Inhomogeneities in the interplanetary magnetic field produced by interplanetary disturbances asso... more Inhomogeneities in the interplanetary magnetic field produced by interplanetary disturbances associated with coronal mass ejections are transmitted fast to remote locations as a directional anisotropy of high-energy cosmic ray intensity due to the high speed and long parallel mean free path of energetic particles. Cosmic ray intensity increases or decreases before the Forbush decreases have been observed with a single directional channel especially for strong geomagnetic storms associated with strong interplanetary shocks. The aim of this work is to study cosmic ray precursory phenomena of small and moderate geomagnetic storms from June 26th 2008 to December 31st 2008 (from Bartels rotation number 2387 to 2393), most of them not associated with shocks, by analyzing data from the Global Muon Detector Network consisting of four multidirectional muon detectors. By analyzing muon count rates in 60 directional channels, the pitch angle distribution in a 48-hour period before the storm sudden commencement was studied by two different methodologies: one using the hourly count rate (MPA) and the other using the time derivative of the count rate (VPA). Possible precursors are clear in 4 of the 7 events registered in the selected period, generally observed by the MPA.
The prediction of cross sections for nuclei far off stability is crucial in the field of nuclear ... more The prediction of cross sections for nuclei far off stability is crucial in the field of nuclear astrophysics. For spherical nuclei close to the dripline the statistical model (Hauser-Feshbach) approach is not applicable and direct contributions may dominate the cross sections. For neutron-rich, even-even Sn targets, we compare the resulting neutron capture cross sections when consistently taking the input for the direct capture calculations from three different microscopic models. The results underline the sensitivity of cross sections calculated in the direct model to nuclear structure models which can lead to high uncertainties when lacking experimental information.
The importance of direct capture for (n,γ)-reactions on intermediateand heavy-mass target nuclei ... more The importance of direct capture for (n,γ)-reactions on intermediateand heavy-mass target nuclei occuring in the sand r-process is investigated. It is shown that the direct mechanism is non-negligible for magic and neutron rich target nuclei. For some double magic and neutron rich nuclei in the r-process direct capture is even the dominant reaction mechanism.
Proceedings of 4th School on Cosmic Rays and Astrophysics — PoS(CRA School), 2011
Inhomogeneities in the interplanetary magnetic field produced by interplanetary disturbances asso... more Inhomogeneities in the interplanetary magnetic field produced by interplanetary disturbances associated with coronal mass ejections are transmitted fast to remote locations as a directional anisotropy of high-energy cosmic ray intensity due to the high speed and long parallel mean free path of energetic particles. Cosmic ray intensity increases or decreases before the Forbush decreases have been observed with a single directional channel especially for strong geomagnetic storms associated with strong interplanetary shocks. The aim of this work is to study cosmic ray precursory phenomena of small and moderate geomagnetic storms from June 26th 2008 to December 31st 2008 (from Bartels rotation number 2387 to 2393), most of them not associated with shocks, by analyzing data from the Global Muon Detector Network consisting of four multidirectional muon detectors. By analyzing muon count rates in 60 directional channels, the pitch angle distribution in a 48-hour period before the storm sudden commencement was studied by two different methodologies: one using the hourly count rate (MPA) and the other using the time derivative of the count rate (VPA). Possible precursors are clear in 4 of the 7 events registered in the selected period, generally observed by the MPA.
In rapid-proton capture (rp-process), N=Z nuclei above Ni are understood to act as waitingpoint n... more In rapid-proton capture (rp-process), N=Z nuclei above Ni are understood to act as waitingpoint nuclei. The N=Z nuclei 68 Se, 72 Kr, 76 Sr and 80 Zr among others are known to give rise to a largeenergy x-ray flux and peaks in abundances of these nuclei synthesized in the astrophysical rp-process. Investigating the experimental isotope shifts in Kr isotopes near the proton drip-line within the framework of the deformed Relativistic Hartree-Bogoliubov theory, we have discovered that N=Z rpprocess nuclei 68 Se, 72 Kr, 76 Sr and 80 Zr exhibit large shell gap both at the proton and neutron numbers in the deformed space with the consequence that pairing correlations for protons and neutrons vanish. This lends a doubly magic character to these nuclei. A significant number of nuclei in this region are also shown to exhibit neutron magicity at N=34, 36, 38, and 40 in the deformed space. A unique case of concomitance of the double magicity and the shape-coexistence is found for 68 Se.
