Effective nucleon mass and the nuclear caloric curve

Assuming a schematic form of the nucleon effective mass as a function of nuclear excitation energy and mass, we provide a simple explanation for understanding the experimentally observed mass dependence of the nuclear caloric curve. It is observed that the excitation energy at which the caloric curve enters into a plateau region, could be sensitive to the nuclear mass evolution of the effective nucleon mass.Comment: 5 pages, 5 figures, Accepted for publication in Phys. Rev. C. Minor changes mad

GEO-ELECTRICAL MAPPING OF BEACHROCK IN VATERA BEACH, LESVOS

Tο Beachrock (Br ή παραλιακοί ψαμμίτες) εμφανίζεται σε παράκτιες ζώνες και έχει σύνθετο ρόλο όσον αφορά στη μορφοδυναμική εξέλιξη τους. Αν και το Br έχει μελετηθεί ευρέως, ωστόσο, δύο βασικά θέματα χρήζουν επιπρόσθετης έρευνας. Το πρώτο αφορά στη σημασία της αλληλεπίδρασης του δυναμικά μεταβαλλόμενου παράκτιου περιβάλλοντος με την χρονικά μεταβαλλόμενη επιφανειακή και υπόγεια υδρογεωλογική ισορροπία. Το δεύτερο θέμα έχει να κάνει με τη χωρική κατανομή και την εξέλιξη του Br σε σχέση με συγκεκριμένο περιβάλλον που το “φιλοξενεί”. H παρούσα εργασία αναδεικνύει τη μέθοδο της ειδικής ηλεκτρικής αντίστασης του υπεδάφους, ως ένα σύγχρονο εργαλείο που μπορεί να συμβάλει στη μελέτη των παραπάνω προβληματισμών. Η έρευνα περιέλαβε μετρήσεις με τη γεωηλεκτρική μέθοδο συνεχούς ρεύματος κατά μήκος δύο τομών στην παραλία των Βατερών της Λέσβου, όπου παρατηρούνται σημαντικές επιφανειακές εμφανίσεις Br. Πραγματοποιήθηκαν δώδεκα γεωηλεκτρικές βυθοσκοπήσεις, με ανάπτυγμα ηλεκτροδίων Axial Pole-Dipole. Οι μετρήσεις της ειδικής ηλεκτρικής αντίστασης επέτρεψαν μία έμμεση εκτίμηση του TDS, το οποίο απεικονίζει την διεπιφάνεια γλυκού-θαλασσινού νερού. Κατά την ερμηνεία του γεωηλεκτρικού μοντέλου αναδείχθηκαν δύο σχηματισμοί που αντιστοιχούν σε Br. Ο πρώτος αποτελεί επέκταση του Br προς την ξηρά και ο δεύτερος πιστεύεται ότι είναι Br σε πρώιμο στάδιο ωρίμανσης.Beachrock (Br) is encountered on the coastal zones, playing an important but also complex role in their morphodynamic evolution. Although Br has been widely studied, two important issues require further investigation. The first concerns the importance of the interaction of the dynamically changing coastal environment with the temporal changing surficial and underground hydrogeological balance. The second has to do with the spatial distribution and the evolution of Br with respect to the specific “host” coastal zone geo environment. This paper designates the electrical resistivity method as a tool that contribute in arguing in the abovementioned issues. The research comprised subsurface measurements with the DC resistivity method along two profiles located on Vatera beach (Lesvos Island), where there is a significant Br outcrops. Twelve geoelectric soundings were carried out using the Axial Pole-Dipole electrode array. The electrical resistively measurements permitted an indirect estimation of TDS, which depicts the coastal interface of fresh water - sea water. The interpreted geoelectric model shows two thin formations attributed to Br. The first is the inland extension of the Br outcrop and the second it is believed to be a primary stage of Br build up

Nuclear expansion and symmetry energy of hot nuclei

The decrease in the symmetry energy of hot nuclei populated in $^{58}$Ni + $^{58}$Ni, $^{58}$Fe + $^{58}$Ni and $^{58}$Fe + $^{58}$Fe reactions at beam energies of 30, 40, and 47 MeV/nucleon, as a function of excitation energy is studied. It is observed that this decrease is mainly a consequence of increasing expansion or decreasing density rather than the increasing temperature. The results are in good agreement with the recently reported microscopic calculation based on the Thomas-Fermi approach. An empirical relation to study the symmetry energy of finite nuclei in various mass region is proposed.Comment: 10 pages, 2 figure

Analysis of fragment yield ratios in the nuclear phase transition

The critical phenomena of the liquid-gas phase transition has been investigated in the reactions 78,86Kr+58,64Ni at beam energy of 35 MeV/nucleon using the Landau free energy approach with isospin asymmetry as an order parameter. Fits to the free energy of fragments showed three minima suggesting the system to be in the regime of a first order phase transition. The relation m =-{\partial}F/{\partial}H, which defines the order parameter and its conjugate field H, has been experimentally verified from the linear dependence of the mirror nuclei yield ratio data, on the isospin asymmetry of the source. The slope parameter, which is a measure of the distance from a critical temperature, showed a systematic decrease with increasing excitation energy of the source. Within the framework of the Landau free energy approach, isoscaling provided similar results as obtained from the analysis of mirror nuclei yield ratio data. We show that the external field is primarily related to the minimum of the free energy, which implies a modification of the source concentration \Delta used in isospin studies

Proton induced reaction cross section measurements on Se isotopes for the astrophysical p process

As a continuation of a systematic study of reactions relevant to the astrophysical p process, the cross sections of the 74,76Se(p,gamma)75,77Br and 82Se(p,n)82Br reactions have been measured at energies from 1.3 to 3.6 MeV using an activation technique. The results are compared to the predictions of Hauser-Feshbach statistical model calculations using the NON-SMOKER and MOST codes. The sensitivity of the calculations to variations in the optical proton potential and the nuclear level density was studied. Good agreement between theoretical and experimental reaction rates was found for the reactions 74Se(p,gamma)75Br and 82Se(p,n)82Br.Comment: 9 pages, 6 figures (in 12 eps files), accepted for publication in Phys. Rev C, RevTeX styl

Asymmetry Dependence of the Nuclear Caloric Curve

A basic feature of the nuclear equation of state is not yet understood: the dependence of the nuclear caloric curve on the neutron-proton asymmetry. Predictions of theoretical models differ on the magnitude and even the sign of this dependence. In this work, the nuclear caloric curve is examined for fully reconstructed quasi-projectiles around mass A=50. The caloric curve extracted with the momentum quadrupole fluctuation thermometer shows that the temperature varies linearly with quasi-projectile asymmetry (N-Z)/A. An increase in asymmetry of 0.15 units corresponds to a decrease in temperature on the order of 1 MeV. These results also highlight the importance of a full quasi-projectile reconstruction in the study of thermodynamic properties of hot nuclei