Gross Theory Of Beta Decay Research Articles

Weak process for Iron isotopes chain used as seed for heavy elements nucleosynthesis

The weak processes are a key to understand the nucleosynthesis of heavy elements in the universe. In this work we have studied weak processes such as β-decay and neutrino capture that are very important for the r-process. This process takes place in a region between neutron drip and β-stability line. For nuclei far from β-stability line the experimental data are very scarce. To study the nucleosynthesis of heavy elements in astrophysics sites like Binary Neutron Star merger (BNS) and Supernova explosions, we have employed the Gross Theory of Beta Decay (GTBD) to evaluate the neutrino-nucleus cross sections and β-decay half-lives. Our 56Fe(νe , e −)56Co cross section show a excelent agreement with microscopic models and the half-lives well reproduce the experimental data with a satisfactory accuracy. We have fitted the neutrino-nucleus cross sections obtained by GTBD using a four degree polynomial dependence of the incident neutrino energy. This dependence allows us to systematically calculate the neutrino-nucleus cross sections for a large amount of nuclei, as occurs in the r-process nucleosynthesis calculation (more than 4000 nuclei). Our fitting and interpolation procedures are shown to be in a good agreement and the GTBD cross sections are successfully reproduced.

Beta Decay Rates Evaluated Within the Gross Theory Using Experimental Data for the Gamow-Teller Resonance Parameter

We improve the results for the β−-decay rates obtained within the context of the Gross Theory of Beta Decay (GTBD) by using new values of the parameter σN related to the standard deviation for the Gamow-Teller resonance: we include experimental data when they are available and, if not, we adopt the value of the nearest neighbor previous (that is, with less mass) that has experimental data. We evaluate the β−-decay rates using a Gaussian energy distribution function with the axial-vector weak coupling constant |gA| = 1, considering updated experimental mass defects and also an improved approximation for the Fermi function. Our sample consists of 94 nuclei with mass in the range 46 < A < 70, all of them decaying by means of allowed transitions, which are of interest in the pre-supernova phase and have experimental data in terrestrial conditions available in the Letter of Nuclides. We compare our result with those obtained within the same GTBD but using values of σN adjusted in Possidonio (Braz. J. Phys. 48:485, 2018) by minimizing the χ2-function, and also with systematic microscopic calculations. We have shown that the substitution of the adjusted parameters by experimental data in GTBD improves the results for β−-decay rates by 6.4%.

Systematic Calculation of Neutrino–Nucleus Cross Section Available for Astrophysical Applications

Assuming the universality of weak interactions, we have studied the weak processes such as β-decay and electron capture using the nuclear gross theory of beta decay (GTBD). We evaluate the β± and electron capture decay rates and the neutrino–nucleus cross sections as a function of the energy of the incident neutrino, for Eν < 250 MeV. The evaluation performed some years ago for the electron neutrino–nucleus reactions in the mass region A < 70 is extended to the heavy one A < 220 for a set of 965 nuclear species of astrophysical interest. The nuclei are separated according to its parity in even–even, even–odd, odd–odd, and odd–even nuclei, both for β±-decay and electron capture. The obtained cross sections are interpolated by means of a fourth-degree polynomial function in Eν. The coefficients in these polynomials are obtained and later fitted as a function of A and Z. The fitting procedure is described in detail paying special attention to the root mean square deviations in the adjustment. These polynomial functions provide a tool for the systematic evaluation of the cross sections needed in astrophysical processes like the r-process during the nucleosynthesis of supernovae.

Effects of Antineutrino mass on β−-Decay Rates Calculated Within the Gross Theory of Beta Decay

We analyze the effect of the antineutrino mass over the β−-decay rates calculated within the scheme of the Gross Theory of Beta Decay (GTBD). We give a non-null value to the mass of the antineutrino participating in β−-decay, $(A,Z)\rightarrow (A,Z+1)+e^{-}+\bar {\nu }_{e}$, which is usually neglected because we know it is small compared with electron mass. We have slightly modified the GTDB by inserting the antineutrino mass in the formalism. We have adopted a Gaussian energy distribution function with the axial-vector weak coupling constant gA = 1, as well as a new set of the adjustable parameter σN related to the standard deviation for the Gamow-Teller resonance, updated experimental mass defects, and also an improved approximation for the Fermi function. Our sample consists of a set of 94 nuclei of interest in the pre-supernova phase, which have experimental data in terrestrial conditions available in the Letter of Nuclide. We have compared the calculation without the inclusion of the antineutrino mass with that adopting a really overestimated value of 50 keV for it to illustrate the effect on the decay rates. We have shown that they are improved only by approximately one per thousand in this case. We conclude that the effect of the antineutrino mass on decay rates is not relevant.

Influence of the Axial-Vector Coupling Constant and the Energy Distribution Function on β-Decay Rates Within the Gross Theory of Beta Decay

We evaluate the β-decay rates within the gross theory of beta decay (GTBD) and compare the results for different values of the axial-vector coupling constant, gA = 0.76, gA = 0.88, gA = 1, gA = 1.13, and gA = 1.26, and also different energy distribution functions like Gaussian, exponential, Lorentzian, and modified Lorentzian ones. We use new sets of parameters as well as updated experimental mass defects and also an improved approximation for the Fermi function. We compare our calculated results for a set of 94 nuclei of interest in pre-supernova phase, with experimental data in terrestrial conditions and also with other theoretical models like the QRPA, the shell model (SM), and different versions of the GTBD. We show that best results are obtained with gA = 1 using Gaussian and Lorentzian distributions, being the rates for the 74 and 80% of our sample, respectively, of the same order of magnitude that of experimental data. Finally, we show that the present results within the GTBD are better than those within the QRPA model and also older versions of the GTBD for the isotopes of cobalt and iron families, and comparable with SM for some elements.

