303 research outputs found
Constraining Big Bang lithium production with recent solar neutrino data
The 3He({\alpha},{\gamma})7Be reaction affects not only the production of 7Li
in Big Bang nucleosynthesis, but also the fluxes of 7Be and 8B neutrinos from
the Sun. This double role is exploited here to constrain the former by the
latter. A number of recent experiments on 3He({\alpha},{\gamma})7Be provide
precise cross section data at E = 0.5-1.0 MeV center-of-mass energy. However,
there is a scarcity of precise data at Big Bang energies, 0.1-0.5 MeV, and
below. This problem can be alleviated, based on precisely calibrated 7Be and 8B
neutrino fluxes from the Sun that are now available, assuming the neutrino
flavour oscillation framework to be correct. These fluxes and the standard
solar model are used here to determine the 3He(alpha,gamma)7Be astrophysical
S-factor at the solar Gamow peak, S(23+6-5 keV) = 0.548+/-0.054 keVb. This new
data point is then included in a re-evaluation of the 3He({\alpha},{\gamma})7Be
S-factor at Big Bang energies, following an approach recently developed for
this reaction in the context of solar fusion studies. The re-evaluated S-factor
curve is then used to re-determine the 3He({\alpha},{\gamma})7Be thermonuclear
reaction rate at Big Bang energies. The predicted primordial lithium abundance
is 7Li/H = 5.0e-10, far higher than the Spite plateau.Comment: Final accepted version, some typos corrected, in the press at Phys.
Rev.
Cosmic-ray induced destruction of CO in star-forming galaxies
We explore the effects of the expected higher cosmic ray (CR) ionization
rates on the abundances of carbon monoxide (CO), atomic carbon
(C), and ionized carbon (C) in the H clouds of star-forming galaxies.
The study of Bisbas et al. (2015) is expanded by: a) using realistic
inhomogeneous Giant Molecular Cloud (GMC) structures, b) a detailed chemical
analysis behind the CR-induced destruction of CO, and c) exploring the thermal
state of CR-irradiated molecular gas. CRs permeating the interstellar medium
with (Galactic) are found to significantly
reduce the [CO]/[H] abundance ratios throughout the mass of a GMC. CO
rotational line imaging will then show much clumpier structures than the actual
ones. For (Galactic) this bias becomes
severe, limiting the utility of CO lines for recovering structural and
dynamical characteristics of H-rich galaxies throughout the Universe,
including many of the so-called Main Sequence (MS) galaxies where the bulk of
cosmic star formation occurs. Both C and C abundances increase with rising
, with C remaining the most abundant of the two throughout
H clouds, when (Galactic). C starts
to dominate for (Galactic). The thermal
state of the gas in the inner and denser regions of GMCs is invariant with
for (Galactic).
For (Galactic) this is no longer the case and
are reached. Finally we identify OH as the key
species whose sensitive abundance could mitigate the destruction
of CO at high temperatures.Comment: 17 pages, 12 figures, accepted by Ap
Cosmic-ray induced background intercomparison with actively shielded HPGe detectors at underground locations
The main background above 3\,MeV for in-beam nuclear astrophysics studies
with -ray detectors is caused by cosmic-ray induced secondaries. The
two commonly used suppression methods, active and passive shielding, against
this kind of background were formerly considered only as alternatives in
nuclear astrophysics experiments. In this work the study of the effects of
active shielding against cosmic-ray induced events at a medium deep location is
performed. Background spectra were recorded with two actively shielded HPGe
detectors. The experiment was located at 148\,m below the surface of the Earth
in the Reiche Zeche mine in Freiberg, Germany. The results are compared to data
with the same detectors at the Earth's surface, and at depths of 45\,m and
1400\,m, respectively.Comment: Minor errors corrected; final versio
Determination of gamma-ray widths in N using nuclear resonance fluorescence
The stable nucleus N is the mirror of O, the bottleneck in the
hydrogen burning CNO cycle. Most of the N level widths below the proton
emission threshold are known from just one nuclear resonance fluorescence (NRF)
measurement, with limited precision in some cases. A recent experiment with the
AGATA demonstrator array determined level lifetimes using the Doppler Shift
Attenuation Method (DSAM) in O. As a reference and for testing the
method, level lifetimes in N have also been determined in the same
experiment. The latest compilation of N level properties dates back to
1991. The limited precision in some cases in the compilation calls for a new
measurement in order to enable a comparison to the AGATA demonstrator data. The
widths of several N levels have been studied with the NRF method. The
solid nitrogen compounds enriched in N have been irradiated with
bremsstrahlung. The -rays following the deexcitation of the excited
nuclear levels were detected with four HPGe detectors. Integrated
photon-scattering cross sections of ten levels below the proton emission
threshold have been measured. Partial gamma-ray widths of ground-state
transitions were deduced and compared to the literature. The photon scattering
cross sections of two levels above the proton emission threshold, but still
below other particle emission energies have also been measured, and proton
resonance strengths and proton widths were deduced. Gamma and proton widths
consistent with the literature values were obtained, but with greatly improved
precision.Comment: Final published version, minor grammar changes, 10 pages, 4 figures,
8 tables; An addendum is published where the last section is revised: T.