We demonstrate that global observations of high‐energy cosmic rays contribute to understanding un... more We demonstrate that global observations of high‐energy cosmic rays contribute to understanding unique characteristics of a large‐scale magnetic flux rope causing a magnetic storm in August 2018. Following a weak interplanetary shock on August 25, 2018, a magnetic flux rope caused an unexpectedly large geomagnetic storm. It is likely that this event became geoeffective because the flux rope was accompanied by a corotating interaction region and compressed by high‐speed solar wind following the flux rope. In fact, a Forbush decrease was observed in cosmic‐ray data inside the flux rope as expected, and a significant cosmic‐ray density increase exceeding the unmodulated level before the shock was also observed near the trailing edge of the flux rope. The cosmic‐ray density increase can be interpreted in terms of the adiabatic heating of cosmic rays near the trailing edge of the flux rope, as the corotating interaction region prevents free expansion of the flux rope and results in the co...
Journal of Geophysical Research: Space Physics, 2019
Cosmic rays are charged particles whose flux observed at Earth shows temporal variations related ... more Cosmic rays are charged particles whose flux observed at Earth shows temporal variations related to space weather phenomena and may be an important tool to study them. The cosmic ray intensity recorded with ground‐based detectors also shows temporal variations arising from atmospheric variations. In the case of muon detectors, the main atmospheric effects are related to pressure and temperature changes. In this work, we analyze both effects using data recorded by the Global Muon Detector Network, consisting of four multidirectional muon detectors at different locations, in the period between 2007 and 2016. For each Global Muon Detector Network directional channel, we obtain coefficients that describe the pressure and temperature effects. We then analyze how these coefficients can be related to the geomagnetic cutoff rigidity and zenith angle associated with cosmic ray particles observed by each channel. In the pressure effect analysis, we found that the observed barometric coefficie...
We analyze the galactic cosmic ray (GCR) density and its spatial gradient in Forbush Decreases (F... more We analyze the galactic cosmic ray (GCR) density and its spatial gradient in Forbush Decreases (FDs) observed with the Global Muon Detector Network (GMDN) and neutron monitors (NMs). By superposing the GCR density and density gradient observed in FDs following 45 interplanetary shocks (IP-shocks), each associated with an identified eruption on the Sun, we infer the average spatial distribution of GCRs behind IP-shocks. We find two distinct modulations of GCR density in FDs, one in the magnetic sheath and the other in the coronal mass ejection (CME) behind the sheath. The density modulation in the sheath is dominant in the western flank of the shock, while the modulation in the CME ejecta stands out in the eastern flank. This east-west asymmetry is more prominent in GMDN data responding to ∼60 GV GCRs than in NM data responding to ∼10 GV GCRs, because of the softer rigidity spectrum of the modulation in the CME ejecta than in the sheath. The geocentric solar ecliptic-y component of the density gradient, G y , shows a negative (positive) enhancement in FDs caused by the eastern (western) eruptions, while G z shows a negative (positive) enhancement in FDs caused by the northern (southern) eruptions. This implies that the GCR density minimum is located behind the central flank of IP-shocks and propagating radially outward from the location of the solar eruption. We also confirmed that the average G z changes its sign above and below the heliospheric current sheet, in accord with the prediction of the drift model for the large-scale GCR transport in the heliosphere.
