The VAMOS++ magnetic spectrometer is characterized by a large angular and momentum acceptance and highly non-linear ion optics properties requiring the use of software ion trajectory reconstruction methods to measure the ion magnetic rigidity and the trajectory length between the beam interaction point and the focal plane of the spectrometer. Standard measurements, involving the use of a thin target and a narrow beam spot, allow the assumption of a point-like beam interaction volume for ion trajectory reconstruction. However, this represents a limitation for the case of large beam spot size or extended gaseous target volume. To overcome this restriction, a seven-dimensional reconstruction method incorporating the reaction position coordinates was developed, making use of artificial deep neural networks. The neural networks were trained on a theoretical dataset generated by standard magnetic ray-tracing code. Future application to a voluminous gas target, necessitating the explicit inclusion of the three-dimensional position of the beam interaction point within the target in the trajectory reconstruction method, is discussed. The performances of the new method are presented along with a comparison of mass resolution obtained with previously reported model for the case of thin-target experimental data.
A new jet gas target system has been developed for the Felsenkeller 5 MV underground ion accelerator for nuclear astrophysics. It provides either a 1.5$\times10^{18}$ cm$^{-2}$ thick cylindrical jet or a 7$\times10^{17}$ cm$^{-2}$ thick wall of nitrogen gas, with a surface of 10$\times$10 mm$^2$ to be seen by the ion beam. The system includes a de Laval type nozzle and altogether five pumping stages: In addition to the jet catcher and the jet chamber surrounding it, there are three stages connecting the jet to the ion accelerator. Behind the jet chamber, as seen from the ion beam, a windowless static-type gas target and, subsequently, a beam calorimeter have been installed. This work describes the offline tests of the gas target system prior to its installation on the beam line of the Felsenkeller accelerator. The thickness of the jet has been determined using three different methods: By computational fluid dynamics simulations, with a Mach-Zehnder interferometer, and by $α$-energy loss using a mixed $α$ source. The three methods were shown to be in agreement. For 0-6 bar inlet gas pressure, a linear relationship between inlet pressure and jet thickness has been found. Different shapes of de Laval type inlet nozzles, both circular and slit-type, have been manufactured from fused silica glass or stainless steel and tested using measurements and simulations. The power and stability of the beam calorimeter have been tested. The interferometry has been shown to work reliably and to give two-dimensional projections of the gas jet with sub-mm resolution.
A series of measurements have been performed with low-energy monoenergetic neutrons to characterise cross-talk between two organic scintillator detectors. Cross-talk time-of-flight spectra and probabilities were determined for neutron energies from 1.4 to 15.5 MeV and effective scattering angles ranging from $\sim$50° to $\sim$100°. Monte-Carlo simulations incorporating both the active and inactive materials making up the detectors showed reasonable agreement with the measurements. Whilst the time-of-flight spectra were very well reproduced, the cross-talk probabilities were only in approximate agreement with the measurements, with the most significant discrepancies ($\sim$40 %) occurring at the lowest energies. The neutron interaction processes producing cross-talk at the energies explored here are discussed in the light of these results.
Thomas Hensel, David Weinberger, Daniel Bemmerer
et al.
