Excited States Of Daughter Nuclei Research Articles

Study of α-Decay Energy by an Artificial Neural Network Considering Pairing and Shell Effects

We build and train an artificial neural network (ANN) model based on experimental α-decay energy (Qα) data. In addition to decays between the ground states of parent and daughter nuclei, decays from the ground states of parent nuclei to the excited states of daughter nuclei are also included. In this way, the number of samples is increased dramatically. The α particle is assumed to have a spherical symmetric shape. The root-mean-square deviation between the calculated results obtained from the ANN model and the experimental data is 0.105 MeV. It shows a good predictive power for α-decay energy with the ANN model. The influence of different inputs is investigated. It is found that both the shell effect and the pairing effect result in an obvious improvement of the predictive power of the ANN model, and the shell effect plays a more important role. The optimal result can be obtained when both the shell and pairing effects are considered simultaneously. The application of the ANN model in predicting α-decay energy indicates a neutron magic number at N=184 in the superheavy nuclei mass region.

Calculation of double-β decay half-lives using an improved Primakoff-Rosen formula * *Supported by the National Natural Science Foundation of China (U1731238, 11761161001, 11105079, 11535004, 11375086, 11975167, 12035011), the Science and Technology Development Fund (FDCT) of Macau (020/2014/A1, 008/2017/AFJ, 0042/2018/A2), the Science and Technology Foundation of Guizhou Province ((2016)4008, (2017)5726-37) and the foundation of Guizhou Provincial education Department (KY(2020)003)

A systematic analysis on experimental data of the half-lives of nuclear double- decays with two neutrinos ( ) is performed based on the analytical formula proposed by Primakoff and Rosen. We improve the formula by considering the shell effects and refining the energy dependence of the phase-space factor. This improved formula can closely describe all available experimental half-lives of decays, both for ground-state transitions and transitions from ground states of parent nuclei to the first excited states of daughter nuclei. The calculated half-lives agree with the experimental data of ground-state transitions of all known eleven nuclei with an average factor of 2.3. Further predictions are provided for -decay candidates with decay energies above 0.5 MeV. We compare different theoretical predictions and emphasize the importance of experimental measurements on the half-lives of double- transitions between the ground state of Ca, Ge, and Xe and the first excited states of their corresponding daughter nuclei, which will be very useful for understanding the underlying mechanisms of double- decays and for further studying the shell effects on nuclear transition matrix elements.

A Silicon 4π Spectrometer of β-Decay Electrons with Energies of up to 3 MeV

A 4π β spectrometer consists of two Si(Li) detectors with a sensitive region that is more than 8-mm thick. Using this total-absorption spectrometer it is possible to make a direct measurement of β spectra without correcting the response function for the electron backscattering from the crystal surface. The β spectra of transitions to the excited states of daughter nuclei have been measured using an additional 3'' BGO detector of γ rays, which is connected in coincidence with the pair of Si(Li) detectors.

Search for evidence of rotational cluster bands in O18

Clustering in $^{18}\mathrm{O}$ is of great interest to the nuclear physics community, due to theoretical predictions of $\mathrm{core}+\ensuremath{\alpha}$ and nuclear molecular structures. An experiment was performed in order to measure branching ratios for states in $^{18}\mathrm{O}$, determining the tendency towards clustering based on the value of ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\alpha}}/{\mathrm{\ensuremath{\Gamma}}}_{\text{tot}}$ for each state, and the reduced widths compared to the Wigner limit. An experimental method that enables the measurement of branching ratios for almost all available decay modes, including $\ensuremath{\gamma}$ decay, $\ensuremath{\alpha}$ decay, and $n$ decay, was employed. The method is also sensitive to the population of excited states in daughter nuclei, allowing for more accurate determination of the ${\ensuremath{\alpha}}_{0}$ branch. The measurements represent, for several states, either the first branching ratio measurement or the first determination of ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\alpha}}/{\mathrm{\ensuremath{\Gamma}}}_{\text{tot}}$. Based on these measurements, no evidence of consistent cluster structure is seen across any of the bands previously proposed, casting doubt on their existence. Despite this, some states displaying cluster structure are observed.

Double Beta Decay to Excited States of Daughter Nuclei

In this paper we review results obtained in the searches of double beta decays to excited states of the daughter nuclei and illustrate the related experimental techniques. In particular, we describe in some detail the only two cases in which the transition has been observed; that is the 2β−(0+→01+) decay of 100Mo and 150Nd nuclides. Moreover, the most significant results in terms of lower limits on the half-life are also summarized.

