Browsing by Author "Nakada, Hitoshi"
Now showing items 1-11 of 11
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Calculating Level Densities of Heavy Nuclei by the Shell Model Monte Carlo Method
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Publisher and Date:(Academic Press Inc Elsevier Science, 2014)The microscopic calculation of nuclear level densities in the presence of correlations is a difficult many-body problem. The shell model Monte Carlo method provides a powerful technique to carry out such calculations using the framework of the configuration-interaction shell model in spaces that are many orders of magnitude larger than spaces that can be treated by conventional methods. We present recent applications of the method to the calculation of level densities and their collective enhancement ...
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Collective enhancement of nuclear state densities by the shell model Monte Carlo approach
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Publisher and Date:(IOP Publishing Ltd, 2015)The shell model Monte Carlo (SMMC) approach allows for the microscopic calculation of statistical and collective properties of heavy nuclei using the framework of the configuration-interaction shell model in very large model spaces. We present recent applications of the SMMC method to the calculation of state densities and their collective enhancement factors in rare-earth nuclei.
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Collectivity in Heavy Nuclei in the Shell Model Monte Carlo Approach
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Publisher and Date:(EDP Sciences, 2014)The microscopic description of collectivity in heavy nuclei in the framework of the configuration-interaction shell model has been a major challenge. The size of the model space required for the description of heavy nuclei prohibits the use of conventional diagonalization methods. We have overcome this difficulty by using the shell model Monte Carlo (SMMC) method which can treat model spaces that are many orders of magnitude larger than those that can be treated by conventional methods. We identify ...
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Crossover from Vibrational to Rotational Collectivity in Heavy Nuclei in the Shell-Model Monte Carlo Approach
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Publisher and Date:(Amer Physical Soc., 2013)Heavy nuclei exhibit a crossover from vibrational to rotational collectivity as the number of neutrons or protons increases from shell closure towards midshell but the microscopic description of this crossover has been a major challenge. We apply the shell model Monte Carlo approach to families of even-even samarium and neodymium isotopes and identify a microscopic signature of the crossover from vibrational to rotational collectivity in the low-temperature behavior of < J(2)>(T) where J is the ...
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Level Densities of Heavy Nuclei in the Shell Model Monte Carlo Approach
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Publisher and Date:(EDP Sciences, 2016)Nuclear level densities are necessary input to the Hauser-Feshbach theory of compound nuclear reactions. However the microscopic calculation of level densities in the presence of correlations is a challenging many-body problem. The configuration-interaction shell model provides a suitable framework for the inclusion of correlations and shell effects but the large dimensionality of the many-particle model space has limited its application in heavy nuclei. The shell model Monte Carlo method enables ...
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Nuclear level density of 161Dy in the shell Model Monte Carlo Method
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Publisher and Date:(EDP Sciences, 2012)We extend the shell-model Monte Carlo applications to the rare-earth region to include the odd-even nucleus Dy-161. The projection on an odd number of particles leads to a sign problem at low temperatures making it impractical to extract the ground-state energy in direct calculations. We use level counting data at low energies and neutron resonance data to extract the shell model ground-state energy to good precision. We then calculate the level density of Dy-161 and find it in very good agreement ...
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Nuclear state densities of odd-mass heavy nuclei in the shell model Monte Carlo approach
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Publisher and Date:(Amer Physical Soc., 2015)The shell model Monte Carlo (SMMC) approach enables the microscopic calculation of nuclear state densities in model spaces that are many orders of magnitude larger than those that can be treated by conventional diagonalization techniques. However it has been difficult to calculate accurate state densities of odd-mass heavy nuclei as a function of excitation energy. This is because of a sign problem that arises from the projection on an odd number of particles at low temperatures making it difficult ...
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Persistence of Vibrational Collectivity in Nuclear Level Densities
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Publisher and Date:(E D P SCIENCES, 2016)By applying the particle-number projection to the finite-temperature BCS theory to the state densities in the rare-earth nuclei and comparing its results to the SMMC ones we investigate effects of the particle-number conservation on the collective enhancement factor for the state densities. Once we restore the particle-number conservation the rapid decay of vibrational enhancement disappears. This suggests that the vibrational collectivity may survive up to higher energy and the relevant enhancement ...
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Recent Advances in the Application of the Shell Model Monte Carlo Approach to Nuclei
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Publisher and Date:(IOP Publishing Ltd, 2015)The shell model Monte Carlo (SMMC) method is a powerful technique for calculating the statistical and collective properties of nuclei in the presence of correlations in model spaces that are many orders of magnitude larger than those that can be treated by conventional diagonalization methods. We review recent advances in the development and application of SMMC to mid-mass and heavy nuclei.
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Recent developments in the shell model Monte Carlo approach to nuclei
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Publisher and Date:(IOP Publishing Ltd, 2012)The shell model Monte Carlo (SMMC) approach provides a powerful method for the microscopic calculation of statistical and collective nuclear properties in model spaces that are many orders of magnitude larger than those that can be treated by conventional methods. We discuss recent applications of the method to describe the emergence of collectivity in the framework of the configuration-interaction shell model and the crossover from vibrational to rotational collectivity in families of rare-earth ...
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Signatures of phase transitions in nuclei at finite excitation energies
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Publisher and Date:(Amer Inst Physics, 2012)The mean-field approximation predicts pairing and shape phase transitions in nuclei as a function of temperature or excitation energy. However in the finite nucleus the singularities of these phase transitions are smoothed out by quantal and thermal fluctuations. An interesting question is whether signatures of these transitions survive despite the large fluctuations. The shell model Monte Carlo (SMMC) approach enables us to calculate the statistical properties of nuclei beyond the mean-field ...
