Synthesis and decay of nuclides in supernovae

Synthesis of chemical elements at conditions of nuclear statistical equilibrium is investigated for the ultramagnetized astrophysical plasma in supernovae and near to neutron stars. For iron group nuclides, the magnetic modification of nuclear structure shifts a maximum of nucleosynthesis products towards smaller mass numbers approaching titanium. Signals of ⁴⁴Ti radioactive decay in the gamma-spectra of the supernova remnant Cassiopeia A were revealed from the integral IBIS/ISGRI observational data. The gamma-ray fluxes for ⁴⁴Sc* lines with energies 67.9 and 78.4 keV are determined. The relationship between model and observational results is discussed.     

40Ca(alpha, gamma)44Ti reaction in the energy regime of supernova nucleosynthesis

The 44Ti(t1/2=59 yr) nuclide, an important signature of supernova nucleosynthesis, has recently been observed as live radioactivity by gamma-ray astronomy from the Cas A remnant. We investigate in the laboratory the major 44Ti production reaction 40Ca(alpha, gamma)44Ti (Ec.m. approximately 0.6-1.2 MeV/u by direct off-line counting of 44Ti nuclei. The yield, significantly higher than inferred from previous experiments, is analyzed in terms of a statistical model using microscopic nuclear inputs. The associated stellar rate has important astrophysical consequences, increasing the calculated supernova 44Ti yield by a factor approximately 2 over previous estimates and bringing it closer to Cas A observations.     

Opportunities for measurements of astrophysical-relevant alpha-capture reaction rates at CRYRING@ESR

The heavy-ion storage ring CRYRING@ESR has recently been installed and commissioned at GSI as one of the first installations of the upcoming Facility for Antiproton and Ion Research (FAIR). It is designed to store highly charged ions in the energy range between 300 keV/u and about 10 MeV/u. It will incorporate a gas-jet target providing high-density jets of, among other gases, hydrogen and helium. This will allow to study alpha-capture reaction rates of astrophysical interest in the energy range of the Gamow window for core-collapse supernovae. Special interest comes from the long-lived radio-isotope ⁴⁴Ti (t_1/2 = 58.9 years), which is supposed to be produced in the alpha-rich freeze-out during such an event. The nucleosynthesis of this isotope is of great interest, as the amount of material produced can be estimated by direct observation in remnants of recent supernovae. The disagreements between the observations and the estimations from astrophysical models show the need of more experimental data for the production and consumption reactions in the energy range of a core-collapse supernova. In this article, we will describe the proposed method of injecting beams of ⁴⁴Ti into CRYRING@ESR and performing the actual reaction rate measurements.     

Magic ultramagnetized nuclei in explosive nucleosynthesis

Direct evidence of the presence of ⁴⁴Ti and content of the isotope in the supernova remnant Cassiopeia A are obtained from the analysis of gamma-ray spectrum of the remnant. A significant excess of observational ⁴⁴Ti volume on predictions of supernova models can be explained as the magnetization effect in the process of explosive nucleosynthesis. The formation of chemical elements is considered accounting for superstrong magnetic fields predicted for supernovae and neutron stars. Using the arguments of nuclear statistical equilibrium, a significant effect of magnetic field on the nuclear shell energy is demonstrated. The magnetic shift of the most tightly ??bound?? nuclei from the transition metals of iron series to titanium leads to an exponential increase in the portion of ⁴⁴Ti and, accordingly to a significant excess of the yield of these products of nucleosynthesis.     

Neutrino-nucleus reactions in terrestrial experiments and astrophysics

We focus on the role and importance of neutrino-nucleus interactions to neutrino detection by terrestrial detector-nuclei and to various processes as well as scattering effects occurring inside the matter of stars (supernova, etc.) that generate the astrophysical neutrino energy spectra. We specifically concentrate on the parameterizations of the supernova neutrino energy distributions and examine the use of the low-energy β-beam spectra, originating from the boosted radioactive nuclei ⁶He and ¹⁸Ne, for such purposes.     

