Decay Of Nuclei Research Articles

Development of a Monte-Carlo Evaporation Code for Multiple-Fragment Emission

An extended Hauser-Feshbach approach has been employed in a multi-step Monte-Carlo evaporation code designed to study the de-excitation of highly excited compound nuclei. The code is intended to account for emission of light particles ($\gamma$, n, $^{1,2,3}$H, $^{3-6}$He) and intermediate mass fragments in their ground and excited states (particle-bound or unbound). As a study case, we consider the decay of the compound nucleus $^{120}$Te$^*$ at excitation energy 100, 200 and 300 MeV. First chance decay widths are compared with treatments based on the Weisskopf and the s-wave approximation. Preliminary calculations are compared with experimental isotopic yields of intermediate mass fragments emitted in E/A = 50 MeV $^{4}$He + $^{116,124}$Sn $\rightarrow$ $^{120,128}$Te$^*$ reactions.

Decay aspects of the compound nuclei formed via CF and ICF path in 12C[formula omitted]Cr reaction

The reaction dynamics of 12C+52Cr reaction induced via a cluster-structured projectile (12C) is examined theoretically using the dynamical cluster decay model (DCM) with respect to the recent experimental data available at wide span of center-of-mass energies (Ec.m.=41.84-71.20 MeV). In view of the cluster-structured projectile, a systematic analysis is carried out for both complete fusion (CF) and incomplete fusion (ICF) channel. The calculations are done by including the quadrupole (β2) deformations and optimum (θiopt.) orientation criteria of the decaying fragments. With an aim to have comprehensive analysis of the decay of compound nuclei formed via CF and ICF processes, the role of center-of-mass energy (Ec.m.) and angular momentum (ℓ) is explored in terms of various parameters of DCM such as fragmentation potential, preformation probability, penetrability and barrier modification. Further, the role of diffuseness parameter is also studied for 12C+52Cr reaction. For the given reaction, the contribution of light particles (LPs), and energetically favored intermediate mass fragments (IMFs) constitutes the decay cross sections. Therefore, the contribution of emitted LPs and IMFs is estimated for the decay of both compound nuclei formed via CF and ICF channels. Furthermore, the comparative analysis of different proximity potentials is also worked out for ICF. Finally, the effect of Ec.m. on the contribution of ICF cross sections is studied and compared with the experimental data.

Decay modes of superheavy nuclei using a modified generalized liquid drop model and a mass-inertia-dependent approach for spontaneous fission

A modified generalized liquid drop model with the proximity 77 parametrization is used for studying the alpha decay of superheavy nuclei in the range $104\ensuremath{\le}Z\ensuremath{\le}118$. The spontaneous fission (SF) half-lives are computed using a new formula which depends on the shells effect (${E}_{\mathrm{shell}}$) and the mass inertia (${I}_{\mathrm{rigid}}$). The modes of decay are predicted by comparing ${T}_{1/2}^{\ensuremath{\alpha}}$ with ${T}_{1/2}^{\mathrm{SF}}$ and are compared with the experimental observations. These studies may induce further investigations in the superheavy region.

Monte Carlo modeling of production of three alpha-particles in low energy n +12C interactions

To describe [Formula: see text] interactions with production of three [Formula: see text]-particles at incident neutron kinetic energy of 14 MeV in a nuclear (photo) emulsion, a Monte Carlo model is proposed for four channels of decay of an excited carbon-12 nucleus into three [Formula: see text]-particles. The Monte Carlo calculation results describe well the experimental data on the distribution of the angle between the three-dimensional momenta of all pairs of [Formula: see text]-particles in a collision event, on the distribution of the angle between the projections of the momentum vectors of all pairs of [Formula: see text]-particles in collision event on each of the coordinate planes, on the distribution of the sum of the kinetic energies of all pairs of [Formula: see text]-particles in a collision event, and the distribution of projections of the momenta of [Formula: see text]-particles on the coordinate planes. The best agreement of the Monte Carlo model results with the experimental data is achieved if the direct decay [Formula: see text] and decay through the formation of an intermediate beryllium nucleus [Formula: see text] are generated with equal probabilities, while the excitation energies of 3.04 MeV, 1.04 MeV, and 0.1 MeV for the beryllium nucleus are generated with relative weights of 75%, 15%, and 10%, respectively.

