Milli-rads vs Sieverts?

Question

Can anyone tell me the difference between rads/rems/seiverts? What are their equivalents? RAD=Radiation Absorbed Dose/REM=Radiation Equiv. Man...Sv=international term for measuring radiation?? Any info would be helpful,thx.

Answer 1

First, this is a topic that is of continual annoyance for people who work with radiation. Let's tackle this in sections...

First let's start with the Roentgen. The Roentgen (R) is defined as charge per unit mass. Historically, it was defined as the amount of gamma or x-rays that produced one electrostatic unit of charge in 1 mL of air at STP (1.293E-3 g). More currently, R=2.58E-4 C/Kg (C=Coulombs).

Ok, back to it. A RAD is defined as 100 erg/g. This is basically the same thing as R; a unit of charge per unit mass. This is the "old" system unit. This was supplanted by the SI unit of the Gray (Gy). A Gy is defined as 1 J/kg (seeing the trend?). Both units are a measure of Absorbed Dose (D). Ok, if you would like to move between them, the conversion is 1 Gy = 100 RAD. Why?

Ok, 1 J/Kg = 10^7 erg/10^3 g = 10^4 erg/g = 100 RAD

Now, onto the Dose Equivalents. A dose equivalent, H, is the effective dose received from ionizing radiation. However, not all radiations are created equal. A 1 RAD exposure to x-rays is far less harmful that a 1 RAD exposure to >10 keV neutrons. So, a sliding scale was introduced. For a given exposure to radiation,

H=QF * D

where QF is the quality factor and D is the absorbed dose. Ok, back to your question. A REM is the Dose Equivalent corresponding to Absorbed Dose in RAD. Confused? Ok, take a dose in RAD, multiply by the quality factor, and you get an answer in REM. For the SI system, take a dose in Gy, multiply by the QF, and your answer is in Sieverts (Sv). Generalized quality factors are:

X and GammaRays - 1
Electrons and Positrons - 1
Neutrons E < 10 keV - 3
Neutrons E > 10 keV - 10
Protons - 1 to 10
Alphas - 1 to 20
Heavy Ions - 20

For reference to the annoyance caused by the dual systems, as a radiological worker, my DOE imposed dose limit is 5 REM. This dose is very easy to remember and seems intuitive. However, under the SI system, my dose limit is 50 mSv, which seems small, though they represent the same physical quantity.

Answer 2

The sievert (symbol: Sv) is the SI derived unit of dose equivalent. It attempts to reflect the biological effects of radiation as opposed to the physical aspects, which are characterised by the absorbed dose, measured in grays. It is named after Rolf Sievert, a Swedish medical physicist famous for work on radiation dosage measurement and research into the biological effects of radiation.

Answer 3

Sieverts = 100 REM and is generally 100 RAD. 1 RAD is 1000 mrad.

A dose in Sieverts would be significant, so generally, microSieverts or milliSieverts are used. The workers I deal with understand mrem very well.

Answer 4

Sieverts To Rem

Answer 5

I don't care what anyone says, I like Milli Vanilli. The actual vocalists who sang on the album, not the Rob & Fab fakers lol. BQ: Erm... what?