We analyze the short cosmic-ray intensity increase ("cosmic-ray burst": CRB) on 2015 June 22 util... more We analyze the short cosmic-ray intensity increase ("cosmic-ray burst": CRB) on 2015 June 22 utilizing a global network of muon detectors and derive the global anisotropy of cosmic-ray intensity and the density (i.e., the omnidirectional intensity) with 10 minute time resolution. We find that the CRB was caused by a local density maximum and an enhanced anisotropy of cosmic rays, both of which appeared in association with Earth's crossing of the heliospheric current sheet (HCS). This enhanced anisotropy was normal to the HCS and consistent with a diamagnetic drift arising from the spatial gradient of cosmic-ray density, which indicates that cosmic rays were drifting along the HCS from the north of Earth. We also find a significant anisotropy along the HCS, lasting a few hours after the HCS crossing, indicating that cosmic rays penetrated into the inner heliosphere along the HCS. Based on the latest geomagnetic field model, we quantitatively evaluate the reduction of the geomagnetic cutoff rigidity and the variation of the asymptotic viewing direction of cosmic rays due to a major geomagnetic storm that occurred during the CRB and conclude that the CRB is not caused by the geomagnetic storm, but by a rapid change in the cosmic-ray anisotropy and density outside the magnetosphere.
The analysis of cosmic ray intensity variation seen by muon detectors at Earthʼs surface can help... more The analysis of cosmic ray intensity variation seen by muon detectors at Earthʼs surface can help us to understand astrophysical, solar, interplanetary and geomagnetic phenomena. However, before comparing cosmic ray intensity variations with extraterrestrial phenomena, it is necessary to take into account atmospheric effects such as the temperature effect. In this work, we analyzed this effect on the Global Muon Detector Network (GMDN), which is composed of four ground-based detectors, two in the northern hemisphere and two in the southern hemisphere. In general, we found a higher temperature influence on detectors located in the northern hemisphere. Besides that, we noticed that the seasonal temperature variation observed at the ground and at the altitude of maximum muon production are in antiphase for all GMDN locations (low-latitude regions). In this way, contrary to what is expected in high-latitude regions, the ground muon intensity decrease occurring during summertime would be related to both parts of the temperature effect (the negative and the positive). We analyzed several methods to describe the temperature effect on cosmic ray intensity. We found that the mass weighted method is the one that best reproduces the seasonal cosmic ray variation observed by the GMDN detectors and allows the highest correlation with long-term variation of the cosmic ray intensity seen by neutron monitors.
We have investigated the nuclear shell effects at N = 126 in the region of the third peak of the ... more We have investigated the nuclear shell effects at N = 126 in the region of the third peak of the r-process nucleosynthesis within the framework of the relativistic mean-field theory using the Lagrangian model NL-SV1 with the vector self-coupling of ω-meson. Our study encompasses even-even nuclei with N = 110 − 140 in the isotopic chains of Hf (Z = 72) down to Ba (Z = 56). It is shown that the nuclear shell effects at N = 126 remain strong even as one moves far away from the line of the β-stability. As the neutron drip line approaches N = 126, nuclei exhibit vanishingly small neutron separation energy. However, going beyond the neutron drip line, we observe an interesting feature in that some nuclei near N ∼ 132 − 134 for the isotopic chains of Z = 62 − 68 show enhanced neutron separation energy. This is especially pronounced for the isotopes of Gd (Z = 64) and Dy (Z = 66). These nuclei exhibit the phenomenon of stability beyond the neutron drip line. Our analysis of the single-particle spectrum shows that this is engendered by the deformation assumed by these nuclei with the consequence that the neutron single-particle spectrum is pushed down in energy, thus leading to enhanced stability beyond the drip line.
The anomalous behaviour of the charge radii of the isotopic chain of Pb nuclei has been studied i... more The anomalous behaviour of the charge radii of the isotopic chain of Pb nuclei has been studied in the relativistic mean field theory. It has been shown that the relativistic mean field provides an excellent description of the anomalous kink in the isotopic shifts about 208 Pb. This contrasts strongly from the Skyrme mean field, where the densitydependent Skyrme forces fail to reproduce the observed trend in the empirical data on the charge radii. The results have been discussed in the perspective of differences in the ansätze of the relativistic and the Skyrme mean-field theories.
We investigate the triple-alpha process and the Oklo phenomenon to obtain constraints on possible... more We investigate the triple-alpha process and the Oklo phenomenon to obtain constraints on possible cosmological time variations of fundamental constants. Specifically we study cosmological temporal constraints for the fine structure constant and nucleon and meson masses.
