Prefixes

k  (kilo)  = 1.0e3  = 1000
M  (mega)  = 1.0e6  = 1_000_000
G  (giga)  = 1.0e9  = 1_000_000_000
T  (tera)  = 1.0e12
P  (peta)  = 1.0e15
E  (exa)   = 1.0e18

c  (centi) = 1.0e-2 = 0.01
m  (milli) = 1.0e-3 = 0.001
mu (micro) = 1.0e-6 = 0.000001
n  (nano)  = 1.0e-9 = 0.000000001
p  (pico)  = 1.0e-12

Units

Newton (N) = \(kg\cdot\cfrac{m}{s^2}\)

Joule (J) = \(kg\cdot\cfrac{m^2}{s^2} = N\cdot m\) . 1 Joule is the energy transferred when a force of 1 Newton is applied to an object, moving it a distance of 1 meter.

Power is given in Watts (W) = \(\cfrac{J}{s}\) .

Pressure is given in Pascal (Pa) = \(\cfrac{J}{m^3}\) (with \(1\,\text{Pa}=10^{-5}\,\text{bar}\) ). Atmospheric pressure is 101325 Pa.

The atomic mass unit is defined such that the atomic weight of a neutral carbon-12 atom in its ground state is exactly 12 amu.

1 amu = 1.66053906660e−27 kg
      = 1.49241808560e−10 J
      = 931.49410242 MeV

The ratio of amu/atom is the same as the ratio of g/mol. Mole is a measure for the amount of a substance, where one mole is the quantity of anything that has the same number of atoms found in 12.000 grams of carbon-12, which are 6.023e23 atoms (Avogadro’s number). So there are 6.023e23 atoms/mol.

The electronvolt is the energy gained or lost by an electron when accelerated through 1 volt of electric potential difference.

1 eV  = 1.602176634e-19 J

Electronvolt can also be used as a unit of mass, which is usually given in \(\cfrac{\text{eV}}{c^2}\) (with \(c\) the speed of light in vacuum).

The conversion factor between amu and MeV is \(931.49 \cfrac{\text{MeV}}{\text{amu}\cdot c^2}\) .

Cross-sections are specified in barn.

1 barn = 10e-28 m^2

Distances on the sub-atomic level are usually given in fermi.

1 fm = 10e-15 m

Activity and radiation dose

The activity of decay is usually given in Curies.

1 Ci = 3.7e10 disintegrations (decayed nuclei) per second

Gray specifies the energy absorption of some mass. Multiplying it by a quality factor gives a risk in Sievert.

1 Gy = 1 J/kg
1 Sv = Q * Gy

The quality factor is the product of a factor for the type of tissue and one for the type of radiation.

• Q=1 for X rays and gamma and beta rays of all energies.
• Q=5...20 for neutrons, depending on their energy (highest for 0.1...2 MeV).
• Q=20 for alpha particles (because they have a very short range and deposit a great amount of energy, so they’re not that harmful when outside the body but very harmful when inside it).
• Q is higher for tissue with more quickly dividing cells (because then the cells divide with the defect before cell repair mechanisms can fix it, more quickly spreading it), and therefore also at younger age.

Corresponding non-SI units are rad (energy absorption, where 1 erg = 10^(-7) J) and rem (Roentgen equivalent man, specifying increased cancer risk).

1 rad = erg/g
1 Gy = 100 rad
1 Sv = 100 rem

Constants

e = 2.718281828459045
c = 299_792_458 m/s