Energy rates due to weak decay rates of vanadium isotopes in stellar environment

The neutrino cooling and gamma heating rates are considered as an important input needed to study the final phases of the evolution of high-mass stars. The weak-interaction mediated processes, namely the $\beta $-decay and electron capture, significantly change the lepton to baryon ratio and accelerate the contraction of the core. The emission of resulting neutrinos/antineutrinos tend to cool the stellar core. On the other hand gamma rays are produced because of electron capture and $\beta $-decay to excited states in daughter nuclei. These gamma rays heat the core and contribute to increase of entropy which may cause convection to occur. In the present work, the weak-interaction heating and cooling rates on a chain of twenty two isotopes of vanadium having mass in the range 43–64 have been estimated using the proton-neutron quasiparticle random phase approximation theory. The rates have been computed for the temperature ranging from ($10^{7}\mbox{--}3\times 10^{10}$) K and for the density range $(10\mbox{--}10^{11})~\mbox{g/cm}^{3}$. Our calculated neutrino energy loss rates have also been compared with the previously reported rates calculated using other theoretical models. At high stellar temperatures, our rates are larger by 1–2 orders of magnitude as compared to previous results.

Registration of Low-Intensity Alpha–Gamma Transitions in the Chain of 226Ra Decay

The results are presented from an experiment to measure the probabilities of γ-quanta emission from the first excited states of daughter nuclei formed in α-decay chain of the 226Ra nucleus. The use of fast temporal digitizers of the shape of the signal from a semiconductor α-detector and a germanium γ-detector of large volume allows the probabilities of the decay of the first excited states to be estimated at the level of 10–5 from the main mode of decay.

Partial α-decay half-lives of ground to ground and ground to excited states of Thorium family

Partial half-lives and Q-values of allowed α-decay for Thorium family are evaluated by using the WKB approximation. In order to calculate the partial half-lives, transition probabilities from ground to ground and ground to excited states of daughter nuclei are obtained. The α-decay potential barrier includes deformed volume, surface, and Coulomb parts in the deformed liquid drop model (DLDM), deformed Woods-Saxon nuclear potential and centrifugal term. The quadrupole and the hexadecapole deformations are considered in the calculations. Calculated half-lives are compared to the results of other theoretical models as well as experimental data. Comparison of the present study and other theoretical methods with experimental data indicated that the predicted half-lives using current approach are well agreed with the experimental data than results of UMADAC and CPPMDN theoretical models. Moreover, the evaluated half-lives correspond well with the Geiger-Nuttall empirical formula.

Branching ratios of α-decay to ground and excited states of Fm, Cf, Cm and Pu

We use the well-known Wentzel–Kramers–Brillouin (WKB) barrier penetration probability to calculate α-decay branching ratios for ground and excited states of heavy even–even nuclei of Fermium (248–254Fm), Californium (244–252Cf), Curium (238–248Cm) and Plutonium (234–244Pu) with 94≤Zp≤100. We obtained the branching ratios for the excited states of daughter nucleus by the α-decay energy (Qα), the angular momentum of α-particle (ℓα), and the excitation probability of the daughter nucleus with the excitation energy of state ℓ in the daughter nucleus (i.e. Eℓ⁎). α-Decay half-lives have been evaluated by using the proximity potential model for the heavy even–even nuclei. We have reported the half-lives and compared the results with the experimental data. The theoretical branching ratios of α-transitions in our calculation are found to agree with the available experimental data well for 0→+ 0+, 0→+ 2+, 0→+ 4+, 0→+ 6+ and 0+ → 8+α-transitions.

Development of the ultra-low background HPGe spectrometer OBELIX at Modane underground laboratory

A new ultra low-background spectrometer based on a HPGe detector with a sensitive volume of 600 cm3 was developed to investigate rare nuclear processes, such as resonant neutrino-less double electron capture (0νEC/EC) and double beta decay processes (2ν2β−, 2νβ+EC, 2νEC/EC) to the excited states of daughter nuclei. The spectrometer was installed at the Modane underground laboratory (LSM, France, 4800 m w.e.). Sensitivity of the spectrometer and its background were tested. A new method for the efficiency calibration in measurements of low-active samples was developed. The spectrometer was used for the measurements of low active materials and samples. Results obtained in 395 h investigation of resonant 0νEC/EC decay of 106Cd to the 2718 keV and 2741 keV excited states of 106Pd with ∼23.2 g of enriched 106Cd and 2ν2β− decay of 100Mo sample with a mass of 2588 g to the 0+, 1130 keV and 2+, 539.5 keV excited states of 100Ru are presented.

