Alain Goasduff

To understand the break-up fusion reaction dynamics, the forward recoil range distribution (FRRD) measurements of 12C + 165Ho system at the incident projectile energy of ≈ 88 MeV has been performed. The recoil catcher activation technique followed by the off-line gamma ray spectroscopy was implemented. It is observed that the FRRD measurements of the evaporation residues (ERs) populated via xn and pxn channels have a single Guassian peak at large cumulative thickness. This is attributed to complete momentum transfer from the projectile to the target nucleus. However, in case of the FRRD measurements of the ERs populated via αxn, αpxn and 2αxn emitting channels, in addition to peak corresponding to complete momentum transfer, the Gaussian peaks at lower cumulative thicknesses are also observed. This is accredited to the breakup fusion. Moreover, the effect of projectile breakup on complete …

The complete and incomplete fusion cross sections for 6 Li+ 209 Bi were measured via the in-beam γ-ray method around the Coulomb barrier. The cross sections of (deuteron captured) incomplete fusion (ICF) products were re-quantified experimentally for this reaction system. The results reveal that the ICF cross section is equivalent to that of complete fusion (CF) above the Coulomb barrier and dominant near or below the Coulomb barrier. A theoretical calculation based on the Continuum Discretized Coupled Channel (CDCC) method is performed for the aforementioned CF and ICF cross sections, and the result is consistent with the experimental ones. The universal fusion function (UFF) is also compared with the measured CF cross section with different barrier parameters, demonstrating that the CF suppression factor is quite sensitive to the choice of potential, which can reflect both dynamic and static effects of …

In this work, we present a novel approach for improving the energy resolution from particles impinging on the interstrip regions of silicon strip detectors. We employed three double-sided strip detectors from the GRIT array and a triple α-source under laboratory conditions. The results showed that the interstrip resolution depends not only on the impinging side but also on whether it is a P- or an N-interstrip. We obtained the interstrip energy resolution down to 0.4%, and, depending on the scenario, the resolution was enhanced by a factor of 2. We believe that this new rotation method allows for the possibility of applying particle identification methods on interstrip events, which in most cases are dismissed during data recording.

Presently, -ray tracking in germanium segmented detectors is realised by applying two advanced, complex algorithms. While they have already triggered an intensive R &D, they are still subject to further improvements. Running the common code for these core algorithms in both the online/real-time and offline data pipelines posed significant challenges. These were addressed in current production software, but also require continued attention in view of significant on-going paradigm shifts in both hardware and software technology. This review paper gives an overview of the various software components produced so far by the AGATA collaboration. It provides hints of what is foreseen for the next phases of the project up to its full configuration namely with 180 capsules in the array.

The AGATA tracking detector array represents a significant improvement over previous Compton suppressed arrays. The construction of AGATA led to numerous technological breakthroughs in order to meet the requirements and the challenges of building a mobile detector across Europe. This paper focuses on the design and implementation of the data acquisition system responsible of the readout and control of the germanium detectors of AGATA. Our system is highly versatile, capable of instrumenting AGATA and seamlessly adapting it to various configurations with a wide range of ancillary detectors and/or spectrometers. It consists of three main components: an autonomous and independent infrastructure, a dedicated application core ensuring overall consistency, and a high-performance software package providing a fully integrated data flow management including the setting-up, the supervision and the slow …

The successful operation of AGATA requires a complex mechanical support structure for the safe and reliable operation of the detectors. Three mechanical structures were designed for the scientific campaigns at LNL, GSI and GANIL, each accommodating an increasing number of detectors. The present phase of the project, to increase the number of detectors from 60 to 180 (the spectrometer), required a new concept in mechanical support. The detectors also require a suite of associated instrumentation, infrastructures and good system design for their optimum performance. This includes the automatic liquid nitrogen filling system, high and low voltage power supplies, and a series of signal cables and distribution systems. A well-designed electromagnetic compatibility across all the sub-systems is essential. An additional requirement is an easily accessible database that records the status of the wide range of …

The excited states of unstable O 20 were investigated via γ-ray spectroscopy following the O 19 (d, p) O 20 reaction at 8 A MeV. By exploiting the Doppler shift attenuation method, the lifetimes of the 2 2+ and 3 1+ states were firmly established. From the γ-ray branching and E 2/M 1 mixing ratios for transitions deexciting the 2 2+ and 3 1+ states, the B (E 2) and B (M 1) were determined. Various chiral effective field theory Hamiltonians, describing the nuclear properties beyond ground states, along with a standard USDB interaction, were compared with the experimentally obtained data. Such a comparison for a large set of γ-ray transition probabilities with the valence space in medium similarity renormalization group ab initio calculations was performed for the first time in a nucleus far from stability. It was shown that the ab initio approaches using chiral effective field theory forces are challenged by detailed high …

