          Estimate of Days of
 Health Risk                              Life Expectancy Lost 

     Smoking 20 cigarettes/day                   2370 (6.5yr)

     Overweight by 20%                            985 (2.7yr)

     Auto accidents                               200

     5 rems/year for 30 years (calculated)        150

     Alcohol consumption (US average)             130

     Home accidents                                95

     Safest jobs (such as teaching)                30

     1 rem/year for 30 years (calculated)          30

     Natural background radiation (calculated)      8

     Medical X-rays (calculated from US average)    6

     Natural disasters                            3.5

     1 Rem occupational dose (calculated)           1

       Adapted from USNRC Regulatory Guide 8.29 

These estimates illustrate that health risks from occupational radiation exposure are of the same order of magnitude as risks that we have historically encountered in normal day-to-day activities. Exposure to radiation should be considered in this perspective when considering its risk. As long as radiation exposure is kept at a value where its contribution to risk is a small part of the total sum of all risks, then it should not be of major concern.

Radiation Exposure Limits

Historical Review

Soon after the discovery of X-rays and radium, the dangers of radiation exposure became well known. Standard setting organizations like the International Council on Radiation Protection (ICRP) and the National Council on Radiation Protection and Measurements (NCRP) were formed to recommend limits on the exposure of radiation. Prior to 1928, the radiation exposure limit was based on the amount of radiation needed to produce reddening of the skin (erythema). When the Roentgen (R) was defined in 1928, this "erythema exposure" was calculated to range from 0.04 R to 2 R per day. In 1935, the NCRP's first recommendation for exposure limitation was 0.1 R/day (31 R/year). This was an arbitrary limit, based on no observable effects on three technicians' exposure to radium gamma rays. In 1949, the NCRP reduced the limit to 0.05 R/day 0.3 R/week; 15 R/year) because radiations then being used were more penetrating. A major revision adopted by both the NCRP and ICRP took place in 1957 and was in effect until January 1, 1994. This limit allowed an individual to receive up to 3 Rem in 13 consecutive weeks, provided that the accumulated dose does not exceed 5(N-18) Rem, where N is the individual's age. The latest revision eliminates what has been called a "bank" of available dose before exceeding the 5(N-18) dose.

Basis for the Current Radiation Exposure Limits

Occupationally exposed individuals are allowed higher radiation exposures than the general population for the following reasons:
1. The radiation worker accepts some small risk balanced against some benefit (through employment).

2. There is a conscious selection of occupationally exposed individuals: minors are excluded, medical histories can be obtained and maintained. Fertile women may be excluded. Preferential treatment is possible to those beyond the reproductive age.

3. There is a limit on the percentage of radiation workers in the total population.

External Exposure

Current State and Federal guidelines describe the radiation exposure limits to an occupational radiation worker as follows:
1. Annual Limit:
   1. An annual limit, which is the more limiting of-
      1. The total effective dose equivalent being equal to 5 rems (0.05 Sv); or

      2. The sum of the deep-dose equivalent and the committed dose equivalent to any individual organ or tissue other than the lens of the eye being equal to 50 rems (0.5 Sv).

   2. The annual limits to the lens of the eye, to the skin, and to the extremities, which are:
      1. An eye dose equivalent of 15 rems (0.15 Sv), and

      2. A shallow-dose equivalent of 50 rems (0.50 Sv) to the skin or to any extremity.

2. Doses received in excess of the annual limits, including doses received during accidents, emergencies, and planned special exposures, must be subtracted from the limits for planned special exposures that the individual may receive during the current year and during the individual's lifetime.

3. The assigned deep-dose equivalent and shallow-dose equivalent must be for the part of the body receiving the highest exposure. The deep-dose equivalent, eye dose equivalent and shallow-dose equivalent may be assessed from surveys or other radiation measurements for the purpose of demonstrating compliance with the occupational dose limits, if the individual monitoring device was not in the region of highest potential exposure, or the results of individual monitoring are unavailable.

