Search

During the last years, the ECOS working group has been considering the construction of a new high-intensity accelerator of stable ion beams for the next Long-Range Plan of the nuclear physics community in Europe. The new facility (LINCE) will be a multi-user facility dedicated to ECOS science: fundamental physics, astrophysics, nuclear structure and reaction dynamics. In this paper, we summarize preliminary design studies of the low-energy part of this facility based on the use of a multi-ion superconducting linac. [ABSTRACT FROM AUTHOR]

Recent results on the reaction dynamics induced by light radioactive ion beams at Coulomb barrier energies are reviewed. As a general feature, the exotic structure and the weak binding energy of most of these projectiles enhance the reaction probability rather than the fusion cross section, as originally expected. The quest has now moved toward understanding which direct reaction mechanism originates the enhancement. Experimental data showed that n-halo and p-halo nuclei are characterized by a different behavior. Transfer processes enhance the reaction probability for n-halo nuclei, such as 6;8He, while for p-halo nuclei, such as 8B, the breakup channel seems to be mainly responsible for the enhancement. [ABSTRACT FROM AUTHOR]

Dipole polarizability, one of the fundamental properties of a nucleus, studied in elastic scattering experiments has been reviewed here. For strongly bound nuclei the effect of dipole polarizability is usually negligible. However, for weakly bound nuclei, where the dipole strength extends to low excitation energies, it does play a major role. This effect has already been examined in the scattering of the lightest weakly-bound stable nuclei, viz., d, ³He, and 7Li. In the present work we have studied it for the weakly bound unstable borromean nucleus, 6He, using the elastic scattering data available at energies around the Coulomb barrier with a 208Pb target. [ABSTRACT FROM AUTHOR]

Experimental reaction cross sections for 6He and 4He projectiles are reduced and are shown to follow well-defined trajectories that can be characterized by respective Wong-type curves. The strong enhancement observed for the 6He data is interpreted as caused by two separate halo effects: a size effect, which affects the whole energy region, and a dynamic effect, important only near and below the barrier. Evidence for a core-halo decoupling is presented for the 6He+64Zn system, which further supports the hypothesis that the decoupling is a characteristic feature of true halo systems. [ABSTRACT FROM AUTHOR]

The angular distribution for 11Be + 120Sn quasielastic scattering at Elab = 32 MeV was measured at REX-ISOLDE, CERN. The interpretation of the data in terms of coupled-channel calculations suggests a strong coupling with the p -states lying in the continuum. [ABSTRACT FROM AUTHOR]

We investigated the performance of synthetic high purity monocrystalline diamond radiation detectors fabricated with TiW, Cr/Au and a novel metallization technique utilising diamond-like carbon tunnelling junction and PtJAu as electrical contacts. The investigation was carried out under irradiation with 60Co γ-rays, 90Sr electrons and 241Am α-particles. The experimental results with respect to I-V dark current levels, irradiation photocurrent, signal-to-noise ratio and time response have been compared and discussed. Results show an ohmic behaviour of the DLC/Pt/Au contact, a charge collection efficiency of 100% at an applied electric field of 0.377 V/μm for all electrical contacts (under 90Sr electrons irradiation) at a correspondent dark current value of less than a picoAmpere. The single crystal CVD DLC/Pt/Au diamond radiation detector reported here shows spectroscopic energy resolution of 1.1% at an applied voltage of +450 volts (0.9 V/μm) under 5.5 MeV alpha particle irradiation. No 'memory' or 'pumping' effect was observed for the DLC/Pt/Au contact at positive bias; the signal was also stable (fluctuations below 0.5%) and reproducible under 60Co~ irradiation, with a signal-to-noise ratio > 10000:1 and a linearity in the, dose rate response. [ABSTRACT FROM AUTHOR]

Abstract: Identification of the interstrip effects using digital pulse shape analysis is for the first time reported. This study is performed on a highly segmented double-sided silicon detector used in a nuclear reaction in which a large range of particles at different energies are produced. The output current pulse of the preamplifier is employed as observable. The interstrip effects diminish the capability of particle identification at energies below 5MeV, especially on the injection side of the detector. [Copyright &y& Elsevier]

