### Regular Series

#### XXXIV Mazurian Lakes Conference on Physics Frontiers in Nuclear Physics

Highlights of the ISOLDE Facility and the HIE-ISOLDE Project

Acta Phys. Pol. B 47, 591 (2016)

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abstract

The ISOLDE radioactive beam facility is the dedicated CERN installation for the production and acceleration of radioactive nuclei. Exotic nuclei of most chemical elements are available for the study of nuclear structure, nuclear astrophysics, fundamental symmetries and atomic physics, as well as for applications in condensed matter and life sciences. In order to broaden the scientific opportunities beyond the reach of the present facility, the on-going HIE-ISOLDE (High Intensity and Energy) project provides major improvements in energy range, beam intensity and beam quality. A major element of the project is the increase of the final energy of the post-accelerated beams to 10 MeV/$u$ throughout the periodic table. Physics with post-accelerated beams at 4 MeV/$u$ has started this autumn. The increase in energy up to 10 MeV/$u$ is fully funded and it will be implemented at the rate of one cryo-module per year reaching 10 MeV/$u$ for $A/q = 4.5$ at the start of 2018. In this contribution, a description of the ISOLDE facility including some highlights will be discussed. The present status of the HIE-ISOLDE project will be described as well as the first experiment realised this year.

all authors

I. Martel, C. Bontoiu, A.K. Orduz, L. Acosta, E. Barrios, R. Carrasco, J.A. Dueñas, D. Gordo-Yañez, A. Peregrín, A.R. Pinto-Gómez, J.A. Prieto-Thomas, M.J. Ruiz-Pomares, T. Junquera, J. Sanchez-Segovia, P.N. Ostroumov, A.C.C. Villari, M.N. Harakeh, L.A. Acosta

ECOS-LINCE: A High-intensity Heavy-ion Facility for Nuclear Structure and Reactions

Acta Phys. Pol. B 47, 607 (2016)

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abstract

During the last years, the ECOS working group has been considering the construction of a new high-intensity accelerator of stable ion beams for the next Long-Range Plan of the nuclear physics community in Europe. The new facility (LINCE) will be a multi-user facility dedicated to ECOS science: fundamental physics, astrophysics, nuclear structure and reaction dynamics. In this paper, we summarize preliminary design studies of the low-energy part of this facility based on the use of a multi-ion superconducting linac.

Studies for a 72.75 MHz Four Vanes CW-RFQ for ECOS-LINCE Project

Acta Phys. Pol. B 47, 619 (2016)

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abstract

The ECOS is considering the construction of a new facility for accelerating high intensity stable beams with energies at and above the Coulomb barrier, the LINCE light and heavy ion accelerator. This facility could be based on a normal conducting CW-RFQ and a superconducting linac, working at 72.75 MHz. This paper presents a design study for the RFQ system which is able to achieve 500 keV/$u$ output for $A/Q = 7$ ions in only 5 m length.

all authors

P.A. Butler, R.D. Page, K. Blaum, M. Grieser, T. Davinson, P.J. Woods, K. Flanagan, S.J. Freeman, I.H. Lazarus, Yu.A. Litvinov, R. Raabe, E. Siesling, F. Wenander

TSR: A Storage Ring for HIE-ISOLDE

Acta Phys. Pol. B 47, 627 (2016)

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abstract

It is planned to install the heavy-ion, low-energy ring TSR, currently at the Max-Planck-Institute for Nuclear Physics in Heidelberg, at the HIE-ISOLDE facility in CERN, Geneva. Such a facility will provide a capability for experiments with stored, cooled secondary beams that is rich and varied, spanning from studies of nuclear ground-state properties and reaction studies of astrophysical relevance, to investigations with highly-charged ions and pure isomeric beams. In addition to experiments performed using beams recirculating within the ring, the cooled beams can be extracted and exploited by external spectrometers for high-precision measurements. The capabilities of the ring facility as well as some physics cases will be presented, together with a brief report on the status of the project.

all authors

S. Lalkovski, Zs. Podolyák, M. Bentley, A.M. Bruce, I. Lazarus, R. Lemmon, P.H. Regan, J. Simpson

The UK NuStAR Project

Acta Phys. Pol. B 47, 637 (2016)

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abstract

The UK NuStAR project is the largest nuclear physics project presently funded by the Science Technology Facilities Council (STFC) in UK. The aim of the project is to design, construct and deliver detectors and sub-detector systems for FAIR. The main project deliverables are a DESPEC multidetector array for fast timing measurements, a HISPEC ToF detector for mass measurements after the secondary target, and the Si tracker for precise vertex determination in R$^3$B experiments with liquid hydrogen target.

all authors

W.R. Hix, E.J. Lentz, S.W. Bruenn, A. Mezzacappa, O.E.B. Messer, E. Endeve, J.M. Blondin, J.A. Harris, P. Marronetti, K.N. Yakunin

The Multi-dimensional Character of Core-collapse Supernovae

Acta Phys. Pol. B 47, 645 (2016)

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abstract

Core-collapse supernovae, the culmination of massive stellar evolution, are spectacular astronomical events and the principle actors in the story of our elemental origins. Our understanding of these events, while still incomplete, centers around a neutrino-driven central engine that is highly hydrodynamically unstable. Increasingly sophisticated simulations reveal a shock that stalls for hundreds of milliseconds before reviving. Though brought back to life by neutrino heating, the development of the supernova explosion is inextricably linked to multi-dimensional fluid flows. In this paper, the outcomes of three-dimensional simulations that include sophisticated nuclear physics and spectral neutrino transport are juxtaposed to learn about the nature of the three-dimensional fluid flow that shapes the explosion. Comparison is also made between the results of simulations in spherical symmetry from several groups, to give ourselves confidence in the understanding derived from this juxtaposition.

The Nuclear Physics of Neutron Stars

Acta Phys. Pol. B 47, 659 (2016)

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abstract

How Does Subatomic Matter Organize Itself? With their enormous dynamic range in density and neutron–proton asymmetry, neutron stars provide unique laboratories to answer this challenging question. Indeed, a neutron star is a gold mine for the study of physical phenomena that cut across a variety of disciplines, ranging from elementary particle physics to general relativity. Although the most common perception of a neutron star is that of a uniform assembly of neutrons packed to enormous densities, the reality is far different and much more interesting. In this contribution, we will focus on the dynamics of neutron-rich matter with special emphasis on its impact on the structure and composition of the outer crust. In particular, we will discuss a novel method that combines modern theoretical approaches with Bayesian Neural Networks to build a new mass formula that is then used to compute the crustal composition.

