Panasonic PT-DZ12000U Operating Instructions Manual page 172

5. Air-proportional alpha detectors have a flatter energy vs
efficiency response than sealed gas-proportional, alpha
scintillator, alpha/beta scintillator, or GM detectors. This is
due to several factors. One factor is the typically thinner
entrance windows on air-proportional alpha detectors
compared to beta detectors and alpha and beta scintillator
detectors whereby more of the initial alpha particle energy
enters the active volume of the air-proportional compared to
other detectors. A second factor is the relatively shallow
depth of the air-proportional detector compared to the path
length of the alpha particle in air which leads to the alpha
pulses being of similar height for any alpha particle energy
above a threshold.
6. Alpha particle energy transfer to air
6 MeV alpha particles produce 40,000 Ion Pairs per cm
4 MeV alpha particles produce 55,000 Ion Pairs per cm
ù for air is 34 eV per Ion Pair
therefore;
6 MeV alpha particles lose 1.18 MeV per cm of air
4 MeV alpha particles lose 1.87 MeV per cm of air
Alpha particle range in cm of air at 1 atmosphere
R = 0.56 E (E <4 MeV)
a
R = 1.24 E - 2.62 (E > 4 MeV)
a
Alpha particles lose about 60 KeV of energy per mm of air
at STP.
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