Experimental Half-lives Research Articles

Theoretical studies on the modes of decay of superheavy nuclei

The decay modes of recently synthesized superheavy nuclei are investigated by comparing the $\ensuremath{\alpha}$-decay half-lives with the spontaneous fission half-lives. $\ensuremath{\alpha}$-decay half-lives are calculated using the Coulomb and proximity potential model for deformed nuclei (CPPMDN). The agreement between theoretical and experimental $\ensuremath{\alpha}$ half-lives shows the predictability of the CPPMDN in the superheavy region. A modified formula is proposed for calculating the spontaneous fission half-lives including the shell correction. The agreement between theoretical predictions and experimental results of spontaneous fission half-lives is satisfactory for heavy and superheavy nuclei ranging from Th to Fl. A comparison between the spontaneous fission half-lives computed using eight different formalisms is performed for even-even superheavy nuclei in the range of $108\ensuremath{\le}Z\ensuremath{\le}120$. Even though all these models can reproduce the experimental spontaneous fission half-lives, model-to-model variations in predicting the fission half-lives in superheavy region is evident from the study.

α-particle preformation of heavy nuclei using proximity potential

The half lives for α decay have been calculated using four different versions of the proximity potential for the even even isotopes of all known α-emitters. Using the experimental half lives, the preformation probability (P0) of α particle before emission is calculated. Also the assault frequency (ν0) is calculated through a modified formula. Half-lives obtained from the potential Prox 76 are minimum, and these values are used for calculating the preformation probability (P0). Use of the potential Prox 76 in calculating P0 is justified as it can best reproduce experimental Coulomb barriers among the four potentials. The trend of the values of P0 versus the neutron number, N, and the proton number, Z, are in agreement with the shell model. The values of P0 are also fitted using a four-parameter formula.

Statistical analysis ofβdecays and the effective value ofgAin the proton-neutron quasiparticle random-phase approximation framework

We perform a Markov Chain Monte Carlo (MCMC) statistical analysis of a number of measured ground-state-to-ground-state single $\beta^+$/electron-capture and $\beta^-$ decays in the nuclear mass range A = 62 - 142. The corresponding experimental comparative half-lives (log ft values) are compared with the theoretical ones obtained by the use of the proton-neutron quasiparticle random-phase approximation (pnQRPA) with G-matrix based effective interactions. The MCMC analysis is performed separately for 47 isobaric triplets and 28 more extended isobaric chains of nuclei to extract values and uncertainties for the effective axial-vector coupling constant g_A in nuclear-structure calculations performed in the pnQRPA framework. As far as available, measured half-lives for two-neutrino double beta-minus decays occurring in the studied isobaric chains are analyzed as well.

Self-consistent approach to beta decay and delayed neutron emission

A brief overview of the recent self-consistent studies of nuclear beta decay is given including the relativistic quasi-particle random-phase approximation or QRPA and Finite Amplitude Method. The results of our self-consistent continuum QRPA model based on the density functional description of the ground states are presented. They are in a good agreement with the recent experimental beta-decay half-lives and delayed neutron emission branchings for the nuclei approaching (and beyond) the neutron closed shells N = 50 near 78Ni and N = 82 near 132Sn. A comparison with the recent calculations from relativistic QRPA model, Finite Amplitude Method and semi-microscopic finite-range droplet model is performed. An importance of the quasi-particle phonon coupling is stressed for the description of the beta decay and delayed multi-neutron emission rates. A strategy of extending our approach to the deformed nuclei and the open problems are discussed.

Proton emission half-lives within a Gamow-like model

Proton emission is described using a model which has previously given good results in the description of $\alpha$ and cluster radioactivity. The simple phenomenological formalism, based on the Gamow theory for alpha decay, is now extended by including the centrifugal term. The model contains only one parameter: the effective nuclear radius constant. Its value was once found for alpha and cluster emitters. A good agreement with the experimental half-lives for proton radioactivity is achieved without any additional fitting procedures to the data for proton emission.