Uncorrelated Nuclear Mass Uncertainties and r-process Abundance Predictions

Acta Phys. Pol. B 47, 673 (2016)

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abstract

Nuclear masses have long been recognized as key nuclear physics inputs for calculations of rapid neutron capture, or r-process, nucleosynthesis. Here, we investigate how uncorrelated uncertainties in nuclear masses translate into uncertainties in the final abundance pattern produced in r-process simulations. These uncertainties can obscure details of the abundance pattern that, in principle, could be used to diagnose the r-process astrophysical site. We additionally examine the impact of reductions of mass uncertainties that will come with new experiments.

all authors

M. La Cognata, C. Spitaleri, S. Cherubini, M. Gulino, I. Indelicato, L. Lamia, R.G. Pizzone, S. Romano, O. Trippella, A. Tumino

Using the Trojan Horse Method to Investigate Resonances Above and Below the Threshold in Nuclear Reactions of Astrophysical Interest

Acta Phys. Pol. B 47, 681 (2016)

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abstract

Resonant reactions play an important role in astrophysics as they might significantly enhance the cross section with respect to the direct reaction contribution and alter the nucleosynthetic flow, namely, the predicted energy production and nucleosynthesis path. Moreover, resonances bear information about states in the intermediate compound nucleus formed in the reaction. Therefore, we have modified the Trojan horse method (THM) to investigate resonant reactions. In this work, we will discuss two examples of reactions of astrophysical interest, whose cross sections show a resonant behavior: the $^{19}$F$(\alpha ,n){}^{16}$O cross section that displays resonances at energies above the particle emission threshold and the $^{13}$C$(\alpha ,n){}^{16}$O reaction, dominated by the $-3$ keV sub-threshold resonance due to the 6.356 MeV level in $^{17}$O.

Nuclear Astrophysics at LNL: the $^{25}$Mg($\alpha$,$n$)$^{28}$Si and $^{10}$B($p,\alpha )^7$Be Cases

Acta Phys. Pol. B 47, 693 (2016)

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abstract

The Legnaro National Laboratories (LNL) has a wealth of experience in nuclear physics measurements. Recently, a new effort to perform nuclear astrophysics studies has been initiated. This effort started with the collaboration of LNL with the LUNA (Laboratory for Underground Nuclear Astrophysics) Collaboration for the study of targets. After that, in 2012, thanks to a fruitful collaboration between nuclear astrophysicist and nuclear physics groups involved in neutron detection, the study of the $^{25}$Mg($\alpha$,$n$)$^{28}$Si reaction was developed in order to help solving the $^{26}$Al puzzle. For the first time, the angular distributions of neutrons emitted by this reaction were studied deeply, founding discrepancies between the previous studies in literature. In 2014, the study of $^{10}$B($p$,$\alpha$)$^7$Be was performed in order to give a precise normalisation to the indirect measurements. This study was done by measuring the activated samples and it is still under analysis. A report of the status of the two experiments will be given in this contribution.

Nuclear Cosmology Deep Underground

Acta Phys. Pol. B 47, 699 (2016)

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abstract

Thanks to the Big Bang Nucleosynthesis (BBN), it is possible to estimate the primordial abundance of all the elements produced in the first few minutes of the Universe. Inputs of the theory are: the cosmological model assumed and the nuclear cross section of the processes involved. The former consists in the $\Lambda$CDM (Lambda-Cold Dark Matter) model or its possible extensions. The latter usually implies low cross section measurements, often extremely difficult in standard nuclear experiments due to the high cosmic background present on the Earth surface. Therefore, the best solution is to go deep underground where this kind of background is much suppressed. As of today, the only facility in the world where it is possible to perform direct measurements of low cross section in a very low background context is LUNA — Laboratory for Underground Nuclear Astrophysics, located in the Laboratori Nazionali del Gran Sasso (LNGS), Italy. Thanks to the background suppression provided by about 1400 meters of rock and to the high current provided by the 400 kV accelerator, LUNA is able to investigate cross sections at energies of interest for the Big Bang Nucleosynthesis using as projectiles protons, $^3$He and alpha particles. In this paper, I will report on the recent results obtained at LUNA for the $^2$H($\alpha$,$\gamma$)$^6$Li reaction. This is the “key-reaction” in the primordial $^6$Li production and the related cross section has never been directly measured before at relevant energies. Another important process in the BBN is the $^2$H($p,\gamma$)$^3$He reaction. The uncertainty on its cross section should explain the small discrepancy between observed and calculated primordial deuterium abundances. In order to reduce it, a new measurement of this cross section in the BBN energy range with an accuracy less than 3% is thus desirable. Such a measurement is planned at LUNA at the beginning of 2016. However, a feasibility test has already been performed. The results obtained are shown. Possible cosmological and theoretical nuclear physics outcomes from future LUNA data is also discussed.

Nuclear Reactions at Astrophysical Energies with $\gamma$-ray Beams: A Novel Experimental Approach

Acta Phys. Pol. B 47, 707 (2016)

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abstract

An active-target Time Projection Chamber is being developed at the University of Warsaw to study photo-disintegration reaction of astrophysical interest at the relevant energies using the intense monochromatic $\gamma$-ray beams that will be available at the ELI–NP facility in Bucharest-Măgurele, Romania. As part of the R$\&$D for this project, a prototype detector was constructed. The first results from tests with charged-particle ion beams are presented.

Exploring Exotic Nuclei with the GRIFFIN Spectrometer at TRIUMF-ISAC

Acta Phys. Pol. B 47, 713 (2016)

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abstract

The new GRIFFIN gamma-ray spectrometer has replaced the 8$\pi$ spectrometer as a dedicated facility for decay spectroscopy experiments at TRIUMF-ISAC. This facility enables a broad program of research in the fields of nuclear structure, nuclear astrophysics and fundamental symmetries using stopped radioactive beams. In this contribution, an overview is given of the detector systems with examples of the experiments performed with the device during the first year of operation at ISAC.

all authors

J. Kownacki, M. Kisieliński, A. Kordyasz, M. Kowalczyk, P. Napiorkowski, J. Srebrny, A. Stolarz, S. Lalkovski, Ch. Droste, E. Ruchowska, W. Czarnacki, A. Korman, P. Sibczyński, J. Andrzejewski, J. Perkowski, Ł. Janiak, J. Samorajczyk

Investigation of $\gamma$-ray Emission in Heavy Ion Induced Fission During the Cyclotron Beam-on Periods

Acta Phys. Pol. B 47, 723 (2016)

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abstract

The delayed coincidence method with special reference to the in-beam experiments is considered as a means of identification and the lifetime measurements of isomeric states, as well as, the method of the investigation of radiations populating isomeric states. Isomers are detected and correlated with prompt events if they occur within a certain time of the prompt event. The $^{16}$O $+\,^{208}$Pb reaction was investigated using the OSIRIS-II and the EAGLE arrays at HIL-UW. About eighty nuclei were identified as fission fragments among the reaction products. Several known isomeric transitions associated with reaction products in neutron-rich nuclei region were detected, as well as some new candidates were observed.

