To grade the "quality" of the radiation
absorbed, the unit defined from the energy is multiplied by a constant
"q".
The values for "q" are: q =1 for gamma and beta radiation; q =3 for
thermal neutrons; q =10 for alpha and heavy neutrons; q =20 for heavy
ions; etc.
Therefore the absorbed radiation (absorbed dose) multiplied by the
factor q gives an equivalent dose in any type of radiation.
Its units are: rem and Sv
We start with the units of absorbed dose (rad and gray) and multiply
them by a factor to find the equivalence of the energy absorbed for any
radiation.
Rem is defined as the radiation of 1 rad exclusively of gamma
radiation; or the radiation of 0.1 rad of alpha radiation.
rem = rad.q
The S.I. defines the sievert (Sv) = 100 Rem
(gamma)
Sievert (sv) = 1 gray of gamma radiation.
Sievert (sv)= 1 gray ·q
The values for "q" are:
| q = 1 |
for gamma and beta
radiation |
| q = 3 |
for thermal neutrons |
| q = 10 |
for alpha radiation and heavy neutrons |
| q = 20 |
for heavy ions, etc |
The absorbed dose may refer to
the whole body or to a concrete organ; it can refer to a single dose or
express the sum of the accumulated doses during a period of time.
The dose of ionizing radiation in France (a country with numerous
nuclear power stations) is 3.5 millisievert per year per inhabitant
(2.4 mSv from natural radiation and 1.1 mSv from artificial radiation).
The prolonged exposition of the whole body to 5 Gray is fatal for 50%
people.
In radiotherapy sessions of 2 to 3 gray are given four days a week on a
part of the oranism.
