Understanding Radiation Quantities and Units: A Comprehensive Guide, Slides of Radiation Quantities and Units

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Lecture 1

QUANTITIES AND UNITS

Quantity: A physical entity used for precise

description of a phenomenon and defined so as to

be measured

Unit: A particular sample of a quantity of such

magnitude that is assigned the measure “1”

Common unit: It is a product or quotient of the

fundamental units, e.g. velocity (m/s)

Special unit: A unit having a special name and is

associated with a particular quantity, eg. joule (J)

Quantity and unit: The quantity specifies the

type of phenomenon under consideration

Radiation

 Radiation is a transport of energy through space  In traversing material, radiation is absorbed

Directly Ionizing Particles

 Charged particles (e’s, p’s, ’s, etc.) having sufficient kinetic energy to produce ionization by collision

Indirectly ionizing particles

 Uncharged particles (n’s, ’s, etc.)

Ionizing radiation

 Any radiation consisting of directly or indirectly ionizing particles or a mixture of both

Nuclide

 A species of atom having specified number of neutrons and protons in its nucleus denoted as e.g.

Energy imparted

 The energy imparted by ionizing radiation to the matter in a vacuum is the difference between the sum of the energies of all the directly and indirectly ionizing particles which have entered the volume and the sum of the energies of all those which have left it, minus the energy equivalent of any increase in rest mass that took place in nuclear or elementary particle reactions within the volume

ZAX (^23592) U

PHYSICAL RADIATION QUANTITIES

Definition

 The quantities that are proportional to the amount of radiation received or the rate at which it is delivered Quantities

 Particle fluence or fluence  Particle flux density of flux density  Energy fluence  Energy flux density of intensity  Kerma and kerma rate  Exposure and exposure rate  Absorbed dose and dose rate  Activity

Particle fluence or fluence ()

 For particle, particle fluence or fluence is

where  N is the number of particles which enter a sphere of cross sectional area  a

a

N

Energy fluence (F)

 For particles, the energy fluence is

where  EF is the sum of the energies, exclusive of rest energies, of all particles which enter a sphere of cross sectional area  a

a

E

F F

Energy flux density of intensity (I)

 It is defined as follows:

where  F is the energy fluence in the time  t

t

I F 

 

Exposure (X)

 The exposure is defined as

where  Q is the sum of the electrical charges on all the ions of one sign produced in air when all the electrons (negatrons and positrons), liberated by photons in a volume element of air whose mass is  m , are completely stopped in air

Exposure rate

m

Q

X

t

X X 

  

Units of exposure

SI unit: Exposure unit (X-unit)

1 X-unit = 1 C/kg air

Old unit: Roentgen (R)

1 R = 1 esu / cm^3 of dry air 1 R = 2.58x10-4^ C/kg

Units of Absorbed dose

SI unit: gray (Gy)

1 Gy = 1 joule/ kg

Old unit: rad (radiation absorbed dose)

1 rad = 100 ergs/ gm 1 rad = 0.01 Gy

Activity (A)

 The activity of a quantity of a radionuclide is

where  N is the number of nuclear transformations

which occur in this quantity in time  t

Units

 SI unit: becquerel (Bq) 1 Bq = 1 dis/sec  Special unit: curie (Ci) 1 Ci = 3.7x10^10 Bq

t

A N 

 

BIOPHYSICAL RADIATION

QUANTITIES

 These quantities depend not only on physical considerations, but also on biological factors of importance in radiation protection

Quantities

 Dose equivalent  Equivalent dose  Effective dose  Population dose  Radon concentration and exposure

Dose equivalent

RBE (Relative biological effectiveness)

 Absorbed dose from different types of radiations have different biological effectiveness  The RBE of one type of radiation in relation to a reference type of a radiation is the inverse ratio of the absorbed doses of two radiations needed to cause the same degree of the biological effect for which the RBE is given

Quality factor (Q)

 The whole number rounded value of RBE