Other Exposure Limits

    Major Organs and Thyroid Gland:         15 rem/yr
    Fetus:                                  0.5 rem

The dose limit to the whole body for non-radiation workers, in addition to natural and medical sources is 0.1 rem/year.

The dose limit to the whole body for the U.S. population from all sources of radiation other than natural and medical sources is 0.1 rem/year per person.

Radiation from Background, Consumer Products, and Medical Exposure

The population as a whole is exposed to radiation whether it be from naturally occurring radioactivity present in the earth, from interstellar space, from medical sources, or from radio-activity contained in consumer products.

Naturally Occurring Radiation

Naturally occurring radiation arises from three sources: cosmic rays entering the earth's atmosphere, naturally occurring radioactive materials in the earth's crust; and naturally occurring radioactive materials within the body.

Cosmic Radiation

Primary cosmic rays are of galactic origin and consists of high energy protons, ⁴He ions, electrons, and photons (X and gamma rays). When these particles enter the atmosphere, they interact with the nuclei of the atoms in the air, giving rise to neutrons, electrons, protons, gamma rays, and other particles which are responsible for most of the observed cosmic ray dose. Because of the earth's magnetic field, the cosmic ray intensity varies with latitude, the lowest value at the geomagnetic equator. The intensity also varies with elevation, the highest levels being in the upper atmosphere. Cosmic rays from solar flares consists of X-Rays, protons, and alpha particles. Because these solar cosmic rays are relatively low in energy, they usually do not contribute significantly to increases in the radiation dose a ground level.

Terrestrial Radiation

Naturally occurring radionuclides in the environment are classed as either cosmogonic or primordial. Cosmogonic nuclides are those nuclides produced in the atmosphere when primary and secondary cosmic rays undergo nuclear reactions with nuclei of atoms in the air. The main contributors to external exposure from cosmogonic nuclides are Be-7, Na-22, and Na-24.

Primordial nuclides are those that are long lived and have existed in the earth's crust throughout history. The main contributors to external exposure from primordial nuclides are K-40, U-238, and Th-232, and their decay products. The concentrations of primordial nuclides in soil are dependent on the process by which the soil was formed. The table below shows the typical activity of these nuclides in various types of rock:

             Typical Activity Concentration (pCi/gm)
                                                    Absorbed dose
                                                     rate in air
 Type of Rock                   K-40     U-238  Th-232  ( rad/hr)   Igneous
   Acidic (e.g. granite)          27      1.6     2.2       12
   Intermediate (e.g. diorite)    19      0.62    0.88       6.2
   Mafic (e.g. basalt)             6.5    0.31    0.30       2.3
   Ultrabasic (e.g. durite)        4.0    0.01    0.66       2.3
 
 Sedimentary
   Limestone                       2.4    0.75    0.19       2.0
   Carbonate                       ---    0.72    0.21       1.7
   Sandstone                      10      0.5     0.3        3.2
   Shale                          19      1.2     1.2        7.9

         Source:  UNSCEAR 1977 Report

In various parts of the world, there are areas with high natural radiation levels. At the beach of the Black Sands in Guarppari, State of Espirto Santos, Brazil, it is possible to receive a radiation exposure of 5 mrad/hr due to the monazite (Thorium bearing minerals) sands. At Pocos de Caldas, State of Gerais, Brazil, the average range of radiation exposure is from 0.1 - 3 mrad/hr.

Naturally occurring radionuclides can give rise to external doses when contained in raw materials used to construct roads and buildings. Uranium and thorium are commonly found in cement, concrete blocks, and masonry products. For example, the possible annual dose near a granite wall at the "Redcap Stand" in Grand Central Station, New York is 200 mrem (assuming an occupancy of 8 hrs/day).

Internal Radiation

Naturally occurring radionuclides enter the body through inhalation and ingestion. Of the cosmogonic nuclides only H-3, C-14, and Na-22 contribute to internal exposure. The major contribution to internal exposure from primordial nuclides are K-40 and the decay products of the uranium and thorium series.
1. Tritium
   Tritium is produced in the atmosphere by secondary cosmic ray neutrons interacting with N-14 nuclides. The global inventory of tritium is calculated to be 34 Mega Curies*. Most (99%) of the H-3 inventory is converted to tritiated water and takes part in the normal water cycle. Approximately 65% of the inventory is in the oceans as a result of transport by rain. About 30% of the inventory is in land surfaces with the remaining in the atmosphere.