We have made a detailed study of the ground-state properties of nuclei in the light mass region w... more We have made a detailed study of the ground-state properties of nuclei in the light mass region with atomic numbers Z=10-22 in the framework of the relativistic mean-field (RMF) theory. The nonlinear σω model with scalar self-interaction has been employed. The RMF calculations have been performed in an axially deformed configuration using the force NL-SH. We have considered nuclei about the stability line as well as those close to proton and neutron drip lines. It is shown that the RMF results provide a good agreement with the available empirical data. The RMF predictions also show a reasonably good agreement with those of the mass models. It is observed that nuclei in this mass region are found to possess strong deformations and exhibit shape changes all along the isotopic chains. The phenomenon of the shape coexistence is found to persist near the stability line as well as near the drip lines. It is shown that the magic number N=28 is quenched strongly, thus enabling the corresponding nuclei to assume strong deformations. Nuclei near the neutron and proton drip lines in this region are also shown to be strongly deformed.
Journal of Physics G: Nuclear and Particle Physics, 2009
We have studied properties and shell structure of the superheavy elements from Z = 102 to Z = 120... more We have studied properties and shell structure of the superheavy elements from Z = 102 to Z = 120 within the framework of the RMF theory. The region of study spans nuclides with neutron numbers N = 150 − 190. The Lagrangian model NL-SV1 with the inclusion of the vector self-coupling of the ω-meson has been employed in this work. We have performed RMF + BCS calculations for an axially deformed configuration of nuclei. The ground-state binding energies, single-particle properties and quadrupole deformation of nuclei have been obtained from the meanfield minimizations. Two-neutron separation energies, Q α values and α-decay halflife have been evaluated. It is shown that a large number of nuclides exhibit the phenomenon of shape-coexistence over a significant region of the superheavy elements. Shape coexistence of a prolate and an oblate shape is prevalent in nuclides far below N = 184, whilst nuclei in the vicinity of N = 184 tend to show a shape coexistence between a spherical and an oblate shape. The shell structure and 2-neutron separation energies obtained with the RMF theory reinforce the neutron number N = 184 as a major magic number. It is shown that the neutron number N = 172 acts akin to a magic number in the deformed region. It is suggested that the combination Z = 120 and N = 172 has the potential of being a doubly magic number in the superheavy region.
Inhomogeneities in the interplanetary magnetic field produced by interplanetary disturbances asso... more Inhomogeneities in the interplanetary magnetic field produced by interplanetary disturbances associated with coronal mass ejections are transmitted fast to remote locations as a directional anisotropy of high-energy cosmic ray intensity due to the high speed and long parallel mean free path of energetic particles. Cosmic ray intensity increases or decreases before the Forbush decreases have been observed with a single directional channel especially for strong geomagnetic storms associated with strong interplanetary shocks. The aim of this work is to study cosmic ray precursory phenomena of small and moderate geomagnetic storms from June 26th 2008 to December 31st 2008 (from Bartels rotation number 2387 to 2393), most of them not associated with shocks, by analyzing data from the Global Muon Detector Network consisting of four multidirectional muon detectors. By analyzing muon count rates in 60 directional channels, the pitch angle distribution in a 48-hour period before the storm sudden commencement was studied by two different methodologies: one using the hourly count rate (MPA) and the other using the time derivative of the count rate (VPA). Possible precursors are clear in 4 of the 7 events registered in the selected period, generally observed by the MPA.
The prediction of cross sections for nuclei far off stability is crucial in the field of nuclear ... more The prediction of cross sections for nuclei far off stability is crucial in the field of nuclear astrophysics. For spherical nuclei close to the dripline the statistical model (Hauser-Feshbach) approach is not applicable and direct contributions may dominate the cross sections. For neutron-rich, even-even Sn targets, we compare the resulting neutron capture cross sections when consistently taking the input for the direct capture calculations from three different microscopic models. The results underline the sensitivity of cross sections calculated in the direct model to nuclear structure models which can lead to high uncertainties when lacking experimental information.
The importance of direct capture for (n,γ)-reactions on intermediateand heavy-mass target nuclei ... more The importance of direct capture for (n,γ)-reactions on intermediateand heavy-mass target nuclei occuring in the sand r-process is investigated. It is shown that the direct mechanism is non-negligible for magic and neutron rich target nuclei. For some double magic and neutron rich nuclei in the r-process direct capture is even the dominant reaction mechanism.
