Overview of the RI beam experiments at RCNP and recent results of the MAIKo active target

The Research Center for Nuclear Physics (RCNP) at Osaka University hosts AVF and ring cyclotrons that can provide high-quality light and heavy ion beams with an energy of up to 100 MeV/u. The projectile fragmentation beamline at the EN course provides various radioactive isotope (RI) beams at tens MeV/u. Using the RI beams, we have investigated several direct reactions including charge-changing reaction [1,2], knockout reaction [3], deuteron elastic scattering [4], and (p,d) reaction[5].

The missing mass spectroscopy is attractive for RI beam experiments because it can be applied to the excited states even above the particle-decay thresholds. However, this spectroscopy at forward angles at the center of the mass frame is extremely difficult because it requires the detection of low-energy recoil particles. Active-target time projection chambers (TPC) overcome this challenge by utilizing the detector gas also as the target material and lower the detection threshold.

We developed an active target named MAIKo at RCNP [6]. The MAIKo TPC has a sensitive volume of 10 x 10 x 15 cm³. Recently, we successfully measured alpha elastic and inelastic scattering on ¹⁰C beam at 68 MeV/u. The nucleon density distribution of the ¹⁰C ground state and the effective interaction between the alpha particles and ¹⁰C were determined from the differential cross section of the elastic scattering. From the cross section of the inelastic scattering to the first 2⁺ state, we determined neutron quadrupole transition matrix element M_n to discuss the Z=6 magicity [7]. We are continuing the analysis of the highly excited states to search for alpha cluster states in ¹⁰C. The MAIKo has been upgraded to MAIKo+ with 20 times larger detection volume.

Having demonstrated the possibilities of the active target method, we are planning a campaign project at RCNP using the world's largest active target system AT-TPC from Michigan State University [8]. The AT-TPC will be operated with C₃D₈ gas to measure the ¹⁷C(d,p)¹⁸C, ¹⁷N(d,³He) ^13,15B(d,³He)^12,14Be, and ¹²C+¹²C reactions.

In the present talk, we will introduce the recent results from the RCNP RI beam experiments and measurements with the MAIKo active target.