Radiation units and Dose.
The radiation units necessary to know the quantity of physical properties of radiation. In 1981, The international commission on Radiation units and Measurements ( ICRU) issued standard radiation units all countries except the united states. In 1990, The NCRP and all U.S scientific and medical societies adopted Radiation units.
The radiation units are given below.A) Activity
B) Exposure
C) Kerma
D) Absorbed dose
E) Equivalent dose
F) Effective dose
A) Activity:- The term activity of a radiation source significant the output of radiation from the source of radiation per unit time. The activity is unit of radioactive ( Becquerel). The activity give an idea about the quantity of radiation released per time from the radiation source.
B) Exposure:- The unit of exposure is Roentgen. The term exposure (X) refers the radiation quantity measured in terms of ionization in air Ina small volume around a point. The exposure from an x-ray source obeys inverse square term. One Roentgen have the quantity of X and gamma radiation such that the emission per 0.001293 grams of air.
The SI unit is Columbia/kg.
C) Kerma:- The Kerma stand for the kinetic energy released in the medium, which describe the initial interaction of photons with an atom in medium. When the x and gamma ray pass through a medium, the transfer kinetic energy to the charged particles. The unit of Kerma is jouls per kilogram (J/kg) . The SI units gray and the special unit is rad. When the reference material is air. The quantity is called air Kerma.
D) Absorbed dose:- The Term absorbed dose refers the amount of energy absorbed per unit mass of the material at the place of interest. The absorbed dose denoted by D. The unit of absorbed dose is rad. 1 rad= 100ergs/ gm. The SI unit of absorbed dose is gray. 1 gray=1 joule per kg.
E) Equivalent dose: The IRCP has introduced radiation weighting factor. It will modify the dose to reflect the relative effectiveness of the type of radiation causing biological damage.
The product of the absorbed dose and radiation weight factor is called equivalent dose. It is denoted by H.
H = D×Wr
Where. D= is the absorbed dose
Wr is the weighting factor for the radiation. The weighting factor is 1 for x-ray, gamma, and all of energies.
The SI unit of equivalent dose is sievert(Sv). 1 Sv= 1 J/ kg. The Rem is the special unit of equivalent dose
1Sv= 1000mSv
100 rem= 1000mSv
1 Sv= 100 reml
F) Effective dose:- The sum of the products of the equivalent dose to each tissue irradiated (Ht) and the corresponding weighting factor of tissue is called effective dose. The Effective dose denoted by E.
E= absorbed dose × Wr×Wt.