Proceedings of 4th School on Cosmic Rays and Astrophysics — PoS(CRA School), 2011
Inhomogeneities in the interplanetary magnetic field produced by interplanetary disturbances asso... more Inhomogeneities in the interplanetary magnetic field produced by interplanetary disturbances associated with coronal mass ejections are transmitted fast to remote locations as a directional anisotropy of high-energy cosmic ray intensity due to the high speed and long parallel mean free path of energetic particles. Cosmic ray intensity increases or decreases before the Forbush decreases have been observed with a single directional channel especially for strong geomagnetic storms associated with strong interplanetary shocks. The aim of this work is to study cosmic ray precursory phenomena of small and moderate geomagnetic storms from June 26th 2008 to December 31st 2008 (from Bartels rotation number 2387 to 2393), most of them not associated with shocks, by analyzing data from the Global Muon Detector Network consisting of four multidirectional muon detectors. By analyzing muon count rates in 60 directional channels, the pitch angle distribution in a 48-hour period before the storm sudden commencement was studied by two different methodologies: one using the hourly count rate (MPA) and the other using the time derivative of the count rate (VPA). Possible precursors are clear in 4 of the 7 events registered in the selected period, generally observed by the MPA.
In rapid-proton capture (rp-process), N=Z nuclei above Ni are understood to act as waitingpoint n... more In rapid-proton capture (rp-process), N=Z nuclei above Ni are understood to act as waitingpoint nuclei. The N=Z nuclei 68 Se, 72 Kr, 76 Sr and 80 Zr among others are known to give rise to a largeenergy x-ray flux and peaks in abundances of these nuclei synthesized in the astrophysical rp-process. Investigating the experimental isotope shifts in Kr isotopes near the proton drip-line within the framework of the deformed Relativistic Hartree-Bogoliubov theory, we have discovered that N=Z rpprocess nuclei 68 Se, 72 Kr, 76 Sr and 80 Zr exhibit large shell gap both at the proton and neutron numbers in the deformed space with the consequence that pairing correlations for protons and neutrons vanish. This lends a doubly magic character to these nuclei. A significant number of nuclei in this region are also shown to exhibit neutron magicity at N=34, 36, 38, and 40 in the deformed space. A unique case of concomitance of the double magicity and the shape-coexistence is found for 68 Se.
We demonstrate that global observations of high‐energy cosmic rays contribute to understanding un... more We demonstrate that global observations of high‐energy cosmic rays contribute to understanding unique characteristics of a large‐scale magnetic flux rope causing a magnetic storm in August 2018. Following a weak interplanetary shock on August 25, 2018, a magnetic flux rope caused an unexpectedly large geomagnetic storm. It is likely that this event became geoeffective because the flux rope was accompanied by a corotating interaction region and compressed by high‐speed solar wind following the flux rope. In fact, a Forbush decrease was observed in cosmic‐ray data inside the flux rope as expected, and a significant cosmic‐ray density increase exceeding the unmodulated level before the shock was also observed near the trailing edge of the flux rope. The cosmic‐ray density increase can be interpreted in terms of the adiabatic heating of cosmic rays near the trailing edge of the flux rope, as the corotating interaction region prevents free expansion of the flux rope and results in the co...
Journal of Geophysical Research: Space Physics, 2019
Cosmic rays are charged particles whose flux observed at Earth shows temporal variations related ... more Cosmic rays are charged particles whose flux observed at Earth shows temporal variations related to space weather phenomena and may be an important tool to study them. The cosmic ray intensity recorded with ground‐based detectors also shows temporal variations arising from atmospheric variations. In the case of muon detectors, the main atmospheric effects are related to pressure and temperature changes. In this work, we analyze both effects using data recorded by the Global Muon Detector Network, consisting of four multidirectional muon detectors at different locations, in the period between 2007 and 2016. For each Global Muon Detector Network directional channel, we obtain coefficients that describe the pressure and temperature effects. We then analyze how these coefficients can be related to the geomagnetic cutoff rigidity and zenith angle associated with cosmic ray particles observed by each channel. In the pressure effect analysis, we found that the observed barometric coefficie...
