Japanese-Russian workshop onStudies of Exotic NucleiDecember 3 - 4, 2004Saitama, Japan

Review of joint RIKEN-Kurchatov-Dubna experiments at Dubna

G.M. Ter-Akopian

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, 2001Isobaric analog state of 5H in 5He (reaction 6He+2H), 20023/2+ and 5/2+ excited 5H states in the t+t reaction, 2003Experiments aimed at the QFS reactions, 2004

Cryogenic targets at ACCULINNATritium target

4H resonance in the 2H(t,p) and 3H(t,d) reactions21qp=18 - 32 degreesqt= 15 39 degreesqn=18 56 degrees2001

p-t Coincidences Unobserved Neutron p-n Coincidences Detected NeutronNeutron Momentum Distribution in the 4H cmsThe 2H(t,p) reactionProcesses 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 + *

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

3.05 0.193.19 (2-)5.42 (2-)

Eres, res, Present work5.14 1.38[Til92]

qn1 (degrees)

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) 2403proton

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).Correlation function

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

20012003

Reactions: 6He+2H3He+5H3H+5He3H+n+n3He+n+n3H+p+nbeam energy: 132 MeV5H and 5He in the 6He+2H reaction

6He+2H 5H+3He, 3He-t coincidence5H 3H+n+n decayqCM=21-40 deg.

Missing mass 5H spectrum obtained from inclusive 3H dataReaction:6He+2H 5H+3He, 5H 3H+n+n decayqCM=21-40 deg.

Reaction:6He+2H 5He+t t-3He coincidencesDecay mode;5He 3He+n+nReaction:6He+2H 5He+t, t-t and t-p coincidencesDecay mode:5He t+p+nqCM=21-40 deg.

6He+2H 5He+3H, t-d coincidenceDecay channel5He t+d qCM=21-40 deg.

6He+2H 5H+3He ~3006He+2H 3H+5He (E*=20MeV, T=1/2) 300 1006He+2H 3H+5He (E*=22MeV, T=3/2) 300 130Isobaric 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)

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

28 MeV/n

p2np6Hepcorepa1pa2Kinematics

-1 -0.5 0 0.5 1 cosq2n160012008004000counts p2nZ (MeV/C)-400 -200 0 200p2nY (MeV/c)3002001000-100-200-300q2nIn PWIA:d3sdWa1dWa2dW2n= Naeff KF F(p2n) 2dsdW aa

0 100 200 300 400 p2n (MeV/c) 0 100 200 300 p2n (MeV/c)qaa cms (degrees)qaa cms (degrees)180

120

60

0180

120

60

01801206000306090countscountsqaa cms = 60-120 deg. 0 100 200 300 p2n (MeV/c) 0 100 200 300 400 p2n (MeV/c)q2n < 120 deg.q2n < 60 deg.

0 100 200 300 400 p2n (MeV/c)3002001000pn-n (MeV/c)

6He+2H 3He+5H5H t+n+n decay3He-t coincidence3H energy in the 5H rest frame5H energy above the decay threshold (MeV)

6He+2H 3H+5He5He 3He+n+n decayt-3He coincidence3He energy in the 5He rest frame5He excitation energy (MeV)

6He+2H 3H+5He5He t+p+n decayt-t coincidenceTriton energy in the 5He rest frame5He excitation energy (MeV)

6He+2H 3H+5He5He t+d decayt-d coincidenceDeuteron energy in the 5He rest frame, (MeV)5He excitation energy (MeV)