scholarly journals A systematic study of proton capture reactions in the Se-Sn region relevant to p-process nucleosynthesis

2019 ◽  
Vol 11 ◽  
Author(s):  
S. Harissopulos ◽  
P. Demetriou ◽  
S. Galanopoulos ◽  
G. Kriembardis ◽  
M. Kokkoris ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Nuclear Physics ◽  
Nuclear Reactions ◽  
Reaction Network ◽  
Reaction Rates ◽  
Compton Suppression ◽  
Experimental Information ◽  
Systematic Investigation ◽  
Model Calculations

The synthesis of the so-called ρ nuclei, i.e. a certain class of proton rich nuclei that are heavier than iron, requires a special mechanism known as ρ process. This process consists of various nucleosynthetic scenaria. In some of them proton and alpha-capture reactions are strongly involved, p-process nucleosynthesis is assumed to occur in the Oxygen/Neon rich layers of type II supernovae during their explosion, ρ nuclei are typically 10-100 times less abundant than the corresponding more neutron-rich isotopes. The prediction of their abundances is one of the major puzzles of all models of p-process nucleosynthesis. Until now all these models are capable of reproducing these abundances within a factor of 3. However, they all fail in the case of the light ρ nuclei with A<100. The observed discrepancies could be attributed to uncertainties in the pure "astrophysical" part of the p-process modelling. However, they could also be the result of uncertainties in the nuclear physics data entering the corresponding abundance calculations. In order to perform these calculations the cross sections of typically 10000 nuclear reactions of an extended reaction network involving almost 1000 nuclei from A=12 to 210 are used as input data. Such a huge amount of experimental cross section data are not available. Hence, all extended network calculations rely almost completely on cross sections predicted by the Hauser-Feshbach (HF) theory. It is therefore of paramount importance, on top of any astrophysical model improvements, to test also the reliability of the HF calculations, i.e. to investigate the uncertainties associated with the evaluation of the nuclear properties, like nuclear level densities and nucleon-nucleus potentials, entering the calculations. Until now, this check has been hindered significantly by the fact that in the Se-Sn region there has been scarce experimental information on cross sections at astrophysically relevant energies. In the present work, a systematic investigation of (p,7) cross sections of nuclei from Se to Sb is presented for the first time. The in-beam cross section measurements reported were carried out at energies relevant to p-process nucleosynthesis, i.e. from 1.4 to 5 MeV. The experiments were performed by using either an array of 4 HPGe detectors of 100% relative efficiency shielded with BGO crustals for Compton suppression, or a 4π Nal summing detector. The resulting cross sections, astrophysical S-factors and reaction rates of more than 10 nuclear reactions are compared with the predictions of various statistical model calculations.

scholarly journals The NUMEN Project: Toward New Experiments with High-Intensity Beams

Universe ◽  
2021 ◽  
Vol 7 (3) ◽  
pp. 72
Author(s):  
Clementina Agodi ◽  
Antonio D. Russo ◽  
Luciano Calabretta ◽  
Grazia D’Agostino ◽  
Francesco Cappuzzello ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
High Intensity ◽  
Particle Physics ◽  
Nuclear Physics ◽  
High Sensitivity ◽  
Experimental Information ◽  
Double Charge Exchange ◽  
Superconducting Cyclotron ◽  
Double Charge

The search for neutrinoless double-beta (0νββ) decay is currently a key topic in physics, due to its possible wide implications for nuclear physics, particle physics, and cosmology. The NUMEN project aims to provide experimental information on the nuclear matrix elements (NMEs) that are involved in the expression of 0νββ decay half-life by measuring the cross section of nuclear double-charge exchange (DCE) reactions. NUMEN has already demonstrated the feasibility of measuring these tiny cross sections for some nuclei of interest for the 0νββ using the superconducting cyclotron (CS) and the MAGNEX spectrometer at the Laboratori Nazionali del Sud (LNS.) Catania, Italy. However, since the DCE cross sections are very small and need to be measured with high sensitivity, the systematic exploration of all nuclei of interest requires major upgrade of the facility. R&D for technological tools has been completed. The realization of new radiation-tolerant detectors capable of sustaining high rates while preserving the requested resolution and sensitivity is underway, as well as the upgrade of the CS to deliver beams of higher intensity. Strategies to carry out DCE cross-section measurements with high-intensity beams were developed in order to achieve the challenging sensitivity requested to provide experimental constraints to 0νββ NMEs.

