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The commissioning of the new fragment separator ACCULINNA-2 at FLNR JINR is accomplished. The separator is destined to expand the possibilities in studies of dripline nuclei performed with the exotic secondary radioactive ion beams (RIBs) at energies of (5 – 50) AMeV. The projected high transmission and purification level were confirmed experimentally for a number of RIBs in the last two years. The ACCULINNA-2 setup will become a backbone facility at FLNR for the research in the field of light exotic nuclei. This report shows the current status of the separator, describes the obtained RIBs parameters and first experiments as well, provides the overview of the developing detection, monitoring and control subsystems.

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

The 7H nucleus most likely possesses an unique decay dynamics: the four-neutron emission (or 5-body decay). We estimated theoretically the 7H width as a function of its decay energy. Uncertainty inherent to the estimated decay energy leaves a room for a possible very small width of 7H. In an attempt to observe a long living quasi stable 7H nucleus, produced in the reaction 2H(8He, 7H)3He, we set an upper limit of 3 nb/sr for the reaction cross section. We utilized a 20.5 MeV/amu 8He beam bombarding a 5.6 cm thick liquid deuterium target, and searched for 7H within 0°–50° CM angles. The obtained cross section limit corresponds to a 7H lifetime less than 1 ns, which allows us to estimate a lower limit of 50–100 keV for the 7H energy above the 3 H +4n breakup threshold.

A resonance state situated at 1.8 +/- 0.1 and, most likely, another state positioned at 2.7 +/- 0.1 MeV above the t+n+n decay threshold were observed in the missing mass energy spectrum of the H-5 nucleus produced in the reaction H-3(t,p)H-5. The peak located close to E-5H = 1.8 MeV also was seen in the H-5 spectrum obtained from the energy distributions of 3H nuclei emitted in the reaction H-2(He-6,H-5)He-3. The width (Gamma(obs) less than or equal to 0.5 MeV) obtained for the two 5H resonance states is surprisingly small. A state of H-4 with E-res = 3.3 MeV and gamma(2) = 2.3 MeV was obtained in the reaction H-2(t,p)H-4 from the proton spectrum.

A cryogenic tritium target and computer-controlled equipment providing for feeding/recovering tritium into/from the target cell and radiation monitoring in technological lines and in workrooms is described. The tritium target set-up showed reliable operation in experiments done with a 58.3 MeV triton beam focused on a 5 mm spot at intensity approaching 3×107 s−1. The t+t elastic scattering cross-section was obtained in a wide angular range.

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 plusmn; 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 = 1.8 MeV was clearly seen in the H spectrum obtained from the energy distributions of 3H nuclei emitted in the reaction 2H(6He, 5H)3He at θ lab = 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. © 2003 MAIK "Nauka/Interperiodica".

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.

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.

Construction and properties of a double ionization chamber (DIC) are described. Heavy ion fusion-evaporation reaction products obtained at the focal plane of the kinematic separator VASSILISSA enter the DIC volume through a thin plastic window. After their thermalization in the gas, they drift in the electric field to the DIC cathode. Their α-decay and/or spontaneous fission are detected in 4π-geometry in two ionization chambers, divided by the common cathode. Using DIC the α-decay of Bi and Pb isotopes produced in the fusion reactions 40 Ar + 159 Tb and 40 Ca + 153 Eu were detected. A new isomer, 189m Bi was observed.

Heavy-ion fusion reaction ER's were studied in a wide excitation energy range of the 199,193,191 Bi and 217 Ac compound nuclei produced with bombarding ions of 40 Ar , 40 Ca and 20 Nc . The problems of the shell effect fading with increasing nucleus excitation energy and the isospin dependence of the macroscopic component of the fission barrier are discussed.

The low-lying spectrum of 8 He was studied in the 3 H( 6 He, p ) 8 He transfer reaction for small center of mass angles. The 0 + ground state (g.s.) of 8 He 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 μ b/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 8 He 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 8 He 2 + state energy.

Low-energy spectra of the He-8,He-10 nuclei were investigated in the (t, p)-type reactions at small centre-of-mass angles using similar to 25AMeV beams of He-6 and He-8 nuclei. The 0(+) ground state (g.s.) of He-8 and excited states, 2(+) at 3.6-3.9MeV and (1(+)) at 5.3-5.5 MeV, were populated with cross-sections of 200, 100-250, and 90-125 mu b/sr, respectively. To account for a near-threshold anomaly observed in the He-8 spectrum the population of a 1(-) continuum (soft dipole excitation) was considered. The lowest-energy group of events in the He-10 spectrum was observed at similar to 3MeV with a cross-section of similar to 140 mu b/sr. This result is consistent with the previously reported observation of He-10 providing a new g.s. position for He-10 at about 3MeV.

The spectrum of $\rm ^He$ was studied by means of the $\rm ^He, p)^He$ reaction at a laboratory energy of 25 $\rm MeV/A$ and small center-of-mass angles. Missing mass spectrum of $\rm ^He$ was derived from the obtained p-8He coincidence. A resolution of 0.7 MeV was achieved in this spectrum for the measured $\rm ^He$ energy. Most likely, a well isolated group of 10 events detected between 2 and 5 MeV and showing a maximum at about 3 MeV in the spectrum of the present work exhibits the $\rm ^He$ g.s. resonance.

