Radiation Units

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Radiation Units

Postby Eric York » Tue Sep 12, 2017 10:39 pm

Can someone please help outline the Si vs US radiation units and which are old and which are just copies of same unit listed differently. For example can you help fill out this:

Si. US
Absorbed Dose: Gray (Gy). RAD?
Effective Dose. Seviert (Sv). REM or R?
Equivelent Dose.Seviert (Sv). REM or R?

I get these all mixed up, especially the non Si units.

Like the difference between RAD, R, REM, roentgen, etc
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Re: Radiation Units

Postby Eric York » Tue Sep 12, 2017 10:40 pm

Well my attempt at making a table failed. That should have been a SI vs US units table.
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Re: Radiation Units

Postby Rich Feldman » Wed Sep 13, 2017 3:54 am

Eric.
Looks like you didn't try using general Internet resources to answer your question.
Starting out with a question to a forum is a method usually reserved for lazy people.

Heck, even Wikipedia seems to have it mostly right. Are you left confused by anything in the table near the bottom of the following page?
https://en.wikipedia.org/wiki/Radiation_exposure

You can easily find much better explanations by following a few results from a search engine. Try, all together: gray sievert rad rem. Please let us know if that leads you to confidence.

By the way, in English those four unit names are conventionally written in lower case, except when they begin a sentence or are part of a title.
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Re: Radiation Units

Postby Richard Hull » Wed Sep 13, 2017 4:16 am

Rem, roentgen, etc. are not U.S. units they were world wide units for many years. SI units are among the newest units in the universe of units. The great thing about units in science.....They will be renamed as often as some highbrow organization feels they need to be changed. CGS became MKS, became SI, some elements have had a couple of different names over the years. Nothing in science is fixed forever. Someone or some group will want to change stuff on a whim. The internet is the place to go to convert poundals to newtons and ergs to joules and the beat goes on and on.

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Re: Radiation Units

Postby Rich Feldman » Wed Sep 13, 2017 4:49 pm

Yes, what Richard said. The nomenclature of scientific units is usually in a state of flux somewhere (pun intended). Like humans fighting somewhere.

What my father would have called micromicrofarads and kilomegacycles are now picofarads and gigahertz.

I wonder if, and how soon, younger techies will call 1,048,576 bytes a mebibyte (MiB)? Mega has stood for 1,000,000 since long before there were address buses for semiconductor memory. It has never meant 2^20, even in "tech", when found on a clock frequency or a data transfer rate.
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Re: Radiation Units

Postby Eric York » Wed Sep 13, 2017 6:04 pm

So R/hr or more commonly mR/hr seen on most US detectors is milliRontgens per hour? Why is exposure used in US but dose equivelent (mSv/hr) used by the rest of the world? Why isn't rem used? Also if rad was replaced by gray (which is SI), then what is used in US? Did the US abandon the rad and accept the SI unit for absorbed dose? Seems like the US should just use all SI units concerning radiation........
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Re: Radiation Units

Postby Dennis P Brown » Wed Sep 13, 2017 8:00 pm

As I understand the 'newer' dose names they are keyed to not just radiation level but depends on the tissue involved (the gray); which from a human health point, is the primary concern for radiation exposure - these units are what health physics people use to determine the exposure of people by radiation. Previous units were more like light illumination - just a standard that didn't need to concern itself if what was happening to the item absorbing the radiation (i.e. brain/organ compared to muscle tissue. Also, type of radiation and tissue comes into play with these units as well.)

As for memory or chips in general, bits and bytes are binary and hexadecimal based. Rather important for that area of technology.

I think this is a good development: that units apply to the engineering area that they are used and be convenient for that purpose.

As for older equipment and that some newer devices still referencing those values, that makes sense. One who is prospecting for uranium does not need to worry about the radiation dose depending on their tissue (lol!) Those older units aren't useless nor shouldn't be used but rather, have a specific application area. But when one talks about radiation exposure by people (a rather critical area even for us fusor people), those SI units are rather important ... . In any case, a torr is still a torr even if it isn't SI.
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Re: Radiation Units

Postby John Myers » Thu Sep 14, 2017 4:02 am

The NRC requires companies to submit paper work with specific unit types which is probably the main reason the US hasn't switched over completely to SI.
There are a plenty of people pushing for unification though.
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Re: Radiation Units

Postby Rich Feldman » Thu Sep 14, 2017 4:23 am

As Richard and Dennis have said, this is not like gallons and liters. I don't see a "rads in USA, grays in rest of the world" dichotomy. More like "rads in old literature, from anywhere, grays in new literature from people who are into SI". The mission statement of Radiation Physics division of NIST (formerly NBS), a U.S. federal government agency, begins with things like "practical realization of the gray". https://www.nist.gov/pml/radiation-physics

We might seek an analogy in vacuum pressure units. European datasheets might be more likely to use pascals or millibars, but that hardly turns the traditional torr into an American unit! Older publications from anywhere in the world use torrs, or mm Hg. Today's torr doesn't depend on density of mercury metal at some standard temperature, or on Earth gravity at some standard latitude. It's defined as exactly 1/760 of a standard atmosphere, which is defined as exactly 101325 pascals. Not that many people care about high precision in torr pressure values.
- - -
Ionizing radiation _exposure_, in roentgens, is fundamentally easy to measure. Electric charge collected in an ionization chamber, divided by the air mass. A good way to start getting quantitative, more than 100 years ago, and no less valid today.

To get from exposure in R to dose in rads (or grays, which are exactly 100 times bigger),
you need adjustments for the type and spectrum of the radiation, as applied to the designated material that's being dosed. If a dose is big enough and fast enough, maybe it can be measured by calorimetry (amount of thermal heating).

Many artificial satellites and space probes need electronics made from radiation-hardened components. Total Ionizing Dose tolerance has been given in rads(silicon) for decades, in fact since before Hal Gray had a unit named for him. For example, in this snippet from an IC catalog:
radhardmem.PNG


[edit] I stumbled upon one article (in Slate) which gives a reason for the "rem" reporting rule John mentioned.
The article also stands with Eric in calling rems a U.S. thing.
http://www.slate.com/articles/news_and_ ... d_rad.html
Capture.JPG
Line three of that snippet misleadingly blames "metricophobia". Rems are as metric as liters, bars, ergs, ångström units, and barns. Each based on a product of SI fundamental units and some whole power of ten. https://en.wikipedia.org/wiki/Non-SI_un ... _in_the_SI
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Re: Radiation Units

Postby Richard Hull » Fri Sep 15, 2017 5:17 am

As always, we old farts have to die out as the youngsters are trained in SI units. Soon these youngsters will be older and have to learn the ISWGU system, (International Scientific World Government Units ). Then they will have their turn to squeal about a shift in their understanding of the old and disused SI system. I was taught in college using the CGS system and never fully accepted or used MKS (units way too big). SI, the Tesla is an outrageous and rarely seen value in the real world. However, I hail the Bequerel as a very sensible unit. (I still use CPM, though) The Curie was another needlessly gigantic unit of activity. Who remembers the unit of activity, (Rutherford) , a big deal in the 50's and in a lot of literature of the period.

Again, as I have said before, if your are doing a scientific paper for publication you must use only SI units! This is send half of the readers to the conversion tables to figure out real activities in Curies and real units they know like Rems and Rads.

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Fusion is the energy of the future....and it always will be
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