Radiative Decay Branching Ratios Research Articles

Clarifying the radiative decay of the Hoyle state with charged-particle spectroscopy

A detailed knowledge of the decay properties of the so called Hoyle state in the 12\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{12}$$\\end{document}C nucleus (Ex=7.654\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E_x=7.654$$\\end{document} MeV, 0+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0^+$$\\end{document}) is required to calculate the rate at which carbon is forged in typical red-giant stars. This paper reports on a new almost background-free measurement of the radiative decay branching ratio of the Hoyle state using advanced charged particle coincidence techniques. The exploitation, for the first time in a similar experiment, of a bidimensional map of the coincidence efficiency allows to reach an unitary value and, consequently, to strongly reduce sources of systematic uncertainties. The present results suggest a value of the radiative branching ratio of Γrad/Γtot=4.2(6)·10-4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Gamma _{rad}/\\Gamma _{tot}=4.2(6)\\cdot 10^{-4}$$\\end{document}. This finding helps to resolve the tension between recent data published in the literature.

Radiative decay branching ratio of the Hoyle state

Radiative decay branching ratio of the Hoyle state

Radiative Decay Branching Ratio of the Hoyle State in 12C via Charged Particle Coincidence Techniques

The properties of the Hoyle state in 12C (7.654 MeV, 0+) affect the rate at which carbon, one of the most abundant elements in the Universe, is forged in stars. Recent experiments reported values of its radiative decay branching ratio that are in tension, posing major implications especially in the astrophysical domain. This work reports on an almost background-free measurement of the radiative decay branching ratio of the Hoyle state that exploits charged particle coincidence techniques. The experiment adopts several methodologies to minimize the background and identify the rare signal associated with the radiative decay. Large care is devoted to having under full control two of the major sources of systematic errors in particle-coincidence experiments: the coincidence efficiency and the spurious coincidence rate. We find a radiative decay branching ratio of Γrad/Γtot = 4.2(6) · 10−4. The new finding helps to resolve the tension between recent data published in the literature.

Study of sublevel population mixing effects in hydrogen neutral beams

Intensity of hydrogen Balmer-alpha line is sensitive to distribution of populations of sublevels of excited state due to difference of radiative decay branching ratio for sublevels with different orbital quantum number. Since these sublevels are degenerate transitions between sublevels and mixing of its population may be caused by very weak action of environment. A beam of fast hydrogen atoms is a system in which these fine effects of population mixing can be observed. Experimental data of Hα line radiation intensities in hydrogen neutral beams are compared with calculations assumed different models of sublevel population. The comparison most probably point out that population mixing effects cause transitions from long-lived 3s to 3p sublevel with corresponding changes in Hα radiation intensities. Discussed effects may influence to results of Doppler-shift spectroscopy measurements of the neutral beam parameters such as species and impurities content and neutralizing efficiency.

J/Ψ→γBB̄ Decaysand the Quark-pair Creation Model

We generalize the quark-pair creation model to a studyof the radiative decays J/Ψ→γBB̄ by assuming thatthe u, d, or s quark pairs are created with the same interactionstrength. From the calculation of the ratio of the decay widthsΓ(J/Ψ→γpp̄)/Γ(J/Ψ→pp̄), we extractthe quark-pair creation strength gI = 15.40 GeV. Based on theSU(6) spin-flavour basis and the ``uds'' basis, the radiative decaybranching ratios containing strange baryons are evaluated.Measurements for these decay widths from the BESII data are suggested.

First observation of radiative photons associated with the μ− transfer process from (tμ−) to 3He through an intermediate (t3Heμ−) mesomolecule

Abstract For the first time, we have observed the 6.76 keV radiative transition photons associated with the μ− transfer process from (tμ−) atoms to 3He nuclei through intermediate (t 3He μ − ) mesomolecule formation in a solid T2 target. The radiative decay branching ratio of the (t 3He μ − ) mesomolecule and the muon transfer rate were determined and compared with theoretical values. We also studied an accumulation process of 3He atoms in a solid T2 target by observing the neutron decay rates originating from t–t muon-catalyzed fusions. Their time dependence indicates a sudden 3He bubble formation in the solid T2 at an atomic concentration of 130 ppm.

