Experimental 7^7Be production cross section from the 7^7Li(p,n)7^7Be reaction at Ep=3.5−13_p = 3.5-13 MeV

The $^7$Li(p,n)$^7$Be reaction is widely used as neutron source for neutron induced reaction cross section measurements, and for $^7$Be radioactive source production. There are two prominent structures in the excitation function, a narrow resonance between $E_\mathrm{p}= 2.2-2.3$ MeV, and a broad peak, around $E_\mathrm{p}= 5$ MeV. There are tension between the experimental data sets both in the position and the width of this latter structure, as well as in the absolute scale of the data. In the present work the $^7$Li(p,n)$^7$Be reaction is investigated using the activation technique, with the aim of providing comprehensive cross section data covering the second structure and connecting prior literature data sets. The irradiations were performed with the Atomki cyclotron accelerator with pairs of thin foil targets, thus with precisely controlled reaction energy in the range of E$_\mathrm{p} = 3.5-13$ MeV. After the irradiations the activity of the samples was measured using a high-purity germanium detector. The energy uncertainty of the new data points is much smaller than in any of the previous works, while the cross section uncertainty is comparable with the most precise literature data. A consistent data set was obtained connecting the most recent and most precise literature data sets. With the new data the absolute magnitude of the $^7$Li(p,n)$^7$Be reaction cross section is constrained and became more precise.Comment: typos correcte

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.

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

Alpha induced reaction cross section measurements on 162Er for the astrophysical γ process

Funding Details: NSF, National Science Foundation. ©2014 Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/). Funded by SCOAP3The cross sections of the Er162(α,γ)Yb166 and Er162(α,n)Yb165 reactions have been measured for the first time. The radiative alpha capture reaction cross section was measured from Ec.m.=16.09MeV down to Ec.m.=11.21MeV, close to the astrophysically relevant region (which lies between 7.8 and 11.48 MeV at 3 GK stellar temperature). The Er162(α,n)Yb165 reaction was studied above the reaction threshold between Ec.m.=12.19 and 16.09MeV. The fact that the Er162(α,γ)Yb166 cross sections were measured below the (α,n) threshold at first time in this mass region opens the opportunity to study directly the α-widths required for the determination of astrophysical reaction rates. The data clearly show that compound nucleus formation in this reaction proceeds differently than previously predicted. © 2014 Elsevier B.V.Peer reviewedFinal Published versio