2. Carbon-14
   Carbon-14 is also produced by cosmic ray neutrons. The global inventory of C-14 is about 300 Mega Curies, with 94% distributed in the ocean, 4% in the land surface and biosphere and the remaining in the atmosphere. The natural specific activity of C-14 is 6.1 pCi/gm of carbon.

3. Potassium-40
   Potassium is an essential element of the body and enters via the food chain. The amount of potassium in the body varies with age and sex. The average whole body activity concentration of K-40 is 1600 pCi/kg. Potassium-40 emits beta and gamma radiations and is, therefore, a source of both internal and external radiation exposure.

4. Uranium and Thorium Series
   The radionuclides that contribute to internal exposure from the uranium series are: U-238, Ra-226, Rn-222, and its decay products Pb-210, Bi-210, and Po-210. The major nuclides that contribute to internal exposure from the thorium series are: Th-232, Ra-228, Ra-220, and its decay products Pb-212, Bi-212, and Po-212. The major contribution to the natural internal dose is from the decay products of Rn-222. The major source of these alpha emitting nuclides is through emanation of Rn-222 from the ground. The decay products form in clusters with water, oxygen, and other gases and attach themselves to aerosol particles. They can be inhaled, ingested, and through direct deposition on plant leaves and root absorption enter the food chain. Cigarettes are estimated to contain 0.6 pCi of Pb-210 and 0.4 pCi of Po-210. Brazil nuts and Pacific salmon have been found to contain larger concentrations (>5 pCi/kg) of radium-226. There are areas in the world in which water concentrations of uranium and radium are high due to isolated deposits. Reindeer and caribou contain elevated levels of Pb-210 and Po-210 mainly because they feed on lichens in the winter which accumulate these isotopes. The Pb-210 in fish and mollusks range between 20-500 pCi/kg.

   The main source of radon indoors is from building materials such as by-product gypsum, used for internal walls and ceilings, and concrete. Increasing the ventilation of the room will significantly reduce the radon levels. The highest levels found in poorly ventilated areas, such as basements, where radon diffuses out of the concrete walls and through cracks in the floor. Sealing the walls and floors with epoxy paint can reduce the emanation rate by a factor of four. Three layers of oil paint can reduce the emanation rate by an order of magnitude.

1. Summary
   The following table summarizes the estimated annual tissue absorbed dose from natural sources:

   
   Source of Irradiation                     Gonads            Lungs
                                             (mrad)            (mrad)
   
   External Irradiation
   
        Cosmic Rays:
            Ionizing component                 28               28
            Neutron component                  0.35             0.35
   
        Terrestrial Radiation: (γ)       32               32
   
   	 
   Internal Irradiation
   
       Cosmogonic radionuclides:
            H-3 (β)                       0.001            0.001
            Be-7 (γ)                     -----            0.002
            C-14 (β)                      0.5              0.6
            Na-22 (β+γ)             0.02             0.02
   
       Primordial radionuclides:
            K-40 (β+γ)              15               17
            Rb-87 (β)                     0.8              0.4
            U-238, U-234 (a)                   0.04             0.04
            Th-230 (a)                         0.004            0.04
            Ra-226, Po-214 (a)                 0.03             0.03
            Pb-210, Po-210 (a+β)          0.6              0.3
            Rn-222, Po-214 (a) inhalation      0.2              30
            Th-232 (a)                         0.004            0.04
            Ra-228, Tl-208 (a)                 0.06             0.06
            Rn-220, Tl-208 (a) inhalation      0.008            4   
                      Total (rounded)          78              110
   
    Source: UNSCEAR 1977 Report
   

Technologically Enhanced Exposures to Natural Radiation

Technologically enhanced exposure to natural radiation is defined as exposure to natural radiation to which man would not be exposed if some kind of technology had not been developed. For example, travel by air, using natural gas for cooking or heating, and living near a coal fired power plant increase an individual's exposure to naturally occurring radiations.

