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Radiation Related Frequently Asked Questions

U of M's Radiation Questions and Answers

Question 1: How much is too much radiation?

That is a very good question and not easy to answer. This will depend on the individual, the risk they are taking and the benefit that they will receive from it. As pointed out in the Radiation and Us page, we receive approximately 360 mrem of radiation every year. The legal limit imposed by the federal government in this country for an occupationally exposed worker is 5,000 mrem per year. If we look first at doses received in a short amount of time, (acute doses), the first biological effect begins to be able to be detected by laboratory analysis at 10,000 to 25,000 mrem. Actual immediate life threatening doses are limited to levels of 100,000 mrem and above. The life shortening doses may be lower than that, and are approximated by taking the data at higher doses where the effects are apparent and extrapolating the risk down to lower doses. Being conservative, the regulators use a model of a straight line from high doses down through the zero dose/zero risk point, so that any dose is assumed to present some small risk. Also you need to know that doses received over a longer period of time allows for repair of cells by the body, and presents less of a risk. See the Radiation and Risk page for more information. So to answer the question, the doses receive by the workers in nuclear power, an extra 100 to 5,000 mrem per year (average about 500 mrem), are seen by most scientific organizations as presenting a low risk compared to normal occupational hazards encountered during a working lifetime. Children, fetuses and embryos are more sensitive and have a longer expression time than adults, and so have smaller allowable doses. It is really a personal choice how much is too much. In some situations, such as to save someone's life, I personally would accept around 100 rem, but in the normal course of my work, I would rather keep my dose to less than 5 rem per year.

See Radiation and Us and Radiation and Risk short essays

Question 2: Do you have any information about Dr. Luckey's work and where can you get more info on "Hormesis"

Dr. Don Luckey is the probably the most famous of the public believers in hormesis, but not the only one. He is a member of Radiation, Science, and Health (web site: http://cnts.wpi.edu/rsh/). More info about his work can be found at the following references:

Dr. Lucky also edited/authored a book for the CRC Press company on Hormesis that is pretty good. The CRC can be reached at:

CRC Press, Inc.
2000 Corporate Blvd., N.W.
Boca Raton, Florida 33431 USA
Phone: (407)-994-0555 or 1-800-272-7737 (US only)

By hormesis, you mean radiation hormesis. The idea of hormesis goes back to ancient Greece, where it was thought that frequent small doses of a poison would fine tune the body and cause positive health effects. The same idea has been thought to apply to radiation, such that small amounts of radiation are actually good for humans, and that without it, our health actually suffers.

Other references for Hormesis:

Health Physics, Vol. 52, No. 5, May 1987, is entitled "Special Issue on Radiation Hormesis," and was edited by Leonard Sagan. The table of contents is a bit lengthy, but here are the section headings:

  • Editorial Comment (by Genevieve Roessler)
  • Preface (by Jerry J. Cohen)
  • Guest Editorial (by Leonard Sagan)
  • Hormesis Overview
  • Cellular and Tissue Level Effects
  • Plant and Animal Effects
  • Alpha-Particle Exposures
  • Human Effects Mechanisms
  • Correspondence (a brief exchange between John Gofman and Leonard Sagan)

Macklis & Beresford published an article "Radiation Hormesis" in the Journal of Nuclear Medicine Vol32, 2, P350, '91 that includes 77 references, that you may find useful.

You can subscribe to the BELLE (Biological Effects of Low Level Exposures) by contacting:

Northeast Regional Environmental Public Health Center
Univ. of Massachusetts Amherst, MA
phone 413-545-1239 or FAX 413-545-4692

This is an informative publication, covering low level exposure to many toxic agents, including radiation. The December 93 issue has a good article by Leonard Sagan of EPRI on "The Low Dose Effects Paradigm", which considers the pluses and minuses of this approach. It is published quarterly and is quite well done.

Question 3: What is the danger of dental x rays?

The danger would be a very slight increase in the risk of cancer. But, from a health standpoint, dental x rays have a much bigger benefit than risk. You will notice though, that your dentist and dental hygienist will not stay in the same room as you, for there is no reason for them to receive doses several times a day, 5 days a week. Their leaving and the lead apron that you may be asked to wear are measures to reduce all of the doses so that they are as low as reasonably achievable.

See Radiation and Us and Radiation and Risk short essays

Question 4: What is the danger of mobile [cellular] phones and can they cause cancer of the face or brain?

Mobile phones radiate and receive electromagnetic radiation in the band of 800 - 900 MHz. This is non-ionizing radiation, but thought by some to have adverse health effects. It would seem that the newest information does not show a link to cancer from the use of mobile phones. For a more definitive page on this topic, please click here to be taken to a FAQ list of Dr. John Moulder (Professor of Radiation Oncology at the Medical College of Wisconsin).

