Fig. 1 Side View of DALI from Up-stream

1H(17C, 16C → 15C + n + γ)X

Event) Total of(Number

keV) 500 with ray γDetecting Events ofNumber

Efficiency

(

)(

Raw

Doppler Effect Corrected

The Excited States of 16C and the Optimization of the DALIγ-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 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.

Jongwon HwangSeoul National University

DALI : γ-ray de-tector

The Excited States of 16C

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 experi-ment• 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

I. DALI is an γ-ray detector, and it was used in the RIPS experiment (R364n).

II. The new state of 16C (5.45 MeV) was found by using the signals from sev-eral detectors including DALI through the 1H(17C, 16C → 15C + n + γ)X reac-tion

III. The optimized position of DALI along the beam line is 40 cm far from the target toward downstream.

IV. The distortion of the γ-ray peak is the problem to be solved. (ex. Assum-ing that the γ-ray source is located at the center of DALI)

Invariant Mass :

Excitation Energy :

(n : neutron, f : fragment)

22 ||)( fnfninv PPEEE *ESMMEE nfninvx

• 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 Coinci-

dence

Newly found state of

16C (R364n at 5.45

MeV)

• 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

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