arXiv subjects

M. Paul

Publications and source records attributed to M. Paul.

At least 19 recordsLinked to original sources

arXiv2025

First experimental determination of the $^{40}$Ar($n,2n$)$^{39}$Ar reaction cross section and $^{39}$Ar production in Earth's atmosphere

The cosmogenic $^{39}$Ar(t$_{1/2}$= 268 years) isotope of argon is used for geophysical dating and tracing owing to its appropriate half-life and chemical inertness as a noble gas; $^{39}$Ar serves also in nuclear weapon test monitoring. We measured for the first time the total cross section of the main $^{39}$Ar cosmogenic production reaction in the atmosphere, namely $^{40}$Ar$(n,2n)^{39}$Ar, using 14.8$\pm0.3$ MeV neutrons. The neutrons, produced by a deuterium-tritium generator, impinged on a stainless steel sphere filled with Ar gas highly enriched in the $^{40}$Ar isotope. The reaction yield was measured by atom counting of $^{39}$Ar with noble gas accelerator mass spectrometry and, independently, by decay counting relative to atmospheric argon. A total $^{40}$Ar$(n,2n)^{39}$Ar cross section of 610$\pm100$ mb was determined. This result serves as a benchmark for recent theoretical calculations and evaluations, found to reproduce well the experimental total cross section. We use these energy-dependent theoretical cross sections together with experimental spectra of cosmogenic neutrons at different altitudes to calculate the global average rate of neutron-induced $^{39}$Ar atmospheric production, resulting in $770\pm240$ $^{39}$Ar atoms/cm$^2$/day. The secular equilibrium between the $^{39}$Ar calculated production rate and radioactive decay rate leads to a partial isotopic abundance $^{39}$Ar/Ar$= (5.9\pm 1.8) \times 10^{-16}$, showing that $\approx$73% of atmospheric $^{39}$Ar is produced by cosmogenic neutrons. The $^{40}$Ar($n,2n$)$^{39}$Ar cross section at 14 MeV is also a key parameter for quantifying the anthropogenic contribution to atmospheric $^{39}$Ar produced during the thermonuclear tests of the 1960s. We estimate that anthropogenic $^{39}$Ar accounts for roughly 20% of the present atmospheric inventory.

nucl-ex↗

arXiv2025

Stellar s-process neutron capture cross sections on A-Se and A-Ce

We report on experiments at the Soreq Applied Research Accelerator Facility - Liquid-Lithium Target (SARAF-LiLiT) laboratory dedicated to the study of s-process neutron capture reactions. The kW-power proton beam at 1.92 MeV (1-2 mA) from SARAF Phase I yields high-intensity 30 keV quasi-Maxwellian neutrons (3-5x10^10 n/s). The high neutron intensity enables Maxwellian averaged cross sections (MACS) measurements of samples with short-lived decay products. Neutron capture reactions on nat-Se and nat-Ce were investigated by activation in the LiLiT neutron beam and {\gamma}-spectrometry measurements of their decay products.

nucl-ex↗

arXiv2024

Stellar s-process neutron capture cross section of Ce isotopes

Stellar abundances of cerium are of high current interest based both on observations and theoretical models, especially with regard to the neutron--magic $^{140}$Ce isotope. A large discrepancy of $s-$process stellar models relative to cerium abundance observed in globular clusters was highlighted, pointing to possible uncertainties in experimental nuclear reaction rates. In this work, the stellar neutron capture cross section of the stable cerium isotopes $^{136}$Ce, $^{138}$Ce, $^{140}$Ce, and $^{142}$Ce, were re-measured. A $^{nat}$Ce sample was irradiated with quasi-Maxwellian neutrons at $kT = 34.2$ keV using the $^{7}$Li($p,n$) reaction. The neutron field with an intensity of $3-5 \times 10^{10}$ n/s was produced by irradiating the liquid-lithium target (LiLiT) with a mA proton beam at an energy (1.92 MeV) just above the threshold at Soreq Applied Research Accelerator Facility (SARAF). The activities of the $^{nat}$Ce neutron capture products were measured using a shielded High Purity Germanium detector. Cross sections were extracted relative to that of the $^{197}$Au(n,$\gamma$) reaction and the Maxwellian-averaged cross section (MACS) of the Ce isotopes were derived. The MACS values extracted from this experiment are generally consistent with previous measurements and show for $^{140}$Ce a value $\approx 15$\% smaller than most recent experimental values.