Recent experiments on 12C + 24Mg and preliminary data on 12C + 26Mg show that we observe the hindrance phenomenon in these two systems that are close to the lighter ones relevant for astrophysics. The cross section at the hindrance threshold has a remarkably high value for 12C + 24Mg, while it is closer to an empirical systematics for 12C + 26Mg. The lowest-energy fusion cross sections of 12C + 24Mg are consistent with simple one-dimensional barrier penetration calculations, i.e. the coupling strengths seem to be strongly damped far below the barrier. Measurements at slightly lower energies would be essential to discriminate between different models and to allow reliably extrapolating to the lighter systems producing energy and elemental synthesis in stellar environments.

The level scheme of Mo 91 has been studied using the GALILEO γ-ray spectrometer at Laboratori Nazionali di Legnaro, INFN. Five transitions together with four levels are identified for the first time by the γ− γ coincidence measurement, considerably enriching the negative band in Mo 91. The discrepancy in the previous parity assignments for the states higher than 3807.5 keV has been clarified with the help of new experimental results. A shell-model calculation employing the JUN45 interaction is performed in order to get a further understanding of the level structure of Mo 91. Being close to N= 50 shell closure, the weak-coupling approximation between the valence g 9/2 neutron-hole with the even-even core (Mo 92) is discussed in Mo 91.

The design study of the AGATA array began with the development of the AGATA simulation code using GEANT4. The latter played a key part in the final design of the array and provided a cost effective solution for the early development of the tracking algorithm. The code has since been maintained and developed by the collaboration to provide more realistic simulations, with reaction chambers, ancillary detectors and surrounding mechanical structures completing the entire setup.

The structure of 74 Se at low energy was investigated via spectroscopy of internal conversion electrons at the INFN Legnaro National Laboratories (LNL). A set of internal K-conversion coefficients and monopole transition strengths was measured. A large ρ 2 (E 0; 2 2+→ 2 1+)⋅ 10 3= 210 (130) value was deduced. This result, in addition to a low upper limit for the 0 3+→ 0 2+ electron transition, casts in doubt a simple interpretation of the 74 Se low-lying structure, in particular the recently proposed spherical, vibrational character. New microscopic beyond-mean-field calculations generally agree with the experimental results and are capable of producing a large ρ 2 (E 0; 2 2+→ 2 1+) value, even if still a factor≈ 7 smaller than the experiment. Triaxiality and a complex shape-coexistence and mixing scenario seem responsible for this unexpected experimental result.

Abstract The Monte-Carlo simulated response for γ-ray detection of the FAst TIMing Array (FATIMA) for exploitation within the DEcay SPECtroscopy (DESPEC) experimental system at the FAIR Phase-0 facility at Darmstadt, Germany is presented. In this configuration, FATIMA consisted of 36 LaBr 3 (Ce) detectors surrounding the AIDA, position-sensitive charged-particle active stopper. The decay of the I π= 8+ isomer-fed decay cascade in 96 Pd, measured in the first DESPEC experiment at the FAIR-0 facility was used to validate the simulations. The experimental data yielded in-situ full-energy peak efficiency values for FATIMA of 11.2 (11)%, 6.8 (7)%, 3.8 (4)% and 2.1 (4)% at 106, 325, 684 and 1415 keV respectively, consistent with the values derived from the simulated response.

Abstract The Advanced GAmma Tracking Array (AGATA) has been installed at Laboratori Nazionali di Legnaro (LNL), Italy. In this installation, AGATA will consist, at the beginning, of 13 AGATA triple clusters (ATCs) with an angular coverage of 1 π, and progressively the number of ATCs will increase up to a 2 π angular coverage. This setup will exploit both stable and radioactive ion beams delivered by the Tandem–PIAVE-ALPI accelerator complex and the SPES facility. The new implementation of AGATA at LNL will be used in two different configurations, firstly one coupled to the PRISMA large-acceptance magnetic spectrometer and lately a second one at Zero Degrees, along the beam line. These two configurations will allow us to cover a broad physics program, using different reaction mechanisms, such as Coulomb excitation, fusion-evaporation, transfer and fission at energies close to the Coulomb barrier …

