The collapse phase of a dense plasma focus gun operating in deuterium was studied using streak photography and time resolved x-ray and neutron measuring techniques. The streak photographs, showing the radial motion of the luminous front at various axial positions, indicate a collapsing luminous front at the time of the current collapse followed by an expanding front and a recompression. The luminosity then disappears for a period of several hundred nanoseconds, during which time the neutrons are emitted. Estimates of shock heating and magnetic compressional heating were made from the streak pictures, and a calculation of plasma heating due to viscous forces arising from axial motion of the plasma was carried out. The effects of shock heating, magnetic compressional heating, and viscous heating are shown to be sufficient to produce an ion temperature of several kilovolts.