Search

We describe the search of the Efimov state in 12C performed by analysing a large set of 3-α particles coincidence data measured at the LNS laboratories with the CHIMERA detector. The data are compatible with the presence of an Efimov state at the excitation energy of 7.485 MeV, with an excitation probability smaller than 0.3% of the population probability of the Hoyle state. The Efimov state gamma decay probability should be around 30%, much larger than the one of the Hoyle state. The population of this level is compatible with the Suda limit for the 3-α reaction rate in stars because its population should be possible only through direct 3-α reaction. More investigations improving the detector angular resolution are needed to confirm these preliminary observations. [ABSTRACT FROM AUTHOR]

The accurate calculations of neutron-induced reaction cross sections are relevant for many nuclear applications. The photon strength functions and nuclear level densities are essential inputs for such calculations. These quantities for 235U are studied using the measurement of the gamma de-excitation cascades in radiative capture on 234U with the Total Absorption Calorimeter at n_TOF at CERN. This segmented 4π gamma calorimeter is designed to detect gamma rays emitted from the nucleus with high efficiency. This experiment provides information on gamma multiplicity and gamma spectra that can be compared with numerical simulations. The code DICEBOXC is used to simulate the gamma cascades while GEANT4 is used for the simulation of the interaction of these gammas with the TAC materials. Available models and their parameters are being tested using the present data. Some preliminary results of this ongoing study are presented and discussed. [ABSTRACT FROM AUTHOR]

The study of the dipole response in atomic nuclei is among the main ELI-NP goals. One of the advantages of ELI-NP is the possibility to use polarized gamma rays, which allow to separate unambiguously the electric and magnetic strength. The ELI-NP facility will provide detailed strength distributions (fine structure), gamma-decay branches, spin and parity of the nuclear dipole response with an important impact both on nuclear structure and astrophysical studies. The theoretical description of the nuclear response requires advanced many body techniques able to go beyond the so called mean-field approximation. In this paper, we will describe a widely employed approach for the microscopic description of the nuclear response, namely the Random Phase Approximation. After that, the need to go beyond this approach will be discussed and an extension of this method will be introduced. An application of these methods will be presented to analyze the dipole strength in 48Ca. Results are illustrated with two Skyrme parametrizations, SGII and SLy4 and compared with the experimental data recently measured. The results obtained with the SGII interaction are particularly satisfactory. In this case, the low–lying strength below the neutron threshold is extremely well reproduced and the giant dipole resonance is described in a very satisfactory way especially in its spreading and fragmentation. Spreading and fragmentation are produced in a natural way within such a theoretical model by the coupling of one particle–one hole and two particle–two hole configurations. [ABSTRACT FROM AUTHOR]

The determination of nuclear level densities and radiative strength functions is one of the most important tasks in low-energy nuclear physics. Accurate experimental values of these parameters are critical for the study of the fundamental properties of nuclear structure. The step-like structure in the dependence of the level densities ρ on the excitation energy of nuclei Eex is observed in the two-step gamma cascade measurements for nuclei in the 28 ≥ A ≥ 200 mass region. This characteristic structure can be explained only if a co-existence of quasi-particles and phonons, as well as their interaction in a nucleus, are taken into account in the process of gamma-decay. Here we present a new improvement to the Dubna practical model for the determination of nuclear level densities and radiative strength functions. The new practical model guarantees a good description of the available intensities of the two step gamma cascades, comparable to the experimental data accuracy. [ABSTRACT FROM AUTHOR]

We present a new method for the measurement of very small Γγ partial width that is important for the synthesis of elements in astrophysics. The method is based on the simultaneous detection of scattered beam, residual nucleus and decay γ rays. This method is optimized for the use of the CHIMERA detector at LNS. Experimental details are described. [ABSTRACT FROM AUTHOR]

Neutron capture on unstable nuclei is important in understanding abundances in r-process nucleosynthesis. Previously, the non-elastic breakup of the deuteron in the (d,p) reaction has been shown to provide a neutron that can be captured by the nucleus and the gamma-ray decay of the subsequent compound nucleus can be modelled to predict the gamma-ray decay of the compound nucleus in the (n,γ) reaction. Preliminary results from the 95Mo(d,pγ) reaction in normal kinematics support the (d,pγ) reaction as a valid surrogate for neutron capture. The techniques to measure the (d,pγ) reaction in inverse kinematics have been developed. [ABSTRACT FROM AUTHOR]