Double internal bremsstrahlung in the electron-capture decay of 55Fe

The energy distribution of photons emitted in double internal bremsstrahlung accompanying the electron-capture decay of ⁵⁵Fe has been investigated. For sum photon energies in the range of 44–230 keV and at an emission angle of 90°, the ratio of transition probabilities of double to single internal bremsstrahlung processes has been found to be (5.6±0.5) × 10^?5. The experimental data are compared with the existing theoretical predictions.     

Axion emission from a hot plasma

We give the technics for the calculation of production and energy loss rates for axion-like particles (scalar or pseudo-scalar coupling to the gauge boson) from a hot QED (or QCD) heat bath. We compute the contribution coming from, the decay mode of a transverse to a longitudinal photon (or gluon). The energy loss rate for this process behaves asT ⁷. Considering the supernova SN1987A event, this behaviour could improve the upper bound on the coupling constant between asions and photons.     

A revised level scheme for 158Tb

Four separate reaction studies have been performed which show how the accepted nuclear level scheme for ¹⁵⁸Tb must be modified. This nuclide is of current interest because of the recent suggestion that its electron-capture decay may yield a means of determining the neutrino mass.     

Few-body Decay and Recombination in Nuclear Astrophysics

Three-body continuum problems are investigated for light nuclei of astrophysical relevance. We focus on three-body decays of resonances or recombination via resonances or the continuum background. The concepts of widths, decay mechanisms and dynamic evolution are discussed. We also discuss results for the triple ?? decay in connection with 2⁺ resonances and density and temperature dependence rates of recombination into light nuclei from ??-particles and neutrons.     

Beta decays of 44V and 52Co

We have studied the prevously unknown β⁺ decay branches from ^44,44mV and ⁵²Co to particle-bound states in ⁴⁴Ti and ⁵²Fe, respectively. These intense branches populate a few states in the daughters from an excitation energy of about 1 MeV up to the isobaric analogue states at about 6 MeV. We have measured the first precise energy values for the latter states as well as the β-branching ratios to all states in this excitation energy region. We have calculated the β⁺ decay of ^44,44mV in the full fp shell model space as well as in a truncated space. Renormalized transition operators are constructed for the truncated space and tested against experimental data in ⁴⁴V and ⁵²Co. In general there is good agreement between theory and experiment for the half-lives, level energies and beta branches, but not all the states found are reproduced by the calculations.     

Search for oscillation of the electron-capture decay probability of Pm

We have searched for time modulation of the electron capture decay probability of ¹⁴²Pm in an attempt to confirm a recent claim from a group at the Gesellschaft für Schwerionenforschung (GSI). We produced ¹⁴²Pm via the ¹²⁴Sn(²³Na, 5n)¹⁴²Pm reaction at the Berkeley 88-Inch Cyclotron with a bombardment time short compared to the reported modulation period. Isotope selection by the Berkeley Gas-filled Separator is followed by implantation and a long period of monitoring the ¹⁴²Nd Kα${\text{K}}_{\alpha }$ x-rays from the daughter. The decay time spectrum of the x-rays is well-described by a simple exponential and the measured half-life of 40.68(53) seconds is consistent with the accepted value. We observed no oscillatory modulation at the proposed frequency at a level 31 times smaller than that reported by Litvinov et al. [Y.A. Litvinov, et al., Phys. Lett. B 664 (2008) 162]. A literature search for previous experiments that might have been sensitive to the reported modulation uncovered another example in ¹⁴²Eu electron-capture decay. A reanalysis of the published data shows no oscillatory behavior.     

The 44Ti(alpha,p) reaction and its implication on the 44Ti yield in supernovae

Cross sections for the 44Ti(alpha,p)47V reaction which significantly affects the yield of 44Ti in supernovae were measured in the energy range 5.7 MeV相似文献   

The decay of 44Sc

The 3.9 h decay of the ⁴⁴Sc ground state has been investigated with a ⁴⁴Ti source. In a singles experiment with a Ge(Li) detector and a γ-γ coincidence experiment with a NaI(Tl)-Ge(Li) detector arrangement a (0.010 ± 0.002)% EC branch to the 3.30 MeV level of ⁴⁴Ca has been found. The γ-decay branching ratio of the 3.30 MeV level has been determined.     

