New articles on Nuclear Experiment

[1] 2208.06621

A new study of the $N=32$ and $N=34$ shell gap for Ti and V by the first high-precision MRTOF mass measurements at BigRIPS-SLOWRI

The atomic masses of $^{55}$Sc, $^{56,58}$Ti, and $^{56-59}$V have been determined using the high-precision multi-reflection time-of-flight technique. The radioisotopes have been produced at RIKEN's RIBF facility and delivered to the newly combined novel designed gas cell and multi-reflection system (ZD-MRTOF), which has been recently commissioned downstream of the ZeroDegree spectrometer following the BigRIPS separator. For $^{56,58}$Ti and $^{56-59}$V the mass uncertainties have been reduced down to the order of $10\,\mathrm{keV}$ for the first time, shedding new light on the $N=34$ shell effect in Ti and V isotopes. With the new precision achieved for the empirical two-neutron shell gaps, we reveal the non-existence of the $N=34$ shell gap for Ti and V isotopes, where the enhanced energy gap above the occupied $\nu p_{3/2}$ orbit is identified as a feature unique to Ca. We perform new Monte Carlo shell model calculations including the $\nu d_{5/2}$ and $\nu g_{9/2}$ orbits and compare the results with conventional shell model calculations, which exclude the $\nu g_{9/2}$ and the $\nu d_{5/2}$ orbits. The comparison indicates that the shell gap reduction in Ti is related to a partial occupation of the higher orbitals for the outer two valence neutrons at $N=34$.

[2] 2208.06696

Fast- and thermal-neutron detection with common NaI(Tl) detectors

Radionuclide Identification Devices (RIDs) or Backpack Radiation Detection Systems (BRDs) are often equipped with NaI(Tl) detectors. We demonstrate that such instruments could be provided with reasonable thermal- and fast-neutron sensitivity by means of an improved and sophisticated processing of the digitized detector signals: Fast neutrons produce nuclear recoils in the scintillation crystal. Corresponding signals are detectible and can be distinguished from that of electronic interactions by pulse-shape discrimination (PSD) techniques as used in experiments searching for weakly interacting massive particles (WIMPs). Thermal neutrons are often captured in iodine nuclei of the scintillator. The gamma-ray cascades following such captures comprise a sum energy of almost 7 MeV, and some of them involve isomeric states leading to delayed gamma emissions. Both features can be used to distinguish corresponding detector signals from responses to ambient gamma radiation. The experimental proof was adduced by offline analyses of pulse records taken with a commercial RID. An implementation of such techniques in commercial RIDs is feasible.

[3] 2208.06839

There and Sharp Again: The Circle Journey of Nucleons and Energy Deposition

A central question in high-energy nuclear phenomenology is how the geometry of the quark-gluon plasma (QGP) formed in relativistic nuclear collisions is precisely shaped. In our understanding of such processes, two features are especially crucial for the determination of the QGP geometry, respectively, the nucleon size and the energy deposition scheme. This contribution reports on the (circular) evolution of such features in state-of-the-art model incarnations of heavy-ion collisions over the past seven years. Ideas for future directions of investigation are pointed out.

[4] 2208.06854

Testing the collectivity in large and small colliding systems with test particles

We propose a test-particle method to probe the transport dynamics of establishment and development of collective flow in large and small systems of heavy-ion collisions. We place test particles as passengers into the partonic medium created by Au$+$Au mid-central collisions at $\sqrt{s_{NN}}$ = 200 GeV and p$+$Pb central collisions at $\sqrt{s_{NN}}$ = 5.02 TeV, using a multiphase transport model. With the help of test particles in two extreme test cases, we demonstrate that parton collisions play an important role in establishing (or destroying) the collectivity in large and small colliding systems. The collectivity established by final state parton collisions is much stronger in large colliding systems compared to small colliding systems. The collectivity from initial state can persist or survive more easily in small colliding systems than in large colliding systems due to fewer parton collisions. Our study provides some new insights to understand the origin of collectivity in large and small colliding systems at RHIC and the LHC.

[5] 2208.07029

Unified description of high-energy nuclear collisions based on dynamical core--corona picture

I establish the dynamical core--corona initialization framework (DCCI2) as a state-of-the-art dynamical framework that is capable of describing small and large colliding systems at the LHC energies. Under the core--corona picture, contributions from both equilibrated (core) and non-equilibrated (corona) components are implemented. I describe the dynamical separation of the system into the core and corona at the initial stage by incorporating the core--corona picture into the novel dynamical initialization framework. With DCCI2, I simulate $p$+$p$ collisions at $\sqrt{s}=7, 13$ TeV and $Pb$+$Pb$ collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV. Especially, I extract the fractions of core and corona components in final hadron yields in $p$+$p$ and $Pb$+$Pb$ collisions as functions of multiplicity, and reveal that the core components become dominant at $\langle dN_{\mathrm{ch}}/d\eta \rangle_{|\eta|<0.5} \approx 20$. I also find that the corona contribution at very low $p_T$ (below $p_T\approx1$ GeV) is non-negligible even in $Pb$+$Pb$ collisions and show that such contributions significantly affect $p_T$-integrated flow coefficients. These results strongly suggest the importance of considering non-equilibrated components to extract transport coefficients of quark-gluon plasma from model-to-data comparisons quantitatively.

[6] 2208.07172

Neinei -- The Neutron Imaging Center at the Brazilian Multipurpose Reactor

Neutron imaging is a non-destructive technique for analyzing a wide class of materials, such as archeologic and industrial structures. Technological advances, in recent decades, have had a great impact on the neutron imaging technique, evolving from simple radiographs using films (2D) to modern tomography systems with digital processing (3D). The Instituto de Pesquisas Energ\'eticas e Nucleares (IPEN), in Brazil, houses a 5MW research nuclear reactor, called IEA-R1, where there is a neutron imaging instrument located at the beam hole 08 (BH08) with $1.0 \times 10^{6}$ $n/cm^{2}s$ at the sample position. IEA-R1 is over 60 years old and the future of nuclear techniques in Brazil, including neutron imaging, depends on a new facility called Brazilian Multipurpose Reactor (RMB). RMB will house a suite of instruments at the Neutron National Laboratory, including the neutron imaging center called Neinei. Inspired by recent works, we have calculated the thermal neutron flux at the sample position, using the Monte Carlo method, in the Neinei and compared it to the results obtained with the Neutra (PSI), Antares (FRM II), BT2 (NIST) and DINGO (OPAL) instruments. The results are promising and provide avenues for future improvements.

[7] 2208.07285

Fluctuations of conserved charges in strong magnetic fields from lattice QCD

We present the first lattice QCD results of the second order fluctuations of and correlations among net baryon number, electric charge and strangeness in (2+1)-flavor lattice QCD in the presence of a background magnetic field with physical pion mass $m_{\pi}=135$ MeV. To mimic the magnetic field strength produced in the early stage of heavy-ion collision experiments we use 6 different values of the magnetic field strength up to $ \sim $10$m_{\pi}^2$. We find that the correlations between baryon number and electric charge along the transition line are substantially affected by magnetic fields in the current $eB$ window, which could be useful for probing the existence of a magnetic field in heavy-ion collision experiments.