Beta-delayed Neutron Emission: First Measurements in the Heavy Mass Region and Future Prospects

Acta Phys. Pol. B 47, 729 (2016)

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abstract

Beta-delayed neutrons play a key role in the formation of heavy elements in explosive stellar environments. The final r-process abundance distribution, including the rare-earth peak, is tailored to a large extent by the neutrons released after the beta decay of very exotic neutron-rich nuclei encountered along the r-process path and during the freeze-out phase. Such scenarios involve a vast amount of — yet undiscovered — nuclei, and most of them are expected to be neutron emitters. In this respect, existing beta-delayed neutron emission data is rather scarce, spanning from the lightest isotopes up to the region of the fission-fragments with masses up to $A\sim 150$. This contribution gives an overview on the latest measurements of neutron branching ratios in the heavy mass region around $N=126$, which was practically unexplored in the past. Present plans to access very exotic nuclei at the RIB-facility of RIKEN in the framework of the BRIKEN project, are presented, together with the expected impact in r-process nucleosynthesis studies.

Studies of Predictive Powers of Beta-delayed Neutron Emission Model Based on Effective Density Parametrization

Acta Phys. Pol. B 47, 739 (2016)

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abstract

Effective density model of beta-delayed neutron emission is studied for its predictive powers. The parameters of the model are fitted to the reduced experimental dataset in order to check for a short-range extrapolation accuracy. Different mass models are used for a study of a long-range extrapolations.

all authors

I. Marroquin, M.J.G. Borge, A.A. Ciemny, H. de Witte, L.M. Fraile, H.O.U. Fynbo, A. Garzón-Camacho, A. Howard, H. Johansson, B. Jonson, O.S. Kirsebom, G.T. Koldste, R. Lica, M.V. Lund, M. Madurga, C. Mazzocchi, C. Mihai, M. Munch, S.A. Nae, E. Nacher, A. Negret, T. Nilsson, A. Perea, J. Refsgaard, K. Riisager, E. Rapisarda, C. Sotty, M. Stanoiu, O. Tengblad, A.E. Turturica, M.V. Vedia

Multi-particle Emission from ${^{31}}$Ar at ISOLDE

Acta Phys. Pol. B 47, 747 (2016)

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abstract

A multi-particle decay experiment was successfully performed at the ISOLDE Decay Station. In this new permanent station, devoted to $\beta$-decay studies, the novel MAGISOL Si-Plugin Chamber was installed to study the exotic decay modes of the proton drip-line nucleus ${^{31}}$Ar. The motivation was to search for $\beta 3p$ and $\beta 3p\gamma$ channels, as well as to provide information on resonances in ${^{30}}$S and ${^{29}}$P relevant for the astrophysical rp-process. Description of the experimental set-up and preliminary results are presented.

all authors

J.A. Briz, A.-A. Zakari-Issoufou, M. Fallot, A. Porta, A. Algora, J.L. Tain, E. Valencia, S. Rice, V. Guadilla, J. Agramunt, J. Äystö, M. Bowry, V.M. Bui, R. Caballero-Folch, D. Cano-Ott, S. Cormon, A. Cucoanes, V. Eloma, T. Eronen, E. Estévez, M. Estienne, G.F. Farrelly, L.M. Fraile, E. Ganioglu, A. Garcia, W. Gelletly, M.B. Gomez-Hornillos, V. Gorlychev, J. Hakala, A. Jokinen, M.D. Jordan, A. Kankainen, F.G. Kondev, M. Lebois, T. Martinez, E. Mendoza, F. Molina, A. Montaner, I. Moore, E. Nácher, S. Orrigo, H. Penttilä, A.B. Pérez, Zs. Podolyak, P.H. Regan, J. Rissanen, B. Rubio, T. Shiba, A. Sonzogni, V. Vedia, C. Weber, J. Wilson

Total Absorption Spectroscopy of Fission Fragments Relevant for Reactor Antineutrino Spectra Determination

Acta Phys. Pol. B 47, 755 (2016)

page 755 •

abstract

The contribution of each fission fragment to the reactor antineutrino spectra was determined using the summation method based on the existing information on fission yields and decay data contained in nuclear databases and the reactor evolution code MURE. The beta decay of some of the main contributors has been studied using the Total Absorption Spectroscopy (TAS) technique during two experimental campaigns at the IGISOL facility, in Jyväskylä (Finland). Results on the decay of $^{92}$Rb, the most important contributor in the $4$–$8$ MeV energy region are reported. The status of the analysis of the second experiment is presented as well.

all authors

W. Luo, M. Bobeica, D. Filipescu, I. Gheorghe, D. Niculae, D.L. Balabanski

Production of Radioisotopes of Medical Interest by Photonuclear Reaction Using ELI–NP $\gamma$-ray Beam

Acta Phys. Pol. B 47, 763 (2016)

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abstract

The radioisotope production has a crucial role in medical diagnosis and therapy. In this work, we investigated the possibility of obtaining radioisotopes of medical interest through photo-neutron reactions using the high-intensity $\gamma$ beams at the Extreme Light Infrastructure — Nuclear Physics (ELI–NP) facility. The specific activity for three benchmark radioisotopes, $^{99}$Mo/$^{99m}$Tc, $^{186}$Re and $^{225}$Ra/$^{225}$Ac, was obtained as a function of $\gamma$-beam energy, target geometry and irradiation time. Optimization for the generation of these radioisotopes at ELI–NP was investigated. We estimated that a saturation specific activity of the order of 1–2 mCi/g could be obtained for a thin target (radius 1–2 mm, thickness 1 cm) and for a conservative $\gamma$-beam flux of 10$^{11}$ s$^{-1}$. The ELI–NP, based on these estimations, could provide the possibility for the production of certain radioisotopes in sufficient quantities for nuclear medicine research.