scholarly journals Global predictions for astrophysics applications

2020 ◽  
Vol 13 ◽  
pp. 18
Author(s):  
P. Demetriou
Keyword(s):  
Nuclear Reaction ◽  
Cross Sections ◽  
Nuclear Reactions ◽  
Nuclear Astrophysics ◽  
Reaction Network ◽  
Reaction Rates ◽  
Reaction Cross ◽  
Hartree Fock ◽  
Microscopic Models ◽  
The Stability

Nuclear reaction rates play a crucial role in nuclear astrophysics. In the last decades there has been an enormous effort to measure reaction cross sections and extensive experimental databases have been compiled as a result. In spite of these efforts, most nuclear reaction network calculations still have to rely on theoretical predic- tions of experimentally unknown rates. In particular, in astrophysics applications such as the s-, r- and p-process nucleosynthesis involving a large number of nuclei and nuclear reactions (thousands). Moreover, most of the ingredients of the cal- culations of reaction rates have to be extrapolated to energy and/or mass regions that cannot be explored experimentally. For this reason it is important to develop global microscopic or semi-microscopic models of nuclear properties that give an accurate description of existing data and are reliable for predictions far away from the stability line. The need for more microscopic input parameters has led to new devel- opments within the Hartree-Fock-Bogoliubov method, some of which are presented in this paper.

scholarly journals Tuning the Re/Os Clock: Stellar-Neutron Cross Sections

2009 ◽  
Vol 26 (3) ◽  
pp. 250-254 ◽  
Author(s):  
A. Mengoni ◽  
M. Mosconi ◽  
K. Fujii ◽  
F. Käppeler ◽  
Keyword(s):  
Cross Sections ◽  
Reaction Rates ◽  
Experimental Information ◽  
Nuclear Model ◽  
Time Duration ◽  
Model Calculations ◽  
Neutron Time ◽  
Neutron Cross Sections ◽  
Capture Cross Sections

AbstractThe neutron-capture cross sections of 186,187Os have been recently measured at the CERN neutron time-of-flight facility n_TOF for an improved evaluation of the Re/Os cosmo-chronometer. This experimental information was complemented by nuclear model calculations for obtaining the proper astrophysical reaction rates at s-process temperatures. The calculated results and their implications for the determination of the time-duration of nucleosynthesis during galactic chemical evolution is discussed.

scholarly journals Measurement of the energy-differential cross-section of the 12C(n,p)12B and 12C(n,d)11B reactions at the n_TOF facility at CERN

2020 ◽  
Vol 239 ◽  
pp. 01045
Author(s):  
M. Barbagallo ◽  
O. Aberle ◽  
V. Alcayne ◽  
S. Amaducci ◽  
J. Andrzejewski ◽  
...  
Keyword(s):  
Differential Cross Section ◽  
Cross Section ◽  
Neutron Energy ◽  
Cross Sections ◽  
Differential Cross ◽  
Nuclear Physics ◽  
Nuclear Reactions ◽  
Present Knowledge ◽  
Graphite Target ◽  
Reaction Thresholds

Although the 12C(n,p)12B and 12C(n,d)11B reactions are of interest in several fields of basic and applied Nuclear Physics the present knowledge of these two cross-sections is far from being accurate and reliable, with both evaluations and data showing sizable discrepancies. As part of the challenging n_TOF program on (n,cp) nuclear reactions study, the energy differential cross-sections of the 12C(n,p)12B and 12C(n,d)11 B reactions have been measured at CERN from the reaction thresholds up to 30 MeV neutron energy. Both measurements have been recently performed at the long flight-path (185 m) experimental area of the n_TOF facility at CERN using a pure (99.95%) rigid graphite target and two silicon telescopes. In this paper an overview of the experiment is presented together with a few preliminary results.

scholarly journals The 55Mn(p,?)56Fe and 55Mn(p,n)55Fe Cross Sections

1983 ◽  
Vol 36 (1) ◽  
pp. 1 ◽  
Author(s):  
LW Mitchell ◽  
DG Sargood
Keyword(s):  
Statistical Model ◽  
Energy Range ◽  
Cross Section ◽  
Cross Sections ◽  
Reaction Rates ◽  
Significant Part ◽  
Thermonuclear Reaction ◽  
Model Calculations ◽  
The Cross

