Constants and Physical Values

The ABR provides candidates with a list of constants, physical values, and related information, which can be found on this page. While the list includes many constants and physical values, the ABR does not warrant the list as a compilation of all constants and physical values needed on the exams. The absence of a value from this list will not be used as a reason to reject a question. Candidates should review the list carefully before their exams to familiarize themselves with the contents and list organization. Prudent candidates also will learn any constants not on the list that they think are important. The value of a constant varies somewhat in the literature. If a question suggests a value different from the value in this table, the candidate should use the value presented in the question. These values are intended for the ABR exam. They should not be used for clinical calculations without confirmation. The ABR has made every effort to use the most current and correct values. If you believe a value is not correct, please contact the ABR. LIST OF CONSTANTS AND PHYSICAL VALUES

Name	Symbol	Value	Units
Planck’s constant	h	6.626 × 10-34	m2 kg / s
Boltzmann’s constant	k	1.38 × 10-23	m2 kg s-2 K-1
Mass of the electron	me	0.511	MeV
Mass of the electron	me	9.11 × 10-31	kg
Charge of the electron	qe	1.60 × 10-19	C
Mass of the proton	mp	938	MeV
Mass of the neutron	mn	939	MeV
Assumed speed of sound in soft tissue	vt	1540	m/s
Speed of light	c	3 × 108	m/s
Mass of standard man		70	kg
Molar gas constant	R	8.31	J mole -1K-1
Avogadro’s Number	NA	6.02 × 1023	Atom/mole
Energy mass conversion	amu	931.48	MeV/amu
Electron Volt	eV	1.60 × 10-19	J/eV
Gyromagnetic ratio - H		42.58	MHz/T
Gyromagnetic ratio - P		17.2	MHz/T
Gyromagnetic ratio - Na		11.26	MHz/T
Ionization constant	Wair/e	33.97	eV/ion-pair in air
Roentgen	R	2.58 × 10-4	C/kg

Half-lives of common radionuclides

Radionuclide	Half-life	Units
18F	110	minute
32P	14.3	day
60Co	5.27	year
67Ga	78.3	hour
68Ga	68	minute
89Sr	50.6	day
90Y	2.67	day
90Sr	28.8	year
99Mo	2.75	day
99mTc	6.01	hour
103Pd	17.0	day
111In	2.80	day
123I	13.2	hour
124I	4.18	day
125I	59.4	day
131I	8.03	day
131Cs	9.69	day
137Cs	30.1	year
153Sm	1.93	day
198Au	2.69	day
192Ir	73.8	day
201Tl	3.04	day
222Rn	3.82	day
223Ra	11.4	day

ICRP 103 tissue weighting factors

Tissue	Tissue weighting factor wT
Bone-marrow (red), Colon, Lung, Stomach, Breast, Remainder tissues*	0.12
Gonads	0.08
Bladder, Oesophagus, Liver, Thyroid	0.04
Bone surface, Brain, Salivary glands, Skin	0.01
*Remainder tissues: Adrenals, Extrathoracic (ET) region, Gall bladder, Heart, Kidneys, Lymphatic nodes, Muscle, Oral mucosa, Pancreas, Prostate (♂), Small intestine, Spleen, Thymus, Uterus/cervix (♀)

PET dose rate constants

Nuclide	Dose rate constant µSv m2 /MBq h	Use
68Ga	0.134	Effective dose equivalent
82Rb	0.159	Effective dose equivalent
124I	0.185	Effective dose equivalent
18F	0.143	Effective dose equivalent

Radiation weighting factors

Radiation Type	Radiation Weighting Factor
Photons, electrons and muons, all energies	1
Protons	5
Fast Neutrons	10
Alpha particles, fission fragments, heavy nuclei	20

Standard Calibration Conditions: Calibrated to deliver 1 cGy/MU at dmax in a 10 x 10 cm2 field at the 100-cm source-to-surface distance (SSD).

Standard Environmental Conditions: Conditions of temperature, pressure, and relative humidity for which ion chamber calibration factors apply. In the US and Canada these are: Temperature, T0 = 22°C, Pressure, P0 = 101.33 kPa, Relative humidity of the air in the ion chamber between 20% and 80%.

IAEA dose rate constants and TVLs

Nuclide	Dose rate constant (µSv/h MBq) @ 1 m	TVL (mm Pb)
24Na	0.500	59
42K	0.038	53
43K	0.147	18
47Ca	0.150	46
51Cr	0.005	7
59Fe	0.170	44
57Co	0.016	0.7
58Co	0.150	28
64Cu	0.032	25
67Ga	0.022	5.3
65Zn	0.085	42
75Se	0.056	5
99mTc	0.017	0.9
111In	0.084	2.5
125I	0.034	0.06
123I	0.044	1.2
131I	0.057	11
192Ir	0.135	12
201Tl	0.012	0.6