Measurements of Thermal and Resonance Neutron Fluence and Induced Radioactivity Inside Bunkers of Medical Linear Accelerators in the Center of Oncology in Opole, Poland

Acta Phys. Pol. B 47, 771 (2016)

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abstract

Emission of high-energy X-ray and electron therapeutic beams from medical linear accelerators is related to undesirable neutron production and to induction of radioactivity. In this work, measurements of thermal and resonance neutron fluence and induced radioactivity were performed inside two bunkers with medical linacs — Elekta in the Center of Oncology in Opole (Poland). The bunkers differ with a construction of their walls. The neutron measurements were performed by means of the induced activity method during emission of the 18 MV X-ray beam. The investigation of radioactivity induced by neutrons was based on the method of off-line gamma-ray spectroscopy measurements. This work has shown that the differences in the considered construction of bunkers do not influence significantly on the thermal and resonance neutron fluence as well as on the induced radioactivity. The greatest thermal neutron fluence ($1.4 \times 10^4$ cm$^{-2}$ MU$^{-1}$) as well as the resonance one ($0.7 \times 10^4$ cm$^{-2}$ MU$^{-1}$) was measured at the isocenter of a rotation of the accelerator head. The radioisotopes of $^{187}$W, $^{56}$Mn, $^{24}$Na and $^{82}$Br originating from the ($n,\gamma$) reactions were identified in the spectral measurements.

all authors

E. Bzymek, A. Konefał, A Orlef, Z. Maniakowski, M. Szewczuk, M. Sokół, W. Zipper

Test of Production of $^{99}$Mo/$^{99m}$Tc by Means of Typical Medical Linear Accelerators Used in Teleradiotherapy

Acta Phys. Pol. B 47, 777 (2016)

page 777 •

abstract

The test of production of the $^{99}$Mo/$^{99m}$Tc complex by means of Varian medical linear accelerators used in teleradiotherapy was performed. The targets made of the natural molybdenum were irradiated by high-energy therapeutic 20 MV X-ray beam. $^{99}$Mo was produced mainly in the photonuclear reaction of $^{110}$Mo($\gamma ,n$)$^{99}$Mo. The obtained specific activities are relatively small in the saturation state (from 155.4 kBq/g to 163.2 kBq/g) because only the high-energetic part of the spectrum of 20 MV X-ray beam covers the energy range of the $^{110}$Mo($\gamma ,n$)$^{99}$Mo reaction cross section. The new application of the $^{99}$Mo/$^{99}$$^m$Tc complex of the low activity was suggested using the molybdenum nanoparticle technology.

Determination of Energy Spectra in Water for 6 MV X Rays from a Medical Linac

Acta Phys. Pol. B 47, 783 (2016)

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abstract

There is a lack of extensive data comprising energy spectra in water for beams generated by medical accelerators applied in radiotherapy. The purpose of this work was the determination of energy spectra in water for the 6 MV X-ray therapeutic beam from the medical linac — Clinac 2300 by Varian. The spectra were derived with the use of Monte Carlo computer simulations basing on MCNPX code in version of 2.7.0. The performed investigations indicate that shapes of the spectra as well as the mean energy of the considered beams depend on a depth in water, a distance from the central-axis of the beam and a radiation field size. The obtained results are valuable for constructors of medical linacs and, additionally, they can be applied in advanced treatment planning systems. Therefore, all obtained spectra in a numerical form are available for common use. They will be sent to users after forwarding e-mail message to the authors of this paper.

all authors

M. Diakaki, A. Kalamara, M. Kokkoris, G. Marangouli, A. Tsinganis, A. Panagiotopoulos, R. Vlastou, E. Berthoumieux, A. Lagoyannis, M. Axiotis, N. Patronis

Measurement of the $^{236}$U$(n,f)$ Cross Section with the MicroMegas Detector

Acta Phys. Pol. B 47, 789 (2016)

page 789 •

abstract

The measurement of the $^{236}$U$(n,f)$ cross section was attempted with a new MicroMegas detector, based on the Microbulk technology. The incident quasi-monoenergetic neutron beams with energies in the range of 4–10 MeV were produced via the $^{2}$H$(d,n)$ reaction at the neutron beam facility of the Institute of Nuclear and Particle Physics at the NCSR “Demokritos” and first results of the analysis are presented.

all authors

A.J. Kordyasz, J. Kownacki, Ł. Kordyasz, M. Konop, A. Bednarek, M. Kowalczyk, J. Tarasiuk, M. Kisieliński, T. Kozik, E. Piasecki, P. Sibczyński, A. Stolarz, J. Kowalska, A. Tucholski, J. Srebrny, M. Wolińska-Cichocka, P. Napiorkowski, J. Sarnecki, D. Lipiński, H. Wodzińska, M. Teodorczyk, M. Gajewski, A. Zagojski, K. Krzyżak

First Tests of Superthin, Ion-implanted Silicon Strip Detectors Produced by Low-temperature Technique

Acta Phys. Pol. B 47, 797 (2016)

page 797 •

abstract

A new technique of producing thin strip detectors was developed. The principle of the technique is the application of a low-temperature baking process instead of high temperature annealing. This thermal treatment follows the $B^{+}$ ion implantation and evaporation of Al as detector contacts, which are created using a single adjusted Al mask in form of a comb. The thickness distribution along $X$ and $Y$ directions for a thin silicon epitaxial membrane was measured by the energy loss of $\alpha$ particles from $^{241}$Am ($\langle E_{\alpha }\rangle =5.5$ MeV). Preliminary tests of the first 5 $\mu$m thin strip detector have been performed with $\alpha$ particles and fission fragments from $^{252}$Cf. The $\Delta E$–$E$ ion identification plots were created using a telescope consisting of our one thin strip of the $\Delta E$ strip detector (5 $\mu$m thick) followed by a typical 300 $\mu$m Ortec E detector.

Transfer Reactions with Radioactive Beams Near the $N=50$ and $N=82$ Shell Closures

Acta Phys. Pol. B 47, 803 (2016)

page 803 •

abstract

Knowledge of single-particle energies is critically important for a microscopic description of the atomic nucleus. In the absence of a model capable of accurate predictions across the whole nuclear chart, realistic calculations still require that effective single-particle energies be empirically determined. Transfer reactions are one of the best tools to determine the single-particle strength of the populated states, by comparing the experimental and theoretical cross sections of the scattered light ejectiles. Radioactive ion beams and new experimental set-ups are being used to study transfer reactions in inverse kinematics in increasingly exotic regions of the nuclear chart. In this context, studies of nuclei neighbouring single and double shell closures are particularly valuable, because they permit direct comparisons with the latest shell model calculations. This paper will focus, in particular, on measurements carried out near the $N=50$ and $N=82$ neutron shell closures, which cross respectively the neutron-rich doubly-magic exotic nuclei $^{78}$Ni and $^{132}$Sn.

