Basic Calculations for Occupational Safety and Environmental Health Professionals - Mathematics and Statistics for the Environment - page 438

Unrestricted area means an area, access to which is neither limited nor controlled by the
licensee.
X-rays is a penetrating type of photon radiation emitted from outside the nucleus of a target
atom during bombardment of a metal with fast electrons.

15.9.2 i ionizing r adiation
Ionization is the process by which atoms are made into ions by the removal or addition of one
or more electrons; they produce this effect by the high kinetic energies of the quanta (discrete
pulses) they emit. Simply, ionizing radiation is any radiation capable of producing ions by inter-
action with matter. Direct ionizing particles are charged particles (e.g., electrons, protons, alpha
particles) having sufficient kinetic energy to produce ionization by collision. Indirect ionizing
particles are uncharged particles (e.g., photons, neutrons) that can liberate direct ionizing par-
ticles. Sources of ionizing radiation can be found in a wide range of occupational settings, includ-
ing healthcare facilities, research institutions, nuclear reactors and their support facilities, nuclear
weapon production facilities, and other various manufacturing settings, just to name a few. These
sources of ionizing radiation can pose a considerable health risk to affected workers if not prop-
erly controlled. Ionization of cellular components can lead to functional changes in the tissues of
the body. Alpha, beta, and neutron particles; x-rays; gamma rays; and cosmic rays are all ionizing
radiations.
Three mechanisms for external radiation protection include time, distance, and shielding. A
shorter time in a radiation field means less dose. From a point source, dose rate is reduced by the
square of the distance and expressed by the inverse square law:

I 1 ( d 1 ) 2 = I 2 ( d 2 ) 2 (15.23)

where
I 1 = Dose rate or radiation intensity at distance d 1 .
I 2 = Dose rate or radiation intensity at distance d 2 .

Radiation is reduced exponentially by thickness of shielding material.

15.9.3 e FFeCtive h alF -l iFe
The half-life is the length of time required for one-half of a radioactive substance to disintegrate.
The formula depicted below is used when the industrial hygienist is interested in determining how
much radiation is left in a worker's stomach after a period of time. Effective half-life is a combina-
tion of radiological and biological half-lives and is expressed as

TT
TT

×
+

b r

T = (15.24)

Teff

b r

where:
T b = Biological half-life.
T r = Radiological half-life.

It is important to point out that T Teff will always be shorter than either T b or T r . T b may be modified
by diet and physical activity.