One-proton Separation Energies Research Articles

Proton drip line nuclei in the Relativistic Hartree-Bogoliubov model

The Relativistic Hartree Bogoliubov (RHB) theory is applied to the description of ground-state properties of proton-rich odd-Z nuclei. The model predicts the location of the proton drip-line, the ground-state quadrupole deformations and one-proton separation energies at and beyond the drip-line, the deformed single-particle Orbitals occupied by the odd valence proton, and the corresponding spectroscopic factors. The results of fully self-consistent RHB calculations are compared with experimental data on deformed and transitional proton emitters and the predictions of various mass models.

α -decay chains of the superheavy nuclei Rg255–350

The decay modes and half-lives of 96 isotopes of the superheavy element roentgenium (Rg) within the range of $255\ensuremath{\le}A\ensuremath{\le}350$ come under investigation in the present paper. The isotopes which lie beyond the proton drip line are identified by calculating the one-proton and two-proton separation energies. The $\ensuremath{\alpha}$-decay half-lives are calculated using the Coulomb and proximity potential model for deformed nuclei (CPPMDN). For a theoretical comparison the $\ensuremath{\alpha}$ half-lives are also evaluated using the Viola-Seaborg semiempirical relation, the universal curve of Poenaru et al., the analytical formula of Royer, and the universal decay law of Qi et al. Spontaneous fission half-lives are computed with the shell-effect-dependent formula of Santhosh and Nithya and the semiempirical formula of Xu et al. The decay modes are predicted by comparing the $\ensuremath{\alpha}$-decay half-lives within the CPPMDN with the corresponding spontaneous fission half-lives computed by the shell-effect-dependent formula of Santhosh and Nithya. In our paper it is seen that the isotopes $^{255\text{--}271,273}\mathrm{Rg}$ lie beyond the proton drip line and hence decay through proton emission. The isotopes $^{272,274\text{--}277}\mathrm{Rg}$ exhibit long $\ensuremath{\alpha}$ chains. Three $\ensuremath{\alpha}$ chains are predicted from the isotopes $^{278\text{--}282}\mathrm{Rg}$. The isotopes $^{283\text{--}345}\mathrm{Rg}$ decay through spontaneous fission. The isotopes $^{346\text{--}350}\mathrm{Rg}$ are found to be stable against $\ensuremath{\alpha}$ decay. The theoretical results are compared with the available experimental results and are seen to be matching well. We hope that our predictions will be useful in future experimental investigations.

Predictions on the modes of decay of even [formula omitted] superheavy isotopes within the range [formula omitted

The decay modes and half lives of all the even Z isotopes of superheavy elements within the range 104≤Z≤136 have been predicted by comparing the alpha decay half-lives with the spontaneous fission half-lives. The Coulomb and proximity potential model for deformed nuclei (CPPMDN) and the shell-effect-dependent formula of Santhosh et al. are used to calculate the alpha half-lives and spontaneous fission half-lives respectively. For theoretical comparison the alpha decay half-lives are also calculated using Coulomb and proximity potential model (CPPM), the Viola–Seaborg–Sobiczewski semi-empirical (VSS) relation, the universal (UNIV) curve of Poenaru et al., the analytical formula of Royer and the universal decay law (UDL) of Qi et al. Another tool used for the evaluation of spontaneous fission half-lives is the semi-empirical formula of Xu et al. The nuclei with alpha decay half-lives less than spontaneous fission half-lives will survive fission and hence decay through alpha emission. The predicted half lives and decay modes are compared with the available experimental results. The one-proton and two-proton separation energies of all the isotopes are calculated to find nuclei which lie beyond the proton drip line. Among 1119 even Z nuclei within the range 104≤Z≤136, 164 nuclei show sequential alpha emission followed by subsequent spontaneous fission. Since the isotopes decay through alpha decay chain and the half-lives are in measurable range, these isotopes are predicted to be synthesized and detected in laboratory via alpha decay. 2 nuclei will decay by alpha decay followed by proton emission, 54 nuclei show full alpha chains, 642 nuclei will decay through spontaneous fission, 166 nuclei exhibit proton decay and 91 isotopes are found to be stable against alpha decay. All the isotopes are tabulated according to their decay modes. The study is intended to enhance further experimental investigations in superheavy region.

Simple relations between masses of mirror nuclei

The difference between the one-neutron and one-proton separation energies is strongly correlated to the difference of Coulomb energies of two mirror nuclei. In this paper we generalize and refine this correlation and then apply it to predict unknown masses of proton-rich nuclei for mass number $A\ensuremath{\le}110$ within competitive accuracy.

