CNS Active Target (CAT) for high-intensity heavy-ion beam experiment*

We developed GEM-based gaseous active targets, CAT-S and CAT-M, aiming at the missing mass spectroscopy in inverse kinematics with high-intensity heavy-ion beams. One of the physics motivation particularly focused is to explore the nuclear incompressibility of asymmetric nuclear matter through the measurements of the isoscalar giant monopole resonance (ISGMR) with high intensity (∼10⁶ Hz) beams of unstable nuclei of A ∼ 100 at an incident energy of ∼100 MeV/u. ISGMR have the forward peak in the center-of-mass angular distribution. For experiments with the unstable nuclei beam, the low energy recoiled particles need to be measured in inverse kinematics, corresponding to the forward angle scattering up to 10 degrees in the center-of-mass frame. A gaseous active target based on a time projection chamber (TPC) enables us to detect such low energy particles and beam particles, simultaneously. The lowest total kinetic energy of recoil particles to be detected by CAT’s is 0.3 MeV. The CAT’s consist of TPC with equilateral triangular readout pads and an array of silicon detectors beside the TPC. Our TPC is operated with low pressure, for instance, 0.4-atm pure deuterium or hydrogen gas. A set of thick GEMs of 0.4-mm thickness or multi-layered thick GEM of 1.2-mm thickness are employed as electron multiplier in CAT-S and CAT-M, respectively. For the operation under high intensity beams, both type of GEMs have segmented electrodes and the gain of the beam region is typically set about 10 times lower than that of the recoil region. The active area of the CAT-S and CAT-M are about 100 × 100 mm² and 280 × 310 mm², respectively. In this talk, the detail of CAT’s and their performances will be presented.