Topics:

         We frequently look back to the ancients and smile smugly because we have an understanding of the world that they seemed to lack. Obviously, the early history of science is one blemished with the fact that the general population was so terribly illiterate compared to the educated few. The ratio of the educated to the general population varied in different parts in the world, but yet it can be said that very few understood simple facts of science. And in light of today's advances, even the educated were far from the truth. Yet it seems that emotion then ruled actions of men rather than reason. Today we may not be very different from the civilizations of old.

         Today we are faced with the radiation controversy, starting in Hiroshima and stretching to the nuclear power industry of the 1980s It seems that fear and misunderstanding guide policy and social reactions to policy
rather than clear, logically developed programs for commercial and governmental uses of nuclear energy. It is
not the intent of this section to criticize past or present governmental and political decisions, but rather to become informed of the physics involved in these policies.

        To approach this in a reasonable manner, let us clarify what is meant by radiation, distinguish between ionizing and non-ionizing radiation, explore today's and future uses of radiation, and finally consider the state of nuclear waste management in today's society.

         One of the major themes of the universe is the interaction of matter and energy. The basic laws and forces are few, but the ways they act sometimes seem overly complicated. We wish to explore the nature of radiation first from the perspective that is a means to transport energy, and then to distinguish between the ionizing and non-ionizing forms of radiation. This allows us to categorize radiation and study certain topics that would otherwise seem disjointed.

        It is very interesting to study science fiction because one can compare what we know about the real world with the fictional story. This comparison allows us the opportunity to apply the laws of physics to some very creative concepts. In fact one does not have to even read science fiction stories to do this, but just read the news reports of UFO sitings and visits to the Earth by extra-terrestial beings. If these space ships really fly, many probably would have utilized new forces that we are unaware of (only four are know to mankind) and even more fantastic methods to transport energy. The Saturday morning cartoons also show rather bizarre happenings that depend on mechanisms unknown to the science world. If in fact these things are really possible, we have much to learn.

Methods of Energy Transport:

At this point, we know of only four ways that energy can be transported. These four ways are:

1. Conduction - suppose we place a metallic object in a fire. Say, for example that we hold an uninsulated handle to a metal pot that is placed over a fire. It soon becomes too hot to hold. This is because the heat travels through the handle to your hand. It does this by conduction. The energy is transferred by direct contact of one molecule or atom with the next in sort of a domino approach.

2. Convection - If our pot over the fire has water in it, eventually the water will boil. As it does this, we observe little bubbles forming on the bottom of the pot (which was heated via conduction) and starting to rise. The bubbles actually involve a phase change from the liquid to the gaseous form, but they rise because they in fact have a lower density than the surrounding medium. This large scale movement of the matter is called convection. The bubbles would rise until they reached a density equivalent to the surrounding medium. On summer days we see thermal currents rise as the lower levels of the air are heated and rise until the hot air meets air of equal density. Glider pilots look for plowed ground which is black because the air above the dark ground heats up and rises faster than that over other surfaces. We can see this dramatically displayed when cumulus clouds form. These clouds are building and rising. In stellar interiors such as our own sun, there is also some convection, mixing in the sublayers and carrying energy to the surface to be radiated to the solar system.

3. Radiation - the classical sense of the word describes a method of transporting energy without a material medium. The previous two mechanisms required matter to transmit the energy. By radiation we do not need a medium for energy transport. Radiation requires the use of waves (essentially a mathematical construct) to transmit energy. The dependence on a medium for transporting energy was so strong that at one time it was thought that there was a medium that filled the universe, called ether. If this existed, then waves could travel through it and transport energy just like water waves do. This idea was eliminated when Einstein pointed out that we don't need such a crutch. Instead, he indicated that there is no such thing as an absolute inertial reference frame that movement could be related to. This is clearly demonstrated when we observed the sun radiating energy to us through the vacuum of space. And that sun energy feels warm, doesn't it?

4. Neutrino transfer - This is the least known and least understood way to transfer energy. We know that the energy of the sun is produced in the P-P cycles when hydrogen is converted to helium. In the process, some energy is given off as gamma rays or photons and some energy , depending on the particular cycle, is removed by the neutrino. This was discussed earlier. The neutrino carries away up to 25% to the energy produced. It has an extraordinarily small cross section for interaction, or the mean free path between interaction is extremely long. It generally doesn't interact. We have built several neutrino detectors in the world. One is in the Homestake gold mine at Lead, South Dakota. It consists of a 100,000 gallon tank of carbon tetrachloride and works when the neutrinos pass through the earth from the far side and finally interact with the detector. Right now there seems to be a lower than expected incidence of reactions so that either something is wrong  with the design of the system or our model of the nuclear reactions in the sun are suspect. It would certainly be a boon to mankind if a solar energy collector could utilize the energy carried by the neutrinos. It would work on cloudy days, and even at night ,. after passing through the entire earth! But, at the present such a device does not exist, and even the neutrino itself is not well understood. In fact there is a massive effort to attempt to measure the mass of a neutrino which is so elusive.

