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).
Table 1004(b).1-Quality Factors and Absorbed Dose Equivalencies
Type of radiation | Quality factor | Absorbed dose equal to a unit dose equivalenta |
(Q) | ||
X-, gamma, or beta radiation | 1 | 1 |
Alpha particles, multiple-charged particles, fission fragments and heavy particles of unknown charge | 20 | 0.05 |
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.
Table 1004(b).2-Mean Quality Factors, Q, and Fluence per Unit Dose Equivalent for Monoenergetic Neutrons
Neutron energy (MeV) | Quality factora (Q) | Fluence per unit dose equivalentb (neutrons cm-2 rem-1) | |
(thermal) | 2.5 * 10-8 | 2 | 980 * 106 |
1 * 10-7 | 2 | 980 * 106 | |
1 * 10-6 | 2 | 810 * 106 | |
1 * 10-5 | 2 | 810 * 106 | |
1 * 10-4 | 2 | 840 * 106 | |
1 * 10-3 | 2 | 980 * 106 | |
1 * 10-2 | 2.5 | 1010 * 106 | |
1 * 10-1 | 7.5 | 170 * 106 | |
5 * 10-1 | 11 | 39 * 106 | |
1 | 11 | 27 * 106 | |
2.5 | 9 | 29 * 106 | |
5 | 8 | 23 * 106 | |
7 | 7 | 24 * 106 | |
10 | 6.5 | 24 * 106 | |
14 | 7.5 | 17 * 106 | |
20 | 8 | 16 * 106 | |
40 | 7 | 14 * 106 | |
60 | 5.5 | 16 * 106 | |
1 * 102 | 4 | 20 * 106 | |
2 * 102 | 3.5 | 19 * 106 | |
3 * 102 | 3.5 | 16 * 106 | |
4 * 102 | 3.5 | 14 * 106 |
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.
10 C.F.R. §20.1004