R. Wolski

High resolution line for secondary radioactive beams at the U400M cyclotron

Abstract For implementation of an experimental program for studying nuclear reactions with radioactive ion beams in the energy domain of 20 through 80 MeV A the high resolution beam line ACCULINNA was put into commissioning on a primary beam line of the JINR U-400M cyclotron. By means of nuclear fragmentation of the 14 N beam with the energy of 51 MeV A on the 170 mg/cm 2 carbon target radioactive beams of 6 He, 8 He and 8 B were obtained. Possibilities of further development of the set-up are discussed.

The 8He and 10He spectra studied in the (t, p) reaction

The low-lying spectra of 8He and 10He nuclei were studied in the 3H(6He, p)8He and 3H(8He, p)10He transfer reactions. The 0+ ground state (g.s.) of 8He and excited states, 2+ at 3.6–3.9 MeV and (1+) at 5.3–5.5 MeV, were populated with cross sections of 200, 100–250, and 90–125 μb/sr, respectively. Some evidence for a 8He state at about 7.5 MeV was obtained. We discuss a possible nature of the nearthreshold anomaly above 2.14 MeV in 8He and relate it to the population of a 1− continuum (soft dipole excitation) with a peak value at about 3 MeV. The lowest energy group of events in the 10He spectrum was observed at ∼ 3 MeV with a cross section of ∼ 140 μb/sr. We argue that this result is consistent with the previously reported observation of 10He providing the new 10He g.s. position at about 3 MeV

Evidences for resonance states in 5H

Resonance states of H-5 were investigated through the two-neutron transfer reaction t(t, P)(5) H. A triton beam at 57.5 MeV and a cryogenic liquid tritium target were used. The H-5 missing mass spectrum in triple coincidence, proton + triton + neutron, shows a resonance at 1.8 +/- 0.1 MeV above the t + 2n decay threshold. This energy is in good agreement with the result reported in Phys. Rev. Lett. 87 (2001) 092501. The resonance width, Gamma(intr) less than or equal to 0.5 MeV, is surprisingly small and difficult to reconcile with theory predictions

Resonance states of hydrogen nuclei 4H and 5H obtained in transfer reactions with exotic beams

Abstract Experimental search for 4 H and 5 H has been performed in the reactions 3 H(t,p) 5 H, 2 H( 6 He, 3 He) 5 H and 2 H(t,p) 4 H. A resonance state situated at 1.8±0.1 MeV above the t+n+n decay threshold is obtained in the missing mass energy spectrum of the 5 H nucleus. Also, there is an indication that another resonance located at 2.7±0.1 MeV presents in this spectrum. Visible peak widths are governed mostly by the instrumental resolution, which came to about 0.4 MeV. We set an upper limit of 0.5 MeV on the true width of any of the two states. The resonance state of 4 H with E res = 3.3 ± 0.2 MeV and Γ res = 4.1 ± 0.3 Mev was obtained in the 2 H(t,p) 4 H reaction.

Isovector soft dipole mode in 6Be

By using the H-1(Li-6,Be-6)n charge-exchange reaction, population of continuum states in Be-6 was observed up to E-T = 16 MeV, E-T being the Be-6 energy above its three-body decay threshold. In kinematically complete measurements performed by detecting alpha + p + p coincidences, an E-T spectrum of high statistics was obtained, containing approximately similar to 5 x 10(6) events. The spectrum provides detailed correlation information about the well-known 0(+) ground state of Be-6 at E-T = 1.37 MeV and its 2(+) state at E-T = 3.05 MeV. Moreover, a broad structure extending from 4 to 16 MeV was observed. It contains negative parity states populated by Delta L = 1 angular momentum transfer without other significant contributions. This structure can be interpreted as a novel phenomenon, i.e. the isovector soft dipole mode associated with the Li-6 ground state. The population of this mode in the charge-exchange reaction is a dominant phenomenon for this reaction, being responsible for about 60% of the cross-section obtained in the measured energy range.

