The mirror extending substantially completely across said internal passageway ensures that {HEAD ~ a maximum} of {TAIL ~ the ultraviolet radiation} entering the housing is available for exciting kerogen in the sample and causing it to fluoresce, i.e. emit radiation at a wavelength higher than said first wave length 
of
The mirror extending substantially completely across said internal passageway ensures that { HEAD ~ a maximum } of { TAIL ~ the ultraviolet radiation } entering the housing is available for exciting kerogen in the sample and causing it to fluoresce , i.e. emit radiation at a wavelength higher than said first wave length
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