nucl-ex↗

arXiv2022

Stellar $s$-process neutron capture cross sections of $^{69,71}$Ga

The stable gallium isotopes, $^{69,71}$Ga, are mostly produced by the weak slow ($s$) process in massive stars. We report here on measurements of astrophysically-relevant neutron capture cross sections of the $^{69,71}$Ga$(n,\gamma)$ reactions. The experiments were performed by the activation technique using a high-intensity ($3-5\times10^{10}$ n/s), quasi-Maxwellian neutron beam that closely mimics conditions of stellar $s$-process nucleosynthesis at $kT \approx$ 40 keV. The neutron field was produced by a mA proton beam at $E_p=1925$ keV (beam power of 2-3 kW) from the Soreq Applied Research Accelerator Facility (SARAF), bombarding the Liquid-Lithium Target (LiLiT). A 473 mg sample of Ga$_2$O$_3$ of natural isotopic composition was activated in the LiLiT neutron field and the activities of $^{70,72}$Ga were measured by decay counting via $\gamma$-spectrometry with a high-purity germanium detector. The Maxwellian-averaged cross sections at $kT$ = 30 keV of $^{69}$Ga and $^{71}$Ga determined in this work are 136(8) mb and 105(7) mb, respectively, in good agreement with previous experimental values. Astrophysical implications of the measurements are discussed.

nucl-ex↗

arXiv2022

A new way of video compression via forward-referencing using deep learning

To exploit high temporal correlations in video frames of the same scene, the current frame is predicted from the already-encoded reference frames using block-based motion estimation and compensation techniques. While this approach can efficiently exploit the translation motion of the moving objects, it is susceptible to other types of affine motion and object occlusion/deocclusion. Recently, deep learning has been used to model the high-level structure of human pose in specific actions from short videos and then generate virtual frames in future time by predicting the pose using a generative adversarial network (GAN). Therefore, modelling the high-level structure of human pose is able to exploit semantic correlation by predicting human actions and determining its trajectory. Video surveillance applications will benefit as stored big surveillance data can be compressed by estimating human pose trajectories and generating future frames through semantic correlation. This paper explores a new way of video coding by modelling human pose from the already-encoded frames and using the generated frame at the current time as an additional forward-referencing frame. It is expected that the proposed approach can overcome the limitations of the traditional backward-referencing frames by predicting the blocks containing the moving objects with lower residuals. Experimental results show that the proposed approach can achieve on average up to 2.83 dB PSNR gain and 25.93\% bitrate savings for high motion video sequences

cs.CV↗

arXiv2020

Ion heating in the PISCES-RF liquid-cooled high-power, steady-state, helicon plasma device

Radio Frequency (RF) driven helicon plasma sources are commonly used for their ability to produce high-density argon plasmas (n > 10^19/m^3) at relatively moderate powers (typical RF power < 2 kW). Typical electron temperatures are < 10 eV and typical ion temperatures are < 0.6 eV. A newly designed helicon antenna assembly (with concentric, double-layered, fully liquid-cooled RF-transparent windows) operates in steady-state at RF powers up to 10 kW. We report on the dependence of argon plasma density, electron temperature and ion temperature on RF power. At 10 kW, ion temperatures > 2 eV in argon plasmas are measured with laser induced fluorescence, which is consistent with a simple volume averaged 0-D power balance model. 1-D Monte Carlo simulations of the neutral density profile for these plasma conditions show strong neutral depletion near the core and predict neutral temperatures well above room temperatures. The plasmas created in this high-power helicon source (when light ions are employed) are ideally suited for fusion divertor plasma-material interaction studies and negative ion production for neutral beams.

