Z. Halász

Hungarian Academy of Sciences, Budapeŝto, Budapest, Hungary

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Publications (21)37.99 Total impact

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    ABSTRACT: The 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.=16.09 MeVEc.m.=16.09 MeV down to Ec.m.=11.21 MeVEc.m.=11.21 MeV, 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 16.09 MeVEc.m.=12.19 and 16.09 MeV. The fact that the Er162(α,γ)Yb166 cross sections were measured below the (α,n)(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.
    Physics Letters B 07/2014; 735:40–44. · 4.57 Impact Factor
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    ABSTRACT: The cross sections of the 162Er(α,γ)166Yb and 162,164,166Er(α,n)165,167,169Yb reactions have been measured at MTA Atomki. The radiative alpha capture reaction cross section was measured between Ec.m. = 11.21 MeV and Ec.m. = 16.09 MeV just above the astrophysically relevant energy region (which lies between 7.8 and 11.48 MeV at T9 = 3 GK). The 162Er(α,n)165Yb, 164Er(α,n)167Yb and 166Er(α,n)169Yb reactions were studied between Ec.m. = 12.19 and 16.09 MeV, Ec.m. = 13.17 and 16.59 MeV and Ec.m. = 12.68 and 17.08 MeV, respectively. The aim of this work is to provide experimental data for modeling the γ process which is thought to be responsible for the production of the proton-rich isotopes heavier than iron.
    04/2014; 1594(1).
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    ABSTRACT: For the better understanding of the astrophysical γ-process the experimental determination of low energy proton- and α-capture cross sections on heavy isotopes is required. The existing data for the Mo92(p,γ)Tc93 reaction are contradictory and strong fluctuation of the cross section is observed which cannot be explained by the statistical model. In this paper a new determination of the Mo92(p,γ)Tc93 and Mo98(p,γ)Tc99m cross sections based on thick target yield measurements are presented and the results are compared with existing data and model calculations. Reaction rates of Mo92(p,γ)Tc93 at temperatures relevant for the γ-process are derived directly from the measured thick target yields. The obtained rates are a factor of 2 lower than the ones used in astrophysical network calculations. It is argued that in the case of fluctuating cross sections the thick target yield measurement can be more suited for a reliable reaction rate determination.
    Nuclear Physics A. 01/2014; 922:112–125.
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    ABSTRACT: For the better understanding of the astrophysical gamma-process the experimental determination of low energy proton- and alpha-capture cross sections on heavy isotopes is required. The existing data for the 92Mo(p,gamma)93Tc reaction are contradictory and strong fluctuation of the cross section is observed which cannot be explained by the statistical model. In this paper a new determination of the 92Mo(p,gamma)93Tc and 98Mo(p,gamma)99mTc cross sections based on thick target yield measurements are presented and the results are compared with existing data and model calculations. Reaction rates of 92Mo(p,gamma)93Tc at temperatures relevant for the gamma-process are derived directly from the measured thick target yields. The obtained rates are a factor of 2 lower than the ones used in astrophysical network calculations. It is argued that in the case of fluctuating cross sections the thick target yield measurement can be more suited for a reliable reaction rate determination.
    12/2013;
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    ABSTRACT: Background: The γ process in supernova explosions is thought to explain the origin of proton-rich isotopes between Se and Hg, the so-called p nuclei. The majority of the reaction rates for γ process reaction network studies have to be predicted in Hauser-Feshbach statistical model calculations using global optical potential parametrizations. While the nucleon+nucleus optical potential is fairly well known, for the α+nucleus optical potential several different parametrizations exist and large deviations are found between the predictions calculated using different parameter sets.Purpose: By the measurement of elastic α-scattering angular distributions at energies around the Coulomb barrier a comprehensive test for the different global α+nucleus optical potential parameter sets is provided.Methods: Between 20^{∘} and 175^{∘} complete elastic alpha scattering angular distributions were measured on the ^{113}In p nucleus with high precision at E_{c}.m.=15.59 and 18.82 MeV.Results: The elastic scattering cross sections of the ^{113}In(α,α)^{113}In reaction were measured for the first time at energies close to the astrophysically relevant energy region. The high precision experimental data were used to evaluate the predictions of the recent global and regional α+nucleus optical potentials. Parameters for a local α+nucleus optical potential were derived from the measured angular distributions.Conclusions: Predictions for the reaction cross sections of ^{113}In(α,γ)^{117}Sb and ^{113}In(α,n)^{116}Sb at astrophysically relevant energies were given using the global and local optical potential parametrizations.