Abstract: We achieved particle separation of proton, deuteron and triton at energies ranging between 2 and 10MeV by the processing of digitized signals obtained with a double-sided, pitch strip, thick neutron transmutation doped (nTD) silicon detector. We produced the light charged particles in a nuclear reaction induced by a 34-MeV beam of 7Li impinging on a 12C target. We analyzed offline the signals with the goal of a simplified, possibly analog, front-end electronics in mind for the processing of the 15,000 channels of the new state-of-the-art detectors for low energy nuclear physics like GASPARD, HYDE and TRACE which should make use of such methods. At the optimum bias, using the current amplitude versus charge correlation, we obtain a separation of 3FWHM between protons and deuteron, and 2FWHM between deuteron and triton at energies as low as 2MeV; with a square bipolar filter, suited for simple implementation, we separate them by 4.3 and 2.7FWHM respectively at 5MeV. [Copyright &y& Elsevier]

Abstract: Proton–deuteron identification at energies between 2.5MeV and 6MeV has been studied as a function of the detector working bias. Digital pulse shape analysis (DPSA) has been used to perform the separation from the two mono-energetic beams. The technique makes use of the current signal delivered by a neutron transmutation doped (NTD) silicon detector, which was setup for low-field injection. It is shown that identification of the H isotopes is better when the detector working bias is close to the depletion voltage rather than over-depletion. The presence of high frequency noise diminished the possibility of identification, however, the use of a simple triangular smoothing algorithm counteracted this. [Copyright &y& Elsevier]

Abstract: A high speed, low power and programmable readout front-end system is presented for silicon detectors to be used in nuclear physics applications. The architecture consists of a folded cascode charge sensitive amplifier, a pole-zero cancellation circuit to eliminate undershoots and a shaper circuit with Gm-C topology. All building blocks include a regulated cascode technique based gain enhancement. Experimental results show that the whole front-end system can be programmed for peaking times of 100ns, 200ns and 400ns maintaining the amplitude of the output voltage. Programmability is achieved by switching different resistors for all poles and zeros. The system has been designed in a 130nm CMOS technology and powered from a 1.2V supply. The output pulse has peak amplitude of 200mV for an input energy of 5MeV from the detector. A power consumption low noise tradeoff will be considered. [Copyright &y& Elsevier]

The elastic scattering and inclusive a-particle yield for the 6He + 206Pb system at an incident energy of 18 MeV, just below the nominal Coulomb barrier, have been measured. The a-particle yield at forward angles is also reported. The data are analyzed by means of continuum-discretized coupled-channels, distorted wave Bom approximation, and coupled reaction channels calculations. Couplings to the one-neutron- and two-neutron-transfer reactions are found to be able to account for most of the absorption in the entrance channel [ABSTRACT FROM AUTHOR]

Since 1970''s when double-folding model, based on M3Y interaction, had to be renormalized to fit the elastic scattering of weakly bound 6,7Li and 9Be nuclei, we learned that preconceptions based on the highly successful experience of the optical model on stable nuclei could not be simply extrapolated to the scattering of exotic nuclei. Recently, we have shown some evidences of long range mechanisms in 6He induced reactions that lead to the loss of flux in the elastic channel at kinematic conditions that suggest the nuclei are well beyond the strong absorption radius [O. R. Kakuee, M. A. G. Alvarez, M. V. Andrés, S. Cherubini, T. Davinson, A. Di Pietro, W. Galster, J. Gómez-Camacho, A. M. Laird, M. Lamehi-Rachti, I. Martel, A. M. Moro, J. Rahighi, A. M. Sánchez-Benitez, A. C. Shotter, W. B. Smith, J. Vervier, P. J. Woods. Nucl. Phys. A 765, (2006) 294]. Even so, the use of nuclear reactions as an spectroscopic tool to investigate the nuclear structure of weakly bound nuclei requires a deep understanding of the reactions induced by these nuclei. Therefore, precise experimental measurements of the elastic scattering of exotic nuclei on a variety of targets, as well as the measurements of the main reaction channels are required in order to converge experimentally and theoretically to this understanding. With this aim a campaign of experiments involving different institutions and collaborations is being carefully established and going ahead at several radioactive ion beam (RIB) facilities: ISOLDE (CERN), CRC (Be), GSI (Ge) and TRIUMPH (Ca). The main idea is to measure the scattering of He, Li, and Be isotopes, and perform an intensive theoretical treatment, besides promoting some necessary instrumental development. In particular we participate in the low energy branch of the FAIR project where we take part in the tracking studies and developments. [Copyright &y& Elsevier]