all authors

C.E. Mertin, L.T. Baby, D.D. Caussyn, K.W. Kemper, N. Keeley, S.A. Kuvin, A.V. Skeeters, I. Wiedenhöver

Population of Levels in $^{15}$O up to 15 MeV in Excitation by the $^{14}$N($^3$He,$d$) Reaction

Acta Phys. Pol. B 47, 815 (2016)

page 815 •

abstract

The $^{14}$N($^3$He,$d)$ reaction was studied at a beam energy of 20 MeV to search for major single-particle strength above 9 MeV in $^{15}$O. No such strength was found up to 15 MeV in excitation. Comparison with the $^{12}$C$(^6$Li,$t)$ reaction allows the firm assignment of $9/2^+$ to the strongly populated state in $^{15}$O at 10.46 MeV. With this result, the mirror $^{15}$N–$^{15}$O spin-parity values can be made up to 11 MeV in both nuclei, which are given in this work.

all authors

A.M. Moro, J. Lei, M. Gómez-Ramos, J.M. Arias, R. de Diego, J. Gómez-Camacho, J.A. Lay

Recent Developments for the Calculation of Elastic and Non-elastic Breakup of Weakly-bound Nuclei

Acta Phys. Pol. B 47, 821 (2016)

page 821 •

abstract

In this contribution, we review some recent theoretical advances for the calculation of breakup cross sections in reactions induced by weakly-bound nuclei.

New Experiments Demand for a More Precise Analysis of Continuum Spectrum in $^6$He: Technical Details and Formalism

Acta Phys. Pol. B 47, 833 (2016)

page 833 •

abstract

A simple three-body model of $^6$He is extended to include $sd$-continuum states in the picture in addition to the already investigated $p$-states. The role of different continuum components in the weakly bound nucleus $^6$He is studied by coupling unbound $spd$-waves of $^5$He by using simple pairing contact-delta interaction. The main focus of this paper is to outline the procedure that allows the calculation of different configurations of $^6$He including continuum states and to set up basic ingredients for computations. The method and results discussed here will be used for the calculation of monopole, dipole, quadrupole and octupole response of $^6$He.

all authors

G. Marquínez-Durán, A.M. Sánchez-Benítez, I. Martel, L. Acosta, K. Rusek, M.A.G. Álvarez, R. Berjillos, M.J.G. Borge, A. Chbihi, C. Cruz, M. Cubero, J.A. Dueñas, J.P. Fernández-García, B. Fernández-Martínez, J.L. Flores, J. Gómez-Camacho, N. Keeley, J.A. Labrador, M. Marqués, A.M. Moro, M. Mazzocco, A. Pakou, V.V. Parkar, N. Patronis, V. Pesudo, D. Pierroutsakou, R. Raabe, R. Silvestri, N. Soic, Ł. Standyło, I. Strojek, O. Tengblad, R. Wolski, A.H. Ziad

Study of the Near-barrier Scattering of $^8$He on $^{208}$Pb

Acta Phys. Pol. B 47, 841 (2016)

page 841 •

abstract

The structure and dynamics of $^{8}$He have been studied through the collision process with a $^{208}$Pb target at energies of 22 and 16 MeV, above and below the Coulomb barrier, respectively. The energy and angular distributions of the elastically scattered $^{8}$He and the $^{6,4}$He fragments were measured. In this paper, we discuss the method used to determine the effective position of the beam spot on the reaction target and the scattering and solid angles of each pixel of the detector array.

all authors

G. Kaur, B.R. Behera, A. Jhingan, B.K. Nayak, R. Dubey, P. Sharma, M. Thakur, R. Mahajan, N. Saneesh, T. Banerjee, Khushboo, A. Kumar, S. Mandal, A. Saxena, P. Sugathan, N. Rowley

Measurement of Quasi-elastic Scattering: to Probe $^{28}$Si+$^{154}$Sm Reaction

Acta Phys. Pol. B 47, 847 (2016)

page 847 •

abstract

We discuss the role of channel coupling of $^{28}$Si on fusion mechanism with permanently deformed target $^{154}$Sm. To this end, we analyze the experimental quasi-elastic cross sections at a large backward angle and quasi-elastic barrier distribution for $^{28}$Si+$^{154}$Sm system using the coupled-channels approach. While earlier studies have reported the rotational excitation of $^{28}$Si playing role on fusion with spherical and near spherical target nuclei, we find its vibrational excitation as origin of observed barrier distribution for $^{28}$Si+$^{154}$Sm system. Our study also reveals significant influence of channel couplings on the surface diffuseness parameter of an inter-nuclear potential supporting the earlier observations.

Approach to High-density Nuclear Matter via Nucleus–Nucleus Elastic Scattering

Acta Phys. Pol. B 47, 853 (2016)

page 853 •

abstract

We investigate the effect of the high-density nuclear matter on the nucleus–nucleus elastic scattering in the framework of the double-folding (DF) model with the complex $G$-matrix interaction. The medium effect including three-body-force (TBF) effect described by the multi-Pomeron exchange potential is investigated with the present methods. One of the methods is to control the medium effect by changing the local density in the DF model calculation. The other is to replace the complex $G$-matrix interaction with the TBF effect by that without the TBF effect in the calculation. With both methods, it is made clear that the heavy-ion elastic scattering is very sensitive to the medium effects in the high-density region. Finally, we make clear the crucial role of the TBF effect up to $k_F=1.6$ fm$^{-1}$ in the nucleus–nucleus elastic scattering.

all authors

M. Krzysiek, M. Kmiecik, A. Maj, P. Bednarczyk, A. Bracco, F.C.L. Crespi, E.G. Lanza, R. Avigo, D. Bazzacco, G. Benzoni, B. Birkenbach, N. Blasi, S. Bottoni, F. Camera, S. Ceruti, M. Ciemała, G. De Angelis, E. Farnea, A. Gadea, A. Giaz, A. Görgen, A. Gottardo, J. Grębosz, R. Isocrate, S. Leoni, S. Lunardi, K. Mazurek, D. Mengoni, C. Michelagnoli, B. Million, A.I. Morales, D.R. Napoli, R. Nicolini, L. Pellegri, F. Recchia, B. Siebeck, S. Siem, C. Ur, J.J. Valiente-Dobon, O. Wieland, M. Ziębliński

Gamma Decay of the Possible $1^-$ Two-phonon State in $^{140}$Ce Excited via Inelastic Scattering of $^{17}$O

