As used in this subpart:
(a) Radiation includes alpha rays, beta rays, gamma rays, X-rays,
neutrons, high-speed electrons, high-speed protons, and other atomic
particles; but such term does not include sound or radio waves, or
visible light, or infrared or ultraviolet light.
(b) Radioactive material means any material which emits, by
spontaneous nuclear disintegration, corpuscular or electromagnetic
emanations.
(c) Restricted area means any area access to which is controlled by
the employer for purposes of protection of individuals from exposure to
radiation or radioactive materials.
(d) Unrestricted area means any area access to which is not
controlled by the employer for purposes of protection of individuals
from exposure to radiation or radioactive materials.
(e) Dose means the quantity of ionizing radiation absorbed, per unit
of mass, by the body or by any portion of the body. When the provisions
in this subpart specify a dose during a period of time, the dose is the
total quantity of radiation absorbed, per unit of mass, by the body or
by any portion of the body during such period of time. Several different
units of dose are in current use. Definitions of units used in this
subpart are set forth in paragraphs (f) and (g) of this section.
(f) Rad means a measure of the dose of any ionizing radiation to
body tissues in terms of the energy absorbed per unit of mass of the
tissue. One rad is the dose corresponding to the absorption of 100 ergs
per gram of tissue (1 millirad (mrad)=0.001 rad).
(g) Rem means a measure of the dose of any ionizing radiation to
body tissue in terms of its estimated biological effect relative to a
dose of 1 roentgen (r) of X-rays (1 millirem (mrem)=0.001 rem). The
relation of the rem to other dose units depends upon the biological
effect under consideration and upon the conditions for irradiation. Each
of the following is considered to be equivalent to a dose of 1 rem:
(1) A dose of 1 rad due to X- or gamma radiation;
(2) A dose of 1 rad due to X-, gamma, or beta radiation;
(3) A dose of 0.1 rad due to neutrons or high energy protons;
(4) A dose of 0.05 rad due to particles heavier than protons and
with sufficient energy to reach the lens of the eye;
(5) If it is more convenient to measure the neutron flux, or
equivalent, than to determine the neutron dose in rads, as provided in
paragraph (g)(3) of this section, 1 rem of neutron radiation may, for
purposes of the provisions in this subpart be assumed to be equivalent
to 14 million neutrons per square centimeter incident upon the body; or,
if there is sufficient information to estimate with reasonable accuracy
the approximate distribution in energy of the neutrons, the incident
number of neutrons per square centimeter equivalent to 1 rem may be
estimated from the following table:
Neutron Flux Dose Equivalents
------------------------------------------------------------------------
Number of
neutrons per Average flux to
square centimeter deliver 100
Neutron energy (million electron equivalent to a millirem in 40
volts [Mev]) dose of 1 rem hours (neutrons/
(neutrons/cm \2\ cm \2\ per sec.)
)
------------------------------------------------------------------------
Thermal........................... 970 x 10 \6\ 670
0.0001............................ 720 x 10 \6\ 500
0.005............................. 820 x 10 \6\ 570
0.02.............................. 400 x 10 \6\ 280
0.1............................... 120 x 10 \6\ 80
0.5............................... 43 x 10 \6\ 30
1.0............................... 26 x 10 \6\ 18
2.5............................... 29 x 10 \6\ 20
5.0............................... 26 x 10 \6\ 18
7.5............................... 24 x 10 \6\ 17
10................................ 24 x 10 \6\ 17
10 to 30.......................... 14 x 10 \6\ 10
------------------------------------------------------------------------
(h) For determining exposures to X-or gamma rays up to 3 Mev., the
dose limits specified in this part may be assumed to be equivalent to
the ``air dose''. For the purpose of this subpart ``air dose'' means
that the dose is measured by a properly calibrated appropriate
instrument in air at or near the body surface in the region of the
highest dosage rate.
