I've been trying to learn about the possible effects of x-ray radiation from dental x-rays and most of the resources I come across compare the exposure to that of natural background radiation.

Here's an example (not specific to dental x-rays): http://www.hpa.org.uk/webw/HPAweb&HPAwebStandard/HPAweb_C/1195733826941?p=1158934607708

I know electro-magnetic-radiation comes in different wavelengths and some are ionizing and some are not. Is this a valid comparison?

Update: Thanks for the helpful responses so far. Looking at the chart here from @anna v, is comparing x-rays with background radiation comparing EMR that is 10^-10 with wavelengths that are longer than infrared? That's what I still don't understand. Wouldn't those different types of waves have different properties?

  • $\begingroup$ I removed 'cosmic' from the characterization of background, because "cosmic background radiation" has an astronomical definition not appropriate to your question. $\endgroup$
    – anna v
    Commented Feb 7, 2012 at 16:48
  • $\begingroup$ @annav I think the cosmic part gives the question a different character than its current form; not really agreeing on your "not appropriate" assessment. $\endgroup$ Commented Feb 7, 2012 at 16:51
  • $\begingroup$ @CaptainGiraffe please read my answer. Background radioactivity is mainly ambient except for the ubiquitous muons. $\endgroup$
    – anna v
    Commented Feb 7, 2012 at 17:22
  • $\begingroup$ @PPC-Coder It's better not to think of waves. Light is made of photons, each traveling at the constant speed of light. Each photon oscillates at a certain frequency. Photons that oscillate 30,000,000 (30 million) cycles per second we call radio waves. X-rays on the other hand are made of photons still traveling at the speed of light but each one oscillating at a frequency of 30,000,000,000,000,000 (30 quadrillion) cycles per second. Therefore having much more energy when it impacts. $\endgroup$ Commented Sep 4, 2017 at 17:26

3 Answers 3


Roughly yes.
Radiation is broadly divided into two from a safety point of view.

Ionising radiation can break chemical bonds and so has an obvious way to cause damage to your body - how much depends on the energy, how much radiation you absorb and where in your body it gets to. Both X-Rays and particles from radioactive material are ionising, as is the UV in sunlight, and all these can cause health issues.

Non-ionising radiation is that where the energy of the individual particles is too low to directly break a chemical bond. This is true of most visible light and radio waves. It's still possible to damage your body with this, but only by some mechanism such as direct heating eg. a microwave oven or an industrial laser.


First of all terminology:

When physicists speak of radiation they primarily speak of electromagnetic radiation. When health physicists speak of radiation they include radiations of other types, alpha and beta and neutrons in addition to gamma and xrays. They have developed a system where radiation is given in Becquerel ignoring the particular source.

So when somebody says that one xray is equivalent to background radiation, they compare the becquerels that one gets from one xray to the equivalent becquerels one would get from the ambient surroundings. This background comes from cosmic ray muons (about 1 per cm^2 per second) to natural radioactivity of stones and materials, to gases in the atmosphere released by volcanoes etc. Natural radiation is mainly non electromagnetic, since high energy photons produced by close by radioactive decays are easily absorbed by the materials intervening, and photons coming from the cosmos are absorbed or interact high in the atmosphere ( another important point for life, to have an atmosphere).

Cosmic background radiation is another story, and is not health physics related :it is photons left over from the Big Bang and has very little energy, it is in the microwave part of the electromagnetic spectrum( mm) whereas x-rays are of higher energy, in the range of nanometers.

The comparison is valid because it is the result of painstaking studies of calibration and measurements.

Response to updated question:

Wouldn't those different types of waves have different properties?

Matter responds differently to the different wavelengths of photons, due to the increasing energy they carry which is proportional to their frequency and inversely proportional to their wavelength.

The column on the far right gives the energy of the photon. A micron wavelength is in the electron Volt range and can affect molecular distances and cohesion and living matter. Below that the interaction with matter is in bulk, not individual molecules and cells after the Ultraviolet level. The electromagnetic radiation that can affect health is ultraviolet and smaller wavelengths. The smaller the wavelength the larger the possibility of destruction of living cells which is the study of health physics: by, as the frequency increases, heating in depth,breaking of chemical bonds, ionizing, and finally destroying complete cell structures when going to MeV energies.

  • $\begingroup$ +1 Good answer. I was considering the fact that the 2.7K CBR does not include the potentially hazardous cosmic HE particles. Please edit your "ad (is not health physics)" -> "and..." I was confused for a little bit there. $\endgroup$ Commented Feb 7, 2012 at 17:43
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    $\begingroup$ Becquerels are not a measure of radiation. They measure radioactivity (i.e., the amount of radioactive substance.) One Becquerel of some substance is the amount in which one nuclear decay occurs per second on average. As a matter of public health, we usually are interested in knowing how much radioactive contamination is present: How many Bq/liter are present in the water or the soil, how many Bq/$m^2$ are present on a surface, etc. It's important because the effects of ingesting radioactive contamination is a very different concern from the effects of accute radiation exposure. $\endgroup$ Commented Sep 4, 2017 at 20:07
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    $\begingroup$ Radiation absorbed dose is measured in Gray One Gray (1 Gy) equals one Joule absorbed per kilogram of exposed matter. For purpose of predicting health effects, doses measured in Gray usually are scaled to a unit called Sievert. This is because one Gray of one particular type of radiation with a particular energy spectrum can have more or less effect on human tissue than one Gray of radiation with a different particle type or a different energy spectrum. $\endgroup$ Commented Sep 4, 2017 at 20:19

This very good article on radiation explains that one unit of uSv measures the amount of damage done by that dose of radiation. If this dose is put entirely in one small part of the body then presumably the damage is confined to that small space. If this is the brain and the mouth then this would appear to be a much bigger potential problem than background radiation of the same quantity that would cover the entire body, especially if it includes radiation that it blocked by the skin etc.



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