Acta Phys. Pol. B 47, 859 (2016)

page 859 •

abstract

The $\gamma$ decay from the low-lying dipole states of $^{140}$Ce excited via inelastic scattering of $^{17}$O at bombarding energy of 340 MeV was measured using the high resolution AGATA-Demonstrator array in coincidence with scattered ions detected in two segmented $\Delta E$–$E$ silicon detectors of the TRACE array. Particular attention is here given to the decay of the first 1$^{-}$ state at 3643 keV which is considered to be of two-phonon character. The gamma–gamma coincidence method was applied to select desired decay branch. No direct decay from this state was observed to 2$^{+}$ and 3$^{-}$ phonon states which would be the proof of the pure harmonic coupling. The comparison between experimentally obtained differential cross sections and analysis with distorted wave Born approximation (DWBA) allowed to conclude that the first 1$^{-}$ state has a different nature than higher-lying pygmy dipole states. This was possible using the form factor obtained by folding a microscopically calculated transition density.

all authors

Y. Fujita, B. Rubio, F. Molina, T. Adachi, H. Fujita, B. Blank, E. Ganioğlu, W. Gelletly, S.E.A. Orrigo

The $T_{z} = \pm 1 \to 0$ and $\pm 2 \to \pm 1$ Mirror Gamow–Teller Transitions in $pf$-shell Nuclei

Acta Phys. Pol. B 47, 867 (2016)

page 867 •

abstract

Gamow–Teller (GT) transitions are the most common weak-interaction processes in the Universe. They play important roles in various processes of nucleosynthesis, for example, in the rapid proton-capture process (rp-process). In the $pf$-shell region, the rp-process runs through neutron-deficient nuclei with $T_{z} = -2$, $-1$, and $0$ mainly by means of GT and Fermi transitions, where $T_{z}$ is the $z$ component of isospin $T$ defined by $T_{z} = (N-Z)/2$. Under the assumption of isospin symmetry, mirror nuclei with reversed $Z$ and $N$ numbers, and thus with opposite signs of $T_{z}$, have the same structure. Therefore, symmetry is also expected for the GT transitions starting from and ending up in mirror nuclei. We have been studying the $T_{z} = -2 \to -1$ and $-1 \to 0$ GT transitions in $\beta$ decays, while those from stable $T_{z}= +2$ and $+1$ nuclei by means of hadronic ($^3{\rm He},t$) charge-exchange (CE) reactions. The results from these studies are compared in order to examine the mirror-symmetry structure in nuclei. In addition, these results are combined for the better understanding of GT transitions in the $pf$-shell region.

Collectivity above the Closed $^{78}$Ni and $^{132}$Sn Cores

Acta Phys. Pol. B 47, 883 (2016)

page 883 •

abstract

We investigate collective features of nuclei with several valence particles outside the closed cores of $^{78}$Ni and $^{132}$Sn. Using the pseudo-SU(3) model and large-scale shell model diagonalizations, we show that quadrupole collectivity should develop in $N=54$ and $N=86$ isotones and that non-axial degrees of freedom may play an important role in both regions.

all authors

E. Sahin, F.L. Bello Garrote, A. Görgen, G. de Angelis, M. Niikura, S. Nishimura, D. Mengoni, Z. Xu, H. Baba, F. Browne, P. Doornenbal, S. Franchoo, G. Guillaume, T. Isobe, P.R. John, H.S. Jung, K.K. Hadyńska-Klęk, Z. Li, G. Lorusso, I. Matea, K. Matsui, P. Morfouace, D.R. Napoli, H. Nishibata, A. Odahara, H. Sakurai, P.-A. Söderström, D. Sohler, I. Stefan, T. Sumikama, D. Suzuki, R. Taniuchi, J. Taprogge, Z. Vajta, H. Watanabe, V. Werner, J. Wu, A. Yagi, K. Yoshinaga

First Results on the Excited States in $^{77}$Cu

Acta Phys. Pol. B 47, 889 (2016)

page 889 •

abstract

The level structure of the $^{77}$Cu nucleus has been studied by means of $\beta$-delayed $\gamma$-ray spectroscopy at RIKEN Nishina Center. Secondary beam particles in the region near $^{78}$Ni were produced via in-flight fission of $^{238}$U on a thick $^9$Be target at a primary beam energy of 345 MeV/nucleon. After identification in atomic number ($Z$) and mass-to-charge ratio ($A/Q$) in the BigRIPS fragment separator, the fission products were delivered to the final focal plane through the ZeroDegree Spectrometer. The WAS3ABI silicon stack array was used for the implantation of the ions, while de-excitation $\gamma$ rays were detected with the EURICA $\gamma$-ray spectrometer at the focal plane. Beta-correlated particle identification of $^{77}$Ni allowed to obtain the $\gamma$-ray spectrum of the daughter $^{77}$Cu in a selective way. Experimental details and first results on the excited states in $^{77}$Cu nucleus will be presented in this contribution.

all authors

P. Bączyk, W. Urban, D. Złotowska, M. Czerwiński, T. Rząca-Urban, M. Konieczka, A. Blanc, M. Jentschel, P. Mutti, U. Köster, T. Soldner, G. de France, G. Simpson, C. Ur

Near-yrast Excitations in Nucleus $^{83\!}$As: Tracing the Deformation in the $^{78}$Ni Region

Acta Phys. Pol. B 47, 897 (2016)

page 897 •

abstract

Medium-spin, yrast excitations in nucleus $^{83}$As have been studied in neutron-induced fission of $^{235}$U. The experiment took place at the Institut Laue-Langevin in Grenoble where gamma rays were registered using the EXILL detector array. Recently, we proposed new tentative $(9/2^+)$ spin assignment for 2777 keV level in $^{83}$As, which is now discussed in the context of deformation showing up in $^{78}$Ni region.

all authors

T.W. Hagen, L. Grente, A. Görgen, M.-D. Salsac, W. Korten, F. Farget, T. Braunroth, B. Bruyneel, I. Celikovic, E. Clément, G. de France, O. Delaune, A. Dewald, A. Dijon, M. Hackstein, B. Jacquot, J. Litzinger, J. Ljungvall, C. Louchart, C. Michelagnoli, D.R. Napoli, A. Navin, F. Recchia, M. Rejmund, W. Rother, E. Sahin, S. Siem, B. Sulignano, Ch. Theisen, J.J. Valiente-Dobon

Lifetime Measurments of Excited States in Neutron-rich Fission Fragments

Acta Phys. Pol. B 47, 903 (2016)

page 903 •

abstract

Lifetimes of short-lived excited states in a wide range of neutron-rich fission fragments were measured using the recoil distance Doppler shift (RDDS) technique, which was applied to fusion-fission reactions in inverse kinematics for the first time. The fission fragments were identified event-by-event in mass, charge, and atomic number using the VAMOS magnetic spectrometer at GANIL. Gamma rays originating from the fission fragments were measured with the EXOGAM array of Ge Clover detectors around the target position. Using a degrader, the change in the Doppler shift of the $\gamma$ ray allows the application of the RDDS method. Details of the experimental technique will be discussed and the status for the ongoing analysis for odd-mass yttrium isotopes will be presented.

