TOPIC 1: Sources of Radiaiton

Let’s explore sources of radiation.

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In the 1980s, the U.S. population averaged 360 mrem per year of dose to radiation from the environment.  Only 15% of that was from medical sources.  That has increased in the following two decades.  Now approximately 48% of the average exposure to radiation comes from medical sources.  The National Council on Radiation Protection & Measurements (NCRP) now estimates the U.S. population averages approximately 600 mrem per year of exposure with 50% coming from background (or radiation from the land, air, cosmos) and 50% coming from man-made sources.

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This chart shows that of the 50% of the exposure to radiation we get, medical dose is predominant.  This comes from the x-rays we get from a broken bone or our dentist.  We also have to take into account that the average age has increased and more people are going to the doctor more often.

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If we flip that chart and look at the dose from natural, background radiation, we see the amount of background exposure each individual receives will vary depending on where they live, what they do, where they travel.  Of the background radiation, the primary source for dose is from Radon gas.

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Examples of background radiation is the Radon gas we inhale and the food and water we ingest which give us doses from inside our bodies.  Then we have the land we walk on, the building materials that surround us, our sun and the cosmos that give us does from outside our bodies.

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Radon is a naturally-occurring radioactive material that is a “daughter” product of radium.  Radium is the “daughter” of natural uranium and thorium ores that have been on earth since the beginning of time.

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Radon gas exposures contribute the most to our annual, background dose. Radon is an inert gas like neon and helium that cannot combine chemically with other elements. So, Radon, for example, can be breathed in and breathed out with no chemical reaction in the body.  However, if the radioactive Radon decays while in our lungs, it emits energy and becomes another element – polonium – which is itself radioactive.  Polonium, a “daughter” of radon, as well as the daughters of Polonium, also emit radioactive particles that emit energy and can damage the lungs.  Areas that have higher deposits of uranium or thorium, such as phosphate mines, will have higher radon concentrations.

Radon is of no consequence as an external source of dose, but it and its “daughters” are the source that will give the lungs a dose of radiation.

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There are many sources of man-made radiation.  We find it in medicine, in industry and of course, nuclear power.  The types of sources range from sources that are sealed in stainless steel and welded to ensure the radioactive material does not leak out.  In these cases only the emissions that can come through the stainless steel are used in industry.  Hopefully you guessed this would be limited to gamma rays or x-rays.  Other sources can be liquids to be mixed with medication or airborne because they volatilized in air.

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In this slide, a herbicide  labelled with C-14 is used in research as “tracers”.  The C-14 replaces stable carbon in the herbicide or pesticide compound.  The herbicide or pesticide is sprayed on the ground and taken up by the plants. Later, the plant’s roots, leaves, stalk, and even fruit is analyzed to identify the efficacy of certain herbicides and pesticides.  Certain personal protective equipment (PPE) is used to ensure that uptake to the worker does not occur.  The radiation levels from the container are minimal as the C-14 emission is weak.  The concern would be uptake through wounds or inhalation if a respirator were not used.

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There are many consumer products that have small amounts of radioactive materials.  They are so small that when the component is no longer desire or no longer works, it can be thrown in the trash.  A primary example is the household smoke detector.

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Medical X-rays will provide the majority of man-made exposures.  However, most people will not receive any doses from nuclear medicines.  Some examples are thallium-201 for cardiac stress tests, fluorine-18 for positron emissions tomography (PET) exams, or iodine-131 for thyroid treatments.  Some sources of radiation therapy can be administered from outside the body.  “Teletherapy” treatments include external beam radiation for the treatment of tumors.  Some sources can be administered inside the body, such as “Brachytherapy” which places the source right in the tumor. Brachytherapy sources are sealed sources implanted in the tissues where only the gamma radiation from the source is used for the treatments, the radiation source may be removed after treatments.  Some sources remain implanted, such as radioactive “seeds” which are tiny sources implanted in the prostate for treatment of prostate cancer.  In this case, the “seeds” remain in the prostate.

Lets take a look at the pie chart which details types of radiation exposures from medical sources.  The amount of exposure each individual receives will vary depending on where they live, what they do, where they travel, and what medical procedures they have had.  From 1980 to present day, the biggest contributor is the Computerized Axial Tomography or CAT scans.

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Here are some examples of medical radiation sources. The CAT scan, nuclear medicine, fluoroscopy (continuous x-ray) and radiography (discrete or individual x-rays).

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Cigarette smoking was not included in the total from man-made sources as not everyone smokes. Cigarettes are “manufactured” by man into a form that can be inhaled, thus creating the exposure source.

So, for those that do smoke one pack a day or more, the dose from background radiation is much higher.  This comes from the naturally occurring polonium-210 that is taken up by tobacco plants.  In addition, Po-210 is an alpha emitter; thus, when inhaled, the smoke gets to aveoli in the lungs, where the transfer of oxygen occurs, to the blood stream.  It is thought that Po-210 could be a major contributor of lung cancers.

One pack a day gives much more dose than multiple chest x-rays in a year.

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When we think of radiation uptake, we think of radioactivity from Chernobyl, Three-Mile Island, or the atomic bomb testing.  But there are a variety of potential sources of radiation uptake.  The picture above shows potential sources.  Uranium, Thorium and all their daughters have been on this planet since it was created.  Additionally, more radioactivity is creating daily in the atmosphere and all around us which we breathe, drink, or consume in food.