Air travel increases the exposure due to comic rays and solar flares when flying at high altitudes. The following table shows calculated doses for various routes:

Comparison of Calculated Cosmic-Ray Doses to a Person Flying in Subsonic and Supersonic Aircraft Average Solar Conditions

                       Subsonic Flight        Supersonic Flight
                          at 11 km                at 19 km
                      _________________       ________________
                                  Dose
                                   per                      per
                       Flight     round        Flight      round
                      duration     trip       duration      trip
Route                   (hr)      (mrad)        (hr)       (mrad)
Los Angles-Paris         11.1       4.0        3.8          3.7
Chicago-Paris             8.3       3.6        2.8          2.6
New York-Paris            7.4       3.1        2.6          2.4
New York-London           7.0       2.9        2.4          2.2
Los Angles-New York       5.2       1.9        1.9          1.3
Sydney-Acapulco          17.4       4.4        6.2          2.1

Source: UNSCEAR 1977 Report

The table below shows the doses received by astronauts on various space missions. The largest part of the dose was received when the spacecraft passed through the earth's radiation belts. The belts contain protons, electrons, and alpha particles trapped by the earth's magnetic fields.

         Absorbed Dose in Chests of Astronauts on Space Missions
  Mission or   Launch Date   Duration of    Type of Orbit   Dose
Mission Series (Yr-Mo-Dy)    Mission (Hr)                  (mrad)
 Apollo VII     68-08-11        260         Earth Orbital    157
 Apollo VIII    68-12-21        147         Circumlunar      150
 Apollo IX      69-02-03        241         Earth Orbital    196
 Apollo X       69-05-18        192         Circumlunar      480
 Vostok 18-6                                 Earth Orbital   2-80
 Voskhad 1,2                                Earth Orbital    30-70
 Soyuz 3-9                                  Earth Orbital    62-234   

Source: UNSCEAR 1977 Report

Individuals living around coal-fired power plants are exposed to enhanced levels of Ra-226, Ra-228, U-238, Th-228, Th-232, and K-40 from gaseous and particulate combustion products of coal. The major contribution to the dose is from the alpha radiation of Pb-210, Th-228, and Th-232.

Phosphate products contain high concentrations of the nuclides in the U-238 decay series. About 1/2 of the phosphate rock that is mined is converted into fertilizer, the rest goes into commodities such as phosphoric acid, gypsum, and land fills. Thus, the use of phosphate fertilizers result in radiation exposures from the following:

1. Absorption of radionuclides by food crops.

2. External radiation from fertilizer storehouses and production plants.

3. Airborne radon decay products over land reclaimed after phosphate mining.

4. Radiation from gypsum used in building products.

Consumer Products

Radiation exposure from consumer products are considered "Enhanced" since the radioactive material is deliberately incorporated into the product to serve a specific purpose.

Radioluminous Products

Products such as time pieces, aircraft instruments, signs, indicators, etc. contain various amounts of Ra-226, Pm-147, or H-3 to provide illumination. Light is generated when the radiations from these nuclides interact with a scintillator, usually zinc sulfide. The scintillator can be in the form of a paint (watch hands) or a coating inside of glass tubes (exit markers) to make the product "glow in the dark". With the exception of Ra-226, the low energy radiations are unable to penetrate watch crystals, glass tubes, etc. Because of the more energetic radiations from Ra-226, it is now rarely used.

Electronic and Electrical Equipment

Radioactive materials are used in lamps and electronic tubes to provide pre-ionization in gases for the purposes of passing an electrical current. This allows the equipment to respond faster and more reliably. Smoke detectors use alpha radiation from Am-241 to provide an ionization current. Smoke or combustion products entering the detection chamber cause a change in resistance (the alpha particles being stopped or absorbed by the smoke) triggering an alarm. Anti-static devices use Po-210 to ionize the air around a charged object, thereby allowing the charge to be neutralized.