Alpha decay half-lives of superheavy nuclei 104 ≤ Z ≤ 125

In order to describe scattering, fusion, fission and ground state masses, Krappe and collaborators developed unified nuclear potential, by generalizing liquid drop model. They have incorporated phenomenological parameters accounting for the attractive force between two separated fragments. One of the phenomenological parameters involved in this model is the range of folded Yukawa function, which accounts for surface diffuseness of the potential and short range attractive interaction. The role of range of folding function of Yukawa-plus-exponential potential is analyzed for alpha decay of heavy and superheavy nuclei. Significant effect of this function is noted in preformation probability which improves the accuracy of half-lives of alpha decay. Half-lives for alpha decay are better obtained for two values of the range of folding function 0.54 and 0.8[Formula: see text]fm for heavy and superheavy mass regions, respectively. The study confirms the associated shell structure [Formula: see text] in heavy nuclei and [Formula: see text] and [Formula: see text] in superheavy nuclei. The calculations are extended to predict the half-lives of superheavy nuclei with [Formula: see text] and [Formula: see text] which are not yet synthesized experimentally.

Multifarious Roles of Hidden Chiral-Scale Symmetry: “Quenching” gA in Nuclei

I discuss how the axial current coupling constant gA renormalized in scale symmetric chiral EFT defined at a chiral matching scale impacts on the axial current matrix elements on beta decays in nuclei with and without neutrinos. The “quenched” gA observed in nuclear superallowed Gamow–Teller transitions, a long-standing puzzle in nuclear physics, is shown to encode the emergence of chiral-scale symmetry hidden in QCD in the vacuum. This enables one to explore how trace-anomaly-induced scale symmetry breaking enters in the renormalized gA in nuclei applicable to certain non-unique forbidden processes involved in neutrinoless double beta decays. A parallel is made between the roles of chiral-scale symmetry in quenching gA in highly dense medium and in hadron–quark continuity in the EoS of dense matter in massive compact stars. A systematic chiral-scale EFT, presently lacking in nuclear theory and potentially crucial for the future progress, is suggested as a challenge in the field.

Nuclear matrix elements of neutrinoless double- β decay in the triaxial projected shell model

The nuclear matrix elements of neutrinoless double-$\beta$ decay for nuclei $^{76}$Ge, $^{82}$Se, $^{100}$Mo, $^{130}$Te, and $^{150}$Nd are studied within the triaxial projected shell model, which incorporates simultaneously the triaxial deformation and quasiparticle configuration mixing. The low-lying spectra and the $B(E2:0^+\rightarrow2^+)$ values are reproduced well. The effects of the quasiparticles configuration mixing, the triaxial deformation, and the closure approximation on the nuclear matrix elements are studied in detail. For nuclei $^{76}$Ge, $^{82}$Se, $^{100}$Mo, $^{130}$Te, and $^{150}$Nd, the nuclear matrix elements are respectively reduced by the quasiparticle configuration mixing by 6%, 7%, 2%, 3%, and 4%, and enhanced by the odd-odd intermediate states by 7%, 4%, 11%, 20%, and 14%. Varying the triaxial deformation $\gamma$ from $0^\circ$ to $60^\circ$ for the mother and daughter nuclei, the nuclear matrix elements change by 41%, 17%, 68%, 14%, and 511% respectively for $^{76}$Ge, $^{82}$Se, $^{100}$Mo, $^{130}$Te, and $^{150}$Nd, which indicates the importance of treating the triaxial deformation consistently in calculating the nuclear matrix elements.

Numerical Solution of Radioactive Core Decay Activity Rate of Actinium Series Using Matrix Algebra Method

The Actinium 235 series is one of the radioactive series which is widely used as a raw material for reactors and nuclear activities. The existence of this series is found in several countries such as West USA, Canada, Australia, South Africa, Russia, and Zaire. The purpose of this study was to determine the activity value and the number of radioactive nucleus decay atoms on the actinium 235 rendered in a very long decay time of 4.3 x 109 years. The decay count in this study uses an algebraic matrix method to simplify the chain decay solution, which generally uses the concept of differential equations. The solution using this method can be computationally simulated using the Matlab program. This study indicates that the value of the decay activity experienced by each element in this series is the same, which is equal to 2,636 x 1011 Bq. This condition causes the actinium 235 series to experience secular equilibrium because the half-life of the parent nuclide is greater than the nuclide derivatives. The decay activity of the radioactive nucleus under the actinium 235 series is strongly influenced by the half-life of the nuclides, the decay constants, and the number of atoms after decay

Correlation in formation of 8Be nuclei and α-particles in fragmentation of relativistic nuclei