Improvement of gross theory of beta-decay for application to nuclear data

A theoretical study of β decay and delayed neutron has been carried out with a global β-decay model, the gross theory. The gross theory is based on a consideration of the sum rule of the β-strength function, and gives reasonable results of β-decay rates and delayed neutron in the entire nuclear mass region. In a fissioning nucleus, neutrons are produced by β decay of neutron-rich fission fragments from actinides known as delayed neutrons. The average number of delayed neutrons is estimated based on the sum of the β-delayed neutron-emission probabilities multiplied by the cumulative fission yield for each nucleus. Such a behavior is important to manipulate nuclear reactors, and when we adopt some new high-burn-up reactors, properties of minor actinides will play an important roll in the system, but these data have not been sufficient. We re-analyze and improve the gross theory. For example, we considered the parity of neutrons and protons at the Fermi surface, and treat a suppression for the allowed transitions in the framework of the gross theory. By using the improved gross theory, underestimated half-lives in the neutron-rich indium isotopes and neighboring region increase, and consequently follow experimental trend. The ability of reproduction (and also prediction) of the β-decay rates, delayed-neutron emission probabilities is discussed. With this work, we have described the development of a programming code of the gross theory of β-decay including the improved parts. After preparation finished, this code can be released for the nuclear data community.

Analysis of Electron and Antineutrino Energy Spectra from Fissile Samples under Irradiation based on Gross Theory of Beta-decay

We applied the gross theory of β-decay to calculate the reactor electron and antineutrino (¯ νe) spectra emitted from 235,238 U and 239,241 Pu by summing up all the contri- butions from a large number of decaying fission-products (FPs). We make it clear what kinds of transition types and FP nuclides are important to shape the lepton spectra. After taking the ambiguity in the current data for fission yields and Qβ-values into account, we suggested a possibility that the high-energy part of the widely referred electron-spectra by Schreckenbach et al., almost only one experimental data set available now, might pos- sibly be too low. Arguments on a special role of the odd(Z)-odd(N) nuclides and on the consistency between U-238 and other fissiles in the experimental data lead to the impor- tance of a new and independent measurement of electron energy spectra which could be converted into the reactore spectra.

Failure of the Gross Theory of Beta Decay in Neutron Deficient Nuclei

The neutron deficient isotopes 117–121 Xe, 117–124 Cs, and 122–124 Ba were produced by a beam of 28 Si from the LBNL SuperHILAC on a target of nat Mo. The isotopes were mass separated and their beta decay schemes were measured with a Total Absorption Spectrometer (TAS). The beta strengths derived from these data decreased dramatically to levels above ≈1 MeV for the even-even decays; 3–4 MeV for even-Z, odd-N decays; 4–5 MeV for the odd-Z, even-N decays; and 7–8 MeV for the odd-Z, odd-N decays. The decreasing strength to higher excitation energies in the daughters contradicts the predictions of the Gross Theory of Beta Decay. The integrated beta strengths are instead found to be consistent with shell model predictions where the single-particle beta strengths are divided amoung many low-lying levels. The experimental beta strengths determined here have been used calculate the half-lives of 143 neutron deficient nuclei with Z=51–64 to a precision of 20% with respect to the measured values.

Estimation of Beta- and Gamma-Ray Spectra for JENDL FP Decay Data File

Beta- and gamma-ray spectra of fission product nuclides were estimated by a theoretical model for the nuclides having no or incompletely measured spectral data. The estimation was performed with Gross Theory of Beta Decay. The estimated spectra were so stored in JENDL FP Decay Data File 2000 as to keep the consistency between the average decay energy value derived from the spectrum and that used for decay heat analysis. The JENDL spectra of FP nuclides and the aggregate beta- and gamma-ray spectra of fission product nuclides calculated using the JENDL spectra showed good agreement with measured data.

Estimation of Beta- and Gamma-Ray Spectra for JENDL FP Decay Data File.

Beta- and gamma-ray spectra of fission product nuclides were estimated by a theoretical model for the nuclides having no or incompletely measured spectral data. The estimation was performed with Gross Theory of Beta Decay. The estimated spectra were so stored in JENDL FP Decay Data File 2000 as to keep the consistency between the average decay energy value derived from the spectrum and that used for decay heat analysis. The JENDL spectra of FP nuclides and the aggregate beta- and gamma-ray spectra of fission product nuclides calculated using the JENDL spectra showed good agreement with measured data.

Calculation of the Delayed Gamma-Ray Energy Spectra from Aggregate Fission Product Nuclides

The beta-delayed emission process of gamma rays was treated with a gross theory of beta decay and a cascade gamma transition model. The method proposed was applied to calculations of the delayed ga...

Estimation of Nuclear Decay Heat for Short-Lived Fission Products

The gross theory of beta decay developed by Takahashi and Yamada has been applied to an estimation of nuclear decay heat of short-lived fission products, that is, to the average energies of emitted beta particles and gamma rays and the half-lives. For short-lived fission products for which no experimental information is available, calculations have been performed with the most probable value of a parameter Q00, which represents the energy of the lowest level actually fed by the beta transition. The results have been summarized in the form of several simple formulas, which are functions of the Q value and mass number of the nuclide in question. When the half-life is determined experimentally, the certainty of the calculated results for the average released energies can be improved by means of a search for the best Q00 value based on the measured half-life for each nuclide. Evaluation of confidence bands is also performed for the calculated results.

On the delayed neutrons at the final stage of the r-process

The gross theory of beta decay is applied to the r-process calculation. In particular, it is explicitly shown that the delayed-neutron emissions at the final stage of the r-process smooth out the abundance curve significantly.