        Let us go back to radiation, the real purpose of this treatise. When we say radiation, we really mean either the mechanism of energy transport, or the resulting decay of radioactive materials. We will examine both of these as they are both significant not only as topics of discussion, but also for the study of interactions of radiation and matter.

Electromagnetic Radiation

        Electromagnetic radiation as mentioned in an earlier section comprises the total spectrum from the very long wavelength of radio waves (several metres to hundreds of metres) through the visible (thousands of angstroms) down to the very short (several angstroms) X-ray and cosmic rays. Not only do these waves have properties of wavelength and frequency and travel at the speed of light, but they exhibit very special characteristics which depend on the nature of electromagnetism. The following few paragraphs are meant to summarize the basic nature of electromagnetism. Complete details can be found in any good textbook on electromagnetic theory.

        We know already that like charges repel and opposite charges attract. That is what is meant by the sign of a charge and the significant difference between positive and negative charges. As a reference, let us choose a positive charge of unit magnitude. Then the effects are such that it will be attracted to negative charges and repelled by positive charges. The magnitude of this interaction can be written as Coulombs Law. Note the similarity in form to Newton's Force of Gravity.
 
 

        The direction of this force can be represented vectorially with field lines where the field lines then are drawn outwards from the positive charge since it repels our positive test charge. Similarly, field lines are directed inward towards negative charges, since the standard test charge is attracted by the negative charge. Negative charges act like "sinks" of field lines whereas positive charges are a "source."
Test

Figure 7-1 Electric Field Lines. Like charges repel the test charge and opposite charges attract it.

        Consider if you will, that our test charge is isolated from the rest of the world. Now, suddenly another charge is placed somewhere in the vicinity of our test charge. The effect of the repulsion or attraction is not felt immediately, but rather requires some time to be felt. The effect is propagated outwards at the speed of light, the same speed that the electromagnetic wave and light travel.
 
 

        Another situation is to take two charges that suddenly affects our positive test charge. For example, let the positive charge be on the bottom and the negative one on top. See Figure 7-3. There is a field line drawn between these two charges. The effect of the field line is to cause a force to act on our test charge. In this casethe force is downwards. The magnitude of the force can be determined by a vector addition of Coulombs Law. The field line acts like it is propagated outwards with a specific direction and magnitude. The direction and magnitude of the field effect is actually perpendicular to the direction of propagation (outwards.)

Figure 7-3 Effects of an oscillating Source.

        Now, let charges in the wire oscillate by varying both the magnitude and polarity of the charges in the wire. Then the effect at the positive test charge is a varying force both in magnitude and direction. This is equivalent to a wave traveling outward from the source (oscillating charges in a wire, or an antenna) and interacting with the test charge. Thus it is common to refer to the phenomenon as an electric field wave.

        It is not realistic to discuss electricity and magnetism separately, although we try to do this for convenience. Basically, electricity makes heat and magnetism. Magnetism makes heat and electricity. The two effects are mutually interactive. Consider the following effect. If a current flows in a wire (the oscillating charge distribution is an oscillating current) a magnetic field is produced. The direction is such that if the the thumb of a persons right hand is aligned with the current, the fingers curl around the wire in the direction of the resultant magnetic field. The magnitude is described by a more complex mathematical expression than Coulombs Law for ther Electric Field Force. That is not our concern here. What is significant is that this magnetic field is also propagated outward as if the electric field effect at the speed of light. Its direction is also perpendicular to the direction of propagation and its effect is also felt at the test charge as if a magnetic field wave were propagated outward from the source current. Actually, both the electric field and magnetic field components are propagated outwards together. Because one is sent out, so is the other. They are mutually induced, and their components are mutually perpendicular. Note the picture below, showing the electric field in the y-direction (upwards) and the magnetic field in the z-direction (perpendicular to the plane of this paper)  while the combined effect travels outward to the rest of the world in the x-direction (to the right, as shown.) Actually, this is a simplified model in one dimension of the real world propagation of electromagnetic waves. Both components are present, they are in phase and mutually perpendicular, and travel at the speed of light.

Figure 7.4  One Dimensional Model of Electromagnetic Wave

        This is a simplified model of how an electromagnetic wave is radiated from a source to an object. We are especially concerned with the effects of this kind of radiation on biological systems. Whether this wave is a radio wave, a microwave, infrared, visible, ultraviolet or x-ray, it has both a magnetic and electric field component and travels at the speed of light. The wavelength and frequency are related by the familiar relations

Types of Electromagnetic Waves:

    Radio waves are used to transmit radio and television signals. Radio waves have wavelengths that range from
    less than a centimeter to tens or even hundreds of meters. FM radio waves are shorter than AM radio waves.
    For example, an FM radio station at 100 on the radio dial (100 megahertz) would have a wavelength of about
    three meters. An AM station at 750 on the dial (750 kilohertz) uses a wavelength of about 400 meters. Radio
    waves can also be used to create images. Radio waves with wavelengths of a few centimeters can be transmitted
    from a satellite or airplane antenna. The reflected waves can be used to form an image of the ground in complete
    darkness or through clouds.