In the events of peripheral dissociation of relativistic nuclei in the nuclear track emulsion, it is possible to study the emerging ensembles of He and H nuclei, including those from decays of unstable 8Be and 9B nuclei, as well as the Hoyle state. These extremely short-lived states are identified by invariant masses calculated from the angles in 2α-pairs, 2αp- and 3α-triplets in the approximation of conservation of momentum per nucleon of the primary nucleus. In the same approach, it is possible to search for more complex states. This paper explores the correlation between the formation of 8Be nuclei and the multiplicity of accompanying α-particles in the dissociation of relativistic 16O, 22Ne, 28Si, and 197Au nuclei. On the above basis, estimates of this correlation are presented for the unstable 9B nucleus and the Hoyle state. The enhancement in the 8Be contribution to dissociation with the α-particle multiplicity has been found. Decays of 9B nuclei and Hoyle states follow the same trend.

Impact of finite-range tensor terms in the Gogny force on the $$\beta $$-decay of magic nuclei

Impact of finite-range tensor terms in the Gogny force on the $$\beta $$-decay of magic nuclei

Predictions for the α decay of superheavy nuclei of Z = 119 − 120 isotopes

A new α preformation factor formula was proposed in the framework of unified fission model (UFM), the coefficients of the formula were obtained by fitting the extracted α preformation factors of 465 nuclei with Z=62−103. The root mean square (RMS) deviation of the calculated α preformation factors with the extracted values is 0.388, indicating that the formula can describe the α particle preformation probability reliably. Then the α decay half-lives for recently observed 76 superheavy nuclei (SHN) are calculated by the UFM with the new α preformation factor formula. The comparison between the calculated values and the experimental data demonstrates that the UFM taking the preformation factor into account is a useful tool to investigate the α decay half-lives of SHN. Encouraged by this, the predictions of α decay half-lives for SHN Z=119,120 isotopes are made by using the theoretical mass tables FRDM2012, WS4 and WS2016+RBFs to determine the Qα values. The predictions can provide references for experiments of synthesizing new SHN if the mass tables are accurate enough.

Extended universal decay law formula for the α and cluster decays

The Universal Decay Law (UDL) formula for the alpha and cluster decays is extended to include the effects of the angular momentum and isospin. The parameters for all formulas are obtained by fitting to available experimental data. We also evaluated the uncertainty of the parameters as well as the uncertainties of predictions of the formulas. The rms values are computed and the best rms among them is obtained for the formula including both the angular momentum and isospin terms. The modified UDL formula is applied to get the half-lives of cluster and alpha decays of nuclei. Branching ratios (alpha/cluster) are calculated and compared with experimental ones. The half-lives for heavier cluster decays are obtained by using UDL and new UDL formulas.

The destruction of the cometary nucleus – The case of 73P/Schwassmann-Wachmann

The paper presents an analysis of the actual brightness change of comet 73P/Schwassmann-Wachmann, which took place in 1995. The consequence of a cometary outburst is the destruction of a fragment of its surface. This causes the emission of comet material from both the surface and from exposed subsurface layers. Therefore, the calculations take into account the scattering cross-sections that come from ice and dust particles. It was assumed that the dust particles are silicates which are characterized by high irregularity of their structure. This assumption is a consequence of the analysis of the results provided by the Rosetta mission to the comet 67P/Churyumov-Gerasimenko. The main factor determining the amplitude of a cometary outburst is the mass ejected as well as the loss of ice that holds the individual nucleus structures together. Consequently, this phenomenon can significantly contribute to the destruction and even decay of the cometary nucleus.

Bayesian analysis of the uncertainty in decay lifetimes in the case of poor statistics

In case of rare decay events the lifetime or the decay width is evaluated with low statistics. The uncertainty has to be carefully evaluated. In this article, we propose a Bayesian analysis of the lifetime and decay width and derive simple formulas for their assigned values and for the limits of the credible interval. The results are applied to the decay of superheavy nuclei as an illustration.

Self-consistent calculations of electron-capture decays in Z=118, 119, and 120 superheavy isotopes

Weak decays in superheavy nuclei with proton numbers Z=118−120 and neutron numbers N=175−184 are studied within a microscopic formalism based on deformed self-consistent Skyrme Hartree-Fock mean-field calculations with pairing correlations. The half-lives of β+ decay and electron capture are compared with α-decay half-lives obtained from phenomenological formulas. The sensitivity of the half-lives to the unknown Q-energies is studied by comparing the results obtained from different approaches for the masses. It is shown that α-decay is always dominant in this mass region. The competition between α and β+/EC decay modes is studied in seven α-decay chains starting at different isotopes of Z=118, 119, and 120.

