共查询到20条相似文献,搜索用时 46 毫秒
1.
The acquisition of precise and reliable nuclear data is a prerequisite to success for stellar evolution and nucleosynthesis studies. Core-collapse simulators find it challenging to generate an explosion from the collapse of the core of massive stars. It is believed that a better understanding of the microphysics of core-collapse can lead to successful results. The weak interaction processes are able to trigger the collapse and control the lepton-to-baryon ratio (Y e ) of the corematerial. It is suggested that the temporal variation of Y e within the core of a massive star has a pivotal role to play in the stellar evolution and a fine-tuning of this parameter at various stages of presupernova evolution is the key to generate an explosion. During the presupernova evolution of massive stars, isotopes of iron, mainly 54–56Fe, are considered to be key players in controlling Y e ratio via electron capture on these nuclides. Recently an improved microscopic calculation of weak-interaction-mediated rates for iron isotopes was introduced using the proton-neutron quasiparticle random-phase-approximation (pn-QRPA) theory. The pn-QRPA theory allows a microscopic state-by-state calculation of stellar capture rates which greatly increases the reliability of calculated rates. The results were suggestive of some fine-tuning of the Y e ratio during various phases of stellar evolution. Here we present for the first time the fine-grid calculation of the electron and positron capture rates on 54–56Fe. The sensitivity of the pn-QRPA calculated capture rates to the deformation parameter is also studied in this work. Core-collapse simulators may find this calculation suitable for interpolation purposes and for necessary incorporation in the stellar evolution codes. 相似文献
2.
Improved values for stellar weak-interaction rates have been recently calculated based upon a large shell-model diagonalization. Using these new rates (for both beta decay and electron capture), we have examined the presupernova evolution of massive stars in the range (15--40)M(o). Comparing our new models with a standard set of presupernova models by Woosley and Weaver, we find significantly larger values for the electron-to-baryon ratio at the onset of collapse and smaller iron core masses. These changes may have important consequences for nucleosynthesis and the supernova explosion mechanism. 相似文献
3.
Microscopic calculations of weak interaction rates of nuclei in stellar environment for A = 18 to 100 总被引:2,自引:0,他引:2
J.-U. Nabi H.V. Klapdor-Kleingrothaus 《The European Physical Journal A - Hadrons and Nuclei》1999,5(3):337-339
We report here the microscopic calculation of weak interaction rates in stellar matter for 709 nuclei with A = 18 to 100
using a generalized form of proton-neutron quasiparticle RPA model with separable Gamow-Teller forces. This is the first ever
extensive microscopic calculation of weak rates calculated over a wide temperature-density grid which includes 107≤ T(K) ≤ 30 × 109 and 10 ≤ρ Ye (gcm−3) ≤ 1011, and over a larger mass range. Particle emission processes from excited states, previously ignored, are taken into account,
and are found to significantly affect some β decay rates. The calculated capture and decay rates take into consideration the
latest experimental energy levels and ft value compilations. Our calculation of electron capture and β-decay rates, in the
fp-shell, show considerable differences with a recently reported shell model diagonalization approach calculation.
Received: 16 April 1999 相似文献
4.
The cross section for the 42Ca(p, γ)43Sc reaction has been measured over the lab energy range from 0.7 to 5.5 MeV using a positron spectrometer to measure the annihilation radiation from the decay of 3.9 h 43Sc. Stellar reaction rates NA〈σv〉 have been calculated from the experimental cross section curve for a series of three temperatures of interest for explosive oxygen and silicon burning in stars. The calculated rates are compared with the theoretical predictions of Woosley et al. and found to be in agreement within the experimental errors and the quoted validity of the theoretical calculation 相似文献
5.
A. De Rújula 《Nuclear Physics B》1981,188(3):414-458
Internal bremsstrahlung electron capture (IBEC) is the decay of an atom into the one preceeding it in the periodic table, a neutrino, and a photon with energy in the X-ray domain. The endpoint shape of the photon spectrum is sensitive to the neutrino mass, mv. IBEC experiments could significantly constrain mv if the rates were sufficient. This is presumably not the case for typical K-capturing nuclides. But, in e-capturing isotopes in which K-(or L-) capture is forbidden, the fractional counting rate at the endpoint is enhanced by several orders of magnitude. The IBEC theory for these isotopes is developed, with emphasis on 193Pt and 163Ho. The theoretical and practical merits of β-decay and IBEC experiments - as tests for massive neutrinos - are compared. 相似文献
6.
Neutrino induced transition rates from205Tl to excited states in205Pb were calculated for neutrino fluxes from the different hydrogen burning reactions in the sun. Suppression factors for electron neutrinos due to flavor oscillations in the sun were obtained. The influence of neutrino oscillations on the neutrino capture rate of205Tl in dependence of the mixing angle and neutrino mass difference is discussed.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday 相似文献
7.