We analyze the galactic cosmic ray (GCR) density and its spatial gradient in Forbush Decreases (F... more We analyze the galactic cosmic ray (GCR) density and its spatial gradient in Forbush Decreases (FDs) observed with the Global Muon Detector Network (GMDN) and neutron monitors (NMs). By superposing the GCR density and density gradient observed in FDs following 45 interplanetary shocks (IP-shocks), each associated with an identified eruption on the Sun, we infer the average spatial distribution of GCRs behind IP-shocks. We find two distinct modulations of GCR density in FDs, one in the magnetic sheath and the other in the coronal mass ejection (CME) behind the sheath. The density modulation in the sheath is dominant in the western flank of the shock, while the modulation in the CME ejecta stands out in the eastern flank. This east-west asymmetry is more prominent in GMDN data responding to ∼60 GV GCRs than in NM data responding to ∼10 GV GCRs, because of the softer rigidity spectrum of the modulation in the CME ejecta than in the sheath. The geocentric solar ecliptic-y component of the density gradient, G y , shows a negative (positive) enhancement in FDs caused by the eastern (western) eruptions, while G z shows a negative (positive) enhancement in FDs caused by the northern (southern) eruptions. This implies that the GCR density minimum is located behind the central flank of IP-shocks and propagating radially outward from the location of the solar eruption. We also confirmed that the average G z changes its sign above and below the heliospheric current sheet, in accord with the prediction of the drift model for the large-scale GCR transport in the heliosphere.
We analyze the short cosmic-ray intensity increase ("cosmic-ray burst": CRB) on 2015 June 22 util... more We analyze the short cosmic-ray intensity increase ("cosmic-ray burst": CRB) on 2015 June 22 utilizing a global network of muon detectors and derive the global anisotropy of cosmic-ray intensity and the density (i.e., the omnidirectional intensity) with 10 minute time resolution. We find that the CRB was caused by a local density maximum and an enhanced anisotropy of cosmic rays, both of which appeared in association with Earth's crossing of the heliospheric current sheet (HCS). This enhanced anisotropy was normal to the HCS and consistent with a diamagnetic drift arising from the spatial gradient of cosmic-ray density, which indicates that cosmic rays were drifting along the HCS from the north of Earth. We also find a significant anisotropy along the HCS, lasting a few hours after the HCS crossing, indicating that cosmic rays penetrated into the inner heliosphere along the HCS. Based on the latest geomagnetic field model, we quantitatively evaluate the reduction of the geomagnetic cutoff rigidity and the variation of the asymptotic viewing direction of cosmic rays due to a major geomagnetic storm that occurred during the CRB and conclude that the CRB is not caused by the geomagnetic storm, but by a rapid change in the cosmic-ray anisotropy and density outside the magnetosphere.
The analysis of cosmic ray intensity variation seen by muon detectors at Earthʼs surface can help... more The analysis of cosmic ray intensity variation seen by muon detectors at Earthʼs surface can help us to understand astrophysical, solar, interplanetary and geomagnetic phenomena. However, before comparing cosmic ray intensity variations with extraterrestrial phenomena, it is necessary to take into account atmospheric effects such as the temperature effect. In this work, we analyzed this effect on the Global Muon Detector Network (GMDN), which is composed of four ground-based detectors, two in the northern hemisphere and two in the southern hemisphere. In general, we found a higher temperature influence on detectors located in the northern hemisphere. Besides that, we noticed that the seasonal temperature variation observed at the ground and at the altitude of maximum muon production are in antiphase for all GMDN locations (low-latitude regions). In this way, contrary to what is expected in high-latitude regions, the ground muon intensity decrease occurring during summertime would be related to both parts of the temperature effect (the negative and the positive). We analyzed several methods to describe the temperature effect on cosmic ray intensity. We found that the mass weighted method is the one that best reproduces the seasonal cosmic ray variation observed by the GMDN detectors and allows the highest correlation with long-term variation of the cosmic ray intensity seen by neutron monitors.
