11Be@RIBLL ExperimentJune 2012

PKU Group + Lanzhou Group

• 名称： 12Be 激发态集团结构研究。• 内容： 1. 11Be@MuNCoS calibration ； 2. 12Be Cluster structure in

excited state

Beams applied

• 18O8+ 70MeV/A 200enA~320enA• 初级靶： 9Be 4527um 降能片： 2759um Al

11Be 12Be

能量 37MeV/A 31.8MeV/A

流强 (T1&T2) 8000~18000 pps 2000~3000 pps

纯度 ~90% ~70%

次级靶 4000um Pb 100mg/cm2 C 靶200um Pb 空靶空靶

Beam time

11Be

靶 4000um Pb 200um Pb 空靶File File 154-167&file 394-399 File 181-215 & file 227-233 File 216-225

time 12h48min 34h53min 8h48minTotal 56h30min

12Be

靶 4He,6He 能量点刻度 100mg/cm2 C 靶 空靶File File 338-348 File 235-309 & file 349-393 File 310-337

Time 2h 9min 92h45min 23hTotal 118h

约 11 天 260 小时

50cm

y

z

初级束 : 18O8+ 70A MeV 200enA~320enA 初级靶 : 9Be次级束 : 11Be@37A MeV ， ~104 pps, 纯度 ~90%, 到靶上能量： 33A MeV次级靶 : 4mm Pb, 200um Pb, 空靶

MuNCos 实验测试

1. 11Be@MuNCoS calibration

Method established

H.B. You et al.

粒子鉴别图

• 0 度望远镜粒子鉴别图– MuNCoS 打火数为 1 ， n 探测单元阈值：

6MeVee– 右图加入中子能量选择，中子能量选择 30-

40MeV– 0 度望远镜挑选出 10Be

与 10Be 符合后的中子能谱

•

&

10

* * * * * *

*(1 )target acceptancecsi al livetime beam telescope

backgroundBe nMuNCoS N N

N

2. 12Be Cluster structure inexcited states

Z.H. Yang et al.

12Be:Generalized Two-Center Cluster model (GTCM) calculation

AO orbit

MO orbit

AO orbit

S↑ S↑

[PRL100(08)182502 ,PRC85(12)044308]

Conflicting results for 12Be*

6He+6He,CH2 4He+8He ， with P 4He+8He ， with C

GANILRef1Freer

MSURef2Charity

Ref1: PRL82(99)1383 Ref2: PRC76(2007)064313

GANIL exp. M.Freer et al. (PRL-1, PRC-1) PRL82(99)1383 12Be, 31.5 MeV/u, 2 x 104 pps, C target, 10 mgcm-2; （ CH2 ） n ,20 mgcm-2. 10 telescopes; each with 500 um-thick 5 x 5 cm2 DSSD 2 mm strip, 20-240 Lab around the beam line. measuring: 6He+6He; 4He + 8He; reconstruct Ex PRC63(01)034301 the same exp. As above. 10Be and 12Be breakup fragments, no neutron detection.

MSU exp., R.J. Charity et al. (PRC-2) PRC76(07)064313 12Be, 50 MeV/u, 105 pps, C target 0.4 mm, CH target 1 mm. beam spot 1 cm x 2 cm 16 HERA telescopes: 2.70-24.80 DSSD(1.5mm thick, 2mm strip) + CsI + 4 LASSA: 29.40-61.50; DSSD(0.5 mm thick, 3mm strip) + CsI very much contradicting GANIL exp. (Freer et al) PRC78(08)054307 the same exp. As above decay to 3H, xLi etc.

12Be + C, MSU exp.

Detector Setup

Beam ： 12Be ， 31.8MeV/u ， ~3000ppsTarget ： Carbon, 100 mg/cm2

DSSD ： 32 2mm-stip,300μm ,CsI ： 2.5cm*2.5cm*3cm,

40cm13.5cm

5.8cm15.5cm18.8cm

PPAC1 DSSDTargetDSSD

SSD

CsI Array

PPAC2

32.3cm

Particle Identification

4He 6He

8He

E

ΔE

Excitation Energy

* 2

2 2 2 2 22( )( ) 2 ( 2 )( 2 ) cos

rel a b a b

a b a a b b a a a b b b

E M M M M M M

M M M T M T M T T M T T M

*MaM

bM

aT

bT

4He+4He 4He+6He 6He+6He 4He+8He

2-xHe events for 12Be

12Be->4He+8He

Erel resolution(σ) Detection effeciency

12Be->4He+8He

107.6KeV 8Be(g.s)

504.1KeV:9Be->8Be(2+)

Excitation Energy---4He+4He

Ref1:PLB580(04)129-14Be breakup

Ref1

Excitation Energy---6He+6He

Ex/MeV 11.7 13.3

◊4He(12Be,6He+6He)---- Saito et al,NPA738(04)337) -----angular distribution analysis

L=0 L=2

GANIL exp@1999 (PRL82(99)1383)

J 4 2 0Ex/MeV 13.2 11.7 10.8

Intercept: 10.8MeVSlope: 0.15MeV

Excitation Energy---4He+8He

Ex/MeV 10.2 12.0 13.4

How to describe the non-resonant breakup process? ---A simple evaporation formula was used here

?√

√

Summary of Ex. States

GTCM calculation by M.Ito(PRL100(08)182502)

4He+8He 6He+6HeAn overal shift of about 1.5MeV for the 6He+6He band---The difference between Ethres(GTCM) and Ethres(exp) is 1.7MeV---This shift may be attributed to the adopted interaction strength.

We agree well with Freer et al and Saito et al., supporting the cluster structure.