Small accelerator based intense positron beam sources

In order to progress positron and antimatter related research, it is highly desirable to develop options for intense sources of positrons capable of fueling positron beams with >10(7) positrons/sec. At the Center for Materials Research at Washington State University, we are investigating N-13 as a positron source based on the nuclear reaction C-12(d,n)N-13. Based on cross section data and earlier tests a source activity of about 11 mCi per [LA of 3 MeV deuterons can be achieved. At 300 mu A a 3 (4) MeV Van de Graaff accelerator will generate 1.2 (2.0)x10(11) positrons/sec in a graphite target. Several methods of utilizing this production rate for moderated positron beams have been tried. These include single crystal CVD diamond, high and low density graphite, frozen source gases, tungsten foil moderation and solid gas moderation. To date, the most successful approach yielded similar to 10(5) moderated positrons per second - efficient moderation of the source flux has not been accomplished. We will present the current status and discuss possible reasons for the poor performance. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.