CALIBRATION OF A HYDROGEN BUBBLE CHAMBER AS A SPECTROMETER FOR LOW MOMENTUM ELECTRONS

A hydrogen bubble chamber has been calibrated at 7, 14 and 21 kG for low momentum electrons by measuring the 0.5 MeV and 1 MeV internal conversion electrons from a 207Bi source. The source was mounted on thin polyester strips which were suspended in the chamber. The two conversion lines are easily resolved at 7 and 14 kG but are only barely resolved at 21 kG. At 14 kG the 1 MeV line has a fwhm, Γ = 25%. The momentum calibration at this energy is good to <2%. The line shape is given by the function ( p pi)0.6 (|p-pi|2.6+S2.6) where pi is the true momentum and S ≈ 0.5piΓ. The variation of Γ with momentum is found by supplementing the 207Bi data with measurements of the high energy end of the μ-decay spectrum. Tests have been made for momentum dependent inefficiencies. © 1968.