    Microwave wavelengths range from approximately one millimeter (the thickness of a pencil lead) to thirty
    centimeters (about twelve inches). In a microwave oven, the radio waves generated are tuned to frequencies
    that can be absorbed by the food. The food absorbs the energy and gets warmer. The dish holding the food
    doesn't absorb a significant amount of energy and stays much cooler. Microwaves are emitted from the Earth,
    from objects such as cars and planes, and from the atmosphere. These microwaves can be detected to give
    information, such as the temperature of the object that emitted the microwaves.

    Infrared is the region of the electromagnetic spectrum that extends from the visible region to about one
    millimeter (in wavelength). Infrared waves include thermal radiation. For example, burning charcoal may not give
    off light, but it does emit infrared radiation which is felt as heat. Infrared radiation can be measured using
    electronic detectors and has applications in medicine and in finding heat leaks from houses. Infrared images
    obtained by sensors in satellites and airplanes can yield important information on the health of crops and can help
    us see forest fires even when they are enveloped in an opaque curtain of smoke.

    The rainbow of colors we know as visible light is the portion of the electromagnetic spectrum with wavelengths
    between 400 and 700 billionths of a meter (400 to 700 nanometers). It is the part of the electromagnetic
    spectrum that we see, and coincides with the wavelength of greatest intensity of sunlight. Visible waves have
    great utility for the remote sensing of vegetation and for the identification of different objects by their visible
    colors.

    Ultraviolet radiation has a range of wavelengths from 400 billionths of a meter to about 10 billionths of a meter.
    Sunlight contains ultraviolet waves which can burn your skin. Most of these are blocked by ozone in the Earth's
    upper atmosphere. A small dose of ultraviolet radiation is beneficial to humans, but larger doses cause skin
    cancer and cataracts. Ultraviolet wavelengths are used extensively in astronomical observatories. Some remote
    sensing observations of the Earth are also concerned with the measurement of ozone.

    X-rays are high energy waves which have great penetrating power and are used extensively in medical
    applications and in inspecting welds. X-ray images of our Sun can yield important clues to solar flares and other
    changes on our Sun that can affect space weather. The wavelength range is from about ten billionths of a meter
    to about 10 trillionths of a meter.

    Gamma rays have wavelengths of less than about ten trillionths of a meter. They are more penetrating than
    X-rays. Gamma rays are generated by radioactive atoms and in nuclear explosions, and are used in many medical
    applications. Images of our universe taken in gamma rays have yielded important information on the life and
    death of stars, and other violent processes in the universe.

        We look now at the effects of this kind of radiation. In general, we will not include the very short wavelength radiation since we cannot distinguish it from X-rays, gamma rays except as to its source. This kind of radiation is usually classified as non-ionizing radiation. Some simple examples of these are Radio and TV Transmission, Flourescence and Phosphorescence, Microwaves, and Power Line Radiation. We explore these few topics to give the reader a foundation in the kinds of non-ionizing radiation we are all generally exposed to on essentially a continuous basis.

        Look briefly at radio and TV radiation. Compare their interaction with particles on the cellular level. In general, if the wave is bigger than the object it interacts with, it acts as if the particle were transparent. If the wave is of the same size, or smaller than the object it interacts with, scattering and possibly absorption resulting in this case in electronic excitation occurs.

Flourescence and Phosphorescence

        Consider a simple Flourescent Tube or "bulb". Typically a Mercury Vapor is placed in the tube which has a Phosphor coating on the inside. The electricity provides energy to "shock" the gas by causing thermally excited electrons to interact with the Mercury atoms. The excited atoms emit an ultraviolet wavelength photon which interacts with the Phosphor coating. The Phosphor atoms which absorbed the U.V. photons then spontaneously decay and give off visible light. The process must be explained in terms of the quantum atom and photon emission from various electronic transitions. The electrons are not removed from the atoms. i.e., the atoms are not ionized. Flourescence is the process by which a material absorbs ultraviolet radiation and de-excites in smaller steps by emitting visible radiation. Phosphorescence is a similar process, but results in glowing for hours after exposure to U-V radiation. The sun is a better source of UV than an incandescent light bulb.

        Laundry is something we all have to do sooner or later, whether we like it or not. "Blueing" is sometimes added to the rinse water to make clothes look whiter. Actually, it gives the clothes a bluish tint that makes them look whiter by leaving small amounts of phosphor in the clothes which flouresces in the blue region under sunlight... Wow, don't your clothes look white when hanging out in the sun? And if your whites are bright, then obviously your whole wash must be clean! At least that is what Madison Avenue advertising tells us.

        "Black Lights" which are used in different kinds of light shows basically emit UV radiation. Remember that UV radiation is shorter in wavelength than the visible region. It would seem that this bulb should be less expensive to manufacture than a typical flourescent tube because it doesn't, even need the phosphor coating. But of course they cost more; after all the public will pay for something special.