Fom more information on EMF and other non-ionizing radiation: Information Source Page

Question 5: Why are some isotopes radioactive and others not? Can you predict which ones will be radioactive?

There are four fundamental forces in nature. They are the strong nuclear, weak nuclear, electro-magnetic, and gravity forces. These all work with and against each other as the universe tries to gain a stable, low ordered state (lowest energy-most random). Also looking at this question, we need to realize that matter is another form of energy and that energy is the ability to do work. The center of an atom, the nucleus, is held together (work) by converting a little of the mass of the particles of the nucleus into a binding energy. This is needed to keep all those positively charged protons so close to each other. For light elements, if the number of protons and the number of neutrons are the same, all the forces acting in the nucleus are well matched and the nucleus is stable. But if there are too many neutrons or protons, then the nucleus has too much energy and will normally transfer energy around until the 1:1 neutron to proton ratio is achieved. This frequently is seen as the emission of the energy, or what is called radiation. At higher atomic numbers, there are so many protons, that you need more than 1 neutron per proton to hold the nucleus together. But there still may be stable configurations for the atoms, and the atoms may try to reach those states by emitting the larger alpha particle. Sometimes, following the initial release of energy, there still may be extra energy in the nucleus, and this can be emitted as a photon, or by transferring the energy to the orbital electrons.

Question 6: What are the different types of radioactive decay?

The forms of radioactive decay and other associated processes are as follows:

Decays -

  • Beta - positive and negatively charged particles that are mass equivalent to electrons that are given off from the nucleus
  • Alpha - the emission of a particle made up of two neutrons and two protons, but no electrons, so it has a mass of four amu and a charge of -2
  • Isomeric transition - a metastable isotope gives off some energy in the form a photon. Can only happen following the formation of a metastable isotope by one of the other modes of decay
  • Internal Conversion - the nucleus gives up some of its energy to a orbital electron
  • Electron capture - the nucleus "captures" an orbital electron
  • fission - division of an atom into two smaller atoms

Other processes related to decay -

  • Characteristic x-rays - the energy of an electron as it falls to a lower energy orbit is given off as a photon
  • Auger processes - the energy of an electron as it falls to a lower energy orbit is given to a neighboring electron

Question 7: What are the different types of natural radiation?

Natural radiation takes the same forms as "human-caused" radiations. All the same decays discussed above happen naturally. Radiation we are exposed to from our environment include Cosmic (high energy particles and EM from outside of our galaxy), Cosmic induced (C-14, Tritium made in the atmosphere by interactions with cosmic radiation), Solar (UV from the sun mostly, but in space can be particles), and terrestrial (Uranium, Thorium, Radon contained in the Earth itself). Life forms have incorporated all of these into their biomass, so all life on Earth has some amount of radioactivity in it. That includes the food and water we ingest, and humans in general.

For more info:

Question 8: What methods are used to detect radiation?

Because ionizing radiation does just that, ionizes, it is easy to see that using a medium like a gas, and a voltage, you can measure the amount of charge liberated in that medium. And that is the most common method of measuring radiation. The infamous Geiger Counter is in reality a small volume of gas, with a voltage applied across it. As the radiation enters the gas, it causes electrons to be formed which are collected and measured to determine the amount of initial radiation present. Another common detection device uses a process similar to the Glow-In-The-Dark plastics, paints, and watches that can be found in every store. While a little more complicated than that, the processes used with radiation detection is called scintillation. Scintillation is the giving off of visible light after interaction with radiation. The light can be collected and used as another measure of the radiation intensity and energy. But, there are many different ways of measuring radiation, using semiconductors, liquids, superheated bubbles, crystals and plastics.

See these pages for more on measuring radiation:

Question 9: What are some examples of applications of constructive uses of radioactive isotopes?

The applications of radiation are numerous. I have listed some below:

Here's just a sampling of radioactive materials...and the many ways they improve lives.


  • Imaging - X-rays, MRI
  • Nuclear medicine - treatment and imaging
  • Treatment - Cancer
  • Sterilization of blood and other items


  • Density Gauging - how dense ground is for roads, in fluids in pipes
  • Well logging - Density of ground for wells
  • Radiography - x-raying pipes, welds, valves for flaws, defects
  • Non-electrical exit signs


  • TV - electron excitation of the screens phosphor
  • Smoke detectors
  • Long lasting light bulbs
  • Food irradiation - longer shelf life, less spoilage, longer transport time
  • Cheap and reliable power source - nuclear power


  • Chemical tracing in humans, animals for new drug development
  • Function tracing - how animals and plants work
  • Analysis of unknown samples by activation
  • Studying the basic building blocks of nature - cyclotrons and accelerators
  • Sterilization of media for experiments
  • Carbon and Potassium dating techniques - aging of biologic specimens

There are many, many more: see Radiation Specialties Section of our site.

Question 10: What are the biological effects of exposure to radiation?