Structure and decay pattern of the linear-chain state inC14

The linear-chain states of $^{14}$C are theoretically investigated by using the antisymmetrized molecular dynamics. The calculated excitation energies and the $\alpha$ decay widths of the linear-chain states were compared with the observed data reported by the recent experiments. The properties of the positive-parity linear-chain states reasonably agree with the observation, that convinces us of the linear-chain formation in the positive-parity states. On the other hand, in the negative-parity states, it is found that the linear-chain configuration is fragmented into many states and do not form a single rotational band. As a further evidence of the linear-chain formation, we focus on the $\alpha$ decay pattern. It is shown that the linear-chain states decay to the excited states of daughter nucleus $^{10}{\rm Be}$ as well as to the ground state, while other cluster states dominantly decay into the ground state. Hence, we regard that this characteristic decay pattern is a strong signature of the linear-chain formation.

Systematic law for half-lives of double-βdecay with two neutrinos

Nuclear double $\beta$-decay with two neutrinos is a rare and important process for natural radioactivity of unstable nuclei. The experimental data of nuclear double $\beta^{-}$-decay with two neutrinos are analyzed and a systematic law to calculate the half-lives of this rare process is proposed. It is the first analytical and simple formula for double $\beta$-decay half-lives where the leading effect from both the Coulomb potential and nuclear structure is included. The systematic law shows that the logarithms of the half-lives are inversely proportional to the decay energies for the ground state transitions between parent nuclei and daughter nuclei. The calculated half-lives are in agreement with the experimental data of all known eleven nuclei with an average factor of 3.06. The half-lives of other possible double $\beta$-decay candidates with two neutrinos are predicted and these can be useful for future experiments. The law, without introducing any extra adjustment, is also generalized to the calculations of double $\beta $-decay half-lives from the ground states of parent nuclei to the first $0^+$ excited states of daughter nuclei and the calculated half-lives agree very well with the available data. Some calculated half-lives are the first theoretical results of double $\beta $-decay half-lives from the ground states of parent nuclei to the first $0^+$ excited states of daughter nuclei. The similarity and difference between the law of $\alpha$-decay and that of double $\beta^{-}$-decay are also analyzed and discussed.

Investigation of double beta decay of 100Mo to excited states of 100Ru

Double beta decay of $^{100}$Mo to the excited states of daughter nuclei has been studied using a 600 cm$^3$ low-background HPGe detector and an external source consisting of 2588 g of 97.5% enriched metallic $^{100}$Mo, which was formerly inside the NEMO-3 detector and used for the NEMO-3 measurements of $^{100}$Mo. The half-life for the two-neutrino double beta decay of $^{100}$Mo to the excited 0$^+_1$ state in $^{100}$Ru is measured to be $T_{1/2}=[7.5 \pm{0.6}(stat) \pm {0.6}(syst)]\cdot 10^{20}$ yr. For other $(0\nu + 2\nu)$ transitions to the 2$^+_1$, 2$^+_2$, 0$^+_2$, 2$^+_3$ and 0$^+_3$ levels in $^{100}$Ru, limits are obtained at the level of $\sim (0.25-1.1)\cdot 10^{22}$ yr.

A highly efficient HPGE gamma-ray spectrometer for investigating ββ decay to excited states

A new low-background spectrometer based on a HPGe detector with a sensitive volume of 600 cm3 is developed to investigate rare nuclear processes such as resonance neutrinoless double electron capture and two-neutrino double beta decay to excited states of daughter nuclei. The spectrometer is installed at the Modane underground laboratory (France) at a depth of 4800 m w.e. The spectrometer background is measured and the spectrometer sensitivity is determined for measuring sources of double beta decay.

Radioactive decays at limits of nuclear stability

The last decades brought impressive progress in synthesizing and studying properties of nuclides located very far from the beta stability line. Among the most fundamental properties of such exotic nuclides, the ones usually established first are the half-life, possible radioactive decay modes, and their relative probabilities. When approaching limits of nuclear stability, new decay modes set in. First, beta decays are accompanied by emission of nucleons from highly excited states of daughter nuclei. Second, when the nucleon separation energy becomes negative, nucleons start being emitted from the ground state. A review of the decay modes occurring close to the limits of stability is presented. The experimental methods used to produce, identify, and detect new species and their radiation are discussed. The current theoretical understanding of these decay processes is reviewed. The theoretical description of the most recently discovered and most complex radioactive process---the two-proton radioactivity---is discussed in more detail.