The nuclear system {sup 5}H was studied using the {sup 3}H(t,p){sup 5}H transfer reaction at a laboratory energy of 57.7 MeV and small center of mass angles. The energy and angular correlations among the {sup 5}H decay fragments were obtained by complete kinematical reconstruction. A broad structure in the {sup 5}H missing mass spectrum above 2.5 MeV with a typical width of several MeV was identified as a mixture of 3/2{sup +} and 5/2{sup +} states. Analysis of interference patterns observed in the measured angular correlations disclosed the 1/2{sup +} ground state of {sup 5}H concealed in the smooth missing mass spectrum. The deduced values for the resonance energy and width are E{sub g.s.}{approx_equal}1.8 MeV and {gamma}{sub g.s.}{approx_equal}1.3 MeV. The estimated cross sections for population of the ground state and the doublet of excited states at {theta}{sub c.m.}=5 deg. are 150{+-}50 {mu}b/sr and 4.6{+-}2 mb/sr, respectively.

International audience; The $^{5}$H system was produced in the $^{3}$H(t, p) $^{5}$H reaction studied at small CM angles with a 58MeV tritium ion beam. High statistics data were used to reconstruct the energy and angular correlations between the $^{5}$H decay fragments. A broad structure in the $^{5}$H missing-mass spectrum showing up above 2.5MeV was identified as a mixture of the $3/2^+$ and $5/2^+$ states. The data also present an evidence that the $1/2^+$ ground state of $^{5}$H is located at about 2MeV. Then, the $^{5}$H and $^{5}$He systems were explored by means of transfer reactions occurring in the interactions of 132MeV $^{6}$He beam nuclei with deuterium. In the $^{2}$H( $^{6}$He, $^{3}$H) reaction a T = 3/2 isobaric analog state of $^{5}$H in $^{5}$He was observed at an excitation energy of 22.0±0.3MeV with a width of 2.5±0.3MeV.

The H-4 resonance was investigated in the transfer reactions H-2(t,p)H-4 and H-3(t,d)H-4 using cryogenic liquid targets of deuterium and tritium and 58 MeV triton beam. The multidetector system with a large angular acceptance was used to measure the recoil protons and deuterons in coincidences with tritons or neutrons from the decay of H-4. Data analysis involved careful considerations made for the competing processes of final state interaction and quasifree scattering. The experimental data show a peak with resonance parameters E-res = 3.05 +/- 0.19 MeV and Gamma(obs) = 4.18 +/- 1.02 MeV. The pole of S-matrix corresponding to the physical values of energy and width, E-0 = 1.99 +/- 0.37 MeV and Gamma(0) = 2.85 +/- 10.3 MeV, has been extracted. (C) 2004 Elsevier B.V. All rights reserved.

Resonance states of 5H 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 5H 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, Γintr ≤ 0.5 MeV, is surprisingly small and difficult to reconcile with theory predictions. © 2003 Published by Elsevier B.V., SCOPUS: ar.j, info:eu-repo/semantics/published

In the fusion reactions of20,22Ne with205Tl,208Pb, and209Bi the absolute production cross-sections of the227Np,222–224Pa,222–224Th, and221Ac isotopes were measured and the products of the xn evaporation channels and theirα-decay properties were investigated. The identified isotope is227Np (7680±10 keV). A newα-line structure of224Pa was established (7460±10 keV (25±3 %) and 7555±10 keV (75±3 %)). Fourα-lines of223Th were identified (7290±10 keV (41±5 %), 7320±10 keV (29±5 %), 7350 ± 15 keV (20±5 %), and 7390±15 keV (10±4 %)). The half life of217Fr was measured to be 16±2 μs and that of220Ra was found to be 17 ±2 ms.

The studies of atomic nuclei with Z > 100 are closely related to the synthesis of new chemical elements and to the investigation of stability limits for the heaviest nuclides. From the mid-50s these studies have been carried out using intense heavy-ion beams and highly sensitive techniques designed for the physical and chemical identification of rare short-lived nuclei. The studies proceeded in two stages, the first one being characterized by the use of hot-fusion reactions between the U, Pu, Am, Cm and Cf target nuclei and the C, N, O, and Ne projectiles and the second being based on the use of the cold-fusion reactions induced by Cr, Mn, and Fe projectiles on Pb and Bi target nuclei. As a result, the chemical elements with atomic numbers from 102 to 109 have first been synthesized. The radioactive properties of over 40 isotopes of these elements have been investigated and unambiguous evidence has been obtained that shell effects play a decisive role for the stability of the Z ≳ 104 nuclei against spontaneous fission. This provides an experimental substantiation for the known hypothesis that the island of nuclear stability should lie around Z ⋍ 114 and N ⋍ 178 or 184. It has been proposed to synthesize elements with Z ≥ 110 by the complete fusion reactions of uranium and adjacent element nuclei with projectile nuclei such as Ar and Ca. The spontaneous fission of a product nucleus (a total of 26 events) has been observed in Dubna experiments with the 232Th + 44Ca and 236U + 40Ar reactions. The authors of those studies tentatively assigned this activity to the decay of the nuclei of element 110.