Fig. 1 Side View of DALI from Up-stream

1. The Excited States of 16C and the Optimization of the DALIγ-ray Detector for a Future Experiment Jongwon Hwang Seoul National University Abstract DALI is a γ-ray detector, which is an array of NaI(Tl) crystal. By incorporating information from DALI signals, an excited state at 5.45 MeV in 16C has newly been identified in a preliminary invariant mass spectrum of the 1H(17C, 16C → 15C + n + γ)X reaction. In order to reproduce the previous result with better statistics and to gain further insights into the spectroscopic nature of this as well as other states in 16C nuclei, another experiment is being planned using the invariant mass method in inverse kinematics. For the future experiment, suitable position of the DALI was determined by a GEANT simulation, and the results will be presented. The Excited States of 16C DALI : γ-ray detector 1H(17C, 16C → 15C + n + γ)X What is DALI? • Invariant Mass Spectrum • Sharp peak at 0.46 MeV • Other small peaks • γ-ray Energy Spectrum • Lower peak : Background • Upper peak : 0.74 MeV(Corresponding to the first excited state of 15C) • γ-ray Detector : An array of NaI(Tl) crystal • 48 NaI Detectors (scintillator & PMT) • Layer Structure : 4 layers • Ring Shape : Beam or target at the center Two peaks in Coincidence Newly found state of 16C (R364n at 5.45 MeV) Invariant Mass : Excitation Energy : (n : neutron, f : fragment) Fig. 1 Side View of DALI from Up-stream Note : The first excited state of 15C is an isomer. (T1/2=2.61 ns) Distortion of the peak (Doppler effect correction) Fig. 2 Top View and Side View of DALI The Optimization of the DALI Raw DALI in R364n experiment Motivation & Method • First Excited State of 15C : Isomer (T1/2=2.61 ns) → γ-ray can be emitted at the place far from the target→ Low efficiency • Adjustment of the Position (to downstream) → Increase efficiency for the future experiment • Geant 3 Simulation : GDALI code • RIPS in RIKEN : RI beam (In-flight separation) • Inverse Kinematics : Unstable isotopes (ex. 17C) • Target : Cryogenic Hydrogen (LH2) • DALI (NaI) Detector • Surrounding the LH2 target • To detect γ-rays from the target (assumption) Result • Best Efficiency at 40 cm (13.5%)to downstream along beam line from the original (R364n) setup. → Gain : 3.8 (R364n setup) • Distortion of the peak due to the isomer state (the small plot) → DALI is farther from the target, more distortion of the γ-ray peak occurs. Doppler Effect Corrected Fig. 3 Experimental Setup of R364 Experiment Summary DALI is an γ-ray detector, and it was used in the RIPS experiment (R364n). The new state of 16C (5.45 MeV) was found by using the signals from several detectors including DALI through the 1H(17C, 16C → 15C + n + γ)X reaction The optimized position of DALI along the beam line is 40 cm far from the target toward downstream. The distortion of the γ-ray peak is the problem to be solved. (ex. Assuming that the γ-ray source is located at the center of DALI) • Collaborators (RIKEN, R364n) • Seoul National University : Y.Satou, J.Hwang • Tokyo Institute of Technology : T.Nakamura, T.Sugimoto, Y.Kondo, N.Matsui, Y.Hashimoto, T.Nakabayashi,T.Okumura, M.Shinohara • RIKEN : N.Fukuda, T.Motobayashi, Y.Yanagisawa, N.Aoi, S.Takeuchi, T.Gomi, Y.Togano, H.Sakurai, H.Otsu, M.Ishihara • RikkyoUniversity : S.Kawai • Tokyo University : H.J.Ong, T.K.Onishi • Center for Nuclear Study (CNS) Tokyo University : S.Shimoura, M.Tamaki • Tohoku University : T.Kobayashi, Y.Matsuda, N.Endo, M.Kitayama