Counting efficiency

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The counting efficiency is the ratio between the number of particles or photons counted with a radiation counter and the number of particles or photons of the same type and energy emitted by the radiation source.[1] Counting efficiency varies for different isotopes, sample compositions and scintillation counters. Poor counting efficiency can be caused by an extremely low energy to light conversion rate, (scintillation efficiency) which, even optimally, will be a small value. It has been calculated that only some 4% of the energy from a β emission event is converted to light by even the most efficient scintillation cocktails.[2]

See also[edit]


  1. ^ IUPAC Compendium of Chemical Terminology (2nd ed.). 1997. 
  2. ^ "Counting efficiency and quenching". National Diagnostics. 2011. Retrieved April 6, 2013. 

SI photon units
Quantity Unit Dimension Notes
Name Symbol[nb 1] Name Symbol Symbol
Photon energy n 1 count of photons n with energy Qp = hc / λ.[nb 2]
Photon flux Φq count per second s−1 T−1 photons per unit time, dn/dt with n = photon number.
also called photon power.
Photon intensity I count per steradian per second sr−1⋅s−1 T−1 dn/dω
Photon radiance Lq count per square metre per steradian per second m−2⋅sr−1⋅s−1 L−2⋅T−1 d2n/(dA cos(θ) dω)
Photon irradiance Eq count per square metre per second m−2⋅s−1 L−2⋅T−1 dn/dA
Photon exitance M count per square metre per second m−2⋅s−1 L−2⋅T−1 dn/dA
See also: Photon counting · SI · Radiometry · Photometry
  1. ^ Standards organizations recommend that photon quantities be denoted with a suffix "q" (for "quantum") to avoid confusion with radiometric and photometric quantities.
  2. ^ The energy of a single photon at wavelength λ is Qp = h⋅c / λ with h = Planck's constant and c = velocity of light.