Resonance States of Hydrogen Nuclei 4H and 5H Obtained in Transfer Reactions with Exotic Beams

To investigate 5H resonance states with a better instrumental resolution, we utilized the two-neutron transfer reaction 3H(t, p)5H accomplished with the use of a cryogenic liquid-tritium target and 57.5-MeV triton beam. As a result of this study, a valuable fraction of protons detected at ϑlab=18°–32° in ptn coincidence events was attributed to the states of the 5H nucleus. Two resonance states situated at 1.8±0.1 and 2.7±0.1 MeV above the t + n + n decay threshold were obtained in the missing mass energy spectrum of the 5H nucleus. The peak located close to E5H was clearly seen in the 5H spectrum obtained from the energy distributions of 3H nuclei emitted in the reaction 2H(6He, 5H)3He at ϑlab=17°–32°. The width (Γobs≤0.5 MeV) obtained for the two 5H resonance states is surprisingly small. A state of 4H with Eres=3.3 MeV and γ2=2.3 MeV was obtained in the reaction 2H(t, p)4H from the spectra of protons leaving the target at ϑlab=18°–32° and detected in coincidence with neutrons emitted in the decay of 4H nuclei.

Soft dipole mode in 8He

The low-lying spectrum of 8He was studied in the 3H(6He, p)8He transfer reaction for small center of mass angles. The 0+ ground state (g.s.) of 8He and excited states, 2+ at 3.6–3.9 MeV and (1+) at 5.3–5.5 MeV, were populated with cross sections of 200, 100–250, and 90–125 μb/sr. Some evidence for the excited state at about 7.5 MeV can be found in the data. The possible nature of the near-threshold anomaly above 2.14 MeV in 8He is related to the population of a 1− continuum (soft dipole excitation) with a peak energy value at about 3 MeV. This assumption can probably resolve the problem of a large uncertainty existing in the experimental data on the 8He 2+ state energy.

Study of complete and incomplete fusion for loosely bound projectiles 6He and 6Li on 165Ho and 166Er targets

Complete fusion (CF) and incomplete fusion (ICF) reactions were studied for the cases of the loosely bound 6He and 6Li projectiles bombarding 166Er and 165Ho targets at energy of about 10 MeV/nucleon. Experiments were carried out to test an approach exploiting the measured intensities of γ rays emitted at the transitions between the yrast-band levels of reaction products formed after the termination of neutron evaporation. Partial waves feeding the CF reactions 165Ho (6Li, 5n) 166Yb and 166Er(6He, 6n) 166Yb as well as ICF 165Ho (6Li, α3n) 164Er and 166Er(6He, α4n) 164Er reaction channels were revealed from the obtained γ-ray data. The method of exit channel identification via the triple coincidence (γ1-γ2-light charged particle) was employed for these reactions study.

High resolution beam line of the U400M cyclotron and a possibility of RIB accumulation and cooling in the K4 storage ring

Abstract The high resolution beam line ACCULINNA put into operation on a primary beam line of the JINR U400M cyclotron is discussed in the framework of the TREBLe project [1]. The capability of the beam line for producing radioactive ion beams is demonstrated by means of nuclear fragmentation of the primary 14 N beam with an energy of 51 MeV. A on a 170 mg/cm 2 carbon target. Characteristics of the obtained 6 He and 8 B radioactive beams are presented. A scheme of accumulation and cooling on the orbit of the storage ring K4 is proposed for a low intensity radioactive beam obtained from this beam line.

Fragment Separator ACCULINNA-2

Project of a new in‐flight fragment separator is proposed as a part of the third generation DRIBs facilities in Dubna. As compared to the existing separator ACCULINNA, beam intensity should be increased by a factor 10–15, the beam quality improved and the RIB assortment should broaden considerably at ACCULINNA‐2. Research program and structure are outlined for the new instrument.