Section 144-220-A-13 - The International system of units (SI)The Metric Conversion Act of 1975 (PL 94-168) urged the increasing awareness and use of the International System of Units (SI). The generally accepted regulatory values in the narrative portions of this document are followed by the SI equivalents in parentheses. Where appropriate, schedules and appendices are provided, with notes concerning conversion factors. The inclusion of the SI equivalent is for informational purposes only unless otherwise specified.
A. Units of Exposure and Dose(1) Absorbed dose. The unit of absorbed dose is the gray (Gy) which is equal to 1 joule per kilogram. One rad is equal to 1 x 10-2 gray. Sub-multiples included in this document are the milligray (mGy) and the microgray (µGy).(2) Dose equivalent. The unit of dose equivalent is the sievert (Sv) which is equal to 1 joule per kilogram. The dose equivalent in sievert is equal to the absorbed dose in gray multiplied by the quality factor. One REM is equal to 1 x 10-2 sievert. Submultiples included in this document are the millisievert (mSv) and the microsievert (µSv).(3) Exposure. The unit of exposure is the coulomb per kilogram (C/kg). One roentgen is equal to 2.58 x 10-4 coulomb per kilogram of air. Submultiples of this unit are the millicoulomb per kilogram (mC/kg) and the microcoulomb per kilogram (µC/kg).(4) Quality factors. As used in this rule, the quality factors for converting absorbed dose to dose equivalent are shown in Table I. TABLE I
Quality Factors and Absorbed Does Equivalencies
Type of Radiation | Absorbed Dose Quality Factor | Equal to a Unit Dose (Q) | Equivalenta |
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 |
aAbsorbed dose in gray equal to 1 Sv or the absorbed dose in rad equal to 1 rem.
(5) If it is more convenient to measure the neutron influence rate than to determine the neutron dose equivalent rate in sievert per hour or rem per hour, as provided in A.13.A(4), 0.01 Sv (1 rem) of neutron radiation of unknown energies may, for purposes of this rule, be assumed to result from a total influence 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 II to convert a measured tissue dose in gray or rad to dose equivalent in sievert or rem. TABLE II
MEAN QUALITY FACT0RS, Q, AND FLUENCE PER UNIT DOSE EQUIVALENT FOR MONOENERGETIC NEUTRONS
Mean Quality Factors Q, and Fluence Per Unit Dose Equivalent for Monoenergetic Neutrons
| Neutron Energy (MeV) | Qualitya Factor (Q) | Fluence per Unit Dose Equivalentb (neutrons cm-2 rem-1) | Fluence/Unit Dose Equiv.b (neutrons-2 cm Sv-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 |
a Value of quality factor (Q) at the point where the dose equivalent is maximum in a 30-centimeter diameter cylinder tissue-equivalent phantom.
b Monoenergetic neutrons incident normally on a 30-centimeter diameter cylinder tissue-equivalent phantom.
B. Units of Activity. For purposes of this rule, activity is expressed in the SI unit of becquerel (Bq) or in the special unit of curie (Ci), or their multiples, or disintegrations or transformations per unit of time.(1) The unit of measurement of radioactivity is the becquerel (Bq) and it is equal to one transformation per second.(2) One curie is equal to 3.7 x 1010 disintegrations or transformations per second (dps or tps) = 3.7E+10 becquerel (Bq) = 2.22E+12 disintegrations or transformations per minute (dpm or tpm). Multiples included in this document are kilobecquerel (kBq), megabecquerel (MBq), gigabecqueral (GBq), and petabecquerel (PBq).10-144 C.M.R. ch. 220, § A-13