Breakup Reactions of 11Li within a Three-Body Model

We use a three-body model to investigate breakup reactions of 11Li (n+n+9Li) on a light target. The interaction parameters are constrained by known properties of the two-body subsystems, the 11Li binding energy and fragmentation data. The remaining degrees of freedom are discussed. The projectile-target interactions are described by phenomenological optical potentials. The model predicts dependence on beam energy and target, differences between longitudinal and transverse momentum distributions and provides absolute values for all computed differential cross sections. We give an almost complete series of observables and compare with corresponding measurements. Remarkably good agreement is obtained. The relative neutron-9Li p-wave content is about 40%. A p-resonance, consistent with measurements at about 0.5 MeV of width about 0.4 MeV, seems to be necessary. The widths of the momentum distributions are insensitive to target and beam energy with a tendency to increase towards lower energies. The transverse momentum distributions are broader than the longitudinal due to the diffraction process. The absolute values of the cross sections follow the neutron-target cross sections and increase strongly for beam energies decreasing below 100 MeV/u.Comment: 19 pages, 14 figures, RevTeX, psfig.st

alpha-decay of excited states in 11C and 11B

Studies of the 16O(9Be,alpha7Be)14C and 7Li(9Be,alpha7Li)5He reactions at E{beam}=70 MeV have been performed using resonant particle spectroscopy techniques. The 11C excited states decaying into alpha+7Be(gs) are observed at 8.65, 9.85, 10.7 and 12.1 MeV as well as possible states at 12.6 and 13.4 MeV. This result is the first observation of alpha-decay for excited states above 9 MeV. The alpha+7Li(gs) decay of 11B excited states at 9.2, 10.3, 10.55, 11.2, (11.4), 11.8, 12.5,(13.0), 13.1, (14.0), 14.35, (17.4) and (18.6) MeV is observed. The decay processes are used to indicate the possible three-centre 2alpha+3He(3H) cluster structure of observed states. Two rotational bands corresponding to very deformed structures are suggested for the positive-parity states. Excitations of some observed T=1/2 resonances coincide with the energies of T=3/2 states which are the isobaric analogs of the lowest 11Be states. Some of these states may have mixed isospin.Comment: accepted for publication in Nuclear Physics

Neutron decay widths of excited states of 11Be

The two neutron transfer reaction 9Be 16O,14C 11Be[10Be n] has been used to measure the branching ratios for the neutron decay of excited states of 11Be. The 14O ejectile was detected by a Q3D spectrometer at foreward angles. The energies and angles of the 10Be fragments of the decaying 11Be recoil were measured in coincidence with the 14O ejectile using a double sided silicon strip detector array at backward angles. This enabled a kinematic reconstruction of the reaction to be performed. Theoretical decay branch ratios were calculated using barrier penetrability factors and were compared to the measured ratios to provide information on the relative reduced widths of the states. The decay widths have been used to link states in 11Be with a common structure and structurally to states in the daughter nucleus 10Be. the 3 2 8.82 MeV state was identified as a candidate for a molecular band hea

Interactions of juvenile Lumbricus terrestris with adults and their burrow systems in a two-dimensional microcosm

The objective of this work was to evaluate interactions of Lumbricus terrestris juveniles with adults and with inherited burrow systems. An experiment was set up using a two dimensional Evans' boxes microcosm. Adult L. terrestris were added to 16 boxes (one individual per box) and kept in darkness at 17ºC along with eight unoccupied boxes for two months. The adult L. terrestris were removed from eight randomly selected boxes, and L. terrestris juveniles were added (one juvenile per box), composing three treatments with eight replicates: 1, with an adult in an inherited burrow (ABJ); 2, alone in an inherited burrow (BJ); and 3, alone in a previously uninhabited box (J). The proportion of juveniles occupying adult burrows observed was significantly different in treatments ABJ (48%) and BJ (75%). The mean mass of juveniles at experimental termination differed significantly among treatments and was greater in treatment J (4.04±0.39 g) in comparison to the BJ (3.09±0.93 g) and ABJ treatments (2.13±0.64 g). Results suggest a negative influence of both the presence of an adult and its burrow system on juvenile growth. Intraspecific competition partially explained this, but further investigation is required to examine how an inherited environment (i.e. burrow) could negatively affect the growth of juveniles.<br>O objetivo deste trabalho foi avaliar as interações de juvenis de Lumbricus terrestris com indivíduos adultos e com sistemas de galerias herdados. O experimento foi realizado usando microcosmos bidimensionais de Evans como unidades experimentais. Adultos de L. terrestris foram colocados em 16 unidades experimentais (um indivíduo por unidade) e mantidos no escuro a 17ºC juntamente com oito unidades experimentais inabitadas, por dois meses. Os adultos foram removidos de oito unidades selecionadas aleatoriamente e juvenis foram adicionados a todas as unidades experimentais (um indivíduo por unidade), em três tratamentos, com oito repetições: 1, com um adulto em um sistema de galerias herdado (ABJ); 2, sozinho em um sistema de galerias herdado (BJ); e 3, sozinho em uma unidade experimental inabitada (J). A proporção de juvenis observados ocupando as galerias feitas pelos adultos foi significativamente diferente nos tratamentos ABJ (48%) e BJ (75%). A biomassa média dos juvenis ao final do experimento diferiu significativamente entre os tratamentos e foi maior no tratamento J (4.04±0.39 g) em comparação com os tratamentos BJ (3.09±0.93 g) e ABJ (2.13±0.64 g). Os resultados sugerem uma influência negativa tanto da presença de um adulto quanto do seu sistema de galerias no crescimento dos juvenis. A competição intraespecífica explica parcialmente este fenômeno, porém novas investigações devem ser feitas para examinar como um ambiente herdado (galerias) pode afetar negativamente o crescimento de juvenis

Structure of the Brunnian nucleus C 10

The 2 2p breakup and structure of the only known Brunnian nucleus, 10C, has been studied at 33.3 MeV nucleon. Detection of the 2 2p breakup fragments using a highly segmented Si Si Si CsI detector array has allowed the 10C rightarrow 9B p, 9B rightarrow 8Be p, 8Be rightarrow and 10C rightarrow 6Be , 6Be rightarrow 5Li p, 5Li rightarrow p decay channels to be reconstructed. Proton emission was seen to be favoured. Resonant breakup was observed from excited states at Ex 4.20, 5.31 and 6.74 MeV. The previously unobserved state at 4.20 MeV may correspond to a 0 2p cluster structur