rem =rad ×Wr (14.7)The International Commission on Radiological Protection (ICRP) has sug-
gested the Wrvalues for different radiations, which are listed in Table 14.1
(ICRP 60, 1991). These values depend on the LET of the radiation. When
a radiation dose comes from several radiations, the total dose equivalent is
calculated by adding the absorbed doses from individual radiations multi-
plied by the Wrof each radiation.
In the past, the Wrvalues were called quality factors, which are somewhat
different from the Wrvalues. The US Nuclear Regulatory Commission
(NRC) still adopts these values for regulatory purposes, and the values are
listed in Table 14.2.
In SI units, the dose equivalent is expressed in sievert, which is defined as
1 sievert (Sv) =100 rem (14.8)
In practical situations, all these radiation units are often expressed in mil-
liroentgens (mR), millirads (mrad), and millirems (mrem), which are 10−^3
times the units, roentgen, rad, and rem, respectively. In SI units, the equiv-
alent quantities are milligrays (mGy) and millisieverts (mSv). A rad is also
commonly expressed as centigray (cGy), one-hundredth of a gray.
210 14. Internal Radiation Dosimetry
Table14.1. Radiation weighting factors.
Type and energy range Radiation weighting factors,Wr
Photons, all energies 1
Electrons, muons, all energies 1
Neutrons, energy <10 keV 5
10 keV to 100 keV 10
100 keV to 2 MeV 20
2 MeV to 20 MeV 10
20 MeV 5
Protons, other than recoil protons, energy >2 MeV 5
Alpha particles, fission fragments, heavy nuclei 20
Adapted with permission from ICRP Publication 60:1990 Recommendations of the Interna-
tional Commission on Radiological Protection.New York: Pergamon Press; 1991.
Table14.2. Quality factors for different radiations.
Type of radiation QF
X-rays,g-rays,b-particles 1.0
Neutrons and protons 10.0
a-Particles 20.0
Heavy ions 20.0