Miscellaneous

Porcelains use in dentistry contain uranium in combination with cerium in order to simulate the natural fluorescence of teeth. Certain glazes used in ceramics contain uranium oxides and sodium uranite as pigments. Glazes ranging from black, brown, green, and the spectrum from yellow to red are used primarily to decorate pottery and tableware. Mantles in gas lanterns and yard lights consist mainly of thorium oxides. Major radiation exposure occurs during the first few hours that a new mantle is used, primarily from the inhalation of the thorium. Color televisions generate X-rays (via Bremsstrahlung) as a result of high speed electrons striking the phosphor screen of the picture tube. Most televisions today have high voltage controls and sufficient thickness of glass to absorb most of these low energy X-rays. The following tables describes various consumer products containing radioactive materials and some annual population dose rates:

Selected Products Containing Radioactive Material

     Product                             Nuclides    Amount

     Radioactive Material Contained in Paint or Plastic:
     Time Pieces                         H-3        1-25 mCi
                                         Pm-147   65-200 µCi	
                                         Ra-226    0.1-3 µCi
     Compasses                           H-3        5-50 mCi
                                         Pm-147       10 µCi
     Thermostat Dials and Pointers       H-3          25 mCi
     Automobile Shift Quadrants          H-3          25 mCi
     Speedometers                        Pm-147      0.1 mCi

Radioactive Material Contained in Sealed Tubes:
     Time pieces, marine navigational 
          instruments                    H-3       0.2-2  Ci
     Exit signs, stepmarkers, public
          telephone dials, light switch
          markers                        H-3      0.2-30  Ci

Electronic and Electrical Devices:
     Fluorescent lamp starters           Ra-226        1 µCi
     Vacuum tubes, electric lamps,
          germicidal lamps               Natural
                                         Thorium      50  mg
     Glow lamps                          H-3        0.01 mCi
     High voltage protection devices     Pm-147        3 µCi
     Low voltage fuses                   Pm-147        3 µCi

Miscellaneous:
     Smoke and fire detectors            Am-241     1-100 µCi
                                         Ra-226   0.01-15 µCi
                                         Kr-85          7 mCi
     Incandescent gas mantles            Natural
                                         Thorium      0.5  gm
     Ceramic tableware glaze             Natural
                                         Uranium      20% by
                                           or       weight of
                                         Thorium    the glaze


      Adapted from UNSCEAR 1977 Report
	

        Average Annual Population Dose Equivalents from
     Selected Consumer Products and Miscellaneous Sources
         Product                              mrem
       TV Receivers                           0.50
       Airport X-Ray                          0.001
       Luminous Watches                       0.05
       Tobacco Products                    2000.00
       Coal Combustion                        1.00
       Natural Gas Combustion                 5.00
       Uranium in Dentures                10000.00

Adapted from NCRP Report No. 56

Medical Exposures

The population receives an exposure of radiation as part of planned medical procedures. This type of exposure is dependent on individual's health needs and is not considered as part of the individual's occupational exposure. Typical radiation exposures for various radiographic techniques are as follows:

        Patient Skin Entrance Exposure, per Film
       Technique                                   mrad

       Sacral Spine                                 2180
       Barium Enema                                 1320
       Upper GI Series                               710
       Dental Bite-Wing                              400
       Skull                                         330
       Chest                                          44

       Source:  Bureau of Radiological Health

Summary

The table below summarizes the annual dose rates received from natural background, medical and other sources of radiation. The values indicated are averages and may vary slightly with other reported values:

Annual Dose Rates to Population in USA    BEIR III (1980)

    Natural Background                             mrem/yr

         Cosmic                                       28
         Terrestrial                                  26
         Internal - C-14, Ra-226, Pm-222, K-40        28 
                                                      82
     Medical

         Diagnosis                                    77
         Dental                                        1.4
         Radiopharmaceutical                          13.6
                                                      92.0 
     Other

         Weapon Tests (Fallout)                        5
         Power Plant and Nuclear Industry            < 1
         Building Materials (brick, masonry)           5
         TV Receivers                                  0.5
         Airline Travel                                0.5
                                                      12.0

                                      Total          186.0 mrem/yr

Problem Set 3

Multiple choice questions may have more than one correct response.

