The observed pattern of the population and decay of the superdeformed band of 152 Dy is related to the large splitting of the giant dipole resonance based on the superdeformed minimum as well as to the low level density associated with it, and to the sudden onset of static pairing correlations taking place at the rotational frequency hco ~ 0.3 MeV. A new method for spectroscopic studies of superdeformed nuclei is suggested.PACS numbers: 21.10. Re, 23.20.Ck, 27.70.+q The recent discovery 1 of a superdeformed band in 152 Dy constitutes a major breakthrough in the study of nuclei at high spin, and confirms theoretical predictions. 2 " 5 However, the finding that the observed discrete band is populated with 0.2% probability at spin 7=60 h, close to the angular momentum limit which nuclei can accommodate, implies the existence of a new process able to cool the compound nucleus an order of magnitude faster than previously observed. Furthermore, the sudden termination of the superdeformed band at I = 24 ft requires a mechanism that within a narrow range of 2-4 units of h can change the tunneling probability between the superdeformed and normal minima by orders of magnitude. In the present paper, a simple model for these phenomena is proposed.The feeding pattern of the superdeformed yrast band is intimately related to the competition between statistical dipole transitions that cool the nucleus without much changing its angular momentum and the collective rotational transitions that take place at constant temperature. The strong population of the superdeformed band then suggests an unusually enhanced E 1 transition rate, more so because the collective El transition probabilities observed 6 are a few times larger than those found in normal deformed rotational bands. This implies that the E 1 cooling leading to the superdeformed yrast band must be enhanced by more than an order of magnitude above standard cooling rates.The integrated £1 transition probability T{E\\Ui) associated with a state at energy [/,-above yrast can be calculated in terms of the strength function /GDR of the gicr Ixl Q_ CO -z. o h-NS
a b s t r a c tThe FIRST (Fragmentation of Ions Relevant for Space and Therapy) experiment at the SIS accelerator of GSI laboratory in Darmstadt has been designed for the measurement of ion fragmentation crosssections at different angles and energies between 100 and 1000 MeV/nucleon. Nuclear fragmentation processes are relevant in several fields of basic research and applied physics and are of particular interest for tumor therapy and for space radiation protection applications.The start of the scientific program of the FIRST experiment was on summer 2011 and was focused on the measurement of 400 MeV/nucleon 12 C beam fragmentation on thin (8 mm) graphite target. The detector is partly based on an already existing setup made of a dipole magnet (ALADiN), a time projection chamber (TP-MUSIC IV), a neutron detector (LAND) and a time of flight scintillator system (TOFWALL). This pre-existing setup has been integrated with newly designed detectors in the Interaction Region, around the carbon target placed in a sample changer. The new detectors are a
Hadrontherapy treatments use charged particles (e.g. protons and carbon ions) to treat tumors. During a therapeutic treatment with carbon ions, the beam undergoes nuclear fragmentation processes giving rise to significant yields of secondary charged particles. An accurate prediction of these production rates is necessary to estimate precisely the dose deposited into the tumours and the surrounding healthy tissues. Nowadays, a limited set of double differential carbon fragmentation cross-section is available. Experimental data are necessary to benchmark Monte Carlo simulations for their use in hadrontherapy. The purpose of the FIRST experiment is to study nuclear fragmentation processes of ions with kinetic energy in the range from 100 to 1000 MeV/u. Tracks are reconstructed using information from a pixel silicon detector based on the CMOS technology. The performances achieved using this device for hadrontherapy purpose are discussed. For each reconstruction step (clustering, tracking and vertexing), different methods are implemented. The algorithm performances and the accuracy on reconstructed observables are evaluated on the basis of simulated and experimental data
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