The cross section of the reaction 55Mn(p, y)56Pe has been measured in the energy range 0�80-2�04 MeV and of the reaction 55Mn(p, n)55Pe from threshold to 2� 04 MeV. Statistical model calculations reproduce the (p, n) cross section to within a factor of 1� 4, but with the (p, y) reaction they fail by a factor ;;;:2 over a significant part of the energy range. Thermonuclear reaction rates are calculated from the data for temperatures in the range (1-5) x 109 K.

scholarly journals Urca nuclide production in Type-I X-ray bursts and implications for nuclear physics studies

2020 ◽  
Vol 500 (3) ◽  
pp. 2958-2968
Author(s):  
Grant Merz ◽  
Zach Meisel
Keyword(s):  
Light Curve ◽  
Nuclear Reaction ◽  
Nuclear Physics ◽  
Thermal Structure ◽  
Reaction Rates ◽  
High Mass ◽  
Type I ◽  
Model Calculations ◽  
X Ray ◽  
Lower Temperature

ABSTRACT The thermal structure of accreting neutron stars is affected by the presence of urca nuclei in the neutron star crust. Nuclear isobars harbouring urca nuclides can be produced in the ashes of Type I X-ray bursts, but the details of their production have not yet been explored. Using the code MESA, we investigate urca nuclide production in a one-dimensional model of Type I X-ray bursts using astrophysical conditions thought to resemble the source GS 1826-24. We find that high-mass (A ≥ 55) urca nuclei are primarily produced late in the X-ray burst, during hydrogen-burning freeze-out that corresponds to the tail of the burst light curve. The ∼0.4–0.6 GK temperature relevant for the nucleosynthesis of these urca nuclides is much lower than the ∼1 GK temperature most relevant for X-ray burst light curve impacts by nuclear reaction rates involving high-mass nuclides. The latter temperature is often assumed for nuclear physics studies. Therefore, our findings alter the excitation energy range of interest in compound nuclei for nuclear physics studies of urca nuclide production. We demonstrate that for some cases this will need to be considered in planning for nuclear physics experiments. Additionally, we show that the lower temperature range for urca nuclide production explains why variations of some nuclear reaction rates in model calculations impacts the burst light curve but not local features of the burst ashes.

ABUNDANCE ANOMALIES PRODUCED BY NUCLEAR REACTIONS IN STELLAR SURFACE LAYERS: I. NUCLEAR-REACTION RATES

1967 ◽  
Vol 45 (10) ◽  
pp. 3275-3296 ◽  
Author(s):  
P. J. Brancazio ◽  
A. Gilbert ◽  
A. G. W. Cameron
Keyword(s):  
Statistical Theory ◽  
Nuclear Reaction ◽  
Cross Sections ◽  
Nuclear Reactions ◽  
Level Density ◽  
Preliminary Investigation ◽  
Computer Time ◽  
Reaction Rates ◽  
Reaction Cross ◽  
Surface Layers

A preliminary investigation of the effects on abundances in stellar surfaces of extensive nuclear bombardment required the calculation of more than 105 nuclear-reaction cross sections. It was necessary to develop simplified methods for using the statistical theory of nuclear reactions to make these calculations in order that the computer time should not be prohibitive. These methods are described here and the results are compared with experiment. The accuracy of the calculations is, in general, about as good as, or somewhat better than, that obtained in previous applications of the statistical theory, probably because the use of an accurate level density formula outweighed the crudity of other approximations.

scholarly journals The 7Be(p, ?)8B Cross Section at Low Energies

1980 ◽  
Vol 33 (2) ◽  
pp. 177 ◽  
Author(s):  
FC Barker
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Solar Neutrinos ◽  
Model Calculations ◽  
Spectroscopic Factors ◽  
Low Energies ◽  
Standard Values ◽  
Experimental Values ◽  
Parameter Values ◽  
Potential Parameters