all authors

M. Ramdhane, G.S. Simpson, F. Drouet, T. Malkiewicz, A. Vancraeyenest, G. Gey, P. Alexa, G. Thiamova, G. Kessedjian, C. Sage, T. Grahn, P.T. Greenlees, K. Hauschild, A. Herzan, U. Jakobsson, P. Jones, R. Julin, S. Juutinen, S. Ketelhut, A. Lopez-Martens, P. Nieminen, P. Peura, P. Rahkila, S. Rinta-Antila, P. Ruotsalainen, M. Sandzelius, J. Saren, C. Scholey, J. Sorri, J. Uusitalo

Study of Intermediate-spin States of $^{98}$Y

Acta Phys. Pol. B 47, 911 (2016)

page 911 •

abstract

The nuclear structure of the odd–odd nucleus $^{98}$Y has been re-investigated by observing prompt $\gamma$ rays emitted following the proton-induced fission of a $^{238}$U target, using the JUROGAM-II multidetector array. New high-spin decays have been observed and placed in the level schemes using triple coincidences. The experimental level energies and $\gamma$-decay patterns are compared to GICM and QPRM calculations, assuming that this neutron-rich $N=59$ isotone is spherical at low energies and prolate deformed at intermediate spins.

all authors

S. Dutt, P.J. Napiorkowski, T. Abraham, Ł. Janiak, M. Kisieliński, M. Komorowska, M. Kowalczyk, R. Kumar, T. Marchlewski, M. Matejska-Minda, M. Palacz, W. Piątek, L. Próchniak, I.A. Rizvi, J. Samorajczyk, M. Saxena, J. Srebrny, A. Tucholski, W. Wróblewski, K. Wrzosek-Lipska, M. Zielińska

Nuclear Structure Study of $^{104}$Pd by Coulomb Excitation at the Warsaw Heavy Ion Laboratory

Acta Phys. Pol. B 47, 917 (2016)

page 917 •

abstract

Low-lying excited states of $^{104}$Pd were investigated by means of Coulomb excitation using the $^{32}$S beam. Gamma-ray spectra resulting from the de-excitation of these levels were measured with the EAGLE gamma-ray spectrometer at the Heavy Ion Laboratory, University of Warsaw. The first three excited states above the ground state up to 6$^{+}$ level were populated along-with the low-lying non-yrast states. Excitation of the 3$^{-}$ state at 2194 keV energy was also observed.

all authors

M. Komorowska, M. Zielińska, P. Napiorkowski, D.T. Doherty, K. Wrzosek-Lipska, P.A. Butler, L. Próchniak, W. Korten, R. Briselet, H. De Witte, L.P. Gaffney, G. Georgiev, A. Goasduff, A. Görgen, A. Gottardo, E.T. Gregor, K. Hadyńska-Klęk, H. Hess, M. Klintefjord, T. Konstantinopoulos, J. Ljungvall, R. Lutter, I. Matea, P. Matuszczak, G.G. O'Neill, W. Piątek, P. Reiter, D. Rosiak, M. Scheck, M. Seidlitz, B. Siebeck, M. Thürauf, N. Warr

Study of Octupole Collectivity in $^{146}$Nd and $^{148}$Sm Using the New Coulomb Excitation Set-up at ALTO

Acta Phys. Pol. B 47, 923 (2016)

page 923 •

abstract

For certain combinations of protons and neutrons in atomic nuclei, a rise of a reflection asymmetry is expected. Experimental E3 strengths, which as a function of the neutron number peak at around $N\approx 88$ and $N\approx 134$, indicate enhanced octupole correlations as predicted by theory. Low-energy Coulomb excitation is a highly successful method for establishing the evolution of nuclear shapes, through the measurement of cross sections, to populate excited states that can be directly related to the static and dynamic moments of the charge distribution of the nucleus. A Coulomb excitation experiment at the ALTO facility, Orsay was performed recently to study collective properties of $^{146}$Nd and $^{148}$Sm. In particular, the strengths of the $\langle 3^- ||$E3$||0^+\rangle$ and $\langle 1^-||$E3$||4^+\rangle$ matrix elements will provide a clear distinction between octupole vibration and rigid deformation.

all authors

M. Cavallaro, F. Cappuzzello, C. Agodi, S. Calabrese, D. Carbone, A. Foti, G. Santagati, V. Zagatto

Using Double Charge Exchange Reactions Towards $0\nu \beta \beta$ Nuclear Matrix Elements

Acta Phys. Pol. B 47, 929 (2016)

page 929 •

abstract

The knowledge of the nuclear matrix elements (NME) for the neutrinoless double beta decay is fundamental for neutrino physics. The NMEs indeed enter in the expression connecting the half-life of the neutrinoless double beta decay to the neutrino mass. Information on the nuclear matrix elements can be obtained by measuring the cross section of double charge exchange nuclear reactions. The basic point is that the initial and final-state wave functions in the two processes are the same and the transition operators are similar. The double charge exchange cross sections can be factorized in a nuclear structure term containing the matrix elements and a nuclear reaction factor. First pioneering experimental results for the $^{40}$Ca($^{18}$O,$^{18}$Ne)$^{40}$Ar reaction at 270 MeV incident energy show that such cross section factorization reasonably holds for the 0$^{+}$ to 0$^{+}$ transition to the $^{40}$Ar$_{\mathrm {gs}}$, at least at very forward angles.

all authors

D. Carbone, C. Agodi, F. Cappuzzello, M. Cavallaro, A. Foti, E. Khan

Collective Excitations in the $^{14}$C Nucleus Populated by the $^{12}$C($^{18}$O,$^{16}$O) Reaction at 84 MeV

Acta Phys. Pol. B 47, 937 (2016)

page 937 •

abstract

The $^{12}$C($^{18}$O,$^{16}$O)$^{14}$C reaction at 84 MeV incident energy has been explored up to high excitation energy of the residual nucleus thanks to the use of the MAGNEX spectrometer to detect the ejectiles. In the region above the two-neutron separation energy, a resonance at 16.9 MeV has been observed. Continuum quasi-particle random phase approximation calculations of the response function, corresponding to the transfer of a neutron pair to the $^{12}$C nucleus, have been performed to investigate the possible presence of the Giant Pairing Vibration in that energy region.

