[Code of Federal Regulations]
[Title 10, Volume 1]
[Revised as of January 1, 2003]
From the U.S. Government Printing Office via GPO Access
[CITE: 10CFR20.1004]

[Page 330-331]
 
                            TITLE 10--ENERGY
 
                CHAPTER I--NUCLEAR REGULATORY COMMISSION
 
PART 20--STANDARDS FOR PROTECTION AGAINST RADIATION--Table of Contents
 
                      Subpart A--General Provisions
 
Sec. 20.1004  Units of radiation dose.

    (a) Definitions. As used in this part, the units of radiation dose 
are:
    Gray (Gy) is the SI unit of absorbed dose. One gray is equal to an 
absorbed dose of 1 Joule/kilogram (100 rads).
    Rad is the special unit of absorbed dose. One rad is equal to an 
absorbed dose of 100 ergs/gram or 0.01 joule/kilogram (0.01 gray).
    Rem is the special unit of any of the quantities expressed as dose 
equivalent. The dose equivalent in rems is equal to the absorbed dose in 
rads multiplied by the quality factor (1 rem=0.01 sievert).
    Sievert is the SI unit of any of the quantities expressed as dose 
equivalent. The dose equivalent in sieverts is equal to the absorbed 
dose in grays multiplied by the quality factor (1 Sv=100 rems).
    (b) As used in this part, the quality factors for converting 
absorbed dose to dose equivalent are shown in table 1004(b).1.

    Table 1004(b).1--Quality Factors and Absorbed Dose Equivalencies
------------------------------------------------------------------------
                                                 Quality   Absorbed dose
                                                 factor     equal to a
               Type of radiation               ----------    unit dose
                                                   (Q)    equivalent \a\
------------------------------------------------------------------------
X-, gamma, or beta radiation..................         1          1
Alpha particles, multiple-charged particles,          20          0.05
 fission fragments and heavy particles of
 unknown charge...............................
Neutrons of unknown energy....................        10          0.1
High-energy protons...........................        10          0.1
------------------------------------------------------------------------
\a\ Absorbed dose in rad equal to 1 rem or the absorbed dose in gray
  equal to 1 sievert.

    (c) If it is more convenient to measure the neutron fluence rate 
than to determine the neutron dose equivalent

[[Page 331]]

rate in rems per hour or sieverts per hour, as provided in paragraph (b) 
of this section, 1 rem (0.01 Sv) of neutron radiation of unknown 
energies may, for purposes of the regulations in this part, be assumed 
to result from a total fluence of 25 million neutrons per square 
centimeter incident upon the body. If sufficient information exists to 
estimate the approximate energy distribution of the neutrons, the 
licensee may use the fluence rate per unit dose equivalent or the 
appropriate Q value from table 1004(b).2 to convert a measured tissue 
dose in rads to dose equivalent in rems.

   Table 1004(b).2--Mean Quality Factors, Q, and Fluence per Unit Dose
                  Equivalent for Monoenergetic Neutrons
------------------------------------------------------------------------
                                                   Fluence per unit dose
                       Neutron energy    Quality       equivalent \b\
                           (MeV)       factor \a\   (neutrons cm-2 rem -
                                           (Q)               1)
------------------------------------------------------------------------
(thermal)...........  2.5x10 -8               2     980x10 \6\
                      1x10 -7                 2     980x10 \6\
                      1x10 -6                 2     810x10 \6\
                      1x10 -5                 2     810x10 \6\
                      1x10 -4                 2     840x10 \6\
                      1x10 -3                 2     980x10 \6\
                      1x10 -2                 2.5  1010x10 \6\
                      1x10 - 1                7.5   170x10 \6\
                      5x10 -1                11      39x10 \6\
                      1                      11      27x10 \6\
                      2.5                     9      29x10 \6\
                      5                       8      23x10 \6\
                      7                       7      24x10 \6\
                      10                      6.5    24x10 \6\
                      14                      7.5    17x10 \6\
                      20                      8      16x10 \6\
                      40                      7      14x10 \6\
                      60                      5.5    16x10 \6\
                      1x10 \2\                4      20x10 \6\
                      2x10 \2\                3.5    19x10 \6\
                      3x10 \2\                3.5    16x10 \6\
                      4x10 \2\                3.5    14x10 \6\
------------------------------------------------------------------------
\a\ Value of quality factor (Q) at the point where the dose equivalent
  is maximum in a 30-cm diameter cylinder tissue-equivalent phantom.
\b\ Monoenergetic neutrons incident normally on a 30-cm diameter
  cylinder tissue-equivalent phantom.