The nonresonant part of the 7Be(p, )I)8B cross section at low energies is recalculated by means of a direct-capture potential model, using parameter values determined by fitting 7Li(n, n)7Li and 7Li(n, )I)8Li data. Standard values of the potential parameters and spectroscopic factors give values of the 7Li(n,)I) cross section that are too large. Modified values that fit the thermal-neutron capture cross section predict 7Be(p,)I) cross sections that are much less than the experimental values. Also, shell model calculations predict resonant 7Be(p,)I) cross sections that are smaller than the experimental values. It is suggested that the accepted experimental values of the 7Be(p, )I) cross section may be too large, perhaps due partly to an overlarge accepted value for the 7Li(d, p)8Li cross section, which has been used for normalization purposes. A decrease in the 7Be(p,)I) cross section would reduce the calculated detection rate of solar neutrinos and lessen the discrepancy with the measured value.

scholarly journals Production of radioisotopes within a plasma focus device

2005 ◽  
Vol 20 (1) ◽  
pp. 33-37 ◽  
Author(s):  
Ergisto Angeli ◽  
Agostino Tartari ◽  
Michele Frignani ◽  
Vincenzo Molinari ◽  
Domiziano Mostacci ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Plasma Focus ◽  
Reaction Rates ◽  
Experimental Production ◽  
Endogenous Production ◽  
The Us ◽  
Further Development ◽  
Radio Isotopes ◽  
Very High

In recent years, research conducted in the US and in Italy has demonstrated production of radioisotopes in plasma focus devices, and particularly, on what could be termed "endogenous" production, to wit, production within the plasma it self, as opposed to irradiation of tar gets. This technique relies on the formation of localized small plasma zones characterized by very high densities and fairly high temperatures. The conditions prevailing in these zones lead to high nuclear reaction rates, as pointed out in previous work by several authors. Further investigation of the cross sections involved has proven necessary to model the phenomena involved. In this paper, the present status of research in this field is re viewed, both with regards to cross section models and to experimental production of radio isotopes. Possible out comes and further development are discussed.

scholarly journals Study of the 232Th(n,f) Cross section at NCSR ‘Demokritos’ using Micromegas Detectors

2020 ◽  
Vol 27 ◽  
pp. 106
Author(s):  
Sotirios Chasapoglou ◽  
A. Tsantiri ◽  
A. Kalamara ◽  
M. Kokkoris ◽  
V. Michalopoulou ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Nuclear Reactions ◽  
Detection Efficiency ◽  
High Energy ◽  
Tandem Accelerator ◽  
Line Detector ◽  
Accelerator Driven Systems ◽  
The Masses

The accurate knowledge of neutron-induced fission cross sections in actinides, is of great importance when it comes to the design of fast nuclear reactors, as well as accelerator driven systems. Specifically for the 232Th(n,f) case, the existing experimental datasets are quite discrepant in both the low and high energy MeV regions, thus leading to poor evaluations, a fact that in turn implies the need for more accurate measurements.In the present work, the total cross section of the 232Th(n,f) reaction has been measured relative to the 235U(n,f) and 238U(n,f) ones, at incident energies of 7.2, 8.4, 9.9 MeV and 14.8, 16.5, 17.8 MeV utilizing the 2H(d,n) and 3H(d,n) reactions respectively, which generally yield quasi-monoenergetic neutron beams. The experiments were performed at the 5.5 MV Tandem accelerator laboratory of N.C.S.R. “Demokritos”, using a Micromegas detector assembly and an ultra thin ThO2 target, especially prepared for fission measurements at n_ToF, CERN during its first phase of operations, using the painting technique. The masses of all actinide samples were determined via α-spectroscopy. The produced fission yields along with the results obtained from activation foils were studied in parallel, using both the NeusDesc [1] and MCNP5 [2] codes, taking into consideration competing nuclear reactions (e.g. deuteron break up), along with neutron elastic and inelastic scattering with the beam line, detector housing and experimental hall materials. Since the 232Th(n,f) reaction has a relatively low energy threshold and can thus be affected by parasitic neutrons originating from a variety of sources, the thorough characterization of the neutron flux impinging on the targets is a prerequisite for accurate cross-section measurements, especially in the absence of time-of-flight capabilities. Additional Monte-Carlo simulations were also performed coupling both GEF [3] and FLUKA [4] codes for the determination of the detection efficiency.

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