On the Possibility to Observe New Shape Isomers in the Po–Th Region

Acta Phys. Pol. B 47, 943 (2016)

page 943 •

abstract

Using the macroscopic–microscopic approach with the macroscopic energy determined by the Lublin–Strasbourg Drop model and the microscopic, shell plus pairing, corrections evaluated through the Yukawa-folded mean-field potential, a certain number of yet unknown super- and hyper-deformed shape isomers in even–even Po, Ra and Th isotopes are predicted. Quadrupole moments and the energies of the lowest rotational state $2^+$ in the local minima of the potential-energy surfaces are evaluated. We show that they turn out to be in good agreement with the available experimental data for the ground state.

all authors

R. Dubey, P. Sugathan, A. Jhingan, T. Banerjee, N. Saneesh, G. Kaur, M. Thakur, R. Mahajan, I. Mukul, D. Siwal

Study the Fission Dynamics of $^{225}$Pa Nuclei Around the Sub-barrier Energy

Acta Phys. Pol. B 47, 953 (2016)

page 953 •

abstract

$^{225}$Pa nuclei exhibit a fusion-fission mechanism below the fusion barrier energy. Mass angle distribution measurements indicate absence of non-compound events at this bombarding energy. The effect of asymmetric fission mode on mass distribution of fission fragments is visible at low excitation energy (31.8 MeV).

Importance of Deformations in Dynamical Evolution of Proton-halo Nuclei

Acta Phys. Pol. B 47, 959 (2016)

page 959 •

abstract

Based on the cluster–core model, we have extended our recent study on neutron-halo structure of light nuclei to investigate the effects of deformations and orientations on the observed and proposed cases of proton-rich light nuclei. The relevance of “hot compact” over “cold elongated” configurations due to orientations is explored along with the possible role of angular momentum effects. The cases of both $1p$- and $2p$-halo nuclei are analyzed in terms of potential energy surfaces calculated as a sum of binding energies, Coulomb repulsion, nuclear proximity attraction and the centrifugal potential for all the possible cluster+core configurations of a nucleus. The halo structures of $^{11}$N and $^{27,28,29}$S nuclei are of special interest as they exhibit strong influence of deformations and angular momentum effects.

Approximate Solution of the Pairing Hamiltonian in the Berggren Basis

Acta Phys. Pol. B 47, 967 (2016)

page 967 •

abstract

We derive the approximate solution for the pairing Hamiltonian in the Berggren ensemble of single particle states including bound, resonance and non-resonant scattering states.

all authors

R. Najman, R. Płaneta, A. Sochocka, F. Amorini, L. Auditore, T. Cap, G. Cardella, E. De Filippo, E. Geraci, A. Grzeszczuk, S. Kowalski, T. Kozik, G. Lanzalone, I. Lombardo, Z. Majka, N.G. Nicolis, A. Pagano, E. Piasecki, S. Pirrone, G. Politi, F. Rizzo, P. Russotto, K. Siwek-Wilczyńska, I. Skwira-Chalot, A. Trifiro, M. Trimarchi, J. Wilczyński, W. Zipper

Investigation of the Freeze-out Configuration in the $^{197}$Au + $^{197}$Au Reaction at 23 $A$ MeV

Acta Phys. Pol. B 47, 975 (2016)

page 975 •

abstract

According to the model predictions, observation of toroidal objects is expected in collisions of heavy ion at low incident energies. Comparison between experimental data and model predictions which may indicate the formation of flat/toroidal nuclear systems is shown.

all authors

T. Cap, K. Siwek-Wilczyńska, J. Wilczyński, F. Amorini, L. Auditore, G. Cardella, E. De Filippo, E. Geraci, L. Grassi, A. Grzeszczuk, E. La Guidara, J. Han, T. Kozik, G. Lanzalone, I. Lombardo, R. Najman, N.G. Nicolis, A. Pagano, M. Papa, E. Piasecki, S. Pirrone, R. Płaneta, G. Politi, F. Rizzo, P. Russotto, I. Skwira-Chalot, A. Trifiró, M. Trimarchi, G. Verde, W. Zipper

Determination of Impact Parameters in Aligned Breakup of Projectile-like Fragments in $^{197}$Au + $^{197}$Au Collisions at 23$A$ MeV

Acta Phys. Pol. B 47, 983 (2016)

page 983 •

abstract

Symmetric and asymmetric aligned breakup of projectile-like fragments in $^{197}$Au + $^{197}$Au collisions at 23$A$ MeV was studied. Independently of the asymmetry, the reaction yields have been found peaked at a common, very narrow range of impact parameters.

Initialization Effects via Nuclear Charge Radii Parameterizations on the Nuclear Stopping and Its Relation to Distribution and Production of Light Mass Fragments

Acta Phys. Pol. B 47, 991 (2016)

page 991 •

abstract

We present the initialization effects on the global stopping parameters and their correlation to the fragment production via different nuclear charge radii parameterizations using isospin-dependent Quantum Molecular Dynamics model at $E = 50$ MeV/nucleon. The results obtained for liquid drop model (LDM) proposed nuclear charge radii parameterization which is isospin-independent — they have been compared with the results of three isospin-dependent nuclear charge radii parameterizations. We conclude that the values of global stopping parameters $R$ and $\frac {1} {Qzz/\mathrm {nucleon}}$ decrease with the increase in nuclear charge radii, while the production of fragments is reported to be enhanced. The influence of nuclear charge radii on nuclear stopping is almost the same for central and semi-central collisions. In addition, we have studied the role of isospin-dependent nuclear charge radii parameterizations on the $N/Z$ dependence of global stopping parameters.

$J/\psi$ Production in U+U Collisions at the STAR Experiment

Acta Phys. Pol. B 47, 997 (2016)

page 997 •

abstract

Quark–gluon plasma (QGP), a novel state of deconfined nuclear matter, has been studied in high-energy heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC). Due to the color screening of the quark–antiquark potential in the QGP, production of heavy quarkonia ($\!$e.g. $J/\psi$, ${\mit \Upsilon }$) is expected to be suppressed. However, there are also other effects that may influence the observed quarkonium yields (e.g. secondary production in the QGP, cold-nuclear-matter effects). To understand those effects, we need to study production of heavy quarkonia in various colliding systems. We present preliminary results on nuclear modification factor of $J/\psi$ production at mid-rapidity via the di-electron decay channel in minimum bias U+U collisions at $\sqrt {s_{NN}}= 193$ GeV at the STAR experiment and the current status of analysis of $J/\psi$ production in central U+U collisions.

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