A systematic calculation of alpha decay half-lives using a new approach for barrier penetration probability

A systematic calculation of alpha decay half-lives of 347 nuclei is considered in the framework of the Wentzel–Kramers–Brillouin (WKB) approximation using two formulas. A recently proposed barrier penetration formula, with some modified parameters, is used first. Second, a new analytic barrier penetration formula is derived by taking into account the centrifugal potential. A good agreement with experimental data is achieved especially for spherical nuclei. The new formula reproduces experimental alpha decay half-lives with a satisfying accuracy especially for penetration energies much lower than the Coulomb barrier.

In Situ Measurement of CuO and Cu(OH)2 Nanoparticle Dissolution Rates in Quiescent Freshwater Mesocosms

Recent studies have characterized copper-based nanoparticles (CBNPs) as relatively insoluble, raising potential persistence, accumulation, and toxicological concerns about their long-term application as agricultural pesticides. The dissolution rates of two CBNPs were measured in natural and artificial waters under both saturated and unsaturated conditions with respect to CuO(s) (total Cu, <1 mg/kg). Kocide 3000, an agricultural pesticide formulation with nanoscale Cu(OH)2 particles, rapidly dissolved with an experimental half-life of <8 h in natural water. Copper oxide nanoparticles were longer-lived, with an experimental half-life of 73 h in natural water. In contrast to prior reports of CuONP dissolution, our results suggest that even in moderately alkaline waters, CuO and Cu(OH)2 NPs may persist as particles for days to weeks under quiescent conditions in a freshwater environment.

Systematic study on α-decay half-lives of Bi isotopes

Systematic calculations on [Formula: see text]-decay half-lives of Bi isotopes are performed by using the generalized liquid drop model (GLDM) and several sets of Royer’s analytic formulas. In calculations, the [Formula: see text] transitions include the ones of (i) ground state (g.s.) to g.s., (ii) g.s. to isomeric state (i.s.), (iii) i.s. to g.s., (iv) i.s. to i.s. According to the comparison between the calculated half-lives and the experimental data, it is found that the experimental half-lives are reproduced well by the GLDM with the cluster-like mode. This indicates that the nuclear structure details play important roles in the [Formula: see text]-decay half-lives. In addition, it is found that the experimental half-lives are not reproduced well by these analytic formulas because the parameters are obtained by fitting the experimental half-lives of g.s. to g.s. transitions. To give better predictions on [Formula: see text]-decay half-lives, the parameters in these formulas should be refitted by including the experimental [Formula: see text]-transition of (ii)–(iv) mentioned above.

Rapid Proteasomal Degradation of Mutant Proteins Is the Primary Mechanism Leading to Tumorigenesis in Patients With Missense AIP Mutations.

Context:The pathogenic effect of mutations in the aryl hydrocarbon receptor interacting protein (AIP) gene (AIPmuts) in pituitary adenomas is incompletely understood. We have identified the primary mechanism of loss of function for missense AIPmuts.Objective:This study sought to analyze the mechanism/speed of protein turnover of wild-type and missense AIP variants, correlating protein half-life with clinical parameters.Design and Setting:Half-life and protein–protein interaction experiments and cross-sectional analysis of AIPmut positive patients' data were performed in a clinical academic research institution.Patients:Data were obtained from our cohort of pituitary adenoma patients and literature-reported cases.Interventions:Protein turnover of endogenous AIP in two cell lines and fifteen AIP variants overexpressed in HEK293 cells was analyzed via cycloheximide chase and proteasome inhibition. Glutathione-S-transferase pull-down and quantitative mass spectrometry identified proteins involved in AIP degradation; results were confirmed by coimmunoprecipitation and gene knockdown. Relevant clinical data was collected.Main Outcome Measures:Half-life of wild-type and mutant AIP proteins and its correlation with clinical parameters.Results:Endogenous AIP half-life was similar in HEK293 and lymphoblastoid cells (43.5 and 32.7 h). AIP variants were divided into stable proteins (median, 77.7 h; interquartile range [IQR], 60.7–92.9 h), and those with short (median, 27 h; IQR, 21.6–28.7 h) or very short (median, 7.7 h; IQR, 5.6–10.5 h) half-life; proteasomal inhibition rescued the rapid degradation of mutant proteins. The experimental half-life significantly correlated with age at diagnosis of acromegaly/gigantism (r = 0.411; P = .002). The FBXO3-containing SKP1–CUL1–F-box protein complex was identified as the E3 ubiquitin-ligase recognizing AIP.Conclusions:AIP is a stable protein, driven to ubiquitination by the SKP1–CUL1–F-box protein complex. Enhanced proteasomal degradation is a novel pathogenic mechanism for AIPmuts, with direct implications for the phenotype.

