Utah Admin. Code 313-12-20

Current through Bulletin 2024-20, October 15, 2024

Section R313-12-20 - Units of Exposure and Dose

(1) As used in these rules, the unit of EXPOSURE is the coulomb per kilogram (C per kg). One roentgen is equal to 2.58 x 10^-4 coulomb per kilogram of air.

(2) As used in these rules, the units of dose are:

(a) Gray (Gy) is the SI unit of absorbed dose. One gray is equal to an absorbed dose of one joule per kilogram. One gray equals 100 rad.

(b) 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. One rad equals 0.01 Gy.

(c) 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. One rem equals 0.01 Sv.

(d) Sievert (Sv) 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. One Sv equals 100 rem.

(3) As used in these rules, the quality factors for converting absorbed dose to dose equivalent are shown in Table 1.

TABLE 1 Quality Factors and Absorbed Dose Equivalencies
Type of Radiation	Quality Factor (Q)	Absorbed Dose Equal to a Unit Dose Equivalent
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
For the column in Table 1 labeled "Absorbed Dose Equal to a Unit Dose Equivalent", the absorbed dose in rad is equal to one rem or the absorbed dose in gray is equal to one Sv.

(4) 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 R313-12-20(3), 0.01 Sv of neutron radiation of unknown energies may, for purposes of these rules, 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 2 to convert a measured tissue dose in gray or rad to dose equivalent in sievert or rem.

TABLE 2 Mean Quality Factors, Q, and Fluence Per Unit Dose Equivalent for Monoenergetic Neutrons
Neutron Energy Mev	Quality Factor Q	Fluence per Unit Dose Equivalent neutrons cm-2 rem-1	Fluence per Unit Dose Equivalent neutrons cm-2 Sv-1
thermal 2.5 x 10-8	2	980 x 106	980 x 108
1 x 10-7	2	980 x 106	980 x 108
1 x 10-6	2	810 x 106	810 x 108
1 x 10-5	2	810 x 106	810 x 108
1 x 10-4	2	840 x 106	840 x 108
1 x 10-3	2	980 x 106	980 x 108
1 x 10-2	2.5	1010 x 106	1010 x 108
1 x 10-1	7.5	170 x 106	170 x 108
5 x 10-1	11	39 x 106	39 x 108
1	11	27 x 106	27 x 108
2.5	9	29 x 106	29 x 108
5	8	23 x 106	23 x 108
7	7	24 x 106	24 x 108
10	6.5	24 x 106	24 x 108
14	7.5	17 x 106	17 x 108
20	8	16 x 106	16 x 108
40	7	14 x 106	14 x 108
60	5.5	16 x 106	16 x 108
1 x 102	4	20 x 106	20 x 108
2 x 102	3.5	19 x 106	19 x 108
3 x 102	3.5	16 x 106	16 x 108
4 x 102	3.5	14 x 106	14 x 108
For the column in Table 2 labeled "Quality Factor", the values of Q are at the point where the dose equivalent is maximum in a 30 cm diameter cylinder tissue-equivalent phantom.
For the columns in Table 2 labeled "Fluence per Unit Dose Equivalent", the values are for monoenergetic neutrons incident normally on a 30 cm diameter cylinder tissue equivalent phantom.

Utah Admin. Code R313-12-20