[Code of Federal Regulations]
[Title 40, Volume 24]
[Revised as of July 1, 2008]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR191 App B]
[Page 15-16]
TITLE 40--PROTECTION OF ENVIRONMENT
CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
PART 191_ENVIRONMENTAL RADIATION PROTECTION STANDARDS FOR MANAGEMENT AND
Subpart C_Environmental Standards for Ground-Water Protection
Sec. Appendix B to Part 191--Calculation of Annual Committed Effective
Dose
I. Equivalent Dose
The calculation of the committed effective dose (CED) begins with
the determination of the equivalent dose, H<INF>T</INF>, to a tissue or
organ, T, listed in Table B.2 below by using the equation:
[GRAPHIC] [TIFF OMITTED] TR20DE93.009
where D<INF>T, R</INF> is the absorbed dose in rads (one gray, an SI
unit, equals 100 rads) averaged over the tissue or organ, T, due to
radiation type, R, and w<INF>R</INF> is the radiation weighting factor
which is given in Table B.1 below. The unit of equivalent dose is the
rem (sievert, in SI units).
Table B.1--Radiation Weighting Factors, wR\1\
------------------------------------------------------------------------
wR
Radiation type and energy range \2\ value
------------------------------------------------------------------------
Photons, all energies........................................... 1
Electrons and muons, all energies............................... 1
Neutrons, energy < 10 keV....................................... 5
10 keV to 100 keV..................................... 10
<ls-thn-eq>100 keV to 2 MeV........................... 20
<ls-thn-eq>2 MeV to 20 MeV............................ 10
<ls-thn-eq>20 MeV..................................... 5
Protons, other than recoil protons, <ls-thn-eq>2 MeV............ 5
Alpha particles, fission fragments, heavy nuclei................ 20
------------------------------------------------------------------------
\1\ All values relate to the radiation incident on the body or, for
internal sources, emitted from the source.
\2\ See paragraph A14 in ICRP Publication 60 for the choice of values
for other radiation types and energies not in the table.
II. Effective Dose
The next step is the calculation of the effective dose, E. The
probability of occurrence of a stochastic effect in a tissue or organ is
assumed to be proportional to the equivalent dose in the tissue or
organ. The constant of proportionality differs for the various tissues
of the body, but in assessing health detriment the total risk is
required. This is taken into account using the tissue weighting factors,
w<INF>T</INF> in Table B.2, which represent the proportion of the
stochastic risk resulting from irradiation of the tissue or organ to the
total risk when the whole body is irradiated uniformly and H<INF>T</INF>
is the equivalent dose in the tissue or organ, T, in the equation:
[GRAPHIC] [TIFF OMITTED] TR20DE93.010
Table B.2--Tissue Weighting Factors, wT \1\
------------------------------------------------------------------------
Tissue or organ wT value
------------------------------------------------------------------------
Gonads.................................................. 0.25
Breast.................................................. 0.15
Red bone marrow......................................... 0.12
Lung.................................................... 0.12
Thyroid................................................. 0.03
Bone surfaces........................................... 0.03
Remainder............................................... \2\ 0.30
------------------------------------------------------------------------
\1\ The values are considered to be appropriate for protection for
individuals of both sexes and all ages.
\2\ For purposes of calculation, the remainder is comprised of the five
tissues or organs not specifically listed in Table B.2 that receive
the highest dose equivalents; a weighting factor of 0.06 is applied to
each of them, including the various sections of the gastrointestinal
tract which are treated as separate organs. This covers all tissues
and organs except the hands and forearms, the feet and ankles, the
skin and the lens of the eye. The excepted tissues and organs should
be excluded from the computation of HE.
III. Annual Committed Tissue or Organ Equivalent Dose
For internal irradiation from incorporated radionuclides, the total
absorbed dose will be spread out in time, being gradually delivered as
the radionuclide decays. The time distribution of the absorbed dose rate
will vary with the radionuclide, its form, the mode of intake and the
tissue within which it is incorporated. To take account of this
distribution the quantity committed equivalent dose, H[Tau]([tau]) where
is the integration time in years following an intake over any particular
year, is used and is the integral over time of the equivalent dose rate
in a particular tissue or organ that will be received by an individual
following an intake of radioactive material into the body. The time
period, [tau], is taken as 50 years as an average time of exposure
following intake:
[GRAPHIC] [TIFF OMITTED] TR20DE93.011
for a single intake of activity at time t<INF>0</INF> where
H<INF>T</INF>(t) is the relevant equivalent-dose rate in a tissue or
organ at time t. For the purposes of this part, the previously mentioned
single intake may be considered to be an annual intake.
[[Page 16]]
IV. Annual Committed Effective Dose
If the committed equivalent doses to the individual tissues or
organs resulting from an annual intake are multiplied by the appropriate
weighting factors, w<INF>T</INF>, and then summed, the result will be
the annual committed effective dose, E([tau]):
[GRAPHIC] [TIFF OMITTED] TR20DE93.012
[58 FR 66415, Dec. 20, 1993]