Talk:Gray (unit)

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pronunciation[edit]

Could use some pronunciation text? Is it "g-ray" or just "gray?" 76.226.54.17 (talk) 20:21, 1 December 2013 (UTC)

Alleged misuse of the unit[edit]

I deleted the following recent addition:

"Some users of very large amounts of nuclear radiation - for example, the food irradiation industry - have shifted from rads to grays, since the larger scale of the unit results in a smaller number. For example, 100,000 rads, an enormous amount of radiation (more than 1,000 times the lethal dose for human beings), can be described as 1 kilogray, or 1kGy, which to the lay audience seems like a smaller amount than a measurement that uses the number 100,000."

Ascribing political motives to a shift to internationally accepted standards seems a bit of a stretch. The food industry could just as well have used the megarad, in which cast the usage cited would be only 1/10 of an Mrad. In any case, this seems inappropriate in an article about the unit. --agr 00:53, 16 September 2005 (UTC)

More Details on risk to Humans[edit]

The Goiânia accident article data suggests that exposure to even 4+ Grays is often fatal for humans.

Dialectric (talk) 21:24, 19 January 2008 (UTC)

R to Gy conversion[edit]

In our laboratory we use 1Gy = 0.00876 R, that gives 114.155 instead of 107.185 from article. Since I don't know the calculations leading to this coefficient, I feel I am not the right person to change it in this article. I have a feeling that this is because of the energy used to create an ion pair in the air is 33.9 [eV] and it is usually not equal to the chemical ionisation energy, even if it is called the same thing.

I don't have access to ICRU report 31 which should be source of this value.

Regards,

213.25.33.100 (talk) 07:16, 13 August 2008 (UTC)Tomasz Sztejka

Really SI base unit?[edit]

I've checked in a lot of places to see if the Gray unit was actually an SI base unit. But I can't find anything. If this isn't actually an SI unit, then the article shouldn't state that it is. I don't know enough about the SI or radiation in general to feel comfortable editing tis article. But could someone please find the truth!

Helixer (talk) 17:05, 5 October 2008 (UTC)

It is a derived unit http://en.wikipedia.org/wiki/SI_derived_unit --Efa (talk) 16:08, 26 November 2009 (UTC)

I am new to this subject and would like somebody to explain to me the following: If the Gray is the unit of absorption of radiation energy, how can a fatal dose be defined as a dose of 5 Grays or more at one time. If the exposure is for only a nanosecond, how can this be a fatal absorbed dose of energy? Maximillions

it can be fatal because you still absorbed the exact same amount of energy during that one nanosecond.145.120.22.201 (talk) 14:38, 17 February 2012 (UTC)

Biological effect centric[edit]

the article is too much focused on Biological effect, while Gy and rad are unit of absorbed dose by matter, inanimated too. They are intended to measure the matter damage, but mainly for non biological matter. For biological effect there's Sievert and rem units.--Efa (talk) 16:14, 26 November 2009 (UTC)

Conversions[edit]

Do we really need to repeat the conversion between rads and grays? This is covered in the first paragraph of the article.

Also do we really need the table listing all the SI prefixes? If the reader has a sufficiently sound scientific background to understand the article, then (s)he almost certainly understands the SI prefixes as well.

I suggest that this section be stripped of everything apart from the discussion on röntgens and that the section be renamed "Grays and röntgens". Martinvl (talk) 20:07, 2 February 2010 (UTC)

Intro Quote[edit]

Where does the "strongly discouraged" quote come from? It is not cited, so it probably shouldn't be there. —Preceding unsigned comment added by 134.174.21.5 (talk) 19:20, 20 August 2010 (UTC)

This has now been clarified by a cut-and-paste job from the rad article. Martinvl (talk) 20:28, 20 August 2010 (UTC)

Energy comparison[edit]

A figure I always find interesting in a discussion about the health effects of radiation, which could be of interest to the reader, is this one:

"The total energy absorbed by a 75 kg individual with a whole body exposure of 600 rads (fatal in most cases) is 450 joules. It is interesting to compare this to the kinetic energy of a .45 caliber bullet, which is about 900 joules." (from http://nuclearweaponarchive.org/Nwfaq/Nfaq5.html but easily calculated)

After some adjustments for context, and taking a smaller bullet, I suggest adding it to the article after the comment about 5 Gy usually being lethal:

The total energy absorbed by a 80 kg individual with a whole body exposure of 5 gray is about 400 joules. It is interesting to compare this to the kinetic energy of a 9 mm bullet, which is about 450 joules."

Thomas Thomasonline (talk) 08:06, 26 September 2010 (UTC)

Roentgen[edit]

There is a dispute regarding the roentgen section of this article. First, I would point out that this article is about the gray, and it might make more sense to take this discussion to the roentgen article. But currently the dispute is here.