NEUTRON–PROTON PAIRING EFFECT ON ONE-PROTON AND TWO-PROTON SEPARATION ENERGIES IN RARE-EARTH PROTON-RICH NUCLEI

The one-proton and two-proton separation energies are studied for "ordinary" and rare-earth proton-rich nuclei by including the isovector neutron–proton (np) pairing correlations using the BCS approximation. Even–even as well as odd nuclei are considered. In the latter case, the wave function is defined using the blocked-level technique. The single-particle energies used are those of a deformed Woods–Saxon mean field. It is shown that the np isovector pairing effects on the one-proton and two-proton separation energies are non-negligible. However, the only isovector BCS approximation seems to be inadequate for a good description of these quantities when including the np pairing effects: either a particle-number projection or the inclusion of the isoscalar pairing effect seems to be necessary. Another possible improvement would be a more realistic choice of the pairing strengths.

Improving nuclear mass predictions through the Garvey-Kelson relations

We describe a procedure to improve the nuclear mass predictions obtained by means of the Garvey-Kelson iterative process. This is achieved by reducing the degrees of freedom involved in the process, expressing the Garvey-Kelson relations in terms of one-neutron and one-proton separation energies, and using a theoretical estimation for them. This approach has the effect that the intrinsic error associated with the iterative process grows significantly more slowly. This leads to a better quality of nuclear mass predictions and therefore extends the range for which the predictions are accurate. We test these ideas using different mass models.

Quenching of the SnSbTe Cycle in therpProcess

The nuclides 104-108Sn, 106-110Sb, 108,109Te, and 111I at the expected endpoint of the astrophysical rp process have been produced in 58Ni+natNi fusion-evaporation reactions at IGISOL and their mass values were precisely measured with the JYFLTRAP Penning trap mass spectrometer. For 106Sb, 108Sb, and 110Sb these are the first direct experimental mass results obtained. The related one-proton separation energies have been derived and the value for 106Sb, Sp=424(8) keV, shows that the branching into the closed SnSbTe cycle in the astrophysical rp process is weaker than expected.

Comment on “Pygmy dipole response of proton-rich argon nuclei in random-phase approximation and no-core shell model”

In a recent article by C. Barbieri, E. Caurier, K. Langanke, and G. Mart\'inez-Pinedo~\cite{;Bar.08};, low-energy dipole excitations were studied in proton-rich ${;32, 34}; Ar with random-phase approximation (RPA) and no-core shell model (NCSM) using correlated realistic nucleon-nucleon interactions obtained by the unitary correlation operator method (UCOM)~\cite{;Fel.98};. The main objective of this Comment is to argue that the article~\cite{;Bar.08}; contains an inconsistency with respect to previous study of excitations in the same UCOM-RPA framework using identical correlated Argonne V18 interaction~\cite{;Paa.06};, it does not provide any evidence that the low-lying state declared as pygmy dipole resonance in ${;32}; $Ar indeed has the resonance-like structure, and that prior to studying exotic modes of excitation away from the valley of stability one should ensure that the model provides reliable description of available experimental data on nuclear ground state properties and excitations in nuclei. Although the authors aimed at testing the UCOM based theory at the proton drip line, available experimental data that are used as standard initial tests of theory frameworks at the proton drip line have not been considered in the UCOM case (e.g., binding energies, one-proton separation energies, two-proton separation energies).

Direct mass measurements beyond the proton drip-line

At GSI in Darmstadt the Penning trap spectrometer SHIPTRAP was set up to perform precision experiments with low-energetic radioactive ions produced in fusion-evaporation reactions at the velocity filter SHIP. First high-precision measurements were performed determining the masses of 18 neutron-deficient isotopes in the terbium-to-thulium region with relative uncertainties of about 10-8. The masses of nine nuclides were measured for the first time. Four of them (144Ho, 145Ho, 147Tm and 148Tm) were determined to lie beyond the proton drip-line. The data were included into the Atomic Mass Evaluation (AME) and showed generally good agreement with previous measurements. The implication of the results on the nuclear structure and on the location of the proton drip-line is discussed by analyzing the two-neutron and one-proton separation energies. Further simulations and off-line measurements were performed to investigate the stopping efficiency in the gas cell, to optimize the contrast and the quality of the measurement and to determine the uncertainties arising from magnetic field fluctuations.