physics.plasm-ph↗

arXiv2020

Comment on: "The interaction of neutrons with 7Be at BBN temperatures: Lack of Standard Nuclear Solution to the Primordial 7Li Problem" by M. Gai et al

The article recently published by M. Gai et al. claims to reach conclusions from a collaborative experiment dedicated to the study of the 7Be(n,alpha) reaction. These claims were published with no authorization from key collaborators, including a PI of the experiment. The Authors of the present Comment reject the conclusions of M. Gai et et al. and condemn the scientific and ethical misconduct involved in their publication. A formal Comment, similarly expressing the Authors' rejection of these conclusions was submitted to EPJ Web of Conferences who published the above article.

nucl-ex↗

arXiv2019

Coherence and indistinguishability of highly pure single photons from non-resonantly and resonantly excited telecom C-band quantum dots

In the present work, the effect of resonant pumping schemes in improving the photon coherence is investigated on InAs/InGaAs/GaAs quantum dots emitting in the telecom C-band. The linewidths of transitions of multiple exemplary quantum dots are determined under above-band pumping and resonance fluorescence via Fourier-transform spectroscopy and resonance scans, respectively. The average linewidth is reduced from $9.74\,\mathrm{GHz}$ in above-band excitation to $3.50\,\mathrm{GHz}$ in resonance fluorescence underlining its superior coherence properties. Furthermore, the feasibility of coherent state preparation with a fidelity of $49.2\,\%$ is demonstrated, constituting a step towards on-demand generation of coherent, single C-band photons from quantum dots. Finally, two-photon excitation of the biexciton is investigated as a resonant pumping scheme. A deconvoluted single-photon purity value of $g^{(2)}_{\mathrm{HBT}}(0)=0.072\pm 0.104$ and a degree of indistinguishability of $V_{\mathrm{HOM}}=0.894\pm0.109$ are determined for the biexciton transition. This represents an important step towards fulfilling the prerequisites for quantum communication applications like quantum repeater schemes at telecom wavelength.

quant-ph↗

arXiv2018

Stellar $^{36,38}$Ar$(n,γ)^{37,39}$Ar reactions and their effect on light neutron-rich nuclide synthesis

The $^{36}$Ar$(n,γ)^{37}$Ar ($t_{1/2}$ = 35 d) and $^{38}$Ar$(n,γ)^{39}$Ar (269 y) reactions were studied for the first time with a quasi-Maxwellian ($kT \sim 47$ keV) neutron flux for Maxwellian Average Cross Section (MACS) measurements at stellar energies. Gas samples were irradiated at the high-intensity Soreq applied research accelerator facility-liquid-lithium target neutron source and the $^{37}$Ar/$^{36}$Ar and $^{39}$Ar/$^{38}$Ar ratios in the activated samples were determined by accelerator mass spectrometry at the ATLAS facility (Argonne National Laboratory). The $^{37}$Ar activity was also measured by low-level counting at the University of Bern. Experimental MACS of $^{36}$Ar and $^{38}$Ar, corrected to the standard 30 keV thermal energy, are 1.9(3) mb and 1.3(2) mb, respectively, differing from the theoretical and evaluated values published to date by up to an order of magnitude. The neutron capture cross sections of $^{36,38}$Ar are relevant to the stellar nucleosynthesis of light neutron-rich nuclides; the two experimental values are shown to affect the calculated mass fraction of nuclides in the region A=36-48 during the weak $s$-process. The new production cross sections have implications also for the use of $^{37}$Ar and $^{39}$Ar as environmental tracers in the atmosphere and hydrosphere.