A technique for improving the observation of CP-nonconservation inB 0 meson decays

In this paper, we show that it may be possible to increase the observability of the CP-violation inB ⁰-meson decays by measuring theB ⁰-meson decay rate as a function of time. We calculate the asymmetry in the time-dependent rate at which aB ⁰-meson and its conjugate particle decay to a given final state. We also calculate the time dependence of the decay rate asymmetry for a correlated \(B - \bar B\) pair. It is suggested that searches for CP-violation lose information by integrating away the time dependence. We then calculate the gain in signal strength from watching the evolution of theB-meson states as a function of time.     

The response of Mo to supernova neutrinos

Knowledge about nuclear responses to neutrinos is essential for both astrophysical applications and studies of neutrino properties. We perform in this paper calculations of the cross sections for neutral-current neutrino scattering off the odd A=95,97 Mo isotopes for energies appropriate for the detection of supernova neutrinos. Both the incoherent and coherent contributions to the cross sections are evaluated. The prominently contributing nuclear final states are identified and analysed. We employ the microscopic quasiparticle-phonon model (MQPM) to construct the wave functions of the initial and final nuclear states. The response of the aforementioned nuclei to supernova neutrinos are computed by folding the obtained cross sections with a two-parameter Fermi-Dirac distribution. The sensitivity of the calculated nuclear responses to the adopted supernova model is also discussed.     

Study of neutrino-recoil produced point defects in InSb by119Sn Mössbauer spectroscopy

We have utilized the electron-capture decay of¹¹⁹ Te to¹¹⁹Sb to produce isolated single Frenkel pairs in InSb. This effect is caused by the neutrino emission in the decay process which imparts a monoenergetic recoil of 12 eV to the¹¹⁹Sb atoms, thereby displacing about 20% of them to interstitial sites. Two distinct interstitial components can be observed. The process is traced by Mössbauer emission spectroscopy following the decay of¹¹⁹Sb to¹¹⁹Sn. The displacement thresholdE _d is confined to 6 eV<E _d <12 eV from auxiliary experiments employing^119mTe isotopes.     

Beyond mean field approach to the beta decay of medium mass nuclei relevant for nuclear astrophysics

The Gamow-Teller strength distributions for the β decay of the ground state as well as the lowest excited states of the rp-process waiting point nuclei ⁶⁸Se and ⁷²Kr are obtained within the complex Excited Vampir variational approach using realistic effective interactions and a rather large model space. The shape mixing is consistently described for both the states in the even-even parent and the states in the odd-odd daugther nucleus. The influence of the shape mixing accounted by the different effective interactions used and comparison with the available data are presented. The possible influence of the decay of the lowest excited states of the parent nuclei in the astrophysical environment of X-ray bursts is discussed.Gamow-Teller strength distributions, β-decay half-lives, and β-delayed neutron emission probabilities for neutron-rich Zr nuclei are investigated for the first time within the complex Excited Vampir approach using a large model space. Comparison with available data and predictions relevant for the astrophysical r process are presented.     

Generation of gravitational radiation in dusty plasmas and supernovae

We present a novel nonlinear mechanism for exciting a gravitational radiation pulse (or a gravitational wave) by dust magnetohydrodynamic (DMHD) waves in dusty astrophysical plasmas. We derive the relevant equations governing the dynamics of nonlinearly coupled DMHD waves and a gravitational wave (GW). The system of equations is used to investigate the generation of a GW by compressional Alfvén waves in a type II supernova. The growth rate of our nonlinear process is estimated, and the results are discussed in the context of the gravitational radiation accompanying supernova explosions.     

Nonextensivity and entropy of astrophysical sources

We study the X-ray intensities of 142 light curves of cataclysmic variables, galaxies, pulsars, supernova remnants and other X-ray sources present in the public data collected by the instrument All Sky Monitor on board the satellite Rossi X-ray Timing Explorer. We show that the X-ray light curves coming from astrophysical systems obey Tsallis’s q$q$-Gaussian distribution as probability density. This fact strongly suggests that these astrophysical systems behave in a non-extensive manner. Furthermore, the q$q$ entropic indices for these systems were obtained and they provide an indication of the nonextensivity degree of each of these astrophysical systems. The q$q$-value increases for systems if the Tsallis entropy decreases.