Tenn. Comp. R. & Regs. 0400-20-05-.33

Current through June 26, 2024

Section 0400-20-05-.33 - UNITS OF RADIATION DOSE

(1) Definitions. As used in these standards the units of radiation dose are:

(a) Gray (Gy) is the SI unit of absorbed dose. One gray is equal to an absorbed dose of 1 joule/kilogram (100 rads).

(b) 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).

(c) 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).

(d) 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).

(2) As used in these standards the quality factors for converting absorbed dose to dose equivalent are shown in Table RHS 5-1.

TABLE RHS 5-1 QUALITY FACTORS AND ABSORBED DOSE EQUIVALENCIES

Type of Radiation	Quality Factor (Q)	Absorbed dose equal to a unit dose equivalent 1
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

¹ Absorbed dose in rad equal to 1 rem or the absorbed dose in gray equal to 1 sievert.

If measuring the neutron fluence rate is more convenient than determining the neutron dose equivalent rate as provided in this paragraph, 1 rem (0.01 Sv) of neutron radiation of unknown energies may 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 RHS 5-2 to convert a measured tissue dose in rads to dose equivalent in rems.

TABLE RHS 5-2 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-2rem-1)
(Thermal). 2.5 x 10-8	2	980x106
1 x 10-7	2	980x106
1 x 10-6	2	810x106
1 x 10-5	2	810x106
1 x 10-4	2	840x106
1 x 10-3	2	980x106
1 x 10-2	2.5	1010x106
1 x 10-1	7.5	170x106
5 x 10-1	11	39x106
1	11	27x106
2.5	9	29x106
5	8	23x106
7	7	24x106
10	6.5	24x106
14	7.5	17x106
20	8	16x106
40	7	14x106
60	5.5	16x106
1 x 102	4	20x106
2 x 102	3.5	19x106
3 x 102	3.5	16x106
4 x 102	3.5	14x106

^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.

Tenn. Comp. R. & Regs. 0400-20-05-.33

Original rule filed February 22, 2012; effective May 22, 2012.

Authority: T.C.A. §§ 68-202-201 et seq., and 4-5-201 et seq.