The effect depends on the amount (dose), ranging from no effect (low) to death (high). For the most part, what radiation does is create ions in our cells, and these ions cause problems in the cell. damage may lead to cancer.

The radiation may interact directly with biologically significant molecules, like DNA and proteins. Radiation may also interact indirectly to cause damage, by interacting with chemicals in our bodies, such as water, and form very active chemicals like free radicals that may cause damage to the biologically significant molecules. The damage can be fixed, or the cell may die, or it may actually affect the tissue/organ if there is enough damage. It is felt that the damage to the DNA is of the most importance, and could lead to increase risk of cancer. The damage could be to a single base pair, could cause the DNA to bind to itself or cause an actually break the DNA on one stand or more rarely, to both DNA strands. If the damage is not fixed or is fixed wrong and the cell escapes apotosis (programmed cell death) it may be one of the several needed steps that results in the cell becoming a tumor. But the chain of events that leads from DNA damage to cancer is a long, multi-step process with many check points along the way where things must go wrong in order to cause cancer.

One of the reasons cancer is not more common is that every minute of the day for your whole life, your body's repair mechanisms are working to fix damage to your DNA. It is surprising how many times each hour, each cell's DNA is damaged:

Rates of DNA Damage in a Mammalian Cell
Damage Events per hour





Deamination of Cytosine


Single-Stranded Breaks


Single-Stranded breaks after depurination


Methylation of Guanine


Pyrimidine (thymine) dimers in skin (noon day sun)

5 x 104

Single-stranded Breaks from Background Radiation

1 x 10-4

Double-stranded Breaks from Background Radiation

4 x 10-6

But, our repair mechanisms fix almost all of these damages at very high rates and efficiencies:

Maximum DNA repair Rates in a Human Cell
Damage Repairs per hour

Single-stranded breaks

2 x 105

Pyrimidine dimers

5 x 104

Guanine methylation


If the damage is in the sex cells, there would be some risk of a DNA change, a mutation, being passed on to the next generation. The physical effects of these radiation induced mutations have never been seen in humans though. Humans have about a one in ten chance of passing along a natural (non-radiation induced) mutation to their offspring. This natural rate normally is of little consequence, either being recessive or not health threatening, but some do cause significant health problems. Many studies have looked for the physical manifestations of the radiation damage in the children, grand children and great grandchildren of the Atomic Bomb survivors, and have not shown an increase above this natural rate.

For more information, recent papers in this topic can be found at the Journal of Nuclear Medicine and RSH Data & Documents compiled by the Center for Nuclear Technology and Society at WPI.

Question 11: How do microwaves heat things?

Microwaves are electromagnetic radiation and part of the Electromagnetic Spectrum, along with radio waves, infared, visable light, ultraviolet, x-rays, and gamma rays. Microwaves do not have enough energy to remove electrons from the orbits of atoms, putting it in the class of non-ionizing radiation. Electromagnetic radiation is energy in transfer by electromagnetic waves. These waves move at the speed of light. Microwaves have a range of frequencies of 0.03 to 300 GHz, placing it between Radio-frequency and Infared radiation in the Electromagnetic Spectrum. Hertz (Hz) is a measure of frequency, the number of times per second that the waves oscillate, in the electric and the magnetic directions. (Note: "GHz" means a billion hertz, or a billion of times per second ). Microwave ovens often use 0.9 or 2.5 GHz for their heating frequencies.

The way microwaves heat things, according to Professor Herman Cember in his book Introduction to Health Physics (Pergamon Press):

In its interaction with matter, microwave energy may either be reflected, as in case of metals, it may be transmitted with little energy loss to the transmitting medium, as in the case of glass, or it may be absorbed by irradiated matter, and thus raise the temperature of the absorber. This heating is attributed to two effects: the main mechanism is believed to be joule heating due to ionic currents induced by the electric fields that are set up within the absorbing medium by the radiation. The second mechanism is due to the interaction between polar molecules in the absorber and the applied high-frequency electric field. The alternating electric field causes these polar molecules to oscillate back and forth in an attempt to maintain the proper alignment in the electric field. These oscillations are resisted by other intermolecular forces, and work done by the alternating electric field in overcoming these resistive forces is converted into heat.

In other words, the EM waves oscillate at high frequency, and set up currents and move molecules. The moving molecules and current generate heat. It has nothing to do with excitation.

Water is a polar molecule and has good heat transfer, so it is a good microwave-able material. Many biological molecules area also polar. The microwaves penetrates most materials to a depth of 1-2 cm. The heat is then transferred by conduction to the whole of the material.

For more info:

Search UofM Web site for Key Words

Risk (UofM)

Radiation around us (UofM)

Information on Specific Radiation Sources (UofM)

Radiation Primer (MIT)


This web page was last updated on Thursday, August 09, 2007 By Michael D. Rennhack.
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