Diamond dE-E-ToF-telescope for heavy ion reactions at the Coulomb barrier

Abstract

Target of our interest is the study of heavy ion reactions, such as multinucleon transfer, quasi-fission and/or fusionfission, at energies close to the Coulomb barrier as well as their possible application for the synthesis of new isotopes, especially in the high-Z neutron-rich region. The conventional time-of-flight technique, combined with the dE-E method, allows us (in general) to identify the mass and the charge of the reaction products and to study the reaction kinematics. Nonetheless, studying heavy particles at low energies needs a special approach. There are some limitations: pulse hight defect, radiation hardness, etc. Moreover, heavy ions at low energy have very short ranges, which means that we have to find a very thin detector capable of measuring energy loss and time simultaneously. Due to their unique properties (a good energy resolution comparable to silicon detectors, e.g. ∆E=20keV for alphas; time resolution on the order of few ten ps due to very high electron and hole mobilities, high count rate up to 10 due to very short rise and fall times (∼20ps) and high radiation hardness[1]) diamonds are good candidates for this application. Very recently, Pomorski et al. succeeded in fabricating ultra-thin diamond membranes with only few micrometers thickness that are able to measure energy loss and produce simultaneously time signals with excellent resolution[2]. Based on these findings we initiated a program to investigate single crystal (sc) diamond detectors for identification of low-energy heavy ion reaction products. For this application we realized the very first dE-E-ToF telescope [3] which consists of 2 sc diamond detectors: ”dE/Start“ and ”E/Stop“. First measurements were carried out with a mixed nuclide α-source. The diamond ”dE/Start“-detector had a thickness of ∼4 μm and the diamond ”E/Stop“detector ∼50 μm. The distance between the detectors was 14 mm. In Fig. 1a-1c the obtained result is shown. Fig. 1a shows the two-dimensional dE versus residual energy Er spectrum measured with the mixed nuclide α-source. There are three well separated ridges which correspond to the three α-lines. Fig 1b shows the one-dimensional energy spectrum where line 1 is the energy loss in the membrane detector, line 2 is the residual energy measured in the stop detector and line 3 is the sum of dE and Er for each event. Fig. 1c shows the time of flight spectrum. Furthermore, we applied the diamond dE-E-ToF telescope to study reaction products from collisions of