Alpha decay of even–even nuclei in the region [formula omitted] to the ground state and excited states of daughter nuclei

Alpha half lives, branching ratios and hindrance factors of even–even nuclei in the range 78 ⩽ Z ⩽ 102 from ground state to ground state and ground state to excited states of daughter nuclei are computed using the Coulomb and proximity potential model for deformed nuclei (CPPMDN). The computed half life values and branching ratios are compared with experimental data and they are in good agreement. The standard deviation of half life and branching ratio are 0.79 and 0.94 respectively. It is found that the standard deviation of branching ratio for the ground state to ground state transition is only 0.25 and it increases as we move to the higher excited states which are due to the effect of nuclear structure. It is evident from the study that our ground state decay model is apt for describing not only the ground state to ground state decay but also decay to excited state.

α-Decay half-lives, α-capture cross sections, and α-nucleous interaction

The expression for the α-nuclear potential was found. This potential describes the α-decay half-lives for the ground states of nuclei and the α-particle capture cross sections for 40Ca, 44Ca, 59Co, 208Pb, and 209Bi nuclei well. The potential was used to calculate the probabilities of α-transitions from the ground states of parent nuclei to different excited states of daughter nuclei. Simple analytical relations for calculating α-decay half-lives for transitions between the ground states of nuclei are determined.

Investigation of ββ decay in 150Nd and 148Nd to the excited states of 150Sm and 148Sm

Double beta decay of 150Nd and 148Nd to the excited states of daughter nuclei have been studied using a 400 cm3 low-background HPGe detector and an external source consisting of 3046 g of natural Nd2O3 powder. The half-life for the two-neutrino double beta decay of 150Nd to the excited 0+1 state in 150Sm is measured to be T1/2 = [1.33+0.36−0.23(stat)+0.27−0.13(syst)] · 1020 y. For other (0ν + 2ν) transitions to the 2+1, 2+2, 2+3, and 0+2 levels in 150Sm, limits are obtained at the level of ~ (2 − 8) · 1020 y. In the case of 148Nd only limits for the (0ν + 2ν) transitions to the 2+1, 0+1, and 2+2 excited states in 148Sm were obtained and are at the level of ~ (4 − 8) · 1020 y.

Investigation ofββdecay inNd150andNd148to the excited states of daughter nuclei

Double beta decay of $^{150}\mathrm{Nd}$ and $^{148}\mathrm{Nd}$ to the excited states of daughter nuclei have been studied using a $400 {\mathrm{cm}}^{3}$ low-background HPGe detector and an external source consisting of 3046 g of natural ${\mathrm{Nd}}_{2}{\mathrm{O}}_{3}$ powder. The half-life for the two-neutrino double beta decay of $^{150}\mathrm{Nd}$ to the excited ${0}_{1}^{+}$ state in $^{150}\mathrm{Sm}$ is measured to be ${T}_{1/2}=[1.33{}_{\ensuremath{-}0.23}^{+0.36}(\mathrm{stat}){}_{\ensuremath{-}0.13}^{+0.27}(\mathrm{syst})]\ifmmode\times\else\texttimes\fi{}{10}^{20}$ yr. For other $(0\ensuremath{\nu}+2\ensuremath{\nu})$ transitions to the ${2}_{1}^{+}$, ${2}_{2}^{+}$, ${2}_{3}^{+}$, and ${0}_{2}^{+}$ levels in $^{150}\mathrm{Sm}$, limits are obtained at the level of $~(2\text{\ensuremath{-}}8)\ifmmode\times\else\texttimes\fi{}{10}^{20}$ yr. In the case of $^{148}\mathrm{Nd}$ only limits for the $(0\ensuremath{\nu}+2\ensuremath{\nu})$ transitions to the ${2}_{1}^{+}$, ${0}_{1}^{+}$, and ${2}_{2}^{+}$ excited states in $^{148}\mathrm{Sm}$ were obtained and are at the level of $~(4\text{\ensuremath{-}}8)\ifmmode\times\else\texttimes\fi{}{10}^{20}$ yr.

Branching ratios of α-decay to excited states of even–even nuclei

We make a systematic calculation on α-decay branching ratios to members of ground-state rotational band and to excited 0 + states of even–even nuclei by a simple barrier penetration approach. The branching ratios to the excited states of daughter nucleus are determined by the α-decay energy, the angular momentum of α-particle, and the excitation probability of the daughter nucleus. Our calculation covers isotopic chains from Hg to Fm in the mass regions 180 < A < 202 and A ⩾ 224 . The calculated branching ratios of α-transitions are consistent with the experimental data. Some useful predictions are made for future experiments.