Maintenance of Certification for Medical Physics

Constants and Physical Values

Last verified on June 19, 2017
 
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 938 MeV
Mass of the neutron 939 MeV
Assumed speed of sound in soft tissue c 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 26.8 × 107 radians 1T-1 s-1
Gyromagnetic ratio - P 10.8 × 107 radians 1T-1 s-1
Gyromagnetic ratio - Na 7.08 × 107 radians 1T-1 s-1
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 min
32P 14.3 da
60Co 5.27 yr
67Ga 78.3 hr
89Sr 50.6 da
90Y 2.67 da
90Sr 28.8 yr
99Mo 2.75 da
99mTc 6.00 hr
103Pd 17.0 da
111In 2.80 da
123I 13.2 hr
124I 4.18 da
125I 60.1 da
131I 8.02 da
131Cs 9.69 da
137Cs 30 yr
153Sm 1.93 da
198Au 2.69 da
192Ir 73.8 da
201Tl 3.04 da
222Rn 3.8 da
 
ICRP 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
Proton 5
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


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