G. Inglima

The heavy-ion magnetic spectrometer PRISMA

Abstract PRISMA is a magnetic spectrometer for heavy ions under construction at Legnaro, with very large solid angle (80 msr), wide momentum acceptance (± 10%) and good mass resolution via TOF measurement; it will be dedicated to the study of nuclear dynamics and nuclear structure with stable and exotic ion beams. This is a review of its main features and of the present status of the project.

Fluctuations in the excitation functions of dissipative heavy ion collisions

Abstract Excitation functions have been measured for different charge products of the 28 Si + 64 Ni reaction in the range 120–126.75 MeV in 250 keV steps (lab). Dissipative cross sections have shown fluctuations with coherence energies in the range 200–800 keV (CM). The formation of a dinuclear intermediate system is suggested.

Quartet states in 20 Ne

T rans f e r r eac t i ons of a, SBe a n d 12C c lus ters on N = Z e v e n e v e n t a rge t s (1) h a v e g i v e n e x p e r i m e n t a l s u p p o r t to t h e q u a r t e t model , f i rs t ly p roposed b y DA~OS a n d GILLET (2). I n t h i s work we h a v e inves t iga t ed , b y m e a n s of t he l~F(p, a)x60 reac t ion , t h e poss ible p resence of q u a r t e t s t a t e s in 2~ co r r e spond ing to exc i t a t i ons f r o m the (0p) to t h e (0d, ls) or (0], lp ) shells. E x c i t a t i o n func t i ons a n d a n g u l a r d i s t r i b u t i o n s r e l a t ive to t he t r a n s i t i o n s to t h e lowest levels in l~0(a0, ~ , a~, ~2, as) h a v e b e e n m e a s u r e d in t h e ene rgy r a n g e 0 . 7 0 < E r < 2 . 6 8 M e V , i .e . in t h e 2~ e x c i t a t i o n region E ~ = ( 1 3 . 5 -15.4) MeV, w h e r e t he b a n d h e a d of t h e 1211[ q u a r t e t conf igura t ion is p r e d i c t e d (3). T h e bas ic idea of t h i s work , t o g e t h e r w i t h t h e e x p e r i m e n t a l se t -up a n d t he f i rs t resul ts , h a s b e e n p r e s e n t e d e l sewhere (a). T he J ~ va lues of t h e i n t e r m e d i a t e s t a t e s

Neutron and proton transfer in 32,36S+ 58,64Ni around the Coulomb barrier

Abstract Quasi-elastic transfer cross sections have been measured for the systems 32,36 S+ 58,64 Ni at three energies around the Coulomb barrier. Q -value distributions have been extracted for each of the neutron and charged particle transfer channels. The influence of the transfer channels on the sub-barrier fusion cross section is discussed, and the importance of the proton stripping in 32 S + 64 Ni is pointed out.

Prompt dipole radiation in fusion reactions

Abstract The prompt γ-ray emission is investigated in the 16 A MeV energy region by means of the 36,40Ar + 96,92Zr fusion reactions leading to a compound nucleus in the vicinity of 132Ce. The dynamical nature of this radiation is confirmed. We show that the prompt γ radiation has an angular distribution pattern consistent with a dipole oscillation along the symmetry axis of the dinuclear system. The data are compared with calculations based on a collective bremsstrahlung analysis of the reaction dynamics.

Statistical multistep compound emission in the /sup 27/Al(/sup 3/He,p)/sup 29/Si reaction

Excitation functions and angular distributions of protons emitted from the reaction /sup 27/Al(/sup 3/He,p)/sup 28/Si have been measured in the energy range from 9 to 14 MeV. Some of the excitation functions show the presence of fluctuations that can be attributed to the statistical multistep compound emission. This effect explains also the shape and absolute value of the emitted proton spectrum measured at 13 MeV incident /sup 3/He beam. This comparison yields the value of the strength of the residual two-body interaction.

The spectral-density method in the analysis of fluctuations in the multistep compound emission

SummaryThe evaluation of coherence energies in the excitation function of reactions proceeding through a multistep compound emission mechanism is examined on the basis of the spectral-density method. This kind of analysis is particularly useful for the extraction of coherence energies when various widths are simultaneously present in the experimental data. The results of the spectral-density method are compared with those from other procedures. The problem of trend elimination is also examined.RiassuntoSi è applicato il metodo della densità spettrale alla determinazione di energie di coerenza in funzioni di eccitazione di reazioni che hanno luogo con un meccanismo composto a molti passi. Questo tipo di analisi è particolarmente utile quando piú di una larghezza di coerenza è presente contemporaneamente nei dati sperimentali. I risultati di questa analisi sono confrontati con quelli di altri metodi. È preso in esame anche il problema dell’eliminazione della tendenza dei dati.

High-energy γ-rays measured in coincidence with α-particles in the reaction 19F + 12C at Elab = 121.7 MeV

The yield of γ-rays emitted in the dissipative reaction 19F + 12C, at Elab = 121.7 MeV has been measured in coincidence with α-particles emitted at θlab = 10°. Comparison with preliminary statistical model calculations shows that assuming only compound nucleaus formation is not sufficient to reproduce the data. Other mechanisms have to be included before information on reaction dynamics can be extracted and definitive conclusions can be drawn.

Pre-equilibrium γ-ray emission in dissipative heavy-ion collisions

Abstractγ-rays are measured in coincidence with the dissipative complex fragments from the35Cl +64Ni reaction at 7.7 A MeV. Theoretical γ-ray coincidence spectra are determined through a fitting procedure using the contribution of the excited fragment statistical γ-decay calculated by means of the CASCADE code. Whereas the expected statistical spectra fit very well the data in the energy regionEν=2 to 8 MeV, above this energy another emission mechanism in addition to the statistical decay has to be considered in order to reproduce the experimental spectra. Simulations based on the Vlasov equation suggest that this emission could come from the decay of dipole strength excited in the intermediate dinuclear system.

Highly excited “nuclear molecules”: A way to explain the fluctuations in DBHIC excitation functions. Study of the28Si +28Si colliding system at 5.3 MeV ·A

The properties of the strong fluctuations observed in the excitation functions of Dissipative Binary Heavy Ion Collisions (DBHIC) have been studied for the system28Si+28Si in the energy range 150 MeV ≤Elab ≤ 156 MeV with 150 keV step laboratory incident energy, by angular distributions and excitation functions measurements. Experimental results are compared to the the recently developed Partially Overlapping Molecular Level Model (POMLM). The parameters of the model have been determined with reasonable accuracy by describing all the quantities characterizing the fluctuations in the excitation functions i.e.: Average Angular Distributions, Energy Autocorrelation Functions, Variances, Angular Correlation Coefficients. The results of the analysis strongly support the idea of a process proceeding through the formation of an highly excited “nuclear molecule”. Experimental data collected at the most forward angles show the effects of strong excitation of a few final channels.