Background: The existence of fusion hindrance in the light heavy-ion systems of astrophysical interest is not well established, so investigating slightly heavier cases may allow a reliable extrapolation towards the lighter ones. The recent observation of a very high hindrance threshold in C 12+ Mg 24 (with a positive Q value for fusion) at σ fus≃ 0.75 mb, misses a valid interpretation within current theoretical models.Purpose: Our aim has been to search evidence for fusion hindrances in the nearby system C 12+ Mg 26 also having Q fus> 0, and to obtain information on the underlying physics from a comparison of the two cases and from coupled-channels calculations.Methods: The experiment was performed in inverse kinematics using the Mg 26 beam from the XTU Tandem accelerator of Laboratori Nazionali di Legnaro (LNL). The targets were thin C 12 evaporations isotopically enriched to 99.9%. The fusion …

The discrepancy between shell-model calculations and intermediate-energy Coulomb excitation measurements in 46 Ar still stands as an unsolved puzzle in understanding the N= 28 shell evolution. This phenomenon has significant relevance considering the remarkable achievements of the shell model and the SDPF-U interaction in the region which is able to predict the fading of the N= 28 shell gap in neutron-rich 44 S. Recent measurements narrowed down this discrepancy to an overestimation of the proton amplitude to the quadrupole transition matrix element. The current work aims to propose a different perspective on the puzzle, by studying a direct proton-transfer reaction on 46 Ar as a means to directly probe the proton wavefunction of the ground state this isotope. By measuring the amount of l= 0 transfer to the ground state (1/2+) of 47 K with respect to the l= 2 to the first excited state (3/2+), we aim to gain …

This work aims at presenting an alternative approach to the long standing problem of the B (E2) values in Sn isotopes in the vicinity of the N= Z double-magic nucleus 100 Sn, until now predominantly measured with relativistic and intermediate-energy Coulomb excitation reactions. The direct measurement of the lifetime of low-lying excited states in odd-even Sn isotopes provides a new and precise guidance for the theoretical description of the nuclear structure in this region. Lifetime measurements have been performed in 105 Sn for the first time with the coincidence Recoil Distance Doppler Shift technique. The lifetime results for the 7/2 1+ first excited state and the 11/2 1+ state, 2+(104 Sn)⊗ ν 1 g 7/2 multiplet member, are discussed in comparison with state-of-the-art shell model and mean field calculations, highlighting the crucial contribution of proton excitation across the core of 100 Sn. The reduced transition …

We measured multinucleon transfer reactions for the Pb 206+ Sn 118 system at E lab= 1200 MeV by employing the large solid angle magnetic spectrometer PRISMA. Differential and total cross sections and Q-value distributions have been obtained for a variety of neutron and proton pick-up and stripping channels. The Q-value distributions show how the quasielastic and deep inelastic processes depend on the mass and charge of the transfer products. The corresponding cross sections have been compared with calculations performed with the grazing code. An overall good agreement is found for most of the few nucleon transfer channels. The underestimation of the data for channels involving a large number of transferred nucleons indicates that more complicated processes populate the given isotopes.

The AGATA collaboration has a long-standing leadership in the development of front-end electronics for high resolution -ray spectroscopy using large volume high purity germanium detectors. For two decades, the AGATA collaboration has been developing state-of-the-art digital electronics processing with high resolution sampling ADC, high-speed signal transfer and fast readout to a high throughput computing (HTC) farm for on-line pulse shape analysis. The collaboration is presently addressing the next challenge of equipping a 4 array with more than 6000 channels in high resolution mode, generating approximately 10 MHz of total trigger requests, coupled to a large variety of complementary instruments. A next generation of front-end electronics, presently under design, is based on industrial products (System on Module FPGA’s), has higher integration and lower power consumption. In this contribution, the …

In the present work the fusion cross section of the 12 C+ 24 Mg system has been measured down to energies far below the coulomb barrier around 4μb. This system is slightly heavier than those of astrophysical interest, like 12 C+ 12 C and 16 O+ 16 O. The data points highlight the presence of hindrance in 12 C+ 24 Mg because the excitation function is over-estimated by standard Coupled-Channels calculations, and a clear maximum of the S factor has been observed. The cross section at hindrance threshold is found to be remarkably large (σ≈ 0.75 mb). The S-factor maximum is nicely fitted using both an empirical interpolation in the spirit of the adiabatic model, and the hindrance parametrisation. The data far below the barrier may suggest that the coupling strengths gradually decrease and vanish, so that the excitation function seems to be well reproduced by a simple one-dimensional tunnelling through the …

NUCLEAR REACTIONS 3 He (32 S, α) 31 S, E= 128 MeV; measured reaction products, Eγ, Iγ; deduced γ-ray energies, levels, T 1/2, resonances. Comparison with the shell-model code NuShellX calculations. Modern Markov chain Monte Carlo-based Bayesian statistical techniques. The Doppler Shift Lifetimes (DSL2) facility at the TRIUMF Isotope Separator and Accelerator (ISAC-II) facility.