The NeuLAND (New Large-Area Neutron Detector) plastic-scintillator-based time-of-flight detector for 0.1-1.6 GeV neutrons is currently under construction at the Facility for Antiproton and Ion Research (FAIR), Darmstadt, Germany. In its final configuration, NeuLAND will consist of 3000 2.7 m $\times$ 5 cm $\times$ 5 cm big plastic scintillator bars that are read out on each end by fast timing photomultipliers. Here, data from a comprehensive study of an alternative light readout scheme using silicon photomultipliers (SiPM) are reported. For this purpose, a NeuLAND bar was instrumented on each end with a SiPM-based prototype of the same geometry as a 1'' photomultiplier tube, including four 6 $\times$ 6 mm$^2$ SiPMs, amplifiers, high voltage supply, and microcontroller. Tests were carried out using the 35 MeV electron beam from the superconducting Electron Linac for beams with high Brilliance and low Emittance (ELBE) with its picosecond-level time jitter in two different modes of operation, namely parasitic mode with one electron per bunch and single-user mode with 1-60 electrons per bunch. Acqiris fast digitisers were used for data acquisition. In addition, off-beam tests using cosmic rays and the NeuLAND data acquisition scheme have been carried out. Typical time resolutions of $σ_t\leq$ 120 ps were found for $\geq$95% efficiency for minimum ionising particles, improving on previous work at ELBE and exceeding the NeuLAND timing goal of $σ_t$ < 150 ps. Over a range of 10-300 MeV deposited energy in the NeuLAND bar, the gain was found to deviate by $\leq$10% ($\leq$20%) from linearity for 35 mm (75 mm) SiPM pitch, respectively, satisfactory for calorimetric use of the full NeuLAND detector. The dark rate of the prototype studied was found to be lower than the expected cosmic-ray induced background in NeuLAND.
A phenomenological extraction of pressure within the proton has recently been performed using JLab CLAS data (arXiv:2104.02031 [nucl-ex]). The extraction used a 3-dimensional Breit frame description in which the initial and final proton states have different momenta. Instead, we obtain the two-dimensional transverse light front pressure densities that incorporate relativistic effects arising from the boosts that cause the initial and final states to differ. The mechanical radius is then determined to be $0.518~ \pm 0.062_{\mathrm{fit}} \pm 0.126_{\mathrm{sys}}~\mathrm{fm}$, which is smaller than the electric charge radius and larger than the light front momentum radius. The forces within the proton are shown to be predominantly repulsive at distances less than $0.43~\pm 0.12~\mathrm{fm}$ from the center, and predominantly attractive further out.
A comparative study of the neutron-$γ$ Pulse Shape Discrimination (PSD) with seven organic scintillators is performed using an identical setup and digital electronics. The scintillators include plastics (EJ-299-33 and a plastic prototype), single crystals (stilbene and the recent doped $p$-terphenyl) and liquids (BC501A, NE213 and the deuterated liquid BC537). First, the overall PSD performance of the different scintillators is compared and threshold neutron energies for a given discrimination quality are determined. Then, using statistical arguments, two intrinsic contributions to the PSD capability of the scintillating materials are disentangled: the light yield and the specific pulse shapes induced by neutrons and $γ$-rays. This separation provides additional insight into the behaviour of organic scintillators and allows a detailed comparison of the discrimination performance of the various materials. On the basis of this analysis, limitations of current organic scintillators and of recently proposed alternative scintillators are discussed.
In the article: A new approach on modelling of the B-VIII, the ultimate achivement of the second ?Uranverain? by Milan P. PESIC, published in the Nuclear Technology & Radiation Protection journal, 33 (2018), 1, pp. 1-23, during the technical preparation of the article, the name of German Evonik Industries AG is wrongly spelled as Evronik Industries AG. This misspelling is entirely author''s omission and he sincerely apologies to the Evonik Industries AG and the readers of the Nuclear Technology and Radiation Protection journal. <br><br><font color="red"><b> Link to the corrected article <u><a href="http://dx.doi.org/10.2298/NTRP1801001P">10.2298/NTRP1801001P</a></b></u>
In the recent years, cluster structures have been evidenced in many ground and excited states of light nuclei [1, 2]. In the currently experimental campaign, the NUCL-EX collaboration has measured the12C+12C and14N+10B reactions at 95 MeV and 80 MeV respectively. The experimental data corresponding to complete fusion of target and projectile into an excited24Mg nucleus was compared to the results of a pure statistical model [3, 4]. In addition, data from12C+12C have been analyzed to investigate the decay of the Hoyle state of12C* [12] obtained as an intermediate step in the 6α decay channel of the24Mg* formed in central events.