nucl-ex↗

arXiv2015

High-Sensitivity Measurement of 3He-4He Isotopic Ratios for Ultracold Neutron Experiments

Research efforts ranging from studies of solid helium to searches for a neutron electric dipole moment require isotopically purified helium with a ratio of 3He to 4He at levels below that which can be measured using traditional mass spectroscopy techniques. We demonstrate an approach to such a measurement using accelerator mass spectroscopy, reaching the 10e-14 level of sensitivity, several orders of magnitude more sensitive than other techniques. Measurements of 3He/4He in samples relevant to the measurement of the neutron lifetime indicate the need for substantial corrections. We also argue that there is a clear path forward to sensitivity increases of at least another order of magnitude.

physics.ins-det↗

arXiv2015

Stellar 30-keV neutron capture in 94,96Zr and the 90Zr(gamma,n)89Zr photonuclear reaction with a high-power liquid-lithium target

A high-power Liquid-Lithium Target (LiLiT) was used for the first time for neutron production via the thick-target 7Li(p,n)7Be reaction and quantitative determination of neutron capture cross sections. Bombarded with a 1-2 mA proton beam at 1.92 MeV from the Soreq Applied Research Accelerator Facility (SARAF), the setup yields a 30-keV quasi-Maxwellian neutron spectrum with an intensity of 3-5e10 n/s, more than one order of magnitude larger than present near-threshold 7Li(p,n) neutron sources. The setup was used here to determine the 30-keV Maxwellian averaged cross section (MACS) of 94Zr and 96Zr as 28.0+-0.6 mb and 12.4+-0.5 mb respectively, based on activation measurements. The precision of the cross section determinations results both from the high neutron yield and from detailed simulations of the entire experimental setup. We plan to extend our experimental studies to low-abundance and radioactive targets. In addition, we show here that the setup yields intense high-energy (17.6 and 14.6 MeV) prompt capture gamma-rays from the 7Li(p,gamma)8Be reaction with yields of ~3e8 gammas/s/mA and ~4e8 gammas/s/mA, respectively, evidenced by the 90Zr(gamma,n)89Zr photonuclear reaction.

nucl-ex↗

arXiv2015

New limit of $^{244}$Pu on Earth points to rarity of actinide nucleosynthesis

Half of the heavy elements including all actinides are produced in r-process nucleosynthesis whose sites and history still remain a mystery. If continuously produced, the Interstellar Medium (ISM) is expected to build up a quasi-steady state of abundances of short-lived nuclides (with half-lives <100My), including actinides produced in r-process nucleosynthesis. Their existence in today's ISM would serve as a radioactive clock and would establish that their production was recent. In particular $^{244}$Pu, a radioactive actinide nuclide (81 My half-life), can place strong constraints on recent r-process frequency and production yield. Here we report on the detection of live interstellar $^{244}$Pu, archived in Earth's deep-sea floor during the last 25 My, at abundances lower by about two orders of magnitude than expected from continuous production in the Galaxy. This large discrepancy may signal a rarity of actinide r-process nucleosynthesis sites, compatible with neutron-star mergers or with a small subset of actinide-producing supernovae.

astro-ph.SR↗

arXiv2013

High-power liquid-lithium jet target for neutron production

A compact Liquid-Lithium Target (LiLiT) was built and tested with a high-power electron gun at Soreq Nuclear Research Center. The lithium target, to be bombarded by the high-intensity proton beam of the Soreq Applied Research Accelerator Facility (SARAF), will constitute an intense source of neutrons produced by the 7Li(p,n)7Be reaction for nuclear astrophysics research and as a pilot setup for accelerator-based Boron Neutron Capture Therapy (BNCT). The liquid-lithium jet target acts both as neutron-producing target and beam dump by removing the beam thermal power (>5 kW, >1 MW/cm3) with fast transport. The target was designed based on a thermal model, accompanied by a detailed calculation of the 7Li(p,n) neutron yield, energy distribution and angular distribution. Liquid lithium is circulated through the target loop at ~200oC and generates a stable 1.5 mm-thick film flowing at a velocity up to 7 m/s onto a concave supporting wall. Electron beam irradiation demonstrated that the liquid-lithium target can dissipate electron power areal densities of > 4 kW/cm2 and volume power density of ~ 2 MW/cm3 at a lithium flow of ~4 m/s while maintaining stable temperature and vacuum conditions. The LiLiT setup is presently in online commissioning stage for high-intensity proton beam irradiation (1.91- 2.5 MeV, 1-2 mA) at SARAF.