Cathode Ray Tubes

        Cathode Ray Tubes, basically like used in oscilloscopes and televisions use a similar process. Electrons are emitted from the filament and accelerated by a high voltage potential. Magnetic coils can cause -the beams of electrons to deflect as desired. They strike a phosphor coating and give off light. Adjustable magnetic fields can deflect the beams back and forth and give rise to a slight vertical motion which gives the effect of a uniformly bright screen. To get a black spot we merely shut off the beam at a specified time for a specific duration. Color TVs have three "guns" - red, blue, and green which combine to make white light or any color in between. (Yes, red, blue, and green are the three primary colors. Combinations of these give all possible colors. Red, yellow, and blue are primary colors in a subtraction process such as painting. See Figure 7-6.)

Figure 7-6a Primary Colors Add to make common colors

Figure 7.6b  Primary colors in the Subtractive Process (eg. painting)

        While radiation from televisions is largely electromagnetic, a small amount of X-rays can also be emitted. It is best not to watch television too closely. Remember thit the electromagnetic radiation intensity falls off as 1/d so that doubling the distance decreases the exposure to 1/4 th and tripling the distance results in 1/9th the effect. See Figure 7-7.
 
 
 
 
 

Figure 7-7. Radiation decreases Is the square of the
distance from the sdurce. I " 1 / R

Microwave Ovens

        Microwaves are electromagnetic waves of wavelengths that are several centimetres long. Some TV stations (such as HB0) broadcast on microwave frequencies. The telephone companies typically send long distance messages via microwave translators. They are common in society today. One interesting application of microwaves is the microwave oven. The nature of microwaves is obviously not well understood by the public. Not long ago I was in a popular department store and overheard a consumer mentioning to the salesman that she would buy a microwave oven for its convenience and energy savings but she did not want her family eating those things!

   Like light waves or radio waves or ultraviolet waves, microwaves carry energy as they propagate outwards. They have a frequency as approved by the FCC of 2450 + 25 MHz or about 12 cm in wavelength. That's about the size of the palm of your hand. They are produced in an oven cavity by a magnetron tube or possibly a klystron assembly. These waves are propagated through a waveguide until they strike a "stir blade" which scatters them to be reflected with in the oven.
 
 

        Microwaves, like other electromagnetic waves, exhibit the property of polarization. Polaroid sunglasses "filter" out one component of the electromagnetic wave. In other words, one component of a wave can be filtered out. For example, a vertically aligned grid can allow one component to cross it while absorbing the other. If a screen is used, or two perpendicularly placed polarizers, the wave is essentially stopped. Polarized glasses considerably cut down light to the eyes by filtering out one component of the light wave. If two such polarizers are rotated until they are perpendicular, the light will stop. The screen on the microwave oven's door doss the same thing. The doornneed not be glass. It can be plastic, but it needs the metallic screen, somewhat small compared to the size of the waves, to effectively stop the emission of microwaves. Leakage should not occur from the screened door, but it is possible that the gasket seal around the door may allow a linearly polarized component to leak out. This is highly unlikely on a door closed properly.

Figure 7-9 Effect of Polarization to stop one component of an electromagnetic wave. Crossed screens effectively stop the entire wave.

        Like other electromagnetic waves, microwaves are subject to superposition. That means that the waves vectorially add and subtract their effects. Below is shown how they may constructively and destructively interfere. While the stir blades reflect the waves about in the cavity, it is possible for some resonant spots to exist. This could result in uneven heating. Sometimes manufacturers utilizes a rotating platform for the food so it gets even exposure.

        Microwaves cook differently than conventional ranges and ovens. Conventional ranges cook by conduction. They heat the pan. The pan gets hot and the food in contact with it gets hot by conduction. Conventional ovens heat the air which then by conduction heats the food from the outside in. The middle is often less cooked than the outside. This is frequently desirable for browning effects. But the Microwave cooks by a different principle. Microwaves penetrate and interact with food molecules which are made mostly of water. These molecules resonate at the same frequency as the microwave radiation. Consequently, they heat by stimulating the vibration of the food molecules. Recall from kinetic
 theory that the average kinetic energy of molecules is measured by temperature. The usual glass or even paper containers do not absorb this radiation and except for the heating of them by contact with the hot food, will usually remain cool. Caution is recommended in heating certain foods such as sugars. Jelly filled rolls can become dangerously hot. The jelly heats faster and gets hotter than the rest of the roll. Documented cases of burns have occurred by eating too ambitiously. Breads are typically dry and get hard if overheated. Steaks, especially those fine rare and medium rare ones are almost impossible to cook properly because of the rather even heating effect.

        But the costs are minimal. It has been reported that the power costs are less than $10 per year for cooking 80% of a family's food with a microwave oven. It is far more efficient than any other oven and possibly safer because burns are unlikely. I~ there were any leakage, the intensity would diminish by 1/d so any possible dangers are lessened by increasing the distance from the observer to the source. Refer to Figure 7-7.

        Two kinds of hazards can occur from microwaves, but the reader is cautioned that these are highly unlikely to result when microwave ovens are used properly. Thermal (heating) effects can result in any tissue that contains fluids which cannot readily dissipate heat. Since microwave ovens have safety locks which prevent them from being activated with the oven door open, we do not discuss that here. If your safety feature becomes inoperative, do not operate the oven until it is serviced by a competent technician.