Optimum orientation versus orientation averaging description of cluster radioactivity

While the optimum-orientation concept is frequently used in studies on cluster decays involving deformed nuclei, the orientation-averaging concept is used in most alpha decay studies. We investigate the different decay stages in both the optimum-orientation and the orientation-averaging pictures of the cluster decay process. For decays of 232,233,234U and 236,238Pu isotopes, the quantum knocking frequency and penetration probability based on the Wentzel–Kramers–Brillouin approximation are used to find the decay width. The obtained decay width and the experimental half-life are employed to estimate the clusters preformation probability. We found that the orientation-averaged decay width is one or two orders of magnitude less than its value along the non-compact optimum orientation. Correspondingly, the extracted preformation probability based on the averaged decay width increases with the same orders of magnitude compared to its value obtained considering the optimum orientation. The cluster preformation probabilities estimated by the two considered schemes are in more or less comparable agreement with the Blendowske–Walliser (BW) formula based on the preformation probability of α ( obtained from the orientation-averaging scheme. All the results, including the optimum-orientation ones, deviate substantially from the BW law based on that was estimated from the optimum-orientation scheme. To account for the nuclear deformations, it is more relevant to calculate the decay width by averaging over the different possible orientations of the participating deformed nuclei, rather than considering the corresponding non-compact optimum orientation.

Systematic study ofαdecay half-lives for even-even nuclei within a two-potential approach

$\ensuremath{\alpha}$ decay is a common and important process of natural radioactivity of heavy and superheavy nuclei. The $\ensuremath{\alpha}$ decay half-lives for even-even nuclei from $Z=62$ to $Z=118$ are systematically studied based on the two-potential approach with a quasistationary state approximation. As for the nuclear potential, the isospin effect is considered, which slightly improves the results by 6.8%. To reduce the deviations between experimental half-lives and calculated results due to the nuclear shell structure, the analytic expression of hindrance factors is employed. Our results can reproduce the experimental half-lives as good as using the density-dependent cluster model and the generalized liquid drop model.

Nuclear β-decay half-lives in the relativistic point-coupling model

The self-consistent proton–neutron quasiparticle random phase approximation approach is employed to calculate β-decay half-lives of neutron-rich even–even nuclei with . A newly proposed nonlinear point-coupling effective interaction PC-PK1 is used in the calculations. It is found that the isoscalar proton–neutron pairing interaction can significantly reduce β-decay half-lives. With an isospin-dependent isoscalar proton–neutron pairing strength, our results well reproduce the experimental β-decay half-lives, although the pairing strength is not adjusted using the half-lives calculated in this study.

Large-scale evaluation ofβ-decay rates ofr-process nuclei with the inclusion of first-forbidden transitions

R-process nucleosynthesis models rely, by necessity, on nuclear structure models for input. Particularly important are beta-decay half-lives of neutron rich nuclei. At present only a single systematic calculation exists that provides values for all relevant nuclei making it difficult to test the sensitivity of nucleosynthesis models to this input. Additionally, even though there are indications that their contribution may be significant, the impact of first-forbidden transitions on decay rates has not been systematically studied within a consistent model. We use a fully self-consistent covariant density functional theory (CDFT) framework to provide a table of $\beta$-decay half-lives and $\beta$-delayed neutron emission probabilities, including first-forbidden transitions. We observe a significant contribution of the first-forbidden transitions to the total decay rate in nuclei far from the valley of stability. The experimental half-lives are in general well reproduced, both for even-even, odd-A and odd-odd nuclei, in particular for short-lived nuclei.

