PH 253 Midterm: PH253_F16_exam2-practice
Document Summary
Exam 2 practice problems: determine the maximum scattering angle in a compton experiment for which the scattered pho- ton can produce a positron-electron pair. Hint: twice the electron"s rest energy mec2 is required of the incident photon for pair production. Solution: in order to produce a positron-electron pair, enough energy must be present to supply the rest energy of a positron and an electron. Both have the same mass, me, so that means the incident photon must supply at least 2mec2 worth of enery. The threshold wavelength is thus hf = hc. Any wavelengths above this value cannot result in pair production. F = i + h mec (1 cos ) = i + 2 th (1 cos ) (2) The right side of the expression is the sum of two positive-de nite terms. The right side can be at most th - if f > th, pair production cannot occur.
