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CLARA is an array of 25 Clover (EUROBALL type) Ge detectors, placed at the target position of the large acceptance magnetic spectrometer PRISMA. Due to the granularity of the CLARA Ge array (100 crystals), the photopeak efficiency (≈3%) and the PRISMA large acceptance (≈80 msr, and 20% Δp/p), the setup is an excellent tool to investigate the structure of neutron-rich nuclei, populated in multinucleon transfer reactions and deep inelastic collisions with stable beams. Since March 2004 the setup is fully operational, and since then several experiments have been performed, with beams delivered by the LNL XTU-Tandem and the ALPI linac. In this contribution the preliminary outcome of the first experiments is shown.

A study of the angular distribution of the high energy γ rays emitted by the giant dipole resonance (GDR) in the compound nuclei 165–167Er, 175,176Hf and 109,110Sn at a variety of excitation energies (E∗= 50–90 MeV)is presented. A comparison of the data with model predictions at the equilibrium deformation and in the adiabatic limit is discussed. In general, the adiabatic calculations give a fair account of the data exception made for Er at very low spin and Sn at very high spin.

The deuteron energy spectrum and the angular distributions to the ground and 2.13 and 3.31 MeV excited states of34S have been measured for the reaction35Cl(n, d)34S. These results and the available experimental data of stripping and pick-up reactions on S and Cl isotopes are analysed using the DWBA and spectroscopic factors for several transitions are obtained. These factors are then compared with those predicted on the basis of the shell and collective rotational models. A good agreement is found with the predictions of the shell model in which phenomenological two-body matrix elements are used. Sono stati misurati nella reazione35Cl(n, d)34S lo spettro di energia e la distribuzione angolare dei deutoni per le transizioni allo stato fondamentale e agli stati eccitati a 2.13 e 3.31 MeV. Questi risultati e i dati sperimentali disponibili sulle reazioni di stripping e di pick-up sugli isotopi dello zolfo e del cloro sono stati analizzati usando la DWBA e sono stati ottenuti i fattori spettroscopici per alcune transizioni. Tali fattori sono stati poi confrontati con quelli previsti sulla base del modello a shell e del modello rotazionale collettivo. Si è trovato un buon accordo con le previsioni del modello a shell nel quale vengano usati elementi di matrice fenomenologici per l’interazione residua a due corpi. Для реакции35Cl(n, d)34S были иэмерены знергетический дейт-ронный спектр и угловые распределения для основного и воэбужденных 2.13 и 3.31 МзВ состояний. Аналиэируются зти реэультаты и имеюшиеся зкспериментальные данные для реакций стриппинга и подхвата на иэотопах 8 и С1, испольэуя DWВА, и вычисляются спектроскопические факторы для некоторых переходов. Затем зти факторы сравниваются с факторами, предскаэанными на основе оболо-чечной и коллективно-ротац ионной моделей. Обнаружено хорощее согласие с предскаэаниями оболочечной модели, в которой испольэуются феноменологические двух-частичные матричные злементы.

The response of a HPGe (82%) detector with a BGO anti-Compton shield has been studied for the 15.1 MeV γ-rays produced by the reaction D(11B,nγ)12C and for the 6.13 MeV γ-rays produced by a 238Pu13C source.

Measurements on proton energy spectra from n, p reactions on Mg, Al, Si and S show the existence of well defined peaks even at excitation energy values where the excitation levels of the residual nucleus are very dense. Comparing our results with some proton spectra from d, p reactions a similarity is found in the position of these peaks on the residual excitation energy scale. By means of this comparison it is possible to establish that the n, p reactions go through a mechanism of the type of surface effect, where the residual nucleus is left preferably in some excited states probably corresponding to single particle excitation. Le misure di spettri di energia di protoni dalla reazione n, p su Mg, Al, Si e S qui presentate mostrano l’esistenza di picchi ben definiti in questi spettri, anche in corrispondenza a valori dell’energia di eccitazione del nucleo residuo dove i livelli eccitati di questo nucleo sono molto fitti. Confrontando i nostri risultati con alcuni spettri di protoni emessi da reazioni d, p, si trova che i picchi esistenti in ambedue queste reazioni si trovano agli stessi valori dell’energia di eccitazione. Questo confronto permette di concludere che le reazioni n, p qui studiate procedono attraverso un meccanismo del tipo ad interazione di superficie, dove il nucleo residuo rimane preferibilmente in stati eccitati che corrispondono a livelli di eccitazione di particella singola.

Energy spectra of protons emitted in (n, p) reactions with 14 MeV neutrons on 13 nuclides from31P to103Rh are presented. The presence of both evaporation and direct mechanisms is put in evidence. By comparing the forward with backward spectra an evaluation of direct effect cross-section is given. Sono presentati gli spettri di energia dei protoni emessi da 13 nuclei compresi tra il31P e il103Rh. Viene mostrata 1’esistenza dei due meccanismi di reazione: l’evaporazione statistica e l’effetto diretto. Confrontando la forma degli spettri dei protoni emessi in avanti con quelli emessi all’indietro si ottiene una valutazione della sezione d’urto dell’effetto diretto.

This work describes a spectrometer for protons of energy between 2 and 14 MeV. This spectrometer is particularly suitable for the study of protons emitted by nuclei bombarded with 14 MeV neutrons. The background of this instrument is particularly low. The resolution of the instrument is discussed.

Accuracy limits of the time of occurrence of an event detected by a scintillation counter are investigated. Two methods « non linear » and « linear » for extracting time information from the output current pulse of the photomultiplier are compared taking into account statistics of photoelectron emission, transit time and multiplication spread in the phototube and finite width of the response of the phototube to one photoelectron. Resolution obtained by the « non linear » method is better, but linear method dispenses from an amplitude selection of pulses.

Energy spectra of the deuterons from the (n, d) reaction on the elements27Al,40Ca,55Mn,63Cu and103Rh are presented. Deuteron peaks corresponding to the fundamental level as well as to some excited levels of residual nuclei are brought into evidence. In Mn and Rh, the existence of gross-structure is shown.

In this paper measurements are presented on the energy distribution of protons emitted in n, p reactions on Al and Ni in the natural isotopic mixture. These measurements have been taken with neutrons of energy of 17.5 and 13.4 MeV, to the purpose of studying how the proton energy distribution varies with the incoming neutron energy, in order to establish which process is responsible for the n, p reaction. The results give evidence to the fact that the statistical evaporation theory is insuitable for explaining the proton spectra obtained, and that the spectrum shape does not depend on the residual nucleus excitation energy but seems more determined by the energy of emitted protons.