First use of HELIOS at forward laboratory angles

The HELIOS spectrometer eliminates the problem of kinematic compression when performing transfer reactions in inverse kinematics, typically resulting in a factor of $\sim$3 improvement in excitation-energy resolution over conventional approaches. To date the instrument has been used primarily for ($d$,$p$) reaction studies with both stable and radioactive ion beams, where the outgoing protons are detected at backwards laboratory angles. Here we report on the first use of HELIOS with negative- Q-value reactions; the ($d$,$t$) and ($d$,$^3$He) reactions induced by a 14-MeV/u $^{28}$Si beam on a CD$_2$ target. For these reactions, outgoing tritons and $^3$He ions are detected at forward laboratory angles along with a range of unwanted reactions products. In HELIOS, particle identification by means of the cyclotron period of the outgoing ion allows unique selection of the low-energy branch of $^3$He or tritons, separating them from the dominant background of protons and alpha particles that arise from fusion-evaporation of the beam with $^{12}$C. This work was supported by the US Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357 and Grant No. DE-FG-2-04ER41320, and NSF Grant No. PHY-08022648, and the UK Science and Technology Facilities Council.