Fig. 1 Side View of DALI from Up-stream - PowerPoint Presentation

Slide1

Fig. 1 Side View of DALI from Up-stream

1

H(

17

C,

16

C →

15

C + n +

γ

)X

Raw

Doppler Effect Corrected

The Excited States of

16

C and the Optimization of the DALI

γ

-ray Detector for a Future Experiment

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

16

C 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.

Jongwon HwangSeoul National University

DALI :

γ

-ray detector

The Excited States of

16

C

The Optimization of the DALI

What is DALI?

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

Fig. 2 Top View and Side View of DALI

DALI in R364n experiment

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)

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 reactionThe 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)

Invariant Mass :

Excitation Energy : (n : neutron, f : fragment)

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)

Two peaks in CoincidenceNewly found state of 16C (R364n at 5.45 MeV)

First Excited State of

15

C : 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

Motivation & Method

Note : The first excited state of

15C is an isomer. (T1/2=2.61 ns)

Distortion of the peak

(Doppler effect correction)

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.

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