REMS, RADS, millisievert, becquerel : anyone want to take on explaining those?

[hedgehog]

I know it's on Wiki, but I suspect a lot of people here have questions. Feel free to discuss various isotopes as well.

[MineralMan]

1. Here's a pretty good rundown on all the measurements,

their comparisons, and more. It's not a complete guide, but it does show you how the measurements compare:

http://orise.orau.gov/reacts/guide/measure.htm

[PoliticAverse]

2. Here...

is short list of the different types of units:
http://www.mcgill.ca/ehs/radiation/basics/units/

There are 2 basic areas of confusion.

1 - Old units (names) vs new.

Just like 'inch/foot/yard/mile' are the old unit (name) of length measure and 'meter' is the new International Standard ('S.I.')
unit of measure radiation has old units and new.

Old unit : New (S.I.) unit
Curie > Becquerel
Rad > Gray
Rem > Sievert

The webpage listed above shows the conversion factors from the old unit to the S.I. unit.

2 - Different measures of radiation.

There are different types of radiation (alpha, beta, gamma, x-rays, neutron) and there
are different ways to measure radiation:

Activity - how fast the radioactive substance is disintegrating:
Units: Curie or Becquerel

Energy - how much energy the radioactivity is imparting to an area:
Units: Rad or Gray

Biological effect - different types of radiation have different effects on biological tissue.
Units: Rems or Sieverts

Note the for the S.I. units prefixes before the name can be used. The common prefixes that are being used
are milli (one thousandth, 'm') and micro (one millionth, 'u').

A milliSievert is one thousand times smaller than a Sievert, and a microSievert is one million times smaller than a Sievert.
A microSievert is one thousand times smaller than a milliSievert, or put in the reverse a milliSievert is one thousand
times larger than a microSievert.

[TheWraith]

3. 1 REM = 1 rad = 0.01 sieverts = 10 millisievert.

All the above are measurements of the dosage rate, i.e. how much radiation a person is absorbing.

25 REM / 0.25 Sievert / 250 millisieverts won't cause perceptible symptoms, but will boost your lifetime risk of cancer by 1.5 percent.

100 REM / 1 Sievert / 1,000 millisieverts will make you sick, but won't kill a healthy person.

500 REM / 5 Sieverts / 5,000 millisieverts will kill more than 50% of exposed people.

Becquerels are a measurement of the number of atomic decays per second. This tends to result in extremely large numbers to measure any noticeable amount of radiation. For instance, 1 Curie, which is the amount of radioactivity demonstrated by one gram of radium, is 37,000,000,000 becquerels. For a point of comparison, the naturally radioactive potassium found in the human body radiates at about 4,000 becquerels.

[leveymg]

4. The confusion is about how becquerel translate into millisievert: they don't.

Millisieverts are a measure of radiation absorption into the body that translates into units (rads) per hour of exposure, whereas becquerel and curie are measures of the rate of radiation emission. One Sievert (1000 millisievert) is considered to be the level at which exposure for an hour will lead to acute radiation poisoning.

One Becquerel is a tiny emission of radiation, only one 37,000 millionth of a single Curie.

[hedgehog]

5. Thank you - the last time I looked, it was rads and rems. I think the

key concept is that it's not the radioactivity per se that's the problem, it's what type of radioactivity is absorbed by which organs.