Delayed neutron emission near the shell-closures

The self-consistent Density Functional + Continuum QRPA approach (DF+CQRPA) provides a good description of the recent experimental beta-decay half-lives and delayed neutron emission branchings for the nuclei approaching to (and beyond) the neutron closed shells N = 28; 50; 82. Predictions of beta-decay properties are more reliable than the ones of standard global approaches traditionally used for the r-process modelling. An impact of the quasi-particle phonon coupling on the delayed multi-neutron emission rates P2n, P3n,… near the closed shells is also discussed.

Calculation of Beta Decay Half-Lives and Delayed Neutron Branching Ratio of Fission Fragments with Skyrme-QRPA

Nuclear β -decay and delayed neutron (DN) emission is important for the r -process nucleosynthesis after the freeze-out, and stable and safe operation of nuclear reactors. Even though radioactive beam facilities have enabled us to measure β -decay and branching ratio of neutron-rich nuclei apart from the stability line in the nuclear chart, there are still a lot of nuclei which one cannot investigate experimentally. In particular, information on DN is rather scarce than that of T 1/2 . To predict T 1/2 and the branching ratios of DN for next JENDL decay data, we have developed a method which comprises the quasiparticle-random-phase-approximation (QRPA) and the Hauser-Feshbach statistical model (HFSM). In this work, we calculate fission fragments with T 1/2 ≤ 50 sec. We obtain the rms deviation from experimental half-life of 3:71. Although the result is still worse than GT2 which has been adopted in JENDL decay data, DN spectra are newly calculated. We also discuss further subjects to be done in future for improving the present approach and making next generation of JENDL decay data.

Half-life determination of the ground state decay of 111Ag

The radioactive decay half-life of the β−-emitter 111Ag has been measured using decay transitions identified using a high purity germanium γ-ray spectrometer. The time series of measurements of the net peak areas of the 96.8keV, 245.4keV and 342.1keV γ-ray emissions following the β− decay of 111Ag were made over approximately 23 days, i.e. ~3 half-life periods. The measured half-life of the ground state decay of 111Ag was determined as 7.423 (13) days which is consistent with the Evaluated Nuclear Structure Data File (ENSDF) recommended half-life of 7.45 (1) days at k=2. Utilising all available experimental half-life values, a revised recommended half-life of 7.452 (12) days has been determined.

Search for double-beta decay of 136Xe to excited states of 136Ba with the KamLAND-Zen experiment

A search for double-beta decays of 136Xe to excited states of 136Ba has been performed with the first phase data set of the KamLAND-Zen experiment. The 01+, 21+ and 22+ transitions of 0νββ decay were evaluated in an exposure of 89.5 kg⋅yr of 136Xe, while the same transitions of 2νββ decay were evaluated in an exposure of 61.8 kg⋅yr. No excess over background was found for all decay modes. The lower half-life limits of the 21+ state transitions of 0νββ and 2νββ decay were improved to T1/20ν(0+→21+)>2.6×1025 yr and T1/22ν(0+→21+)>4.6×1023 yr (90% C.L.), respectively. We report on the first experimental lower half-life limits for the transitions to the 01+ state of 136Xe for 0νββ and 2νββ decay. They are T1/20ν(0+→01+)>2.4×1025 yr and T1/22ν(0+→01+)>8.3×1023 yr (90% C.L.). The transitions to the 22+ states are also evaluated for the first time to be T1/20ν(0+→22+)>2.6×1025 yr and T1/22ν(0+→22+)>9.0×1023 yr (90% C.L.). These results are compared to recent theoretical predictions.

