S. V. Stepantsov

TWO-NEUTRON EXCHANGE OBSERVED IN THE 6HE + 4HE REACTION. SEARCH FOR THE DI-NEUTRON CONFIGURATION OF 6HE

Differential cross sections for the elastic scattering of 6 He exotic nuclei from a gaseous helium target has been measured in a wide angular range in the CM system at a 6 He beam energy of 151 MeV. The large cross-sections obtained at backward angles are discussed in terms of a two-neutron exchange process. The results of DWBA calculations show that this effect can account for the cross sections obtained between 1208 and 1608 assuming the spectroscopic factor to be about 1 for the di-neutron cluster as was predicted by theory for 6 He. q 1998 Published by Elsevier Science B.V. All rights reserved.

Cluster structure of 6He studied by means of 6He + p reaction at 25 MeV/n energy

Abstract Angular distributions for elastic scattering and 1n and 2n transfer reactions were measured for the 6 He + 1 H system at 25 MeV/nucleon. The experimental data were analyzed in the framework of the one-step finite range DWBA model. The results suggest a lower triton spectroscopic amplitude for the 6 He nucleus as compared to the shell model calculation.

The Vassilissa facility for electrostatic separation and study of complete fusion reaction products

Abstract The Vassilissa facility is described. The main component is an electrostatic separator of complete-fusion reaction products from the ion beam. The facility is capable of transmitting recoil nuclei emitted by the target in the beam direction within a solid angle of 10 −2 sr and has a ± 10% spread in energy and ionic charge. The time required to transport the nuclei to the detectors is 3 × 10 −6 s The separation of scattered ions is performed using a system of three electrostatic condensers. Separation factors obtained for Ar, P and Ne are equal to 10 10 , 10 11 and 10 12 , respectively.

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

24.5 A MeV 6He+p elastic and inelastic scattering

The structure of 6 He is explored with proton elastic and inelastic scattering to the first 2 + excited state (Q =− 1. 8M eV) of 6 He in the inverse kinematics using a 24.5 A MeV 6 He beam. The distorted wave approximation (DWA) with an optical potential obtained by folding an effective nucleon–nucleon (NN) g-matrix with the 6 He density matrix elements as given by a large basis shell model is used to analyse the data. The comparison of predictions with the data confirms the view that 6 He has

Status of ACCULINNA beam line

AbstractTheseparatorACCULINNAwasupgradedtoachievenewexperimentalrequirements.Thebeamlinewasextendedbynewion-opticalelementsbeyondthecyclotronhall.Thenewarrangementsyieldmuchbetterbackgroundcondi-tions.Theintensitiesof 6 Heand 8 Heradioactivebeamsproducedinfragmentationof35AMeV 11 Bionswereincreaseduptoafactorof10.Theupgradedbeamlinewasusedinexperimentstostudythe 5 Hresonancestatespopulatedinthet þt reaction.Acryogenicliquidtritiumtargetwasdesignedandinstalledattheseparatorbeamline. 2002ElsevierScienceB.V.Allrightsreserved. PACS:25.70.Mn;29.25.RmKeywords:Radioactive ion beams;Productiontarget;Profileddegrader;Liquidtritiumtarget 1.IntroductionTheseparatorACCULINNA[1]isinoperationsince1996.Highintensityprimarybeamsof 7 Li, 11 B, 13 C, 15 Nand 18 Owithenergyvaluesrangingbetween32and50AMeVaredeliveredbytheU-400Mcyclotrontotheproductiontargetoftheseparator.Thesecondarybeamsof 6 Heand 8 Henucleiwithenergiesofabout25AMeVallowedustogainnewinsightsintothestructureofneutronhalonucleithroughthestudyofone-andtwo-neutrontransferreactionsmadewithhydrogenandheliumtargets[2–5].Suchbeamsofferfavor-ableconditionsfortheproductionofsofarun-knownparticle-unstablenucleibeyondtheneutrondripline.Forthispurposeonecoulduseone-stepone-proton and two-neutron transfer reactionsoccurringwheneither

The project of the mass separator of atomic nuclei produced in heavy ion induced reactions

Abstract A new separator and mass analyzer, named MASHA (mass analyzer of super heavy atoms), has been designed at the Flerov Laboratory JINR Dubna to separate and measure masses of nuclei and molecules with precision better than 10−3. The set up can work in the wide mass range from A≈20 to A≈500, its mass acceptance is as large as ±2.8%. In particular, it allows unambiguous mass identification of super heavy nuclei with a resolution better than 1 amu at the level of 300 amu. Synthesized in nuclear reactions nuclides are emitted from an ECR ion source at energy E=40 kV and charge state Q=+1. Then they pass the following steps of separation and analysis: the first section of rough separation, the second section of separation and mass analysis and the final section of separation with a 90° electrostatic deflector. In the focal plane of the device, a focal plane detector determines positions (masses) of studied nuclei. Ion optics of the analyzer, optimized up to the second order, is considered. Description of its elements and subsystems is given.

New insight into the low-energy

The spectrum of