A systematic study of neutron magic nuclei with N = 8, 20, 28, 50, 82 and 126 in the relativistic mean-field theory

We perform a systematic study of all the traditional neutron magic nuclei with N = 8, 20, 28, 50, 82 and 126, from the neutron drip line to the proton drip line. We adopt the deformed relativistic mean-field theory as our framework and treat pairing correlations by a simple BCS method with a zero-range δ-force. Remarkable agreement with the available experimental data is obtained for the binding energies, the two- and one-proton separation energies, and the nuclear charge radii. The calculated nuclear deformations are compared with the available experimental data and the predictions of the FRDM mass formula and the HFBCS-1 mass formula. We discuss, in particular, the appearance of sub-shell magic nuclei by observing irregular behaviour in the two- and one-proton separation energies.

Proton-Rich Nuclei at and beyond the Proton Drip Line in the Relativistic Mean Field Theory

Ground state properties of proton-rich odd-$Z$ nuclei in the region $55\le Z \le 73$ are studied in the relativistic mean field (RMF) theory. The RMF equations are solved by using the expansion method in the Harmonic-Oscillator basis. In the particle-particle channel, we use the state-dependent BCS method with a zero-range $\delta$-force, which has been proved to be effective even for neutron-rich nuclei. All the ground state properties, including the one-proton separation energies, the ground state deformations, the last occupied proton orbits and the locations of proton drip line, are calculated. Good agreement with both the available experimental data and the predictions of the RHB method are obtained.

Proton drip-line calculations and therpprocess

One-proton and two-proton separation energies are calculated for proton-rich nuclei in the region $A=41--75.$ The method is based on Skyrme Hartree-Fock calculations of Coulomb displacement energies of mirror nuclei in combination with the experimental masses of the neutron-rich nuclei. The implications for the proton drip line and the astrophysical $\mathrm{rp}$ process are discussed. This is done within the framework of a detailed analysis of the sensitivity of $\mathrm{rp}$ process calculations in type I x-ray burst models on nuclear masses. We find that the remaining mass uncertainties, in particular for some nuclei with $N=Z,$ still lead to large uncertainties in calculations of x-ray burst light curves. Further experimental or theoretical improvements of nuclear mass data are necessary before observed x-ray burst light curves can be used to obtain quantitative constraints on ignition conditions and neutron star properties. We identify a list of nuclei for which improved mass data would be most important.

The Proton Drip Line betweenZ= 31 andZ= 49

The Relativistic Hartree Bogoliubov (RHB) model is applied in the description of ground-state properties of proton-rich odd-Z nuclei in the region 31 ≤Z ≤49. The model predicts the location of the proton drip-line, the ground-state quadrupole deformations and one-proton separation energies at and beyond the drip-line, the deformed single-particle orbitals occupied by the odd valence proton, and the corresponding spectroscopic factors.

Mapping the proton drip line from [formula omitted] to [formula omitted

The structure of proton drip line nuclei in the 60<A<100 mass range is studied with the relativistic Hartree–Bogoliubov (RHB) model. For the elements which determine the astrophysical rapid proton capture process path, the RHB model predicts the location of the proton drip-line, the ground-state quadrupole deformations and one-proton separation energies at and beyond the drip-line. The results of the present theoretical investigation are compared with available experimental data. For possible odd- Z ground-state proton emitters, the calculated deformed single-particle orbitals occupied by the odd valence proton and the corresponding spectroscopic factors are compared with predictions of the macroscopic–microscopic mass model.

Relativistic Hartree-Bogoliubov Description of the Deformed Ground-State Proton Emitters

Ground-state properties of deformed proton-rich odd- $Z$ nuclei in the region $59\ensuremath{\le}Z\ensuremath{\le}69$ are described in the framework of relativistic Hartree-Bogoliubov (RHB) theory. One-proton separation energies and ground-state quadrupole deformations that result from fully self-consistent microscopic calculations are compared with available experimental data. The model predicts the location of the proton drip-line, the properties of proton emitters beyond the drip-line, and provides information about the deformed single-particle orbitals occupied by the odd valence proton.

Ground-state properties of deformed proton emitters in the relativistic Hartree-Bogoliubov model

The relativistic Hartree-Bogoliubov (RHB) model is applied in the description of ground-state properties of proton-rich odd- Z nuclei in the region 53 ⩽ Z ⩽ 69. The NL3 effective interaction is used in the mean-field Lagrangian, and pairing correlations are described by the pairing part of the finite-range Gogny interaction D1S. The model predicts the location of the proton drip-line, the ground-state quadrupole deformations and one-proton separation energies at and beyond the drip-line, the deformed single-particle orbitals occupied by the odd valence proton, and the corresponding spectroscopic factors. The results of fully self-consistent RHB calculations are compared with available experimental data, and with predictions of the macroscopic-microscopic mass model.