Applications to nuclear properties of the microscopic–macroscopic model based on the semiclassical Wigner–Kirkwood method

Some time ago we proposed a new microscopic–macroscopic model where the semiclassical Wigner–Kirkwood expansion of the energy up to fourth-order in ℏ is used to compute the shell corrections in a deformed Woods–Saxon potential instead of the usual Strutinsky averaging scheme. For a set of 558 even–even nuclei computed with this new model, we found a rms deviation of 610 keV from the experimental masses, similar to the value obtained using the well-known finite range droplet model and the Lublin–Strasbourg drop model for the same set of nuclei. In this paper we analyze the α radioactivity in nuclei with mass number , finding good agreement with the available experimental results. We have also estimated spontaneous fission half-lives for superheavy nuclei in the region between Z = 102 and Z = 110. We find that our model predicts reasonably well the experimental half-lives in the considered nuclei, in spite of the fact that the fission barriers turn out to be somewhat too high.

Preformation probability inside α emitters having different ground state spin-parity than their daughters

The ground-state spin and parity of a formed daughter in the radioactive Alpha-emitter is expected to influence the preformation probability of the Alpha and daughter clusters inside it. We investigate the Alpha and daughter preformation probability inside odd-A and doubly-odd radioactive nuclei when the daughter and parent are of different spin and/or parity. We consider only the ground-state to ground-state unfavored decays. This is to extract precise information about the effect of the difference in the ground states spin-parity of the involved nuclei far away any influences from the excitation energy if the decays are coming from isomeric states. The calculations are done for 161 Alpha-emitters, with Z=65-112 and N=84-173, in the framework of the extended cluster model, with WKB penetrability and assault frequency. We used a Hamiltonian energy density scheme based on Skyrme-SLy4 interaction to compute the interaction potential. The Alpha plus cluster preformation probability is extracted from the calculated decay width and the experimental half-life time. We discussed in detailed steps the effect of angular momentum of the emitted Alpha-particle on the various physical quantities involved in the unfavored decay process and how it is finally increases the half-life time. We found that if the ground states spin and/or parity of parent and daughter nuclei are different, then the preformation probability of the Alpha-cluster inside parent is less than it would be if they have similar spin-parity. We modified the formula that gives the Alpha preformation probability in terms of the numbers of protons and neutrons outside the shell closures of parent, to account for this hindrance in the preformation probability for the unfavored decays between ground states.

Are Quasi-Steady-State Approximated Models Suitable for Quantifying Intrinsic Noise Accurately?

Large gene regulatory networks (GRN) are often modeled with quasi-steady-state approximation (QSSA) to reduce the huge computational time required for intrinsic noise quantification using Gillespie stochastic simulation algorithm (SSA). However, the question still remains whether the stochastic QSSA model measures the intrinsic noise as accurately as the SSA performed for a detailed mechanistic model or not? To address this issue, we have constructed mechanistic and QSSA models for few frequently observed GRNs exhibiting switching behavior and performed stochastic simulations with them. Our results strongly suggest that the performance of a stochastic QSSA model in comparison to SSA performed for a mechanistic model critically relies on the absolute values of the mRNA and protein half-lives involved in the corresponding GRN. The extent of accuracy level achieved by the stochastic QSSA model calculations will depend on the level of bursting frequency generated due to the absolute value of the half-life of either mRNA or protein or for both the species. For the GRNs considered, the stochastic QSSA quantifies the intrinsic noise at the protein level with greater accuracy and for larger combinations of half-life values of mRNA and protein, whereas in case of mRNA the satisfactory accuracy level can only be reached for limited combinations of absolute values of half-lives. Further, we have clearly demonstrated that the abundance levels of mRNA and protein hardly matter for such comparison between QSSA and mechanistic models. Based on our findings, we conclude that QSSA model can be a good choice for evaluating intrinsic noise for other GRNs as well, provided we make a rational choice based on experimental half-life values available in literature.