Nuclear level densities and $γ$-ray strength functions of $^{56,57}$Fe have been extracted from proton-$γ$ coincidences. A low-energy enhancement in the $γ$-ray strength functions up to a factor of 30 over common theoretical E1 models is confirmed. Angular distributions of the low-energy enhancement in $^{57}$Fe indicate its dipole nature, in agreement with findings for $^{56}$Fe. The high statistics and the excellent energy resolution of the large-volume LaBr$_{3}$(Ce) detectors allowed for a thorough analysis of $γ$ strength as function of excitation energy. Taking into account the presence of strong Porter-Thomas fluctuations, there is no indication of any significant excitation-energy dependence in the $γ$-ray strength function, in support of the generalized Brink-Axel hypothesis.
A recent reconsideration of a theoretical process of a neutrinoless double beta decay points out that a signal of the decay should be shifted by a few keV from the Q-value for the 2ß0ν-decay. The conclusion was based on an analysis of the experimental data of the HEIDELBERG-MOSCOW experiment and a reconsideration of the Cuoricino data. Still the recent CUORE results contradicted the conclusions completely. No trace of a 2ß0ν-decay was found and only a limit T1/2 > 2.8*10^24 y was postulated. The problem was very serious and the CUORE results have deserved a more careful consideration.
The extreme back-angle evaporation spectra of α, Li, Be. B and C from different compound nuclei near A≈100 (Ex = 76-210MeV) have been studied and compared with the predictions of standard statistical model codes such as CASCADE and GEMINI. The temperatures of the ensembles of residual nuclei were extracted by fitting the back-angle spectra of the fragments emitted from 16O+89Y[E(16O)lab = 96MeV)], 16O+93Nb[E(16O)lab = 116MeV] and 3He+Ag[(E(3He)lab = 90and198MeV] reactions with the statistical evaporation formula given by Moretto [Nucl. Phys. A 247, 211 (1975] and similar analysis were also done for the corresponding calculated statistical spectra obtained from CASCADE and GEMINI codes. It was found that the shapes of the α-spectra agree well with the predictions of the Statistical Model. However, the spectra of Li, Be, B and C show significantly gentler slopes implying higher temperatures of the residual nuclei, even though the spectra satisfy all other empirical criteria of statistical emissions. The obs...
Peter Sorensen, Mike Heffner, Adam Bernstein
et al.
We make a proof-of-principle demonstration that improved energy resolution can be obtained in a negative-ion time projection chamber, by individually counting each electron produced by ionizing radiation.
Jefferson Lab Experiment E04-001 used the Rosenbluth technique to measure R=σ_{L}/σ_{T} and F_{2} on nuclear targets. This experiment was part of a multilab effort to investigate quark-hadron duality and the electromagnetic and weak structure of the nuclei in the nucleon resonance region. In addition to the studies of quark-hadron duality in electron scattering on nuclear targets, these data will be used as input form factors in future analysis of neutrino data which investigate quark-hadron duality of the nucleon and nuclear axial structure functions. An important goal of this experiment is to provide precise data which to allow a reduction in uncertainties in neutrino oscillation parameters for neutrino oscillation experiments (K2K, MINOS). This inclusive experiment was completed in July 2007 at Jefferson Lab where the Hall C High Momentum Spectrometer detected the scattered electron. Measurements were done in the nuclear resonance region (1 < W^{2} < 4 GeV^{2}) spanning the four-momentum transfer range 0.5 < Q^{2} < 4.5 (GeV^{2}). Data was collected from four nuclear targets: C, Al, Fe and Cu.
The reaction 12 C+ 12 C at 95 MeV beam energy has been measured using the GARFIELD+RCo apparatuses at Laboratori Nazionali di Legnaro LNL - INFN, Italy, in the framework of an experimental campaign proposed by the NUCL-EX collaboration. The aim is to progress in the understanding of statistical properties of light nuclei at excitation energies above particle emission thresholds, by measuring exclusive fusion-evaporation data. A theoretical study of the system, performed with a newly developed Monte Carlo Hauser-Feshbach code, is shown, together with preliminary results of the data analysis.