G. Giardina

Semi-empirical determination of the shell correction temperature and spin dependence by means of nuclear fission

We study the temperature and angular momentum dependence of the shell effects in the fissioning nucleus by means of a theoretical analysis of the total fission probability. We find clear evidence of the disappearance of the shell correction to the fission barrier with both increasing spin and temperature and propose a general method to determine the level density at the saddle-point configuration. The results of the present study might explain the differences between the fission barriers extracted from the heavy-ion reactions and those obtained using light-particle induced fission.

Energy and Width Measurement of the 9B First Excited State Observed by the 10B(3He, α)9B(p)8Be and 10B(3He, α)9B(α)5Li Reactions

An appropriate choice of the beam energies and detector geometries allowed us to observe the first excited 9B state through the p-8Be and α-5Li decay channels populated by the 10B(3He, α)9B(p)8Beg.s. and 10B(3He, α)9B(α)5Lig.s. reactions at E(3He) = 2.3 and 5 MeV, respectively. The excitation energy Ex and the state width Γ have been deduced.

5Lig.s. energy spectrum deduced by the6Li(3He, αp) α reaction

SummaryThe αα bidimensional spectra of the6Li(3He, αp)α reaction atE(3He)=2.5 MeV were analysed. The peak energyE* and the Γ width of the5Lig.s. nucleus were deduced. Each energy spectrum was fitted by an incoherent sum of the contributions coming from the g.s. and the first excited state of the5Li nucleus. A test was performed to verify whether experimental data could be fitted by a single-levelR-matrix calculation.RiassuntoSono stati analizzati gli spettri bidimensionali αα della reazione6Li(3He, αp) α ad energia incidente di 2.5 MeV e sono state misurate l’energia di piccoE* e l’ampiezza Γ dello stato fondamentale del5Li. Ogni spettro energetico è stato trattato con una somma incoerente dei contributi dovuti allo stato fondamentale ed al primo stato eccitato del5Li. Utilizzando la matriceR, è stato eseguito un fit dei dati sperimentali allo scopo di verificare se lo spettro energetico del5Li potesse essere riprodotto solo con l’ausilio di un singolo livello.РезюмеАнализируются двумерные спектры αα из реакции6Li(3He, αp) α приE (3He)=2.5 МэВ. Определяются положение максимальной энергииE* и ширины Γ для основного состояния5Li. Каждый энергетический спектр представляется в виде некогерентной сумму вкладов от основного состояния и первого возбужденного состояния ядер5Li. ИспользуяR-матрицу, предпринимается попытка объяснения экспериментальных данных, если предположить, что энергетический спектр может быть воспроизведен с помощью толяко одного уровня.

Measurement of the 4. 8-MeV /sup 9/B state width by the reaction /sup 10/B(/sup 3/He,. cap alpha. )/sup 9/B(. cap alpha. ) /sup 5/Li at E( /sup 3/He) = 2. 3 and 5. 0 MeV

The analog of the 4.7-MeV state of the /sup 9/Be nucleus has been observed in its mirror /sup 9/B by the reaction /sup 10/B(/sup 3/He, ..cap alpha..)/sup 9/B(..cap alpha..) /sup 5/Li (g.s.) at E( /sup 3/He) = 2.3 and 5.0 MeV. The excitation energy and width of the state have been deduced. The value of 1.5 +- 0.3 MeV found for the width is in line with the value deduced by the reaction /sup 7/Li(/sup 3/He,n) /sup 9/B, but it is larger by a factor of about 4 than the one measured by the proton following the ..beta../sup +/ decay of the /sup 9/C nucleus.

Measurement of the 4.8-MeV 9B state width by the reaction 10B(3He, alpha )9B( alpha ) 5Li at E( 3He

The analog of the 4.7-MeV state of the /sup 9/Be nucleus has been observed in its mirror /sup 9/B by the reaction /sup 10/B(/sup 3/He, ..cap alpha..)/sup 9/B(..cap alpha..) /sup 5/Li (g.s.) at E( /sup 3/He) = 2.3 and 5.0 MeV. The excitation energy and width of the state have been deduced. The value of 1.5 +- 0.3 MeV found for the width is in line with the value deduced by the reaction /sup 7/Li(/sup 3/He,n) /sup 9/B, but it is larger by a factor of about 4 than the one measured by the proton following the ..beta../sup +/ decay of the /sup 9/C nucleus.

The short-lived 8Be level at Ex=11.4 MeV

Measurements of the differential cross section for the 7Li(d, alpha alpha n) reaction have been performed at incident deuteron energy Ed=19.7 MeV. An appropriate kinematical configuration was chosen to observe the population of the second excited 8Be level. The values of (11.3+or-0.2) MeV for the excitation energy and of (3.7+or-0.2) MeV for the width of the above level were found. The influence of the transformation Jacobian on the determination of the two spectroscopic parameters is discussed.

Reaction mechanism and nuclear-rainbow effect in the3He+12C interaction atE(3He)=98 MeV

SummaryNuclear-rainbow effects in elastic and inelastic scattering and transfer reactions by the3He+12C interaction atE(3He)=98 MeV are observed, analyzing the angular distributions of the3He,2H and4He particles. The data are analyzed by a near/far-side formalism using Fullers model. We also observe the different characteristics of the rainbow effects and of the shape of the angular distributions for various reaction mechanisms.

Alpha-proton coincidence spectra from the6Li(3He, ααp) reaction

SummaryThe αp coincidence spectra coming from the6Li(3He, ααp) reaction at 1.6 MeV3He incident energy and at various telescope-detector angles were analysed. Each asymmetric energy spectrum was fitted by an incoherent sum of the two contributions coming from the ground and first excited5Li states. The deduced Γ width values of the5Lig.s. prove to be angle-independent, at least within the limits of the confidence level of the analysis method used and of the experimental errors, and are in line with the one adopted in the literature.

Angle independence of the5Lig.s. Γ width

SummaryWe measured the differential cross-sections for the6Li(3He, ααp) reaction at various detector angles in a kinematical complete way by 7 and 9 MeV energy3He beams. The analysis of the αp bidimensional spectra allowed us to separate the5Lig. s. contributions from the first excited state ones of the same nucleus. The Γ(5Lig. s.) values deduced from both the experiments atE(3He)=7 and 9 MeV do not appear to be dependent on the: i)5Lig. s. emission angle, ii)5Lig. s. decay proton angle when correlated to the various α-particle emission angles.

The energy independence of the 5Ligs Gamma width

The differential cross sections for the 6Li(3He, alpha alpha p) reaction were measured at 1.6, 3.5, 7.0 and 9.0 MeV 3He incident energies. Each 5Li energy spectrum was analysed by an incoherent sum of the contributions coming from the ground and first excited states of the same nucleus. The Gamma values found are in line with the one adopted in the literature and with the ones deduced from the above reaction at E(3He)=2.5 MeV and from the 7Li(p, t)5Li reaction at E(p)=43.7 MeV. No dependence of the 5Ligs Gamma width on the 3He incident energy has been observed.