IR(E): Response in terms of emissions per unit area

where R_i is the observed reading (s^-1)

            B is the background count rate (s^-1)

SER is the surface emission rate per unit area (α, β or photon) s^-1cm^-2

E.g. If an instrument reading of 80 βs^-1 were obtained on exposure to a ³⁶Cl reference source of emission rate 25 β s^-1 cm^-2

This is the response to beta radiations of maximum energy 708 keV in terms of surface emission rate.

2π eff: Efficiency in terms of SER

 

E.g. Using the example above and where A_p = probe area (10 cm² in this example)

This is the efficiency to beta radiations of maximum energy 708 keV  in terms of surface emission rate.

CF_E: Calibration factor in terms of SER.  Note CF_E is the reciprocal of IR(E)

                                 

This is the calibration factor for ³⁶Cl. The net instrument reading should be multiplied by this to obtain the number of beta particles detected per unit area.

IR(A): Instrument response  in terms of activity

The calibration laboratory may provide the instrument’s response to the source activity. For the calibration sources involved, in a controlled environment, this is relatively easy to estimate

Where P = P-factor and describes the relationship between the particle or photon generation rate and the emission rate from the surface.³⁶Cl has a P factor of 2 because there is a simple relationship between the number of beta emissions that emerge (SER) and the source activity. Other radionuclides may have more complicated decay schemes, further guidance on this can be found in the module ‘estimating surface activity’

E.g. ³⁶Cl response {for an ideal source of ³⁶Cl, P=2}

This is the response to beta radiations of max energy 708 keV in terms of activity.