Wikipedia:Writing about radiation

Ionizing radiation warning symbol

Readers and editors alike have a fascination with nuclear accidents, atomic bombs, and all the other peculiar ways that radiation can find its way into our lives. But read enough articles mentioning radiation, and you might start to notice a pattern: radiation is very poorly described on Wikipedia. Radiation doses are almost never broken down into an understandable number. Readers are provided a number and expected to know what 200 Roentgen means (spoiler alert: don't use Roentgen!). Radiation exposures range from "mundane" to "instantly lethal." Without context, readers are left to assume that any radiation number is Big and Scary and Terrible. But most radiation doses are survivable. It is our job as editors to make sure that readers understand radiation in context.

Radiation dose primer

Radiation means ionizing radiation. Some kinds of electromagnetic radiation are ionizing, such as X-rays, whereas other kinds of electromagnetic radiation are not, like visible light or radio waves. This guide is not a comprehensive primer on radiation; it helps to have read about ionizing radiation before going through this guide.

For comparison, the average background radiation in the United States is 310 (.003 Sv) millirem a year. Chronic doses above 20 rem (200 mSv), or acute doses above 10 rem (200 mSv) increase the risk of cancer. Acute doses of 500 rem (5 Sv) kill half of those affected without medical treatment. Doses up to 900 rem may be survivable with prompt and intensive treatment. Doses received only to one part of the body are more survivable than doses absorbed to the whole body. For example, a whole body dose of 2,000 rem is always deadly and kills within 2 weeks. But localized doses of above 8,000 rem may be used in radiation therapy to target a tumor. The tumor absorbs the dose and dies, but the rest of the body is relatively unharmed. Chronic doses (received over a longer period of time) are less damaging than acute doses.

You are free, and encouraged, to cut-and-paste relevant cited sections (along with their citations) in this guide to provide context where necessary in radiation articles.

Best practices on writing about radiation

So a source has provided a measurement of radiation. How should you best include that in an article?

• Ensure correctness: Make sure the measurement is appropriate in context. Many lay authors do not understand the difference between kinds of radiation unit, and may thus confuse exposure with dose. More rarely, authors may conflate dose or exposure with activity. If the author has used the wrong kind of dose, look for a better source, or at least make sure to use a source which explains the underlying radiation science, thereby pointing out the erroneous aspects.
• Provide a comparison: the average reader has no clue what a 20 mSv dose of radiation is. The uninitiated might assume this to be a rather scary amount of radiation. But it is in fact the amount of radiation absorbed from a typical chest CT scan. Conversely, the average reader might assume a 20 Sv dose to be relatively safe. But such a dose, absorbed by the whole body, is an inescapable death sentence. The reader needs something to understand what these rarely encountered numbers mean.
  • Incorrect: Johnson received a 20 mSv dose of radiation.
  • Correct: John received a 20 milliSievert (mSv) dose of radiation. That is roughly equivalent to the amount of radiation absorbed from a chest CT scan.
  • Incorrect: Johnson received a 20 Sv dose of radiation.
  • Correct: John received a 20 Sievert (Sv) dose of radiation. Such a dose, absorbed over the whole body, is almost invariably fatal. For comparison, acute radiation syndrome begins at doses of approximately 1 Sv, and doses above 6 Sv are 95% lethal even with medical intervention.
• Do the math: Simple math is one of the few aspects of Wikipedia which does not require citation (see Wikipedia:No original research#Routine calculations). Therefore, you can convert units where necessary, so long as you provide a citation to the original number, and where necessary, a citation to the conversion numbers you have used. This can also be used to provide mathematical context. A classic good comparison number is 50 mSv a year, the United States yearly exposure limit for radiation workers in non-emergency situations. If you are comparing a 1.23 mSv dose, you could state this as about 2.5% of the yearly exposure limit for American radiation workers. Percentages are helpful when dealing with radiation.
• Standardize units: This is not always possible, but standardizing units across an article is ideal. If your reader is constantly having to juggle Sieverts and rem, they're going to lose the plot somewhere. Some simplification to this end can be useful. For example, 1 Gray is roughly equal to 1 Sievert, assuming that Sievert is fully absorbed across the whole body. Thus, unless there is some extenuating circumstance, it can be more effective to go with one unit or the other (so long as an appropriate explanatory note is added). When using Rem, it is often helpful to convert to Sieverts as well, i.e., 20 rem (200 mSv).
• Beware: While the different kinds of dose are somewhat interchangeable, dose cannot be conflated with activity. Dose may be calculated from exposure, given enough information and some assumptions. But while converting activity to exposure or dose is not technically impossible, it is so beyond the scope of the Wikipedia writer that it should not be attempted. (See this source for a discussion of just how hard it is to calculate a dose from activity).

