GDR decay in hot Hg isotopes. An approach to improve the sensitivity to GDR decay following fusion reactions

Ataç, A.; Gaardhøje, J. J.; Herskind, B.; Iwata, Y.; Ogaza, S.; Bracco, A.; ruce, A.M.; James, A.N.; Chapman, R.; Khazaie, F.; Lisle, J.C.; Mo, J.N.; Connell, K.A.; Simpson, John

doi:10.1016/0370-2693(90)90480-t

Cited by 19 publications

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“…Exclusive experiments studying the GDR strength at a given excitation energy (or T ) of the nucleus have been carried out in refs. [1,2,3,4]. The understanding of these phenomena is relevant because it affects important features like the fission barriers and the stability of the nucleus itself.…”

Section: Introductionmentioning

confidence: 99%

Thermal shape fluctuation effects in the description of hot nuclei

2003

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The behavior of several nuclear properties with temperature is analyzed within the framework of the Finite Temperature Hartree-Fock-Bogoliubov (FTHFB) theory with the Gogny force and large configuration spaces. Thermal shape fluctuations in the quadrupole degree of freedom, around the mean field solution, are taken into account with the Landau prescription. As representative examples the nuclei 164 Er, 152 Dy and 192 Hg are studied. Numerical results for the superfluid to normal and deformed to spherical shape transitions are presented. We found a substantial effect of the fluctuations on the average value of several observables. In particular, we get a decrease in the critical temperature (Tc) for the shape transition as compared with the plain FTHFB prediction as well as a washing out of the shape transition signatures. The new values of Tc are closer to the ones found in Strutinsky calculations and with the Pairing Plus Quadrupole model Hamiltonian. IntroductionSince the advent of the new generation of 4π gamma ray detectors and the improved accuracy in the channel selection new possibilities have opened up in the study of nuclear structure. Besides this, the availability of faster computers has made possible to perform realistic theoretical investigations with large configuration spaces. The high excitation energy is specially interesting since new features may take place. For example, in the quasicontinuum, the high level density gives rise to the unexpected phenomenon of the damping of the rotational motion. In the limit of high excitation energies (or temperature T ) quantum effects become less relevant or may even disappear. Thus one expects that in a heated nucleus physical effects like superfluidity or shape deformations are washed out when T increases. This expectation can be easily understood in terms of the shell model since, by increasing T , one promotes particles from levels below the Fermi surface to levels above it. In the case of pairing correlations, blocking levels amounts to destroying Cooper pairs. In the case of shape deformation, by depopulating the deformation driving levels (intruders) one gets on the average less deformation. Experimental information about nuclear shape changes can be obtained by means of the Giant Dipole Resonance (GDR) built on excited states. Exclusive experiments studying the GDR strength at a given excitation energy (or T ) of the nucleus have been carried out in refs. [1,2,3,4]. The understanding of these phenomena is relevant because it affects important features like the fission barriers and the stability of the nucleus itself. For a recent review on hot nuclei see ref. [5].The shape transitions have been object of many studies, most of them with schematic models, separable forces, and small configuration spaces [6,7,8,9,10]. The theoretical approaches used in the calculations are based on the mean field approximation, mainly the Finite Temperature Hartree-Fock-Bogoliubov theory (FTHFB). The mean field approximations predict sharp shape transitions, wherea...

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Section: Introductionmentioning

confidence: 99%

Thermal shape fluctuation effects in the description of hot nuclei

2003

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“…Two issues involvingnuclear data have emergedrecently concerning these materials: i) What amounts of hydrogen would be generatedby D-T neutrons on vanadium?ii) What levels of 2SA1 activity, with a half life of (7.4+0.3)x105y [2], might be produced in silicon carbide within the reactor blanket. '1V(n,p)5*Ti and 51V(n,np+d)50Ti are considered to be the principal sources of hydrogen in vanadium.The two-step process 28Si(n,np+d)27Al(n,2n)2GAl is mainly responsible for the formation of 2GA1 in a fhsion reactor [3].…”

Section: Introductionmentioning

confidence: 99%

Exclusive studies of the GDR in excited nuclei

et al. 1999

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Current designs of fision-reactor systems seek to use radiation-resistan$ low-activation materials that support long service lifetimes and minimize radioactive-waste problems atler decommissioning. Reliable assessment of. fusion materials perfonrmnce requires accurate neutronreaction cross sections and radioactive-decay constants. The problem areas usually involve cross sections since decay parameters tend to be better known. The present L stud was motivated by two specific questions: i) Why are the V(n,np)sOTi cross section values in the ENDFLB-VI library so large (a gas production issue)? ii) How well known are the cross sections associated with producing 7.4X105 y 'Al in silicon carbide by the process 28Si(n,np+d)27Al(n,2n)2sAI (a long-lived radioactivity issue)? The energy range 14-15 MeV of the D-T fhsion neutrons is emphasized. Cross-section error bars are needed so that uncertainties in the gas and radioactivity generated over the lifetime of a reactor can be estimated. We address this issue by comparing values obtained from prominent evaluated cross-section libraries. Small differencesbetween independent evaluations indicate that a physical quantity is well known while the opposite signals a problem. Hydrogen from 51 V(n,p)5% and helium from 5*V(n,a)4*Scare also important sources of gas in vanadium, so they too were examined. We conclude that 'lV(n p)5*TIis adequately known but 51 V(n,np+d)50Tiis not. he status for helium generation data is quite good. Due to recent experimental work, 2'Al(n,2n)2GAl seems to be fairly well known. However, the situation for %i(n,np+d)27Alremains unsatisfactory.

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