Large-area detector for position and energy resolving detection of molecular fragments

To study reactions like the dissociative recombination in laboratory environment, the MPI-K Heidelberg is building a cryogenic storage ring to prepare molecular ions in their rotational groundstate. The kinematics of these processes can be resolved by a position and energy sensitive detection of the produced molecule fragments. Previously, we described a magnetic calorimeter for position and energy sensitive detection of massive particles. The detector encompasses 16 large-area absorbers, the temperature of each is monitored by a paramagnetic sensor located at a short edge of the absorber. Due to the finite thermal diffusivity in the absorber material, the rise-time of the detector depends on the impact location of the particle. Now, we compare the expected energy resolution and position sensitivity of this detector to experimental results where energy was deposited at different positions. We investigate the impact of backscattering, sputtering and lattice damage effects on the instrumental linewidth by means of Monte Carlo simulations and measurements performed with a similar detector that was irradiated with ions and small molecules. We find that the degradation of energy resolution is less than predicted and show that molecular fragments differing by only 1 mass unit can clearly be resolved.