Search for light exotic fermions in double-beta decays

The Standard Model of Particle Physics predicts the double-β decay of certain nuclei with the emission of two active neutrinos. In this letter, we argue that double-β decay experiments could be used to probe models with light exotic fermions through the search for spectral distortions in the electron spectrum with respect to the Standard Model expectations. We consider two concrete examples: models with light sterile neutrinos, singly produced in the double-β decay, and models with a light Z2-odd fermion, pair produced due to a Z2 symmetry. We estimate the discovery potential of a selection of double-β decay experiments and find that future searches will test for the first time a new part of the parameter space of interest at the MeV-mass scale.

A systematic study of alpha decay in actinide nuclei using modified generalized liquid drop model

The alpha decay half-lives of actinides within modified generalized liquid drop model (MGLDM) are investigated by the Wentzel–Kramers–Brillouin (WKB) barrier penetration probability. The potential barrier was studied taking in to account of nuclear proximity, coulomb interaction and centrifugal potential with the inclusion of angular momentum. This work predicts the alpha decay half-lives of unknown actinide nuclei such as [Formula: see text]Am, [Formula: see text]Cm, [Formula: see text]Bk, [Formula: see text]Es and [Formula: see text]No. The calculated alpha decay half-lives reproduce accurately the experimental data. The predictions provided for the alpha decay half-lives within the MGLDM may be helpful for identifying the new isotopes in this field.

Experimental taphonomy of organelles and the fossil record of early eukaryote evolution.

The timing of origin of eukaryotes and the sequence of eukaryogenesis are poorly constrained because their fossil record is difficult to interpret. Claims of fossilized organelles have been discounted on the unsubstantiated perception that they decay too quickly for fossilization. We experimentally characterized the pattern and time scale of decay of nuclei, chloroplasts, and pyrenoids in red and green algae, demonstrating that they persist for many weeks postmortem as physical substrates available for preservation, a time scale consistent with known mechanisms of fossilization. Chloroplasts exhibit greater decay resistance than nuclei; pyrenoids are unlikely to be preserved, but their presence could be inferred from spaces within fossil chloroplasts. Our results are compatible with differential organelle preservation in seed plants. Claims of fossilized organelles in Proterozoic fossils can no longer be dismissed on grounds of plausibility, prompting reinterpretation of the early eukaryotic fossil record and the prospect of a fossil record of eukaryogenesis.

Ab initio benchmarks of neutrinoless double- β decay in light nuclei with a chiral Hamiltonian

We report ab initio benchmark calculations of nuclear matrix elements (NMEs) for neutrinoless double-beta ($0\nu\beta\beta$) decays in light nuclei with mass number ranging from $A=6$ to $A=22$. We use the transition operator derived from light-Majorana neutrino exchange and evaluate the NME with three different methods: two variants of in-medium similarity renormalization group (IMSRG) and importance-truncated no-core shell model (IT-NCSM). The same two-plus-three-nucleon interaction from chiral effective field theory is employed, and both isospin-conserving ($\Delta T=0$) and isospin-changing ($\Delta T=2$) transitions are studied. We compare our resulting ground-state energies and NMEs to those of recent ab initio no-core shell model and coupled-cluster calculations, also with the same inputs. We show that the NMEs of $\Delta T=0$ transitions are in good agreement among all calculations, at the level of 10%. For $\Delta T=2$, relative deviations are more significant in some nuclei. The comparison with the exact IT-NCSM result allows us to analyze these cases in detail, and indicates the next steps towards improving the IMSRG-based approaches. The present study clearly demonstrates the power of consistent cross-checks that are made possible by ab initio methodology. This capability is crucial for providing meaningful many-body uncertainties in the NMEs for the $0\nu\beta\beta$ decays in heavier candidate nuclei, where quasi-exact benchmarks are not available.

Predictions for the α decay of proton-rich nuclei in the range of 86⩽Z⩽98

The α decay half-lives of odd-A and odd-odd nuclei ranging in 65⩽Z⩽112 are investigated by employing the modified universal decay law and the unified fission model, both of them take into account the contribution of centrifugal potential. The good agreement with the experimental data indicates that the modified universal decay law and the unified fission model are useful tools to investigate these α-decays when they contain the effect of centrifugal potential. Relatively long half-lives are predicted by using the new mass table WS2016+RBFs to determine the Qα for many unknown proton-rich nuclei between Rn and Cf, sufficient to detect them if synthesized in a laboratory.