Japanese-Russian workshop on Studies of Exotic Nuclei December 3 - 4, 2004 Saitama, Japan

1. Japanese-Russian workshop on Studies of Exotic Nuclei December 3 - 4, 2004 Saitama, Japan Review of joint RIKEN-Kurchatov-Dubna experiments at Dubna G.M. Ter-Akopian

2. Collaboration overview: (activity in Dubna) • First series of experiments, 1999 – 2000 • 5H nucleus in the 6He+p 5H+2He reaction, • attempt to find a p1/2 resonance in 7He. • Development of experimental set-ups: • tritium target, acceleration of tritons at U-400M, • upgrade of separator ACCULINNA, • new detector arrays, the use of DEMON modules. • 4H and 5H in the 2H(t,p), 3H(t,d), and 3H(t,p) reactions, 2001 • Isobaric analog state of 5H in 5He (reaction 6He+2H), 2002 • 3/2+ and 5/2+ excited 5H states in the t+t reaction, 2003 • Experiments aimed at the QFS reactions, 2004

5. Cryogenic targets at ACCULINNA Tritium target

10. 4H resonance in the 2H(t,p) and 3H(t,d) reactions 2001 qp=18 - 32 degrees qt= 15 – 39 degrees qn=18 – 56 degrees 21

11. The 2H(t,p) reaction Neutron Momentum Distribution in the 4H cms p-n Coincidences – Detected Neutron p-t Coincidences – Unobserved Neutron • Processes in the t+p+n Output Channel: • Transfer Reaction t + d → p + 4H • p-n Final State Interaction (FSIpn) • Quasi-free Scattering (QFS) of the beam triton on the proton bound in the deuteron • Transfer Reaction t + d → n +α*

12. Parameters of the 4H g.s. obtainedin the reaction 2H(t,p)4H 3.05 ± 0.19 3.19 (2-) 5.42 (2-) [Til92]. D.R. Tilley et al., Nucl. Phys. A541 (1992). Charge-symmetric reflection of the4LiR-matrix parameters

16. qn1 (degrees)

17. 13C(6Li,d)17O*(a)13Cg.s. K.P. Artemov et al., Yad.Fiz., 28 (1978) 288. G. Cardella et al., Phys. Rev., C36 (1987) 2403 proton

18. Correlation function Similar analysis was made for 6Be(2+) in paper O.V. Bochkarev et al., Sov. J. Nucl. Phys. 55, 955 (1992). Hyperspherical expansions of decay amplitudes were made in Refs. B.V. Danilin et al., Sov. J. Nucl. Phys. 46, 225 (1987), O.V. Bochkarev et al., Nucl. Phys. A505, 215 (1989).

20. Strong correlation patterns observed for the broad structure in the 5H spectrum above 2.5 MeV allows one to unambiguously identify this structure as a mixture of the 3/2+ and 5/2+ states. This imposes an upper limit (Eres<2.5 MeV) the energy of the 5H ground state resonance. Correlation picture seen in the 5H spectrum below 2.5 MeV evidences for the interference of the 3/2+-5/2+ doublet and the 1/2+ ground state in 5H.

21. 2001 2003

22. 5H and 5He in the 6He+2H reaction beam energy: 132 MeV 3He+5H 3H+n+n Reactions: 6He+2H 3He+n+n 3H+p+n 3H+5He

23. 6He+2H 5H+3He, 3He-t coincidence 5H 3H+n+n decay qCM=21-40 deg.

24. Reaction: 6He+2H 5H+3He, 5H 3H+n+n decay Missing mass 5H spectrum obtained from inclusive 3H data qCM=21-40 deg.

25. qCM=21-40 deg. Reaction: 6He+2H 5He+t t-3He coincidences Decay mode; 5He 3He+n+n Reaction: 6He+2H 5He+t, t-t and t-p coincidences Decay mode: 5He t+p+n

26. Decay channel 5He t+d 6He+2H 5He+3H, t-d coincidence qCM=21-40 deg.

27. Isobaric analog state of 5H was for the first time obtained in 5He by means of the 2H(6He,t)5He reaction. The excitation energy and the width of this resonance are: • Eres=22.0 0.3 MeV, Gobs=2.5 0.4 MeV. • The following proves this conclusion: • In this state 5He shows the three-body decay modes: 5He 3He+n+n and • 5He t+p+n. • Two-body decay mode 5He t+d was not revealed at a 10% probability. • The known 20-MeV, Jp=3/2- resonance of 5He does not contribute in the • observed three-body decay modes. • Within error bars, the obtained energy of this resonance fits the 5H g.s. energy • reported by our collaboration. Evidence was obtained for the Jp=1/2+ ground state resonance of 5H lying at about 2 MeV above the 5H t+n+n decay threshold. Following cross sections were estimated (qCM range of 21-40 degrees: Reaction Cross section (mb/sr) 6He+2H 5H+3He ~300 6He+2H 3H+5He (E*=20MeV, T=1/2) 300 100 6He+2H 3H+5He (E*=22MeV, T=3/2) 300 130

28. Quasi-free scattering in the 4He(6He,2a) reaction at E6He=28 MeV/n Data have been collected also for the 4He(8He,2a) and 4He(8He,a6He) reactions Note the quasi-free scattering study made at Osaka, Japan e.g. A. Okihana et al., Nucl. Phys. A617, 71 (1997)

29. 28 MeV/n

30. Kinematics pa2 p2n pcore p6He pa1

31. 300 1600 200 1200 q2n 100 0 p2nY(MeV/c) 800 counts -100 400 -200 0 -300 -1 -0.5 0 0.5 1 cosq2n -400 -200 0 200 p2nZ(MeV/C) In PWIA: d3s dWa1dWa2dW2n 2 ds dW aa = NaeffKFF(p2n)

32. q2n< 120 deg. q2n< 60 deg. 180 120 60 0 180 120 60 0 qaacms (degrees) qaacms (degrees) 0 100 200 300 400 p2n (MeV/c) 0 100 200 300 p2n (MeV/c) 180 90 120 60 counts counts 60 30 0 0 0 100 200 300 400 p2n (MeV/c) 0 100 200 300 p2n (MeV/c) qaacms = 60-120 deg.

33. 300 200 pn-n (MeV/c) 100 0 0 100 200 300 400 p2n (MeV/c)

34. 6He+2H 3He+5H 5H t+n+n decay 3He-t coincidence 3H energy in the 5H rest frame 5H energy above the decay threshold (MeV)

35. 6He+2H 3H+5He 5He 3He+n+n decay t-3He coincidence 3He energy in the 5He rest frame 5He excitation energy (MeV)

36. 6He+2H 3H+5He 5He t+p+n decay t-t coincidence Triton energy in the 5He rest frame 5He excitation energy (MeV)

37. 6He+2H 3H+5He 5He t+d decay t-d coincidence Deuteron energy in the 5He rest frame, (MeV) 5He excitation energy (MeV)