        The nonthermal effects result when molecular bonds are stressed or altered. The greatest hazards are to the eyes. They are of course sensitive to thermal effects too, but the nonthermal aspects of the radiation can cause cataracts to form prematurely. Research shows that the effects depend of the level of radiation and the time of exposure. On exposure at 300 mW/cm for T>15 min will, but at 200 mW/cm for T>30 min does not. There is an obvious threshold value of intensity. There also seemed some inhibitions of the nervous systems and reflexes in rabbits after repeated exposures, but that they returned to normal two months later. It is probable that some regeneration is involved therein. It is documented that workers such as welders, TV transmitter technicians and particle accelerators workers experienced fatigue, excitability and anxiety. These occupations result in microwave exposure. Generally, the shorter the microwaves, the more the damage possible.
 
 

Electric Transmission Lines

            Transmission lines carry electricity from the power plants which are normally remote from the point of where the electricity is used. Since the energy lost due to-heating is proportional to the square of the current, the power is usually carried at a high voltage and low current value. Some of these voltages are of the order of 115 kilo-volts (kV) to a maximum of 765 kV in North America. There has been some recent publicity and concern about these power lines and possible harmful effects to living beings and the environment.

        Like any other line carrying electricity, they are sources of electromagnetic waves and can affect electrical charges. We do not discuss obvious hazards such as direct contact with them through kite flying or similar incidents, but rather look at the field effects. The lines are placed on high poles to minimize the effects near the ground. At ground level the magnitude of the elctromagnetic field effects is about 5 to 10 times less than that of a color TV, and about 50 times less than that of an electric hair dryers It is possible, however, that directly under them that electrostatic shocks can be experienced. These are similar to walking across a carpet in a dry house. Typically these are harmless.

         Long term studies have been conducted by Johns Hopkins University and the University of Toronto. No long term effects have been identified, but the Soviet Union reported that workers exposed to much stronger fields than exist at North American transmission lines did experience fatigue and headaches. It was difficult to correlate these effects with causation. In the last ten years, more than $30 million dollars has been spent investigating the phenomena and no  !
evidence of harmful effects was demonstrated.  The basic hazards are not from the electromagnetic fields, but mostly from the power lines themselves.

         There is a coronal effect associated with them.  The corona is the ionization of the air surrounding the wires
when the insulating capability of the wires are exceeded. In the dark, especially during a drizzle, tiny fingers spark
out and appear to make the vicinity glow. It does make a crackling sound and sometimes even produces that ozone smell which accompanies electrical burning. This is essentially harmless to persons nearby although radio and TV
interception may be somewhat disturbed.  Generally, unless further information is available to demonstrate other effects, it seems unlikely that any harm  can come to humans from the radiation itself.  The usual
hazards accompanying any electrical line apply.    !

Ionizing Radiation

         Non-ionizing radiation is present in many forms all around us. We live with it on a contnuous basis. Effects are
subtle and perhaps minimal in most cases. But results of ionizing radiation (radiation so energetic that  it causes
orbital electrons to be removed from atoms) are more complex and potentially damaging to biological systems.
 Regardless of whether the source of ionizing radiation is natural or man-made,  the mechanisms responsible for it
effects are well known:

• Charged particles interacting directly with electrons in an atom through Coulomb's Law. (Equation 5-2.)
• Electromagnetic radiation or photons may transfer energy through matter-radiation interactions. We already studied such effects as the photoelectric Effect, Chapter 5.

Biological Effects of Radiation

        Two basic effects of radiation are important - the somatic and genetic effects. The somatic effects pertain to the health of the affected individual while genetic effects are transmitted through the reproductive process. Regardless of the source, when radiation affects a biological system, the following, three phase sequence occurs.

First, the physical phase, in which energy is absorbed. Typically, a single orbital electron is removed from an atom by one of the physical processes (particles or waves interacting with atomic electrons.) At this point, the molecule to which the damaged atom belongs, is consequently, altered. This is called the chemical phase, wherein chemical changes affect the cells. Only a fraction of a second has elapsed thus far. Now, the biological phase of the sequence begins. This could take years or decades of years.
 
 

        It may very well be that the body itself can repair any damage, or perhaps it will take a long time, perhaps years, before the damaged cells affect the overall health of the body. Human cells reproduce, dividing perhaps fifty times before they die. Cells are continuously regenerating. Radiation can affect cells particularly sensitive to this process. Embryos, because of the rapid growth process, are especially sensitive to radiation. Not only can cells develop abnormally, but cancer, an uncontrolled growth of cells, can also be induced.

        It has been estimated that if the entire population of the United States were exposed to 5 rems additional radiation over the next 30 years (this is double our normal background level) there would be an increase of 2% in the present cancer rate and. 0.3% in the total death rate. The risk analysis calculations can become quite complex. Any time that affects applied to human beings are considered, it is difficult to fully include other intervening variables. For example, Merril Eisenbud remarked ("Nuclear Power and the Public", University of Minnesota Press, 1970) that "... temperature, like ionizing radiation, can cause genetic mutations and that as much as 50% of the mutations that occur normally in contemporary man might be due to the increase in testicular temperature caused by the male practice of wearing trousers."
 

