Katz, L.2010-07-222013-01-042011-07-222013-01-04196419641964http://hdl.handle.net/10388/etd-07222010-104859The shape of the photon spectrum due to the annihilation of positrons in flight has been calculated. Multiple scatterings and energy losses of the positrons before annihilation have been taken into account in the calculation. It was found that multiple scattering tends to narrow, rather than broaden, the photon spectrum. Calculations are done to show that this result is to be expected.en-UStext