CLHEP Units

The CLHEP Units module has been supplied by GEANT4. It consists of two header files which contain definitions of some frequently used physical constants and units:

To make them available it is enough to insert in your program the following line:

All constants and units are defined via few so called basic units. The following units have been choosen as basic:

The CLHEP Units module can be considered as an attempt to provide a practical System of Units for HEP applications. Many standard HEP classes, for example in GEANT4 and CLHEP, assume that data are given in the System of Units defined in the CLHEP Units module. For this reason it is recommended to define any physical data with its units, e.g.

Tables 1 and 2 represent physical units and physical constants defined in the CLHEP Units module. Most of the physical constants have been taken from the Particle Data Book: "Phys. Rev. D volume 50 3-1 (1994) page 1233".

Physical quantity	CLHEP Units name	Name of unit	Symbol, equation
Length, area, volume	`mm,mm2,mm3`	millimeter
	`cm,cm2,cm3`	centimeter
	`m,m2,m3`	meter
	`km,km2,km3`	kilometer
	`parsec`		$pc=3.0856775807\times 10^{16}\,m$
	`microm`	micro meter
	`nanom`	nano meter
	`fermi`		$10^{-15}\,m$
	`barn`		$10^{-28}\,m^2$
	`millibarn`
	`microbarn`
	`nanobarn`
Angle	`rad`	radian
	`mrad`	milli radian
	`deg`	degree	$(\pi/180)\,rad$
	`st`	steradian
Time	`s`	second
	`ms`	milli second
	`ns`	nano second
Frequency	`Hz,kHz,MHz`	hertz
Energy	`eV,keV,MeV,GeV,TeV`	electron volt
	`joule`		$J=6.24150\times 10^{12}\,MeV$
Mass	`kg`	kilogram	$kg=J\,s^2/m^2$
	`g`	gram
	`mg`	milli gram
Force	`newton`
Power	`watt`
Pressure	`pascal`	pascal
	`bar`		$10^5 \, Pa$
	`atmosphere`		$1.01325\times 10^5\,Pa$
Electric charge	`eplus`	positon charge
	`coulomb`		$C=6.24150\times10^{18}\,e$
Electric current	`ampere`
Electric potential	`volt`
	`kilovolt`
	`Megavolt`
Electric resistence	`ohm`		$\Omega$
Electric capacitance	`farad`
	`millifarad`
	`microfarad`		$\mu F$
	`nanofarad`
	`picofarad`
Magnetic flux	`weber`
Magnetic field	`tesla`
	`gauss`		$G=10^{-4}\,T$
	`kilogauss`
Inductance	`henry`
Temperature	`kelvin`
Amount of substance	`mole`
Activity	`becquerel`
	`curie`		$3.7\times10^{10}\,Bq$
Absorbed Dose	`gray`

Physical quantity	CLHEP Units name	Symbol, equation
positon charge in coulomb	`e_SI`	$1.60217733\times10^{-19}$
speed of light in vacuum	`c_light`
	`c_squared`
Plank constant	`h_Planck`
Plank constant, reduced	`hbar_Planck`	$\hbar$
	`hbarc`	$\hbar\,c$
	`hbarc_squared`	$(\hbar\,c)^2$
electron charge	`electron_charge`
	`e_squared`
atomic equivalent mass unit	`amu_c2`	$931.49432\,MeV$
atomic mass unit	`amu`
electron mass	`electron_mass_c2`	$m_e\,c^2$
proton mass	`proton_mass_c2`	$m_p\,c^2$
neutron mass	`neutron_mass_c2`	$m_n\,c^2$
permeability of free space	`mu0`	$\mu_0$
permittivity of free space	`epsilon0`	$\epsilon_0$
electromagnetic coupling	`elm_coupling`	$e^2/4\pi\epsilon_0$
fine-structure constant	`fine_structure_const`	$\alpha$
classical electron radius	`classic_electr_radius`
electron Compton wavelength	`electron_Compton_length`	$\makebox[0mm][l]{\hspace{.1em}\rule[.9ex]{.4em}{.4pt}}\lambda _e$
Bohr_radius	`Bohr_radius`	$a_\infty$
	`alpha_rcl2`	$\alpha\,r_e^2$
	`twopi_mc2_rcl2`	$2\pi\,m_e\,c^2\,r_e^2$
Avogadro constant	`Avogadro`
Boltzmann constant	`k_Boltzmann`
	`STP_Temperature`	$273.15\,K$
	`STP_Pressure`	$1\,atmosphere$
	`kGasThreshold`	$10^{-2}\,g/cm^3$
	`pi`	$\pi$
	`twopi`	$2\pi$
	`halfpi`	$\pi/2$
	`pi2`	$\pi^2$
	`perCent`	$10^{-2}$
	`perThousand`	$10^{-3}$
	`perMillion`	$10^{-6}$