        Genetic effects are caused in the same manner as radiation damage. In affecting cells which reproduce, DNA molecules may be damaged. Reproductive cells contain chromosones. Human cells have 23 pairs of chromosones, each with thousands of genes. On reproduction, 23 single cells from both male and females combine to make the 23 pairs of chromosones. This process is particularly sensitive to radiation.  The reader is advised to investigate the extreme effects of radiation from the WWII bombings of Hiroshima and Nagasaki. Radiation Effects Research Foundation is a Cooperative Japan-United States Research Organization which (RERF) conducts research and studies--for peaceful purposes--on the effects of radiation exposure on humans  with a view toward contributing to the maintenance of the  health and welfare of atomic-bomb survivors and to the enhancement of the health of all people. It provides answers to such questions as How many persons died in the atomic bombings?  or How many cancer deaths have occurred among atomic-bomb survivors and how many of these can be attributed to radiation?

Background Radiation

        Let us look at typical quantities of radiation people are exposed to naturally from various sources. Since normal levels are quite low, far far below a rem, the quantity milli-rem (one-thousandth of a rem) or mrem, is used. According to the National Research Council, the average exposure per person, consists of natural background radiation plus radiation from man-made sources. It should be obvious that there is little that can be done to protect oneself from naturally occuring sources, on the average.

        Natural background radiation generally amounts to about 102 mrems per person per year. Cosmic rays from the sun and stars, reaching the surface of the earth after interacting with the upper atmosphere, consists of mesons, electrons, and protons. About 1 strikes every square centimetre of area per minute at sea level. The atmosphere protects us since this exposure doubles every 2000 m in altitude. Cosmic rays account for about 44 mrems per year. People living in Cheyenne, Wyoming, for example, receive about twice the average exposure as do people living at sea level.

Table 7-4  Background Radiation

Radioactive Decay

        Radioactivity is essentially a natural phenomena. When the numbers of protons and neutrons in a nucleus is unbalanced (there are "magic", stable ratios for each element) the nucleus becomes unstable. Nature's way of bringing the nucleus back to a stable situation is to spontaneously emit radiation. (All nuclei with more that 83 protons are radioactive.) This radiation is in the form of alpha, beta or gamma emission. These come directly from the nucleus. Alpha particles are the nuclei of a helium - 4 atom. i.e., Alpha particles have two protons and two neutrons. They are not atoms for there are no electrons attached to them. Alpha particles are ejected from the nucleus through the process of radioactive decay. In doing so, the "parent" nucleus loses 2 protons and 2 neutrons and is thus itself, transmuted into something else. This can, for example, be written as:

        Some say that all materials will decay if we wait long enough. Verification of the half-life of the proton will support this concept. See Chapter 6.
 

Interactions between the electric field of an alpha and orbital electrons in the absorber cause ionization and excitation events.Because of their double charge and low velocity (due to their large mass), alpha particles lose their energy over a relatively short range. Alpha particles interact through electrostatic forces as their positive charge attracts the extranuclear electrons of the surrounding material through which they pass.

One alpha will cause tens of thousands of ionizations per centimeter in air. The range in air of the most energetic alpha particles commonly encountered is about 10 centimeters (4 inches). In denser materials, the range is much less. Since an alpha particle is about 7300 times heavier than an electron, it does not easily scatter and generally travels in a straight line through matter.

Alpha particles are easily stopped by a sheet of paper. Because of their limited range, they are unable to penetrate the outer, dead layer of skin on the body; therefore, they are not an external hazard to the body. Alpha emitting radioactive material is a concern when it enters the body through inhalation, ingestion, or an open wound. In the body, alphas are able to interact with living tissue and deposit large amounts of energy in small volumes of tissue.

.

Again, the same notation is used. Note that to conserve charge in this decay, internally, a neutron must be converted to a proton. The total number of neutrons and protons is conserved. An anti-neutrino accompanies the decay.
 

Normally, a beta particle loses its energy in a large number of ionization and excitation events. Due to the smaller mass, higher velocity and single charge of the beta particle, the range of a beta is considerably greater than that of an alpha . An average energy beta particle may travel about three meters in air. Since its mass is equal to that of an electron, a large deflection may occur with each interaction, resulting in many path changes in an absorbing medium. Like alpha particles, beta particles
primarily undergo electrostatic interactions with orbital electrons.

If a beta particle passes close to a nucleus, it decreases in velocity due to interaction with the positive charge of the nucleus, emitting x-rays known as bremsstrahlung radiation. The energy of the bremsstrahlung x-rays has a continuous spectrum from zero up to a maximum equal to the maximum kinetic energy of the betas. The production of bremsstrahlung increases with the atomic number of the absorber and the energy of the beta. Therefore, low Z materials are used as beta shields.

A positron will lose its kinetic energy through ionizations and excitations in a similar fashion to a negatron. However, the positron will then combine with an electron. The two particles are annihilated, producing two 511 keV photons called annihilation radiation.

