Proton resonance scattering of 7 Be H. Yamaguchi, Y. Wakabayashi, G. Amadio, S. Kubono, H. Fujikawa, A. Saito, J.J. He, T. Teranishi, Y.K. Kwon, Y. Togano,

Proton resonance scattering of Proton resonance scattering of 77BeBe

H. Yamaguchi, Y. Wakabayashi, G. Amadio, S. Kubono, H. Fujikawa, A. Saito, J.J. He, 　　 T. Teranishi, Y.K. Kwon, Y. Togano, N. Iwasa,

　 K. Inafuku, M. Niikura, and L.H. Khiem

Center for Nuclear Study, Univ. of Tokyo,Kyushu University, RIKEN, Chung-Ang Univ.

Rikkyo Univ., Tohoku Univ., IPE

• Introduction of CRIB

• Motivation of the measurement

• Method

• Result

• Summary

2006 Jun 29 Nuclei in the Cosmos IX

CRIB IntroductionCRIB Introduction CNS Radio Isotope Beam separator

Low energy(<10MeV/u) RI beams, in-flight method Primary beam from K=70 AVF cyclotron Momentum (Magnetic rigidity) separation by “double achromatic” system, an

d velocity separation by a Wien filter. Orbit radius: 90 cm, solid angle: 5.6 msr, momentum resolution: 1/850.


Low-Energy RI beam Low-Energy RI beam Productions at CRIBProductions at CRIB

Reactions such as (p,n), (d,p) and (3He,n) in inverse kinematics are used.

RI beam Primary beam Reaction Cross section

Target Intensity

10C6.1 A MeV

10B(4+) 7.8 A MeV (200 pnA)

p(10B,10C)n 2 mb CH4 gas

1.3 mg/cm2

(1.6105 pps)

14O6.7 A MeV

14N(6+) 8.4 A MeV(500 pnA)

p(14N,14O)n 8 mb CH4 gas

1.3 mg/cm2

(1.7106 pps)

12N3.9 A MeV

10B(4+) 7.8 A MeV200 pnA

3He(10B,12N)n 5 mb 3He gas0.25 mg/cm2

2.5103 pps

11C3.4 A MeV

10B(4+) 7.8 A MeV200 pnA

3He(10B,12N*)n12N* 11C+p

20 mb

3He gas0.25 mg/cm2

1.6104 pps

Other RI beams have been produced at CRIB: 7Be, 8Li, 13N, 17N, 18F, 21Na, 22Mg , 23Mg, 25Al, 26Si, 39Ar,… typically 104-106 pps


low-T production targetlow-T production target

Features:Lq. N2 cooling

for a better cooling power (~100 W) and thicker target.

Forced target gas flow (30 l/min) for an efficient cooling of the gas.

Oxygen density monitoring


Recent experiments at CRIB (2005-2006)Recent experiments at CRIB (2005-2006) 39Ar production for its lifetime (~269 y) measurement

geochemical studies, distribution of cosmic ray that produces 39Ar. 8Li(,n)11B

Primordial nuclear synthesis in big bang model. 25Al+p resonance scattaring

Production of 26Si in explosive hydrogen burning. 7Be+p resonance scattaring

Related to 7Be(p,)8B reaction and astrophysical S-factor S17(E). 8B’s 2- state and higher excited states.

8Li+p resonance scattaring Nuclear structure and isotope shift

16N , 18N polarized beam production Intense 7Be beam production by Lq.N2-cooled gas target

For the direct measurement of 7Be(p,)8B reaction Beam production by 40Ca+ 12C fusion reaction

….and some more experiments are in the test phase.Collaborating with ATOMKI, McMaster U, INFN (Catania), ANU, Chung-Ang U, Ew

ha U., VAST(Vietnam), RIKEN, Kyushu U., TITech,...


77Be+p resonance scattering; Motivation (I)Be+p resonance scattering; Motivation (I) Astrophysically important reactio

n: 7Be(p,)8B 8B neutrino … high energy (1

0MeV), the largest component detected by most of the major neutrino detectors in the world.

Astrophysical S-factor S17(0)…determined by 7Be(p,)8B cross section.

For a direct measurement of the above reaction in inv. kinematics Intense 7Be Beam productio

n 8B structure may affect the r

esults

)}(2exp{)(

)( EE

ESE

• S17(0)=0.019+0.004 -0.002 (keV b) (recommended value by Adelberger et al., 1997)


Motivation (Motivation (IIII))

Nuclear synthesisUsually, triple-

process is important to pass over the instability at A=8.