One editor wishes to include a definition of the roentgen, along with some calculations to arrive at a conversion of 1 Gy = 111 R, supported by a citation to an online dictionary. There are several problems with this. First, the citation does not support any conversion from Gy to R. As a minor note, a dictionary is not necessarily the most reliable source for this kind of thing anyway, but in this case it's OK as far as it goes. Second, the air ionization energy of 35 J/C is unsupported. A google search finds alternate values of 36.16 J/C and 33.97 J/C just on the first page of results, so it seems to be a contested value that needs a citation. Another reader disputed the figures 4 years ago, see above on this talk page. Third, the way the statement is written suggest that 1 Gy = 111 R is a conversion constant. In fact it is not constant; it depends on the material exposed, and I provided citations to support that.--Yannick (talk) 12:37, 12 May 2012 (UTC)

I agree that this section needs attention, but then so does the article on the Roentgen. The formal defininiton of the the roentgen involving dry air looks like a good definition to me (in the sense that it is probably verifiable - it has a 1900 "feel" about it), but in terms of physics it looks shaky. In this artcile we should be describing how to relate the roentgen to the gray and the unreliability of the defintion is part fo the argument (if a suitable reference can be found). In conclusion then, in my view the formal definition must stay, but if somebody else can find references for the ionisation energy of dry air, please add them. If there is a range, then clearly one cannot directly equate roentgens and grays.Martinvl (talk) 16:40, 12 May 2012 (UTC)
Well, as it happens, I've recently done a lot of work on the roentgen article, and included citations. You should take a look at it and let me know what you think. Maybe you need to refresh your cache? I've found some reasonable citations for the key definitions, (and they don't exactly match your dictionary definition) so I don't think there's any need to guess whether one definition or another is "probably" verifiable. In terms of physics it is shaky. That's why it was abandoned. I think the reliability issues are best discussed in the roentgen article, and we should only give a practical summary of that here. That's what I was trying to do, anyway.--Yannick (talk) 18:03, 12 May 2012 (UTC)
I have reintroduced the original definiton of the roentgen. I am not happy with the introduction of the words "Kerma" and "deposits", the latter in the context "deposits N grays" - neither words appear in the references. One major reason for keeping the original definition of the roentgen is that it was Hal Gray who realised the inadequacy of the legacy definition of the roentgen which is why the gray was named after him. Martinvl (talk) 14:22, 15 May 2012 (UTC)

OK, I think I see what you're getting at, and I would like to work with you to figure out what's the best way to explain everything. I was not aware that Gray was the first to see the flaws in the roentgen unit, and I'm wondering where you got that from. I'm aware of him defining a roentgen equivalent quantity for neutrons in 1940, but I was under the impression that this was a common and evident thing to do at the time as scientists realized that particles did not ionize matter the same way as photons do. Your citation from Guill and Moteff (great find, by the way!) seems to suggest that V. I. Ivanov was first. The verbal lore that I was taught was that Sievert's and Gray's roles as the chairman and vice chairman of the ICRU had more to do with the naming of the units. See for example here.

I am not comfortable with the word "kerma" myself because it is inconsistently used, but it does appear in many important texts. It's right in the SI brochure in table 3 as one of the quantities that can be measured in Gray, so technically we could open the article by saying the Gray is a unit of absorbed dose or kerma. But my personal experience, and what I think I've seen most often in writing, is that it's primarily the radiologists who use the word "kerma." The explanation they usually give me is that their ionization chamber (used for calibration) measures radiation concentration, or kerma, in roentgen or C/kg, and they assure me that this is a different quantity from absorbed dose that the doctor prescribes in Gy. So I'm trying to reflect that prevalent practice. Another way I've seen the word used is to describe the calibration medium, e.g. 5 roentgen air kerma. Used this way, "kerma" doesn't quite match it's written definition, but that's real-life for you. Here are some sources that try to explain kerma, though they don't fully support what I've just said: [1] [2] [3] [4] [5]

As for the word "deposits," I really don't see what's wrong with it. I have commonly seen it used in serious radiation protection texts. See for example the SI brochure or this radiation protection manual. I could come up with a thousand citations for this. Could you clarify your objection?

