NuclearInstruments andMethods203 (1982) 93-95 North-Holland Publishing Company THIN-FILM CRYOGENIC ACCELERATORTARGETS

Studiesof nuclearor atomic reactionsinvolving neon. argon, krypton, xenon, fluorine, sulfur, chlorine, nitrogen, and other elements as targets have required use of gas cells, differentially pumped chambers [l1, or compound solid targets (e.g. melamine). The large spatial extent of a gas cell target can cause severe geometrical problems, e.g . at small scattering angles where good angular resolution is required . Also, measurements at 0=0° are usua!ly not feasible. Compound solid targets often contain unsuitable elements. Many of theselimitations can be minimized if the target material is wndensed as a thin film onto a thin substrate using cryogenic techniques [2-4]. A short report by Fulbright [5] describes an apparatus used to condense water vapor onto thin foils for usein a nuclear reaction study161of 111 .0(p t)" In this note we describe tests of several thin-film cryogenic targetsoperatingat 20 K e T< 80 Ksuitable for use in nuclear and atomic reaction studies. The cryostat consisted of a commercial LN/LHe cryo-pump [71 modified [8) for use as an accelerator target holder (rig . 1). Provisions were made forpumping the inner cryostat with a high capacity rotary oil pump to further reduce the temperature of the inner cryostat liquid when using LN . The temperature of the LN cryostat, outer heat shield, inner cryostat, and target frame were monitored by carbon and Pt resistors . The target holder consisted of a slotted 5 mm thick, 30 X 50 mm2copper block (OFHC) fastened with indium gaskets (for thermal conductivity) to the inner LHe cryostat