1. The primary indirect effect of ionizing radiation upon biological target is:
   1. erythema response.

   2. free radical formation.

   3. leukegenic response.

   4. target absorption of the radiation.

2. The LD_50/30 for humans is approximately
   1. 100 mrem.

   2. 1 rem.

   3. 25 rem.

   4. 450 rem.

3. The primary cause of death following and LD₅₀³⁰ in humans is directly associated with irreparable and irreversible damage to:
   1. the nervous system.

   2. the heart, liver, and kidneys.

   3. the hematopoietic organs (blood tissue producing).

   4. the skeletal bone.

4. Which of the following cells are correctly grouped from radiosensitive to radioresistant?
   1. lymphocytes (white blood cells), endothelial cells (cells lining the GI tract), nerve cells

   2. nerve cells, lymphocytes, endothelial cells

   3. endothelial cells, lymphocytes, nerve cells

   4. endothelial cells, nerve cells, lymphocytes

5. Late Effects (5 - 20 yrs) of a large exposure to ionizing radiation may result in:
   1. death as predicted by the LD₅₀ concept.

   2. carcinogenesis.

   3. a change in skin pigmentation.

   4. significant blood changes.

6. Immediate effects (within 30 days) of a large exposure to ionizing radiation may result in:
   1. bacterial infections.

   2. deaths.

   3. development of tumors.

   4. erythema.

7. Radiation damage to the body depends on:
   1. the type of energy of the radiation.

   2. the absorbed dose.

   3. the time the radiation was distributed.

   4. the area of the body affected.

8. An acute dose of 1 rem to the whole body may result in:
   1. significant blood changes.

   2. nausea, vomiting.

   3. sterility.

   4. no observable effects.

9. The "Law of Bergionie and Tribondeau" explains the radiosensitivity of tissues as:
   1. directly proportional to the growth rate and inversely proportional to the degree of specialization.

   2. directly proportional to the degree of specialization and inversely proportional to the growth rate.

   3. directly proportional to the growth rate and directly proportional to the degree of specialization.

10. Name five factors that determine a given tissue's radiosensitivity:

        __________________________________________________________________________
    
        __________________________________________________________________________ 
    
        __________________________________________________________________________ 
    
        __________________________________________________________________________ 
    
        __________________________________________________________________________ 

11. What are the allowed Federal Exposure Limits for radiation workers?

    
                    Rems per Calendar Year
    
                              Average    Maximum
               Whole Body     _______    _______
               Skin           _______    _______
               Extremities    _______    _______
    

12. __________________ is the formula used to compute the maximum allowable accumulated lifetime exposure to ionizing radiation to the whole body for radiation workers.

13. Under what conditions can the maximum whole body exposure limits be applied?

    ________________________________________________________________________________
    
    ________________________________________________________________________________
    
    ________________________________________________________________________________
    

14. The yearly Federal whole body exposure limits for individual non-radiation workers is _______ rem.

15. The yearly whole body exposure limit for the U.S. population is __________ rem per person.

16. Occupational radiation dose limit for a minor is __________ % of the exposure limit for an adult.

17. A person becomes a radiation worker (with no previous radiation exposure history). What would be the maximum allowable whole body dose this person could receive in this year?

18. What are three major sources of natural background radiation?

             _________________________________________________________________   
    
             _________________________________________________________________   
    		 
             _________________________________________________________________

19. Why may the levels of natural radiation exposure be greater inside of some buildings than in open spaces?

    
             _________________________________________________________________
    
             _________________________________________________________________
    
             _________________________________________________________________

20. What naturally occurring isotopes contribute to external radiation exposure? Internal radiation exposure?

             _________________________________________________________________
    
             _________________________________________________________________
    
             _________________________________________________________________
    

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