Sources of the temperature dependence of rates of nuclear beta processes in matter of massive stars are systematized. Electron and positron beta decays and electron capture (K capture and the capture of unbound electrons) fromexcited nuclear states (thermal decays) are considered along with the photobeta decays from ground and excited nuclear states. The possible quantum degeneracy of an electron gas in matter and the degree of ionization of an atomic K shell in a high-temperature field are taken into account. For a number of multidecay odd-nuclei, the temperature dependences of the ratios of the total rates of their β ? decays to the sum of the total rates over all of decay modes for the same nuclei are calculated in the range of nuclear temperature from 2 to 3 × 109 K. It is shown that the deviation of this ratio from the experimental value obtained at “normal” temperature may be quite sizable. This circumstance should be taken into account in models that consider the problem of synthesis of nuclei in matter of massive stars. 相似文献
8.
O. Dumbrajs R. Koch H. Pilkuhn G.C. Oades H. Behrens J.J. de Swart P. Kroll 《Nuclear Physics B》1983,216(2):277-335
The electron capture decay occurs with a record low energy release, Q ~ 2.6 keV. The daughter DyH atom has an electron hole, H, and predominantly decays by electron ejection DyH→DyH1H2+e?. We investigate the neutrino mass sensitivity of the electron spectrum in the overall process Ho→DyH1H2+e?+νe. In this spectrum, the fraction of events sensitive to a fixed non-zero neutrino mass in one to two orders of magnitude smaller than in the standard case of tritium β decay. But the electron energies in 163Ho decay are considerably smaller than in 3H decay (Q ~ 18 keV). This suggests experiments whose energy resolution could be much better than that of the magnetic spectrometers conventionally used in the tritium case. 相似文献
9.
研究了超强磁场对中子星外壳层核素56Fe,56Co,56Ni,56Mn和56Cr电子俘获过程中微子能量损失的影响.结果表明,就大部分中子星表面的磁场B<1013G,超强磁场对中微子能量损失率的影响很小.对于一些磁场范围为1013—1015G的超磁星,超强磁场可使中微子能量损失率大大降低,甚至超过5个数量级. 相似文献
10.
A. N. Ivanov H. Oberhummer N. I. Troitskaya M. Faber 《The European Physical Journal A - Hadrons and Nuclei》2000,8(2):223-250
A dynamics of low-energy nuclear forces is investigated for low-energy electromagnetic and weak nuclear reactions with the
deuteron in the Nambu-Jona-Lasinio model of light nuclei by example of the neutron-proton radiative capture (M1-capture) n
+ p → D + γ, the photomagnetic disintegration of the deuteron γ + D → n + p and weak reactions of astrophysical interest. These are the solar proton burning p + p → D + e+ + ν
e, the pep-process p + e− + p → D + ν
e and the neutrino and antineutrino disintegration of the deuteron caused by charged ν
e + D → e− + p + p, + D → e+ + n + n and neutral ν
e() + D → ν
e() + n + p weak currents. 相似文献
11.
We present and discuss differential cross sections for the 128,130Te isotopes, contents of the COBRA double beta decay detector. The response of these isotopes to energy spectra of supernova neutrinos is explored by convoluting the original results, calculated in the context of the quasi-particle random phase approximation (QRPA) using realistic two-body forces, with a two-parameter Fermi-Dirac (FD) and a Power-Law (PL) neutrino energy distributions. 相似文献
12.
The lepton-charge (L e , L μ , L τ ) nonconserving interaction leads to the mixing of the electron, muon, and tau neutrinos, which manifests itself in spatial oscillations of a neutrino beam, and also to the mixing of the electron, negative muon, and tau lepton, which, in particular, may be the cause of the “forbidden” radiative decay of the negative muon into the electron and γ quantum. Under the assumption that the nondiagonal elements of the mass matrices for neutrinos and ordinary leptons, connected with the lepton charge nonconservation, are the same, and by performing the joint analysis of the experimental data on neutrino oscillations and experimental restriction for the probability of the decay µ? → e ? + γ per unit time, the following estimate for the lower bound of neutrino mass has been obtained: m (ν) > 1.5 eV/c 2. 相似文献
13.
The probability of generation of an e+ e– pair by a neutrino moving in a magnetic field is calculated in the low energy approximation of the Weinberg-Salam model with consideration of electron and positron spin states.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 30–34, August, 1983.The authors thank A. A. Sokolov forhis kind evaluation of the study. 相似文献
14.
A statistical theory is proposed for the calculation of the total capture cross section of a neutrino by a nucleus. Close references are made to the statistical theory of β-decay and electron capture developed by Yamada and his collaborators. As a test of the theory, we calculate the total cross section for the capture of a solar neutrino by a 37Cl nucleus. 相似文献
15.