Reaction path through 7Be might be important in special environments (e.g. high-temperature and metal-deficient stars).


Motivation (Motivation (IIIIII))

Study the structure of 8 Ｂ States at 0.77 MeV and 2.32 MeV

are well known, but no clear knowledge above 3.5 MeV.

A wide (>4 MeV) state at 3.5 MeV …2- 　 ; low-lying 2s state?

the resonance may contribute to the cross section even at 0 energy (3% of on resonance).

V.Z. Gol’dberg et al, JETP Lett. (1998), another measurement in G.V. Rogachev et al, Phys. Rev. C (2001).


Method (RI beam production)Method (RI beam production)

Primary beam: 7Li3+,8.76 MeV/u (61.9 MeV), ~100 pnA Production target: Hydrogen gas (0.67 mg/cm2), 7Li3+(p, n) 7Be4+. Secondary beam: 7Be4+, 53.8 MeV (@ secondary target)

3 x 105 pps.


Method (Experimental setup)Method (Experimental setup)

Thick target method: all the 7Be were stopped in the CH2 target, and recoil protons (Emax=23 MeV) were detected by silicon detector telescopes (60 msr x 4 sets, covering up to 45 degree).

Eproton⇒Ecm⇒Eex


Experimental Setup (picture)Experimental Setup (picture)


Advantages over past measurementsAdvantages over past measurements

Wide energy rangeEcm up to 6.7 MeV (< 3.5MeV in the past

measurements). Wide angle

0-45 degree in LAB (fixed angles in the past).

Inelastic scattering 7Be(p,p)7Be* Inelastic events to the 7Be excited state

at 429 keV may affect the measurements.

NaI detectors were used to detect 429 keV gamma rays.


Result (RI beam production)Result (RI beam production) PI by TOF and energy: 7Be was clearly identified. The measurement

(left) and calculation (right) were in good agreement.

Purity 56% (above figure, before the Wien Filter), 100% (after the Wien filter with high voltages of ±40 kV).

Intense 7Be4+ beam was successfully produced (3 x 105pps).

F0-F2 TOF(ns)

Part

icle

Ene

rgy(

MeV

)


Selection of proton eventsSelection of proton events

Proton was the largest component and colud be identified by the E-E relationship.

Considerable amount of 3He and 4He are also seen (break up of 7Be?).


Carbon background subtractionCarbon background subtraction

Preliminary


Cross section spectrum (Cross section spectrum (LABLAB=0~5 deg)=0~5 deg)

Good agreement with Rogachev et al. (2001), for the energies around the 2.3 MeV resonance.

Wide state expected at 3.5 MeV was not clearly seen (so far). Indication of a new state around Eex=4.6 MeV.

Preliminary


Resonance parameters Resonance parameters

We can make sure the spin and parity by analyzing the angular distribution. Contribution from inelastic scattering, three-body decay, and so on must be considered.

R-matrix analysis… resonance parameters can be deduced by the resonance shape in the excitation function.

Preliminary results (assuming continuum b.g.): E~4.7 MeV, keV Spin, parity 0- (or 1-) fits

better than 1+, 3+ and 4+, which were identified in the mirror nucleus (8Li).

E,,Jof 8Li levels:

3.21 MeV, ~1000 keV, 1+

5.4 MeV, ~650 keV, (0,1)+

6.1 MeV, ~1000 keV, 3+

6.53 MeV, 35 keV, 4+

4.7 0-?


Summary and future analysisSummary and future analysis

For the future: Complete spin, parity etc. determination by the R-

matrix analysis. Analysis for the angular distribution. Consideration of inelastic events by the NaI data.

We have measured proton elastic scatterings of 7Be with thick target method, using 7Be4+ beam produced in CRIB facilty (CNS, Univ. of Tokyo).

Cross section spectrum against center-of-mass energy was obtained for LAB deg. (CMdeg.).

Cross section is in good agreement with the past measurements for the energy region of 1~2.5MeV.

Indication of a new state of 8B is seen at Eex~4.7 MeV.

Documents

Proton resonance scattering of 7 Be H. Yamaguchi, Y. Wakabayashi, G. Amadio, S. Kubono, H. Fujikawa, A. Saito, J.J. He, T. Teranishi, Y.K. Kwon, Y. Togano,