Specific units

There are more than a dozen different ways to describe ionizing radiation, but only a few are actually useful to the average reader. The rem and sievert are effectively interchangeable: 1 Sv = 100 rem. They are useful for a wide range of radiation types, and are useful even for very small doses.

The Gray (unit) is useful mostly for acute doses that are fairly large. At small doses, it is better to use Sv or rem. The Gray is best suited for radiation accidents and deaths. The chart at Acute_radiation_syndrome#Dose_effects does a good job of showing acute radiation injury at high levels. This chart should not be used for chronic exposures. Unfortunately, the research regarding chronic exposure is much poorer than that of acute exposure, usually because the latencies of symptoms can be years or decades, and oftentimes the only effect is a slightly elevated cancer risk, which itself is disputed and hard to measure.

The Gray (Gy) describes deterministic effects, which conveniently become noticeable at about 1 Gy. See this chart for a breakdown of the health effects of radiation doses above 1 Gy.

External radiation exposure is different than internal exposure. Alpha radiation is effectively harmless outside the body since a thin sheet of paper, clothes, or skin blocks it. But inside the body, there is nothing to protect organs from its very damaging particles. Thus ingested or inhaled particles of alpha emitters (like plutonium) are much more dangerous.

The radiation chart

Ionizing radiation related quantities

Quantity	Unit	Symbol	Derivation	Year	SI equivalent
Activity (A)	becquerel	Bq	s−1	1974	SI unit
	curie	Ci	3.7×1010 s−1	1953	3.7×1010 Bq
	rutherford	Rd	106 s−1	1946	1000000 Bq
Exposure (X)	coulomb per kilogram	C/kg	C⋅kg−1 of air	1974	SI unit
	röntgen	R	esu / 0.001293 g of air	1928	2.58×10−4 C/kg
Absorbed dose (D)	gray	Gy	J⋅kg−1	1974	SI unit
	erg per gram	erg/g	erg⋅g−1	1950	1.0×10−4 Gy
	rad	rad	100 erg⋅g−1	1953	0.010 Gy
Equivalent dose (H)	sievert	Sv	J⋅kg−1 × WR	1977	SI unit
	röntgen equivalent man	rem	100 erg⋅g−1 × WR	1971	0.010 Sv
Effective dose (E)	sievert	Sv	J⋅kg−1 × WR × WT	1977	SI unit
	röntgen equivalent man	rem	100 erg⋅g−1 × WR × WT	1971	0.010 Sv

Outdated units and how to convert them

Merely because radiation has been measured in a particular unit, and written down by a reliable source, does not mean that we should report that amount of radiation using that unit. For one, converting to an SI unit is preferred for reader friendliness. If all of our articles used SI radiation units, reader comprehension would improve, not least of which because the modern world tends to use more modern units. Further, unlike other Imperial units such as the inch, readers are not entrenched in their familiarity with outdated radiation units.

Many simple conversions may be done using this lovely calculator http://www.radprocalculator.com/RadProDownloads.aspx (they also have a web-only version).

For example, units given in Roentgen (unit) should be avoided. The Roentgen is an exposure unit whose derivation is silly because it is not an SI unit. The Roentgen is only useful for electromagnetic ionizing energy (think X-Rays and Gamma). It will not work with particles (Alpha, Beta, Neutron). If an old source used it to describe a particle radiation, toss it and find something better. 1 Roentgen = .00877 Sieverts = 0.877 rem. Different texts give slightly different values for this. If you really must use a Roentgen, you should convert it to a usable unit using an appropriate calculator. The weighting factor for conversion is always 1 for X-ray or Gammas, which means the answer is multiplied by 1, making no difference.

Note that Geiger counters most often provide an exposure, not an absorbed, dose value. If a Geiger counter is providing a value in rem or Sv, it is probably making some assumptions.

To convert to rem or Sv, a few assumptions are needed, and the results will only be somewhat accurate, but this is passable enough for most Wikipedia purposes. First, you'll need the weighting factor (W_R). For alpha particles, this factor is 20. For neutron radiation, it is 5–20. Beta radiation, X-ray, and gamma radiation all have a factor of 1. (see a pdf here ). This means that Alpha radiation does 20 times more damage than beta radiation. This isn't exactly true though. Alpha particles are stopped by skin or even a thin sheet of paper, and don't go more than about 10 cm in air. So for most practical purposes, the radiation that is actually doing harm is the other kinds which can travel further through air. Alpha radiation is usually only a problem if consumed or otherwise enters the body (such as through a wound), then the injury can be catastrophic.