Constants and Physical Values
Last verified on December 8, 2020
Name | Symbol | Value | Units |
Planck’s constant | h | 6.626 × 10^{-34} | m^{2} kg / s |
Boltzmann’s constant | k | 1.38 × 10^{-23} | m^{2} kg s^{-2} K^{-1} |
Mass of the electron | m_{e} | 0.511 | MeV |
Mass of the electron | m_{e} | 9.11 × 10^{-31} | kg |
Charge of the electron | q_{e} | 1.60 × 10^{-19} | C |
Mass of the proton | m_{p} | 938 | MeV |
Mass of the neutron | m_{n} | 939 | MeV |
Assumed speed of sound in soft tissue | v_{t} | 1540 | m/s |
Speed of light | c | 3 × 10^{8} | m/s |
Mass of standard man | 70 | kg | |
Molar gas constant | R | 8.31 | J mole ^{-1}K^{-1} |
Avogadro’s Number | N_{A} | 6.02 × 10^{23} | Atom/mole |
Energy mass conversion | amu | 931.48 | MeV/amu |
Electron Volt | _{eV} | 1.60 × 10^{-19} | J/eV |
Gyromagnetic ratio - H | 26.7522 × 10^{7} | radians T^{-1 }s^{-1} | |
Gyromagnetic ratio - P | 10.8291 × 10^{7} | radians T^{-1 }s^{-1} | |
Gyromagnetic ratio - Na | 7.0761 × 10^{7} | radians T^{-1 }s^{-1} | |
Ionization constant | W_{air}/e | 33.97 | eV/ion-pair in air |
Roentgen | R | 2.58 × 10^{-4} | C/kg |
Radionuclide | Half-life | Units |
^{18}F | 110 | minute |
^{32}P | 14.3 | day |
^{60}Co | 5.27 | year |
^{67}Ga | 78.3 | hour |
^{68}Ga | 68 | minute |
^{89}Sr | 50.6 | day |
^{90}Y | 2.67 | day |
^{90}Sr | 28.8 | year |
^{99}Mo | 2.75 | day |
^{99m}Tc | 6.00 | hour |
^{103}Pd | 17.0 | day |
^{111}In | 2.80 | day |
^{123}I | 13.2 | hour |
^{124}I | 4.18 | day |
^{125}I | 59.4 | day |
^{131}I | 8.02 | day |
^{131}Cs | 9.69 | day |
^{137}Cs | 30 | year |
^{153}Sm | 1.93 | day |
^{198}Au | 2.69 | day |
^{192}Ir | 73.8 | day |
^{201}Tl | 3.04 | day |
^{222}Rn | 3.8 | day |
^{223}Ra | 11.4 | day |
Tissue | Tissue weighting factor w_{T} |
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 (♀) |
Nuclide | Dose rate constant µSv m^{2} /MBq h | Use |
^{68}Ga | 0.134 | Effective dose equivalent |
^{82}Rb | 0.159 | Effective dose equivalent |
^{124}I | 0.185 | Effective dose equivalent |
^{18}F | 0.143 | Effective dose equivalent |
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 d_{max }in a 10 x 10 cm^{2} 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, T_{0} = 22°C, Pressure, P_{0} = 101.33 kPa, Relative humidity of the air in the ion chamber between 20% and 80%. |
Nuclide |
Dose rate constant (µSv/h MBq) @ 1 m |
TVL (mm Pb) |
^{ 24}Na |
0.500 |
59 |
^{ 42}K |
0.038 |
53 |
^{ 43}K |
0.147 |
18 |
^{47}Ca |
0.150 |
46 |
^{ 51}Cr |
0.005 |
7 |
^{ 59}Fe |
0.170 |
44 |
^{57}Co |
0.016 |
0.7 |
^{58}Co |
0.150 |
28 |
^{64}Cu |
0.032 |
25 |
^{67}Ga |
0.022 |
5.3 |
^{65}Zn |
0.085 |
42 |
^{75}Se |
0.056 |
5 |
^{99m}Tc |
0.017 |
0.9 |
^{111}In |
0.084 |
2.5 |
^{125}I |
0.034 |
0.06 |
^{123}I |
0.044 |
1.2 |
^{131}I |
0.057 |
11 |
^{ 192}Ir | 0.135 | 12 |
^{ 201}Tl |
0.012 |
0.6 |
Concept | Unit | Clinical Alternatives |
Mass | Kilogram (kg) | AMU |
Length | Meter (m) | |
Time | Second (s) | Minutes, Hours, Days, Years |
Amount of a Substance | Mole (mol) | |
Electric Current | Ampere (A) | |
Thermodynamic Temperature | Kelvin (K) | Celsius (C): C = K - 273.15 |
Luminous Intensity | Candela (cd) |
Concept | Unit | Clinical Alternatives |
Force | Newton (N); (kg-m-s^{-2}) | |
Pressure | Pascal (Pa); (N-m^{-2}) | |
Absorbed Dose | Gray (Gy); (J-kg^{-1}) | |
Dose Equivalent | Sievert (Sv); (J-kg^{-1}) | |
Energy, Work | Joule (J); (N-m) | eV |
Power | Watt (W); (J-s^{-1}) | |
Activity | Becquerel (Bq); (s^{-1}) | Curie (Ci) Ci=3.7 × 10^{10} Bq, mCi |
Frequency | Hertz (Hz); (s^{-1}) | |
Magnetic Flux | Weber (Wb); (V-s) | |
Inductance | Henry (H); (kg-m^{2}-s^{-2}-A^{-2}) | |
Magnetic Flux Density also Magnetic Field | Tesla (T); (Wb-m^{-2}) | Gauss T=10^{4} G; Magnetic Field Strength (B) is measured in Tesla |
Electric Charge | Coulomb (C); (A-s) | |
Electric Potential | Volt (V); (W-A^{-1}) | |
Capacitance | Farad (F); (s^{4}A^{2}m^{-2}kg^{-1}) | |
Resistance | Ohm (Ω); (V-A^{-1}) | |
Luminous Flux | Lumen (lm) |
eV | Used as an energy unit |
amu | Used as a mass unit |
minutes, days and years | Used as a time unit |
bel | Used to express power ratios |
roentgen | Equal to 2.58 × 10^{-4} C/kg |