IC MP Constants & Physical Values

Initial Certification

Initial Certification > Medical Physics > Constants & Physical Values

 

Medical Physics

List of Constants and Physical Values for Use on the Part 1 and Part 2 Physics Exams

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 examinations. 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 examinations 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