Finally, I take issue with saying that the reference to x-rays or gamma rays was dropped. Although you are technically correct on paper, this restriction is still widely seen as implicit. See this recent textbook for example. The reason is that using roentgens or C/kg generally reflects the use of an ionization chamber, which won't work right under particle radiation. You might say that I have a double standard here, with the dry air restriction on one hand and the gamma restriction on the other, but from my experience and reading, that reflects how the roentgen has been used and abused in practice.--Yannick (talk) 01:09, 16 May 2012 (UTC)

Looking through the history of the article, the section on the Roentgen appears to be the remnant of a poorly written section entitled "Conversions" that catalogued a few different units of radiation including everything from a gigagray to a picogray. Personally I woudl like to replace the section entitled "Roentgen" by one called "Historic background" which would trace the original definition of the roentgen, Gray's proposal to use energy absorbed per unit mass of tissue, the rad and the adoption of the name, the gray as the SI unit. This is what I beleive an encyclopeadia should contain.
The comments that I have about the verbal lore are that Gray died in 1965 and that in addition to his work in dosimetry, he was also a Methodist lay preacher and in 1939 had declined a post a Cambridge (from which he had graduated) as the work invovled war-effort work. In 1940 he published his paper proposing the use of energy per unit mass. Martinvl (talk) 04:57, 16 May 2012 (UTC)
Really, I think you should look at what I've done with the roentgen (unit) article. I think it might help you build that historic background section you want. Regarding Louis Harold Gray, I guess you've answered lore with legend, and what you want to do sounds reasonable. Regarding my points that you haven't answered, I guess you accept my views for now, or are you still thinking?--Yannick (talk) 05:59, 16 May 2012 (UTC)
Hi Yannick
Thank you for yoru reply. Yes, I think that we are on the same track. I am totally rewritiung the section "Roentgen" and renaming it "Leading up to the gray" in which I trace the developemnt of the roentgen (1928), the gram roentgen (1940), the rem (1953) showing how these built on each other, resulting in the gray in 1975. I will certainly look at what you have written. Martinvl (talk) 20:36, 16 May 2012 (UTC)

Why must we use the german google site?[edit]

There were a couple of citations that originally pointed to books.google.de, with a long untrimmed URL. I switched them to point to books.google.com and trimmed the URL to the minimum using the tool. But now I see that they've been switched back to the books.google.de, and seemingly back to their original length. What's the logic for preferring the german version on english wikipedia, and what's the benefit of the additional URL queries?--Yannick (talk) 03:10, 20 May 2012 (UTC)

Hi Yannick - I am currently working in Germany - my office PC seems to pick up the German site. In addition, the office seems to pick up a bigger extract of Lovell's book than does my personal PC, other than than I have no preference as to which site is used. Martinvl (talk) 06:13, 20 May 2012 (UTC)
I would guess your laptop has some kind of UK setting because one of your cites uses the google.co.uk site. The different country sites have different missing pages: In Guill, UK is missing page 66-67, DE is missing 67-68, and CA is only missing 65. Linking the COM site should automatically bounce the user to the site in his home country, so it wouldn't change what you see. The extra length in URL queries does things like highlight search terms and force all the buttons, etc. to show up in German regardless of which nation's site you use. I can read enough german to get by, but it would make more sense to link to English on English wikipedia. If I fix the URL's could you try to preserve them in future edits? Thanks.--Yannick (talk) 12:14, 20 May 2012 (UTC)
My appologies. Martinvl (talk) 15:35, 20 May 2012 (UTC)

Measuring the dose in gray?[edit]

Hello, there is one thing I do not understand about this unit. Can someone enlighten me? Gray is defined as absorption of one joule by one kilogram of matter. But I suppose that one kg of lead absorbs more energy that 1 kg of iron when exposed with the same "amount" of radiation. So when I set my X-ray unit to let's say 70 kV, 500 mAs and I expose 1 kg of iron and then 1 kg of lead, it will be a different dose expressed in grays (even when the setting of X-ray device stays the same)? Or maybe better question - my Unfors measuring unit does show me the dose in grays. But to which matter is this dose calculated? Is it the average human tissue?

Chrabros (talk) 10:22, 30 May 2012 (UTC)

The same beam with the same energy fluence will deposit a different absorbed dose in iron than in lead, even when the settings of your X-ray device stays the same. For your Unfors unit, you'll have to read the manual or contact the manufacturer. But from the specs on their ThinX RAD, I would guess it's actually measuring kerma in air, as similar devices from other manufacturers usually do. (Both kerma and absorbed dose are measured can be measured in gray, but only kerma is measured in roentgen. And then their conversion factor tips me off that they're assuming air.) If I'm right, then the absorbed dose to your patient will be about 10% higher than what your instrument says.--Yannick (talk) 13:32, 30 May 2012 (UTC)

Plural[edit]

Is the plural "gray" or "grays". I checked the Oxford English Dictionary and they gave two instances of the word "grays" being used, one of which was taken from New Scientist. I checked the SI brochure. It was silent apart from saying that the normal rules of English grammar are applied. Does anybody have access to any other authoritative view on the matter? Martinvl (talk) 18:16, 8 May 2013 (UTC)