Beta particles may be an external, as well as an internal, hazard because with sufficient energy they may penetrate the outer, dead layer of skin. The radiation from an external beta source is primarily a hazard to the skin and lens of the eye. Alpha particles and beta particles are forms of directly ionizing radiation. Provided the individual particles have sufficient energy, they may directly disrupt the atomic structure of matter

Gamma rays and x-rays differ only in their origin. Both are electromagnetic radiation, and differ only from radio waves and visible light in having much shorter wavelengths. They have zero rest mass and travel at the speed of light. They are basically distortions in the electromagnetic field of space, and interact electrically with atoms even though they have no net electrical charge. While alphas and betas have a finite maximum range and may therefore be completely stopped with a sufficient thickness of absorber, photons interact in a probabilistic manner. This means that an individual photon has no definite maximum range. However, the total fraction of photons passing through an absorber decreases exponentially with the thickness of the absorber. There are three mechanisms by which photons lose energy.

The photoelectric effect is one in which the photon imparts all its energy to a tightly bound orbital electron. The photon simply vanishes, and the absorbing atom becomes ionized as an electron (photoelectron) is ejected. This effect has the highest probability with low energy photons.

Compton scattering provides a means for partial absorption of photon energy by interaction with a 'free' (loosely bound) electron. The electron is ejected, and the photon continues on to lose more energy in other interactions. In this mechanism of interaction, the photons in a beam are scattered, so that radiation may appear around corners and in front of shields.

Pair production occurs only when the photon energy exceeds 1.022 MeV. In pair production, the photon simply disappears in the electric field of a nucleus, and in its place two electrons, a negatron and a positron, are produced from the energy of the photon. The positron will eventually encounter a free electron in the absorbing medium. The two particles annihilate each other and their mass is converted into energy. Two photons are produced each of 0.511 MeV and are emitted in opposite directions(180 degrees). The ultimate fate of these two photons is energy loss by Compton scattering or the photoelectric effect. For a given energy, pair production is more likely to occur in high atomic number materials than low atomic number materials.

Photons ionize matter indirectly. They do not produce chemical and biological damage by themselves, but when absorbed in material they give up their energy to produce ionized electrons with enough kinetic energy to produce further ionization. Photons may travel great distances and penetrate the body. A gamma ray or x-ray source may cause damage to deep-seated organs and tissues without being in the body. They are both an external and internal hazard to the body.
 

        The three major particles ejected from radioactive sources, again, are the alpha, beta, and gamma. Additionally, while not ejected from the nucleus of radioactive atoms, a study of radiation effects must include (from other sources) protons and neutrons. Alpha particles can be "stopped" in a few centimetres of travelling through air. If human tissue were exposed to the, alpha particles (because they are so heavy) would penetrate only aboiut one micron (one-millionth of a metre.) i.e., normal clothing is suffciient protection. Remember that alphas consist of 2 protons and 2 neutrons. An electron or beta particle, is almost 7500 times less massive. They move much faster and penetrate about 180 times deeper than do alphas. Still, clothing may provide protection. Simple barries are effective. But highhly energetic photons, or gammas are entirely different. They travel at the speed of light and can penetrate concrete walls. They can be extremely harmful to biological systems. The alpha and beta become real problems when their "parents" are ingested and the radioactive decay occurs internally. Radon, if breathed in through the air, decays via alpha emission in less than 4 days.

        It should be emphasized at this point that the alpha, beta and gamma are not radioactive. They are the same particle as if coming from other sources. Following is an example of the repeated decays in some elements and the times required in the process. Risk and hazard depends on the quantity, the energy of the decay products, and the rate of decay. Just because some things, like Uranium, have a long half-life in decay, they may not be as hazardous as something that decays evry quickly and gives off massive amounts of dangerous particles. On the other hand, respect for hazards is always wise.

We said that on the average, a person is exposed to about 102 mrems of natural radiation. In certain places on the earth this may be more or less. In one place in India, the population is exposed to more that 1300 mrems per year. Some of this other naturallky occuring radiation is due to internal and external sources.

Radium Dial Painters - 1926

        The internal radioactive sources come to us in forms of food we ingest (perhaps radioactive isotopes of iodine or patassium) or even the air we breathe. One indeed unfortunate incident involves women, who in the 1920s, were employed to paint watch dials with luminous paint containing radium mixed with zinc sulfide. Those of us who have painted very fine objects know well the technique of "tipping" the brush with the tongue to keep the point sharp. These women ingested radium.

Radon- Halitosis of the Earth

        Ed Ney, University of Minnesota researcher, describes Radon gas, a naturally occuring daughter of uranium, as a halitosis of the Earth. It can be ingested with the air we breathe if quantities are sufficient.

        Radium ( Ra) decays to Radon (Rn) with a 1600 year half-life. (Half-life is merely the time for half of the radioactive material to decay, so it is a good measure of how rapidly an object decays. Total radiation depends more on the quantity present.) Radon then decays in 3.8 days giving off an alpha particle as it transmutes to Polonium. Suffciient quantities can be quite hazardous.

