Anonymous

# what is the unit of radiation?

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• Anonymous

Radiation measurement units are confusing. I hate them. But I do know what they are. The röntgen was taken out of the SI system in 2006, and is no longer used in the scientific community in common terms.

The original unit for measuring the amount of radioactivity was the curie (Ci), which today is defined as exactly, 1 Ci = 3.7E+10 radioactive decays per second, referencing one gram of Radium-226.

Today, using SI units (International System), the curie has been replaced by the becquerel (Bq), defined as 1 becquerel = 1 radioactive decay per second = 2.703E-11 Ci.

There are also the units of measuring radiation exposure, and the magnitude of radiation exposure is specified in terms of the radiation dose. This comes in two categories:

(1) The absorbed dose, (or physical dose), is defined by the amount of energy deposited in a unit mass in human tissue (or whatever). The original unit is the rad [100 erg/g], it is now widely replaced by the SI unit, the gray (Gy) [1 J/kg], where 1 gray = 100 rad.

(2) The biological dose, (or dose equivalent), was previously in rem, and now in SI units, the sievert (Sv).

This dose reflects the fact that the biological damage caused by a particle depends not only on the total energy deposited but also on the rate of energy loss per unit distance traversed by the particle (linear energy transfer). For example, alpha particles do much more damage per unit energy deposited than do electrons. This effect can be represented, in rough overall terms, by a quality factor, Q. Over a wide range of incident energies, Q is taken to be 1.0 for electrons (and for x-rays and gamma rays, both of which produce electrons) and 20 for alpha particles. For neutrons, the adopted quality factor varies from 5 to 20, depending on neutron energy.

But wait, there's more!

The biological impact is specified by the dose equivalent H, which is the product of the absorbed dose D and the quality factor Q: H = Q D.

The unit for the dose equivalent is the rem if the absorbed dose is in rads and the sievert (Sv) if the absorbed dose is in grays. Thus, 1 Sv = 100 rem. 1 rem is roughly the average dose received in 3 years of exposure to natural radiation. 1 Sv is at the bottom of the range of doses that, if received over a short period of time, are likely to cause noticeable symptoms of radiation sickness.

The dose equivalent isn't the whole story. If only part of the body is irradiated, the dose must be discounted with an appropriate weighting factor if it is to reflect overall risk. The discounted dose is termed the effective dose equivalent or just the effective dose, expressed in rems or sieverts.

Okay, have you gone crazy yet?

• earles
Lv 4
4 years ago

the fashionable time period is rads. the unique time period develop into curies after the discoverer of the phenomenon Eve Curie. probably a present day radiologist does no longer even understand what a curie is! each and every career has to have a language with a view to be more effective above we mere mortals.