We have investigated the nuclear shell effects at N = 126 in the region of the third peak of the ... more We have investigated the nuclear shell effects at N = 126 in the region of the third peak of the r-process nucleosynthesis within the framework of the relativistic mean-field theory using the Lagrangian model NL-SV1 with the vector self-coupling of ω-meson. Our study encompasses even-even nuclei with N = 110 − 140 in the isotopic chains of Hf (Z = 72) down to Ba (Z = 56). It is shown that the nuclear shell effects at N = 126 remain strong even as one moves far away from the line of the β-stability. As the neutron drip line approaches N = 126, nuclei exhibit vanishingly small neutron separation energy. However, going beyond the neutron drip line, we observe an interesting feature in that some nuclei near N ∼ 132 − 134 for the isotopic chains of Z = 62 − 68 show enhanced neutron separation energy. This is especially pronounced for the isotopes of Gd (Z = 64) and Dy (Z = 66). These nuclei exhibit the phenomenon of stability beyond the neutron drip line. Our analysis of the single-particle spectrum shows that this is engendered by the deformation assumed by these nuclei with the consequence that the neutron single-particle spectrum is pushed down in energy, thus leading to enhanced stability beyond the drip line.
The anomalous behaviour of the charge radii of the isotopic chain of Pb nuclei has been studied i... more The anomalous behaviour of the charge radii of the isotopic chain of Pb nuclei has been studied in the relativistic mean field theory. It has been shown that the relativistic mean field provides an excellent description of the anomalous kink in the isotopic shifts about 208 Pb. This contrasts strongly from the Skyrme mean field, where the densitydependent Skyrme forces fail to reproduce the observed trend in the empirical data on the charge radii. The results have been discussed in the perspective of differences in the ansätze of the relativistic and the Skyrme mean-field theories.
We investigate the triple-alpha process and the Oklo phenomenon to obtain constraints on possible... more We investigate the triple-alpha process and the Oklo phenomenon to obtain constraints on possible cosmological time variations of fundamental constants. Specifically we study cosmological temporal constraints for the fine structure constant and nucleon and meson masses.
We have made a detailed study of the ground-state properties of nuclei in the light mass region w... more We have made a detailed study of the ground-state properties of nuclei in the light mass region with atomic numbers Z=10-22 in the framework of the relativistic mean-field (RMF) theory. The nonlinear σω model with scalar self-interaction has been employed. The RMF calculations have been performed in an axially deformed configuration using the force NL-SH. We have considered nuclei about the stability line as well as those close to proton and neutron drip lines. It is shown that the RMF results provide a good agreement with the available empirical data. The RMF predictions also show a reasonably good agreement with those of the mass models. It is observed that nuclei in this mass region are found to possess strong deformations and exhibit shape changes all along the isotopic chains. The phenomenon of the shape coexistence is found to persist near the stability line as well as near the drip lines. It is shown that the magic number N=28 is quenched strongly, thus enabling the corresponding nuclei to assume strong deformations. Nuclei near the neutron and proton drip lines in this region are also shown to be strongly deformed.
Journal of Physics G: Nuclear and Particle Physics, 2009
We have studied properties and shell structure of the superheavy elements from Z = 102 to Z = 120... more We have studied properties and shell structure of the superheavy elements from Z = 102 to Z = 120 within the framework of the RMF theory. The region of study spans nuclides with neutron numbers N = 150 − 190. The Lagrangian model NL-SV1 with the inclusion of the vector self-coupling of the ω-meson has been employed in this work. We have performed RMF + BCS calculations for an axially deformed configuration of nuclei. The ground-state binding energies, single-particle properties and quadrupole deformation of nuclei have been obtained from the meanfield minimizations. Two-neutron separation energies, Q α values and α-decay halflife have been evaluated. It is shown that a large number of nuclides exhibit the phenomenon of shape-coexistence over a significant region of the superheavy elements. Shape coexistence of a prolate and an oblate shape is prevalent in nuclides far below N = 184, whilst nuclei in the vicinity of N = 184 tend to show a shape coexistence between a spherical and an oblate shape. The shell structure and 2-neutron separation energies obtained with the RMF theory reinforce the neutron number N = 184 as a major magic number. It is shown that the neutron number N = 172 acts akin to a magic number in the deformed region. It is suggested that the combination Z = 120 and N = 172 has the potential of being a doubly magic number in the superheavy region.
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Papers by Madan Sharma