N.M. Code R. § 20.3.4.8 – Units of Exposure and Dose

A. As used in these regulations, the unit of exposure is the coulomb per kilogram (C/kg) of air. One roentgen is equal to 2.58E-4 coulomb per kilogram of air.
B. As used in these regulations, the units of dose are:
1. (1) gray (Gy) is the SI unit of absorbed dose; one gray is equal to an absorbed dose of 1 joule per kilogram (1 gray = 100 rads);
2. (2) rad is the special unit of absorbed dose; one rad is equal to an absorbed dose of 100 erg per gram or 0.01 joule per kilogram (1 rad = 0.01 gray);
3. (3) rem is the special unit of any of the quantities expressed as dose equivalent; the dose equivalent in rem is equal to the absorbed dose in rad multiplied by the quality factor (1 rem = 0.01 sievert); and
4. (4) sievert is the SI unit of any of the quantities expressed as dose equivalent; the dose equivalent in sievert is equal to the absorbed dose in gray multiplied by the quality factor (1 sievert = 100 rems).
C. As used in these regulations, the quality factors for converting absorbed dose to dose equivalent are shown in table 8.1.
TABLE 8.1 QUALITY FACTORS AND ABSORBED DOSE EQUIVALENCIES Type of Radiation Quality Factor (Q) Absorbed Dose Equal to A Unit Dose Equivalent¹ X, gamma, or beta radiation and high-speed electrons 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
TABLE 8.1
QUALITY FACTORS AND ABSORBED DOSE EQUIVALENCIES
Type of Radiation
Quality Factor (Q)
Absorbed Dose Equal to A Unit Dose Equivalent¹
X, gamma, or beta radiation and high-speed electrons
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
Table 8.1 note: ¹absorbed dose in gray equal to 1 sievert or the absorbed dose in rad equal to 1 rem.
D. If it is more convenient to measure the neutron fluence rate than to determine the neutron dose equivalent rate in sievert per hour or rem per hour, as provided in Subsection C of this section, 0.01 sievert (1 rem) of neutron radiation of unknown energies may, for purposes of these regulations, 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 or registrant may use the fluence rate per unit dose equivalent or the appropriate Q value from table 8.2 to convert a measured tissue dose in gray or rad to dose equivalent in sievert or rem (Note: The values in table 8.2 are presented in the “E” notation. In this notation a value of 5E-1 represents a value of 5x10^-1 or 0.5. A value of 4E+2 represents 4x10² or 400.)
TABLE 8.2 MEAN QUALITY FACTORS, Q, AND FLUENCE PER UNIT DOSE EQUIVALENT FOR MONOENERGETIC NEUTRONS Neutron Energy (megaelectronvolt) Quality Factor¹ (Q) Fluence per Unit Dose Equivalent² (neutrons centimeter^-2 rem^-1) Fluence per Unit Dose Equivalent (neutrons centimeter^-2 sievert^-1) (thermal) 2.5E-8 2 980E+6 980E+8 1E-7 2 980E+6 980E+8 1E-6 2 810E+6 810E+8 1E-5 2 810E+6 810E+8 1E-4 2 840E+6 840E+8 1E-3 2 980E+6 980E+8 1E-2 2.5 1010E+6 1010E+8 1E-1 7.5 170E+6 170E+8 5E-1 11 39E+6 39E+8 1 11 27E+6 27E+8 2.5 9 29E+6 29E+8 5 8 23E+6 23E+8 7 7 24E+6 24E+8 10 6.5 24E+6 24E+8 14 7.5 17E+6 17E+8 20 8 16E+6 16E+8 40 7 14E+6 14E+8 60 5.5 16E+6 16E+8 1E+2 4 20E+6 20E+8 2E+2 3.5 19E+6 19E+8 3E+2 3.5 16E+6 16E+8 4E+2 3.5 14E+6 14E+8
TABLE 8.2
MEAN QUALITY FACTORS, Q, AND FLUENCE PER UNIT DOSE EQUIVALENT FOR MONOENERGETIC NEUTRONS
Neutron Energy
(megaelectronvolt)
Quality Factor¹ (Q)
Fluence per Unit Dose
Equivalent² (neutrons
centimeter^-2 rem^-1)
Fluence per Unit Dose
Equivalent (neutrons
centimeter^-2 sievert^-1)
(thermal) 2.5E-8
2
980E+6
980E+8
1E-7
2
980E+6
980E+8
1E-6
2
810E+6
810E+8
1E-5
2
810E+6
810E+8
1E-4
2
840E+6
840E+8
1E-3
2
980E+6
980E+8
1E-2
2.5
1010E+6
1010E+8
1E-1
7.5
170E+6
170E+8
5E-1
11
39E+6
39E+8
1
11
27E+6
27E+8
2.5
9
29E+6
29E+8
5
8
23E+6
23E+8
7
7
24E+6
24E+8
10
6.5
24E+6
24E+8
14
7.5
17E+6
17E+8
20
8
16E+6
16E+8
40
7
14E+6
14E+8
60
5.5
16E+6
16E+8
1E+2
4
20E+6
20E+8
2E+2
3.5
19E+6
19E+8
3E+2
3.5
16E+6
16E+8
4E+2
3.5
14E+6
14E+8
Table 8.2 notes:
¹ value of quality factor (Q) at the point where the dose equivalent is maximum in a 30-centimeter diameter cylinder tissue-equivalent phantom;
² monoenergetic neutrons incident normally on a 30-centimeter diameter cylinder tissue-equivalent phantom.

[20.3.4.8 NMAC - Rp, 20.3.1.117 NMAC, 4/30/2009]