    Physical Review C 10/2013; 88(4). · 3.72 Impact Factor
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    ABSTRACT: The astrophysically important He3(α,γ)Be7 reaction was studied at high energies where the available experimental data are in contradiction. A thin window 3He gas cell was used and the cross section was measured with the activation method. The obtained cross sections at energies between Ec.m.=1.5 and 2.5 MeVEc.m.=1.5 and 2.5 MeV are compared with the available data and theoretical calculations. The present results support the validity of the high energy cross section energy dependence observed by recent experiments.
    Nuclear Physics A 04/2013; 908:1–11. · 1.53 Impact Factor
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    ABSTRACT: A thin-window gas target system was designed in order to fulfill the requirements of the measurement of low energy α-inducedα-induced reaction cross-sections relevant for nuclear astrophysics using the activation method. The properties of the gas cell system, its characterization and the results of the first feasibility studies on the View the MathML sourceHe3(α,γ)Be7 and View the MathML sourceXe124(α,γ)Ba128 reactions are summarized.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 11/2012; 693:220-225. · 1.14 Impact Factor
  • Physical Review C 10/2012; 86(4). · 3.72 Impact Factor
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    ABSTRACT: The total reaction cross section is related to the elastic scattering angular distribution by a basic quantum-mechanical relation. We present new experimental data for alpha-induced reaction cross sections on 64Zn which allow for the first time the experimental verification of this simple relation at low energies by comparison of the new experimental reaction data to the result obtained from 64Zn(alpha,alpha)64Zn elastic scattering.
    Physical Review C 09/2012; 86(4). · 3.72 Impact Factor
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    ABSTRACT: Background: The γ process in core-collapse supernova explosions is thought to explain the origin of proton-rich isotopes between Se and Hg, the so-called p nuclei. The majority of the reaction rates for γ process reaction network studies has to be predicted in Hauser-Feshbach statistical model calculations. Recent investigations have shown problems in the prediction of α widths at astrophysical energies. This impacts the reliability of abundance predictions in the upper mass range of the p nuclei.Purpose: Our purpose is to measure the 127I(α,γ)131Cs and 127I(α,n)130Cs reaction cross sections close to the astrophysically relevant energy range to test the predictions, to derive an improved reaction rate, and to extend the database required to define an improved global optical α+nucleus potential.Methods: The cross sections are derived using the activation technique and the yield of the emitted γ, and characteristic x-ray photons are measured using a LEPS and an HPGe detector.Results: Cross sections of the 127I(α,γ)131Cs reaction are determined for the first time, at energies 9.50⩽Ec.m.⩽15.15 MeV. The 127I(α,n)130Cs reaction is studied in the range 9.62⩽Ec.m.⩽15.15 MeV. Furthermore, the relative intensity of the 536.1-keV γ transition is measured precisely; its uncertainty is reduced from 13% to 4%. The results are then compared to Hauser-Feshbach calculations which are also used to extend the cross sections into the astrophysically relevant region and to compute the reaction rate.Conclusions: The comparison to statistical Hauser-Feshbach model calculations shows that the α width can be described well in the measured energy range using a standard, energy-independent global optical potential. The newly derived stellar reaction rates at γ process temperatures for 127I(α,γ)131Cs and its reverse reactions, nevertheless, are faster by factors of 4–10 than those from previous calculations, owing to further improvements in the reaction model. The importance of the inclusion of complete level schemes in the Hauser-Feshbach calculations is illustrated by comparing the impacts of two level schemes, one of them extending to higher excitation energies but not containing all relevant levels.
    Physical Review C 09/2012; 86(3). · 3.72 Impact Factor
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    ABSTRACT: Reaction cross sections of 169Tm(alpha,gamma)173Lu and 169Tm(alpha,n)172Lu have been measured in the energy range 12.6<=E_alpha<=17.5 MeV and 11.5<=E_alpha<=17.5 MeV, respectively, using the recently introduced method of combining activation with X-ray counting. Improved shielding allowed to measure the (alpha,gamma) to lower energy than previously possible. The combination of (alpha,gamma) and (alpha,n) data made it possible to study the energy dependence of the alpha width. While absolute value and energy dependence are perfectly reproduced by theory at energies above 14 MeV, the observed change in energy dependence at energies below 14 MeV requires a modification of the predicted alpha width. Using an effective, energy-dependent, local optical alpha+nucleus potential it is possible to reproduce the data but the astrophysical rate is still not well constrained at gamma-process temperatures. The additional uncertainty stemming from a possible modification of the compound formation cross section is discussed. Including the remaining uncertainties, the recommended range of astrophysical reaction rate values at 2 GK is higher than the previously used values by factors of 2-37.
