Cryogenic System for the Production of Very Thin Targets

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Abstract
A windowless gas target chamber has been developed for the production of very thin, but uniform, targets to be used with accelerated charged particle beams. The target reaction chamber is appended to a cryostat which is capable of containing liquid helium as the primary refrigerant. The temperature of this chamber can be adjusted so that condensation of the gas in the vicinity of the beam path is minimized. The cryostat freezes out the gas which escapes the reaction chamber. To date, we have used this new cryogenic technique to observe the 2D(d,n) reaction and the (p,n) reactions in 11B, 40A, and 37Cl. Very narrow resonances (widths ≤450 eV) were discovered in the 40A(p,n)40K reaction near the neutron threshold. The narrowest observed widths in the yield curve are 140±10 eV. These were observed with a target whose effective density was found to be 3.0±0.3×1016 atoms/cm2.