Investigation of alpha-induced reactions on 130Ba and 132Ba and their importance for the synthesis of heavy p nuclei

Captures of alpha particles on the proton-richest Barium isotope, 130Ba, have been studied in order to provide cross section data for the modeling of the astrophysical gamma process. The cross sections of the 130Ba(alpha,gamma)134Ce and 130Ba(alpha,n)133Ce reactions have been measured with the activation technique in the center-of mass energy range between 11.6 and 16 MeV, close above the astrophysically relevant energies. As a side result, the cross section of the 132Ba(alpha,n)135Ce reaction has also been measured. The results are compared with the prediction of statistical model calculations, using different input parameters such as alpha+nucleus optical potentials. It is found that the (alpha,n) data can be reproduced employing the standard alpha+nucleus optical potential widely used in astrophysical applications. Assuming its validity also in the astrophysically relevant energy window, we present new stellar reaction rates for 130Ba(alpha,gamma)134Ce and 132Ba(alpha,gamma)136Ce and their inverse reactions calculated with the SMARAGD statistical model code. The highly increased 136Ce(gamma,alpha)132Ba rate implies that the p nucleus 130Ba cannot directly receive contributions from the Ce isotopic chain. Further measurements are required to better constrain this result.Comment: Accepted for publication in Phys. Rev.

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

Chaotic Phase Synchronization in Bursting-neuron Models Driven by a Weak Periodic Force

We investigate the entrainment of a neuron model exhibiting a chaotic spiking-bursting behavior in response to a weak periodic force. This model exhibits two types of oscillations with different characteristic time scales, namely, long and short time scales. Several types of phase synchronization are observed, such as 1 : 1 phase locking between a single spike and one period of the force and 1 : l phase locking between the period of slow oscillation underlying bursts and l periods of the force. Moreover, spiking-bursting oscillations with chaotic firing patterns can be synchronized with the periodic force. Such a type of phase synchronization is detected from the position of a set of points on a unit circle, which is determined by the phase of the periodic force at each spiking time. We show that this detection method is effective for a system with multiple time scales. Owing to the existence of both the short and the long time scales, two characteristic phenomena are found around the transition point to chaotic phase synchronization. One phenomenon shows that the average time interval between successive phase slips exhibits a power-law scaling against the driving force strength and that the scaling exponent has an unsmooth dependence on the changes in the driving force strength. The other phenomenon shows that Kuramoto's order parameter before the transition exhibits stepwise behavior as a function of the driving force strength, contrary to the smooth transition in a model with a single time scale

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

Precise half-life measurement of the 10 h isomer in 154Tb

The precise knowledge of the half-life of the reaction product is of crucial importance for a nuclear reaction cross section measurement carried out with the activation technique. The cross section of the 151Eu(alpha,n)154Tb reaction has been measured recently using the activation method, however, the half-life of the 10 h isomer in 154Tb has a relatively high uncertainty and ambiguous values can be found in the literature. Therefore, the precise half-life of the isomeric state has been measured and found to be 9.994 h +- 0.039 h. With careful analysis of the systematic errors, the uncertainty of this half-life value has been significantly reduced.Comment: Accepted for publication in Nuclear Physics

Measurement of (α,n) reaction cross sections of erbium isotopes for testing astrophysical rate predictions

Date of Acceptance: 30/01/2015The γ-process in core-collapse and/or type Ia supernova explosions is thought to explain the origin of the majority of the so-called p nuclei (the 35 proton-rich isotopes between Se and Hg). Reaction rates for γ-process reaction network studies have to be predicted using Hauser-Feshbach statistical model calculations. Recent investigations have shown problems in the prediction of α-widths at astrophysical energies which are an essential input for the statistical model. It has an impact on the reliability of abundance predictions in the upper mass range of the p nuclei. With the measurement of the 164,166Er(α,n)167,169Yb reaction cross sections at energies close to the astrophysically relevant energy range we tested the recently suggested low energy modification of the α+nucleus optical potential in a mass region where γ-process calculations exhibit an underproduction of the p nuclei. Using the same optical potential for the α-width which was derived from combined 162Er(α,n) and 162Er(α,γ) measurement makes it plausible that a low-energy modification of the optical α+nucleus potential is needed.Peer reviewedFinal Accepted Versio