Muon catalyzed fusion and muon to 3 He transfer in solid T 2 studied by X-ray and neutron detection

X-ray and neutron measurements were carried out for muon catalyzed fusion and related phenomena in solid T2. The X-ray originated from the μ- to α sticking in muon catalyzed fusion; t + t + μ-→ (μ-α) + 2n was measured for the first time, yielding Kα X-ray intensity of (μα) atom and the intensity ratio of Kβ to Kα. Utilizing the phenomena of 3He accumulation in solid T2, the X-ray in the μ- transfer process from (tμ) to 3He was detected, providing a formation rate and radiative decay branching-ratio of (t3Heμ) molecule. From fusion neutron measurements, estimated values were obtained for (ttμ) molecular formation rate as well as sticking probability ωt in ttμ fusion. A possible new insight in t + t fusion reaction process at a low energy limit is also obtained.

The radiative charmed baryon decay [formula omitted

U-spin symmetry ( s ↔ d symmetry) forbids the radiative decay Ξ c2 0∗ a ̊ Ξ c1 0γ in the SU(3) limit. The quark mass term breaks U-spin symmetry and the leading nonanalytic contribution to the radiative decay amplitude is computable in heavy baryon chiral perturbation theory. The radiative decay branching ratio is determined by the coupling constant g 2 and at leading order in chiral perturbation theory is given by Br c2(Ξ 0∗ a ̊ Ξ c1 0γ) = 1.0 × 10 −3g 2 2 . Measurement of this branching fraction will determine ∥ g 2∥.

Constraints on massive unstable dark matter from ultrahigh-energy γ-ray flux

We ruled out regions in parameter space of the mass, lifetime and branching ratio for radiative decay of massive unstable dark matter particles based on upper limits to the ultrahigh-energy cosmic diffuse γ-ray spectrum. The lifetime of massive unstable particles is shown to be no shorter than ∼ 1017 s if they exist at a density equal to the cosmological critical density. The branching ratio for radiative decay of such massive unstable particles is less than 10-11 at mass of 1 GeV and 10-2 at 105 GeV.

Strong radiative decay of double Rydberg states in high-q ions

We have measured cross sections for true double-electron capture (DC) and transfer ionization (TI) in slow Xeq+-(Ar, He, Xe) collisions in the charge-state regime 15⩽q⩽44. Following the extended classical over-the-barrier model we assume that the first step in the population mechanism is the same for both processes and that the two transferred electrons initially go to a double Rydberg state. We define total probabilities for radiative stabilization as Prad=σDC/(σDC+σTI). These quantities represent products of the branching ratios for radiative decay of all the individual intermediate states in the decay processes averaged over the possible cascade paths. Within the experimental uncertainties there is no difference for Prad measured for two-electron transfer from He, Ar, or Xe. The common q-behaviour of Prad consists of a strong increase in the region 26 < q < 36 to a level of about 0.35, a "flat top" for 37 < q < 42, and a rather steep decrease for q=43 and 44. Apparently, a substantial fraction of the intermediate states have high branching ratios for radiative decay. Electron emission seems to occur late in the cascade when one of the electrons is close to the core. We offer a qualitative explanation for these observations and discuss the possible influence from configuration mixing with strongly asymmetric doubly excited states at high q.

Variational theory of the radiant emittance of the mercury argon discharge and the effects of isotopic enrichment

A variational theory of the radiant emittance of the mercury-argon discharge is developed and applied to an investigation of the effects of alterations of the isotopic composition of the mercury. The theory includes the effects of transport of resonance radiation, elastic and inelastic collisions, resonant exchange of excitation, diffusion of the mercury atoms, the isotope- and hyperfine-shifted structure of the resonance line, and the surfaces of the discharge on the emittance. Two sensitive parameters—the branching ratio for radiative decay of the resonance state and the rate constant for resonant exchange of excitation—are fitted to data on natural mercury. The remaining insensitive parameters are given values based on microscopic estimates. The resulting theory reproduces the experimentally observed results for mercury—196 enhanced mixtures. We predict small effects for mixtures with other isotopes enhanced. The crucial role played by resonant exchange of excitation is emphasized.

Molecular hydrogen n=3 triplet gerade complex disentangled.

