The concentration of primary fluor is higher than around ten times of wavelength shifter (secondary fluor). What the main reason behind this?
The wavelength shifter absorbs the first fluorescence emitted by the scintillator and emits a second fluorescence with a longer wavelength. Since the probability of converting the first fluorescence into the second one is less than 100%, the number of photons is reduced; however, the amount of signal increases because the wavelength of the second photon is more effectively sensed by the photodetector.
Wavelength shifters also have self-absorption and re-emission, so if too much is added, the number of second photons will decrease and the amount of signal will decrease. Whether 1/10 is optimal depends on the degree of overlap between the emission and absorption spectra of the scintillator and wavelength shifter, respectively. The balance is considered.
@Kengo Shibuya Thanks for your answer. self absorption will be important paramter..
What I was thinking that primary fluor concentration is kept high to allow beta/gamma radiation interaction with primary flurophore rather with secondary.
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