V. Dexheimer G. Pagliara L. Tolós J. Schaffner-Bielich S. Schramm 《The European Physical Journal A - Hadrons and Nuclei》2008,38(1):105-113
The equation of state of beta-stable and charge neutral nucleonic matter is computed within theSU(2) parity doublet model in mean-field and in the relativistic Hartree approximation. The mass of the chiral partner of the
nucleon is assumed to be 1200MeV. The transition to the chiral restored phase turns out to be a smooth crossover in all the
cases considered, taking place at a baryon density of just 2ρ0 . The mass-radius relations of compact stars are calculated to constrain the model parameters from the maximum mass limit
of neutron stars. It is demonstrated that chiral symmetry starts to be restored, which in this model implies the appearance
of the chiral partners of the nucleons, in the center of neutron stars. However, the analysis of the decay width of the assumed
chiral partner of the nucleon poses limits on the validity of the present version of the model to describe vacuum properties. 相似文献
16.
Catherine Silvestre 《The European Physical Journal C - Particles and Fields》2009,61(4):841-845
In this paper, we calculate the decay rates of the D
+→D
0
e
+
ν, D
S
+→D
0
e
+
ν,
, D
S
+→D
+
e
−
e
+ and B
S
0→B
0
e
−
e
+ semileptonic decay processes, in which only the light quarks decay, while the heavy flavors remain unchanged. The branching
ratios of these decay processes are calculated with the flavor SU(3) symmetry. The uncertainties are estimated by considering
the SU(3) breaking effect. We find that the decay rates are very tiny in the framework of the standard model. We also estimate
the sensitivities of the measurements of these rare decays at future experiments, such as BES-III, super-B and LHC-b. 相似文献
17.
The statistical theory of nuclear neutrino capture is extended to include first-forbidden transitions. A comparison with the theory of Bahcall and Frautschi is made. It is found that the present theory predicts neutrino capture cross sections which are smaller than those of Bahcall and Frautschi by a factor 2–3 for neutrino energies less than 50 MeV when first-forbidden transitions are dominant. Calculation of the cross section is made for the process in which 37Cl nuclei capture electron neutrinos that are emitted in muon decay. The present calculation gives a cross section which is around one half of that of Donnelly and Haxton. Finally the contributions of the highly excited states in 37Ar to the neutrino capture cross section are evaluated. It is shown that the contributions from the highly excited states (E > 6.02 MeV) to the neutrino capture cross section amount to 60% for Ev = 50 MeV. 相似文献
18.
S. Baeßler F. Ayala Guardia M. Borg F. Glück W. Heil G. Konrad I. Konorov R. Muñoz Horta G. Petzoldt D. Rich M. Simson Yu. Sobolev H. -F. Wirth O. Zimmer 《The European Physical Journal A - Hadrons and Nuclei》2008,38(1):17-26
The neutron decay spectrometera SPECT has been built to perform a precise measurement of the proton spectrum shape in the decay of free neutrons. Such a
measurement allows a determination of the neutrino electron angular-correlation coefficienta . The present best experiments have an uncertainty of Δa/a = 5% and since the seventies there is no substantial improvement. Witha SPECT, we aim for an uncertainty which is lower by more than an order of magnitude, thus enabling us to perform several precise
tests of the Standard Model. In our first beam time at the particle physics beam MEPHISTO at the Forschungsneutronenquelle
Heinz Maier-Leibnitz, we studied the properties of the spectrometer. The most serious problem turned out to be the situation-
and time-dependent behavior of the background. From the data sets from this beam time in which a background problem was not
obvious, we could extract a value ofa = - 0.1151±0.0040stat , but we could not quantify the background uncertainty. We show ways to deal with the background and other problems for future
beam times. 相似文献
19.
《Physics letters. [Part B]》1987,198(3):403-405
If the deficit of the solar neutrino (νe) flux is caused by the neutrino oscillation, there exists a lower bound of an effective neutrino flux detectable by electron scattering experiment, since the converted neutrino can also interact with atomic electron via neutral current effect. The effective reduction factor and day-night asymmetry for the 8B flux is calculated and plotted in the mixing parameter space, when matter oscillation effects both in the sun and in the earth are included, yielding a lower flux bound, ∼ 14% of the standard value. 相似文献
20.
《Physics letters. [Part B]》1987,186(2):211-216
The resonant neutrino oscillations in matter are assumed to be responsible for the observed reduction in the capture rate for the 37Cl detector. The expression of the probability that a solar ve reaches the Earth as a ve is given in the case of three generations. In the small mixing angle approximation, we describe all the regions of neutrino parameters which give rise to a capture rate of 2.1 SNU for 37Cl and we give the corresponding prediction for the 71Ga detector. 相似文献