Nonadiabatic calculations have been performed for the {ital g}, {ital h}, {ital i}, and {ital j} states of H{sub 2}, HD, and D{sub 2}, yielding the lowest rovibrational levels ({nu},{ital N}=0,1,2,3). Born-Oppenheimer potential-energy curves were taken from literature. Irregularly shaped rotational and vibrational couplings were significantly reduced by an appropriate electronic basis transformation. In the diabatic electronic basis introduced here the rotational matrix elements were fixed to their united-atom-limit values, and the vibrational matrix elements were adjusted to reproduce experimental data. Apart from the hydrogen {sup 3}{Sigma}{sub g}{sup +} state {nu}=2 and 3 series that we suspect are misassigned, we obtained agreement with experiment down to a wave number for all calculated energy levels. Calculated branching ratios for radiative decay, which are very sensitive to the excited-state electronic composition, are found to agree with experimental data (following paper, Phys. Rev. A 44, 4171 (1991)). The confusion in the nomenclature of the adiabatic electronic {sup 3}{Sigma}{sub {ital g}}{sup +} states is addressed.

A measurement of the branching ratio for the∑ + →pγ decay

We have measured the weak radiative decay branching ratio (∑+ →pγ)/(∑+ →pπ0). The experiment was carried out at Brookhaven National Laboratory using a low-energy separatedK− beam stopping in liquid hydrogen. The∑+ was tagged by observing the pion fromK−K+p→∑+π− in a range telescope, and the gamma was detected in a segmented NaI detector. The result is (2.81±0.39−0.43+0.21)×10−3, which is consistent with previous measurements. This corresponds to a branching ratio for (∑+ →pγ)/(∑+ → all) of (1.45±0.20−0.22+0.11)×10−3, where the quoted errors are statistical and systematic, respectively. A total of 408 signal events were observed, doubling the previous world total.

Decay of H atoms excited in small electric fields.

The branching ratios for radiative decay of H atoms excited in small electric fields (0--5 V/cm) have been calculated for the nl states up to n=6. A simple computational procedure was employed, allowing only for Stark-effect mixing of levels with the same values of the quantum numbers (n,j,${m}_{j}$). The results are compared with more detailed calculations available for 3l-state decay made using the density-matrix formalism, and new calculations of this type reported here for 4l-state decay. In conjunction with theory, this allowed the domain of validity of the simple computational procedure to be established as a function of n. The results show that the branching ratios depend quite strongly on electric-field magnitude, pointing to the need to exercise caution in measurements of H emissions, and in application of the available data to other problems.

L2,3 subshell X-ray fluorescence yields and Coster-Kronig transition probabilities of Nd and Yb

X-ray spectra emitted in the radioactive decay of 17.7y 145Pm and 1.9y 171Tm were studied using a three-parameter technique for XX · t coincidence measurements. The following L2 and L3 subshell X-ray fluorescence yields, ω2, ω3, Coster-Kronig transition probabilities, f23, and radiative decay branching ratios, s2, s3, were determined for Nd (Z = 60) and Yb (Z = 70); At Z = 60, ω3 = 0.108 ± 0.010, ω2 = 0.128 ± 0.018, f23 = 0.123 ± 0.013, s3 = 0.178 ± 0.006, and s2 = 0.205 ± 0.010. At Z = 70, ω3 = 0.227 ± 0.022, ω2 = 0.217 ± 0.030, f23 = 0.141 ± 0.007, s3 = 0.175 ± 0.003, and s2 = 0.197 ± 0.004. These results are compared with available theoretical calculations.

Model potential calculations and spectroscopic observations of some doubly excited states in beryllium-like Ne VII

Energy level positions and branching ratios for radiative decay have been calculated for a number of doubly excited states in beryllium-like Ne VII using the SUPERSTRUCTURE code. These are compared with weak unidentified features observed in spectra obtained from foil-excited neon beams at energies of 6, 13 and 18 MeV.

Electron capture decay of181W: L subshell fluorescence and Coster-Kronig yields in Ta

The TaL x-ray spectrum from the 140 d electron capture decay of181W was studied with high resolution semiconductor detectors and fast coincidence techniques. Measurement ofL x-ray-K x-ray andL x-ray—γ-ray coincidence rates yielded the followingL shell fluorescence and Coster-Kronig yields and radiative decay branching ratios: ω2=0.250±0.013, ω3=0.228±0.013 (corrected for angular correlation effects),f23=0.180±0.007,v1=O.218±0.016,s3=0.205+-0.010,s2=0.215+-0.010,f13+f12f23=0.36+-0.02, and ω1+f12ω2=0.14±0.02, from which upper limits were obtained off13<0.36 and ω1<0.14.