Sz\"ucs and P. Mohr, Phys. Rev. C 92, 044328 (2015) [arXiv:1510.04956
Successful Prediction of Total α-Induced Reaction Cross Sections at Astrophysically Relevant Sub-Coulomb Energies Using a Novel Approach
The prediction of stellar (,) reaction rates for heavy nuclei
is based on the calculation of (,) cross sections at
sub-Coulomb energies. These rates are essential for modeling the
nucleosynthesis of so-called -nuclei. The standard calculations in the
statistical model show a dramatic sensitivity to the chosen -nucleus
potential. The present study explains the reason for this dramatic sensitivity
which results from the tail of the imaginary -nucleus potential in the
underlying optical model calculation of the total reaction cross section. As an
alternative to the optical model, a simple barrier transmission model is
suggested. It is shown that this simple model in combination with a well-chosen
-nucleus potential is able to predict total -induced reaction
cross sections for a wide range of heavy target nuclei above
with uncertainties below a factor of two. The new predictions from the simple
model do not require any adjustment of parameters to experimental reaction
cross sections whereas in previous statistical model calculations all
predictions remained very uncertain because the parameters of the
-nucleus potential had to be adjusted to experimental data. The new
model allows to predict the reaction rate of the astrophysically important
W(,)Os reaction with reduced uncertainties,
leading to a significantly lower reaction rate at low temperatures. The new
approach could also be validated for a broad range of target nuclei from up to .Comment: 6 pages, 3 figures; 6 pages supplement with 3 additional figures and
3 tables; Physical Review Letters, accepted for publicatio
Cross section measurements for γ-process studies using a LEPS detector
T Szücs, GG Kiss, T Rauscher1, Zs Török, Z Halász, Zs Fülöp, Gy Gyürky and E Somorjai, 'Cross section measurements for Y-process studies using a LEPS detector', Journal of Physics: Conference Series, Vol 665(1), 012041, Jan 2016, Published under licence by IOP Publishing Ltd. The version of record is available online via doi: 10.1088/1742-6596/665/1/012041 Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.In this paper we present the ongoing experiments at ATOMKI related to our systematic γ-process studies. These studies are intended to enlarge the limited experimental database from α-induced reactions on nuclei in the heavier mass range of the γ -process. In all presented cases the activation method was used. The details of the cross section measurements and preliminary results on115In(α,n)118mSb, 115In(α,γ)119Sb; 162Er(α,n)165Yb, 162Er(α,γ)166Yb, 164Er(α,n)167Yb, 166Er(α,n)169Yb; 191Ir(α,n)194Au, 191Ir(α,γ)195Au, 193Ir(α,n)196mAu, 193Ir(α,n)196Au reactions are presented.Peer reviewedFinal Published versio
Dynamic clamp with StdpC software
Dynamic clamp is a powerful method that allows the introduction of artificial electrical components into target cells to simulate ionic conductances and synaptic inputs. This method is based on a fast cycle of measuring the membrane potential of a cell, calculating the current of a desired simulated component using an appropriate model and injecting this current into the cell. Here we present a dynamic clamp protocol using free, fully integrated, open-source software (StdpC, for spike timing-dependent plasticity clamp). Use of this protocol does not require specialist hardware, costly commercial software, experience in real-time operating systems or a strong programming background. The software enables the configuration and operation of a wide range of complex and fully automated dynamic clamp experiments through an intuitive and powerful interface with a minimal initial lead time of a few hours. After initial configuration, experimental results can be generated within minutes of establishing cell recording
