Reactions of the halo systems lIBe and 11Li (at 460 and 280 MeV/nucleon) with a carbon target demonstrate that (n + 9Li) has an (unbound) l = O ground state very close to the threshold. The neutron halo of 11Li has appreciable (1S 1 / 2 )2 and (OP1/2)2 components. PACS numbers: 25.60.+v, 21.10.Pc, 25.70.Mn, 27.20.+n There is currently a surge of interest in the IOLi problem caused by the work of Kryger et al. [1], who reported a narrow central peak in the relative velocity spectrum of the fragments (n + 9Li) produced in fragmentation of an 18 0 beam at 80 MeV/nucleon. The peak was interpreted as evidence either for the ground state of IOLi, in this case probably the missing s state, or for an l = 0,1 resonance near 2.5 MeV. Weak evidence for a structure close to threshold [2] favors the first interpretation. A low-Iying P state is also present near 0.5 MeV according to very similar data presented by Young et al. [2] and by Bohlen el al. [3]. These two papers give a detailed summary of previous work on lOLi.The properties of IOLi are essential for the understanding of the neutron halo associated with the 11 Li ground state [4]. Thompson and Zhukov [5] found that a neutron s state at low energy would lead to an 11 Li halo with about egual admixtures of (lS 1 / 2 )2 and (OP1/2)2. This gave much better agreement with the narrow momentum distributions observed in fragmentation experiments and was in line with the suggestion by Barranco, Vigezzi, and Broglia [6], who attributed the forward-peaked angular distributions of neutrons from 11 Li incident on light targets to the decay in ftight of lOLi. (The 5He intermediate state also dominates the breakup of 6He [7]. ) We have produced the intermediate state lOLi in singlenucleon stripping reactions of the halo states 11 Be and 11 Li. The word "stripping" is employed here in the sense introduced in 1947 by Serber to describe reactions of 190 MeV deuterons; see his recent remarks on the subject [8]. At high bombarding energies, the sudden approximation is valid, and the halo neutron will, after the collision, to a good approximation be in a state characteristic of the projectile and not in an eigenstate of (9Li .+ n). We shall in the following develop a line of arguments that first infer the properties of IOLi from the known structure of 11 Be and then use the results to draw conclusions about the 11 Li halo.The radioactive beams were generated in a 8 g/cm 2 Be target by fragmentation of a 18 0 beam from the heavy-ion synchrotron SIS at GSI aod separated io the fragment separator [9] FRS by magnetic analysis. The secondary beams of 280 MeV / nucleon for 11 Li and 460 MeV / nucleon for 11 Be were transported via the storage ring ESR to a carbon target (thickness 1.29 g/cm 2 ) placed directIy in front of the large-gap magnetic spectrometer [10,11] ALADIN. Neutrons coincident with the nuclear fragment were detected in the calorimeter LAND [12] placed 11 m behind the carbon target and having an active detector area of 2 X 2 m 2 and a total thickness of 1 m. The neutron ...
Very neutron-deficient isotopes of rhodium, palladium, silver, cadmium and indium in the N= 50 region were studied at the GSI on-line mass separator following bombardment of 58, 60, 62Ni and 63, 65Cu targets with 4.0 MeV/u ions of 4~The known 'properties of the t-delayed proton precursor 95mpd were confirmed, but a search for direct proton decay of 95mAg was not successful. Beta-delayed proton activities observed at mass-numbers 94, 96, 97 and 100 were assigned to the precursors 94Rh(66_+14 s), 96Ag(5.1 + 0.4 s), 97 +4 lOOin" . _ Cd(3 z s) and In addition. 94pd(9.0+0.5 s) was identified from fl-y-X studies. Individual decay schemes of 95~, 96pd and 96, 9SAg are reported.
Using the on-line mass separator at the Gesellschaft fur Schwerionenforschung Unilac we produced Ba through the Ni( Ni, 2n) Ba reaction and measured its production cross section to be 0.20+o 09 pb. The new isotope Ba represents the heaviest N = Z+ 2 nucleus known to date. With KE-E telescopes we measured the total (P-decay) half-life to be Tp = 0.43+o~s s and the partial o.-decay half-life to be T ) 1.2 x 10 s (1 Mev( E' ( 4 MeV) for Ba. With track detectors we found a half-life for spontaneous C emission T& & 1.1 x 10 s based on three carbon events. PACS number(s): 23.70. +j, 23.60.+e, 25.70.Jj, 27.60. +jCluster radioactivity is now a well established, although rare, decay mode of heavy nuclei. Intense experimental research in the last decade has led to the detection of 20 cases of spontaneous emission of clusters ranging from C to Si from trans-lead nuclei, with branching ratios relative to o, decay &om 10 down to 10 and partial half-lives from 10~u p to 10 s [1]. The general features of this new radioactive decay mode have been established; above all, its strong dependence on the barrier penetration factor and consequently on the Q value, which must be large in order to compensate for the small preformation factors typical of such complew clusters [2]. For this reason, all heavy residual nuclei resulting &om cluster emission have been found so far to differ &om the doubly magic Pb by three nucleons at most. Analogously, a new island of cluster radioactivity having residual nuclei close to doubly magic Sn has been predicted by Greiner et al. and Poenaru et al. [3,4]. They found the most favorable case to be C emission from Ba and calculated the decay rate using various mass predictions [5] for the then unknown Ba nucleus. The results of their predictions strongly depend on the adopted Q value: a 2-MeV spread in the Q values results in a factor 10 spread in the partial half-lives. More recently others [6 -10] have taken up the challenge of calculating the decay rate for C emission from~~Ba; their results for the same choice of Q value span more than eight orders of magnitude. This situation is in complete contrast with what is found in the translead region of cluster radioactivity, where Q values are generally known and all models predict half-lives for the same decay mode that typically agree within an order of magnitude [11]. It is clear that the possible island of cluster radioactivity in the trans-tin region would be interesting to ex-plore. Apart &om the possibility of discriminating among different theoretical approaches, the mere detection and measurement of the partial C decay rate of 4Ba could shed light on the behavior of cluster radioactivity in this region of the Chart of the Nuclides far below Pb, possibly providing information on the interplay with o. decay and on the role of the nearly double shell closure in a nucleus such as Sn far from the stability line. The first searches for
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