    Physical Review C 06/2012; 86(1). · 3.72 Impact Factor
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    ABSTRACT: 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.
    Physical Review C 02/2012; · 3.72 Impact Factor
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    ABSTRACT: For the synthesis of the heavy, proton rich isotopes in the astrophysical γ-process the precise knowledge of α-induced cross sections is of high importance. We have initiated a comprehensive study of the 64Zn + α system involving the cross section measurement of different reaction channels as well as the elastic scattering at low, astrophysically relevant energies. In this paper the experimental technique and some preliminary results of the 64Zn(α,p)67Ga cross section measurement are presented.
    Journal of Physics Conference Series 01/2012; 337(1).
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    ABSTRACT: The activation technique has proven to be a very successful tool in measuring charged particle induced reaction cross sections relevant for the astrophysical γ-process. This method is, however, only applicable when the product nucleus of the reaction is radioactive and its decay can well be measured. In other cases the technically much more challenging in-beam measurements are inevitable. Here we present the first steps of a new research program aiming at the in-beam measurements of (α, γ) cross sections. As a first test case, the study of the 116Sn(α,γ)120Te reaction has been started.
    Journal of Physics Conference Series 01/2012; 337(1).
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    ABSTRACT: For the synthesis of the heavy, proton rich isotopes in the astrophysical gamma-process the precise knowledge of alpha-induced cross sections is of high importance. We have initiated a comprehensive study of the 64Zn+alpha system involving the cross section measurement of different reaction channels as well as the elastic scattering at low, astrophysically relevant energies. In this paper the experimental technique and some preliminary results of the 64Zn(alpha,p)67Ga cross section measurement are presented.
    11/2011;
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    ABSTRACT: The half-life of (66)Ga, an isotope very important for high-energy efficiency calibration of γ-detectors, has been measured using γ-spectroscopy. In order to reduce systematic uncertainties, different source production methods and γ-counting conditions have been applied. A half-life value of t(1/2)=(9.312±0.032)h has been obtained in agreement with a recent measurement but in contradiction with some of the earlier results.
    Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine 08/2011; 70(1):278-81. · 1.09 Impact Factor
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    ABSTRACT: The half-life of 66Ga, an isotope very important for high-energy efficiency calibration of gamma-detectors, has been measured using gamma-spectroscopy. In order to reduce systematic uncertainties, different source production methods and gamma-counting conditions have been applied. A half-life value of 9.312 +- 0.032 h has been obtained in agreement with a recent measurement but in contradiction with some of the earlier results.
    08/2011;
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    ABSTRACT: In order to extend the available experimental database for the astrophysical gamma-process, the cross section measurement of the 130Ba(alpha,gamma)134Ce and 130Ba(alpha,n)133Ce reactions is in progress. The measurements are carried out using thin layers of evaporated BaCO3 as target. Since the target thickness enters directly into the calculation of the cross sections, the reliability of its determination is of crucial importance. Three different methods have been used to determine the target thickness. Details of these experiments and the obtained results are presented.
    03/2011;
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    ABSTRACT: In this paper we describe our experiment determining the half-life of 133mCe . An activation-based nuclear-reaction cross-section measurement has been carried out for the 130Ba(a \alpha, n)133mCe reaction, in order to improve our knowledge of the astrophysical p-process. For the analysis of such a measurement, the precise knowledge of the decay half-life of the reaction product is desired. In the case of 133mCe the literature half-life value has only been known with a high relative uncertainty. A measurement utilizing g \gamma -spectrometry has been carried out to refine the half-life of 133mCe . As a result, the new recommended half-life is t 1/2 = (5.326±0.011) h. This value has been found to be consistent with the previous literature value, while its uncertainty has been reduced by more than a factor of 30.
    European Physical Journal A 01/2011; 47(1):1-4. · 2.04 Impact Factor
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    ABSTRACT: In order to extend the experimental database relevant for the astrophysical gamma-process towards the unexplored heavier mass region, the cross sections of the 151Eu(alpha,gamma)155Tb and 151Eu(alpha,n)154Tb reactions have been measured at low energies between 12 and 17 MeV using the activation technique. The results are compared with the predictions of statistical model calculations and it is found that the calculations overestimate the cross sections by about a factor of two. A sensitivity analysis shows that this discrepancy is caused by the inadequate description of the alpha+nucleus channel. A factor of two reduction of the reaction rate of 151Eu(alpha,gamma)155Tb in gamma-process network calculations with respect to theoretical rates using the optical potential by McFadden and Satchler (1966) is recommended.
    Journal of Physics G Nuclear and Particle Physics 08/2010; 37(11). · 5.33 Impact Factor