Direct presynaptic and indirect astrocyte-mediated mechanisms both contribute to endocannabinoid signaling in the pedunculopontine nucleus of mice
The pedunculopontine nucleus (PPN), a cholinergic nucleus of the reticular activating system, is known to be involved in the regulation of sleep and wakefulness. Endogenous and exogenous cannabinoids, by systemic or local administration to the pedunculopontine nucleus, can both influence sleep. We previously demonstrated that activation of astrocytes by cannabinoid type 1 (CB1) receptor agonists was able to modulate the membrane potential of PPN neurons, even in the presence of blockers of fast synaptic neurotransmission. In the present work, we provide evidence that synaptic inputs of PPN neurons are also affected by activation of presynaptic and astrocytic CB1 receptors. Using slice electrophysiology combined with calcium imaging, optogenetics and immunohistochemistry, we revealed a direct presynaptic inhibitory action on inhibitory postsynaptic currents, along with a mild increase of excitatory postsynaptic currents during CB1 receptor stimulation. Besides inhibition of excitatory and inhibitory neurotransmission through stimulation of presynaptic CB1 receptors, astrocyte- and mGluR-dependent tonic inhibition and excitation also developed. The mild stimulatory action of CB1 receptor activation on excitatory neurotransmission is the combination of astrocyte-dependent tonic excitation on excitatory neurons and the canonical presynaptic CB1 receptor activation and consequential inhibition of excitatory synaptic neurotransmission, whereas the astrocyte-dependent stimulatory action was not observed in inhibitory neurotransmission within the PPN. Our findings demonstrate that endocannabinoids act in the PPN via a dual pathway, consisting of a direct presynaptic and an indirect, astrocyte-mediated component, regulating synaptic strength and neuronal activity via independent mechanisms
Consistency and diversity of spike dynamics in the neurons of bed nucleus of Stria Terminalis of the rat: a dynamic clamp study
Neurons display a high degree of variability and diversity in the expression and regulation of their voltage-dependent ionic channels. Under low level of synaptic background a number of physiologically distinct cell types can be identified in most brain areas that display different responses to standard forms of intracellular current stimulation. Nevertheless, it is not well understood how biophysically different neurons process synaptic inputs in natural conditions, i.e., when experiencing intense synaptic bombardment in vivo. While distinct cell types might process synaptic inputs into different patterns of action potentials representing specific "motifs'' of network activity, standard methods of electrophysiology are not well suited to resolve such questions. In the current paper we performed dynamic clamp experiments with simulated synaptic inputs that were presented to three types of neurons in the juxtacapsular bed nucleus of stria terminalis (jcBNST) of the rat. Our analysis on the temporal structure of firing showed that the three types of jcBNST neurons did not produce qualitatively different spike responses under identical patterns of input. However, we observed consistent, cell type dependent variations in the fine structure of firing, at the level of single spikes. At the millisecond resolution structure of firing we found high degree of diversity across the entire spectrum of neurons irrespective of their type. Additionally, we identified a new cell type with intrinsic oscillatory properties that produced a rhythmic and regular firing under synaptic stimulation that distinguishes it from the previously described jcBNST cell types. Our findings suggest a sophisticated, cell type dependent regulation of spike dynamics of neurons when experiencing a complex synaptic background. The high degree of their dynamical diversity has implications to their cooperative dynamics and synchronization
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