Does Radon make a difference? Does smoking matter with radon exposure? If 1,000 people were exposed to this level over a life time who are:

         Scientists estimate that 2,000 to 20,000 Americans die each year from cancer caused by radon. This is perhaps the single most important radiation problem in the world. Most soils in the United States contain between 0.33 and 1 pCi of radium per gram of mineral matter and between 200 and 2,000 pCi of radon per liter of soil air. Radon gas enters homes, from wells, open pits and pipes in basements. Well sealed homes are worse, especially in winter months, because of the lack of ventilation. There are ways, fortunately, to seal foundations as well as air exchangers, to decrease radon levels, but at some expense. It is tasteless, odorless, and can't be filtered with home filtration systems. Public buildings, because of larger volumes for the same floor space, usually are safer.

Radiation from Medical Practices

        The largest single source of man-made radiation is from the diagnostic use of x-rays. Most of this will be covered in class as it is a bit sketchy here.

1. X-Rays:

 a. Characteristic x-rays- emitted in atomic transitions when an electron in an inner shell of an atom is removed an electron from an outer shell drops down to take its place. Electrons sort of want to find the lowest energy state to be in. In any case, in making this transition a high energy photon is released, of x-ray wavelength and frequency.

b. Bremsstrahlung(braking radiation) x-rays are emitted when an electron passes close to the nucleus of a massive atom. As it turns and is accelerated it emits an x-ray. This is generally the process used in x-ray tubes.

2. Radio-Isotopes in Medicine:
 

3. Flouroscopy instead of x-ray film,. allow photons to pass to a flourescent screen - can see organs moving - eg. use barium liquid passing through esophagus

4. Tomography - see difference between diseased and healthy tissue - move x-ray source and/or the film to see different layers.

•  Linear tomography
• Axial tomography - rotoate film and source along axis of patient
• Computer Axial Tomography  (CAT Scans)

5. Dental x-rays

• Are dental x-rays necessary?
• Digital x-rays

6. Radioactive Tracers

Food and Sewage Sludge Irradiation
 

1. DOE Byprdducts Utilization Program

2. Disinfection of sewage sludge

3. Food treatment

a. Trichenella Spiralis - pork!

b. Caribbean fruit fly

c. 3rd world food preservation - Bangladesh

4. Medical products treatment

Summary:

Ionizing Radiation:

Types of Particles: Alpha (He ++ nucleus)
 Beta (electron or positron)
 Gamma (a form of wave energy)

Also included are neutrons, protons, X-rays, cosmic rays, etc as sources of radiation. Only the first three come directly from the nucleus.

Sources

Natural Background - Cosmic Rays

Roentgen - describes INTENSITY of radiation

Rad - describes amount of energy absorbed
 

rem - rad equivalent on man

 background levels < 200 mrem per year

Range of charged particvles - 4 MeV alpha, about 2.5 cm in air; about .003 cm in H20. - easy to shield against.

 Range of gamma type (including X-rays) depends on
processes involved: photoelectric effect
  Compton
  pair production
 

Know 1/2 Life of radioactive materials

Effects on humans:

3 stages: 1) Physical - energy absorbed by electron

2) Chemical - molecule & surrounding effects

3) Biological proceses affected

Levels - 20 - 100 rems subtle effects

100 - 300 rems - vomiting ; radiation sickness; loss of hair, teeth?

500 rems - 50% chance of survival or death, depending on if you are an optimist or pessimist
 

Medical Uses - is risk worth the benefit?

X-rays

Flouroscopy

CAT - Computer Axial Tomography

Angiograms

other medical imaging

QUESTIONS

1. Tanning booths - ionizing or non-ionizing? Can they be harmful?

2. Microwave and normal ovens for cooking:

    a. Mechanism of energy delivery

    b. Time involved

    c. quality of cooking
 

3. Check with your doctor and dentist about levels of radiation involved in chest x-rays; dental x-rays.
 

4. Make a list of background radiation for your lifestyle.
 

5.  What is Half-Life?
 
 

BIBLIOGRAPHY

1. Nuclear Waste Management, Chautauqua Course, National Science Foundation, Argonne National Laboratories, 1984.
 

2. Loeb, Paul, Nuclear Culture , New Society Publishers, Philadelphia, 1986.
 

3. Ney, Ed, Radon - Halitosis of the Earth, University of Minnesota, 19 8.
 

4. Power Lines - Answers to Questions, MAPP - Mid Continent Area Power Pool, 25 Soo Building, 507 Marquette Avenue, Minneapolis, MN 55402.
 

5. Midfield, Peter, Radioactive Radiations and Their Biological Effects, AAPT, Stony Brook, NY, 1977.
 

6. Laws, Pricsilla, Ionizing Radiation in Health Care, AAPT, Stony Brook, NY
 

7. Cosmic Ray Dosage, Apollo-Soyuz Pamphlet #6, NASA, 1977.
 

8. "Juarez: An Unprecedented Radiation Accident". Science, Vol 223, 16 March 1984.
 

9. Inman, Virginia, "Risk of Cancer from Radon", Wall Street Journal, Feb 23, 1984.
 

10. Curnette, B., "Principles of Microwave Radiation",
Journal of Food Protection, Vol 43, Aug 1980.
 

11. Lambert, John P, "Biological Hazards of Microwave
Radiation", Journal of Food Protection, Vol 43, Aug 1980.