physics.ins-det↗

arXiv2012

A Shorter 146Sm Half-Life Measured and Implications for 146Sm-142Nd Chronology in the Solar System

The extinct p-process nuclide 146Sm serves as an astrophysical and geochemical chronometer through measurements of isotopic anomalies of its alpha-decay daughter 142Nd. Based on analyses of 146Sm/147Sm alpha-activity and atom ratios, we determined the half-life of 146Sm to be 68 \pm 7 (1sigma) million years (Ma), which is shorter than the currently used value of 103 \pm 5 Ma. This half-life value implies a higher initial 146Sm abundance in the early solar system, (146Sm/144Sm_0 = 0.0094\pm0.0005 (2sigma), than previously estimated. Terrestrial, Lunar and Martian planetary silicate mantle differentiation events dated with 146Sm-142Nd converge to a shorter time span and in general to earlier times, due to the combined effect of the new 146Sm half-life and (146Sm/144Sm)_0 values.

astro-ph.EP↗

arXiv2011

Fusion reactions with the one-neutron halo nucleus 15C

The structure of 15C, with an s1/2 neutron weakly bound to a closed-neutron shell nucleus 14C, makes it a prime candidate for a one-neutron halo nucleus. We have for the first time studied the cross section for the fusion-fission reaction 15C + 232Th at energies in the vicinity of the Coulomb barrier and compared it to the yield of the neighboring 14C + 232Th system measured in the same experiment. At sub-barrier energies, an enhancement of the fusion yield by factors of 2-5 was observed for 15C, while the cross sections for 14C match the trends measured for 12,13C.

nucl-ex↗

arXiv2010

The Structural Analysis Possibilities of Reflection High Energy Electron Diffraction

The epitaxial growth of complex oxide thin films provide three avenues to generate unique properties: the ability to influence the 3-dimensional structure of the film, the presence of a surface, and the generation of an interface. In all three cases, a clear understanding of the resulting atomic structure is desirable. However, determining the full structure of an epitaxial thin film (lattice parameters, space group, atomic positions, surface reconstructions) on a routine basis is a serious challenge. In this paper we highlight the remarkable information that can be extracted from both the Bragg scattering and inelastic multiple scattering events that occur during Reflection High Energy Electron Diffraction. We review some methods to extract structural information and show how mature techniques used in other fields can be directly applied to the {\em in-situ} and real-time diffraction images of a growing film. These collection of techniques give access to both the epitaxially influenced 3 dimensional bulk structure of the film, and any reconstructions that may happen at the surface.

cond-mat.mtrl-sci↗

arXiv2009

Epitaxial growth of Fe3O4 thin films on ZnO and MgO substrates

Magnetite thin fims have been grown epitaxially on ZnO and MgO substrates using molecular beam epitaxy. The film quality was found to be strongly dependent on the oxygen partial pressure during growth. Structural, electronic, and magnetic properties were analyzed utilizing Low Energy Electron Diffraction (LEED), HArd X-ray PhotoElectron Spectroscopy (HAXPES), Magneto Optical Kerr Effect (MOKE), and X-ray Magnetic Circular Dichroism (XMCD). Diffraction patterns show clear indication for growth in the (111) direction on ZnO. Vertical structure analysis by HAXPES depth profiling revealed uniform magnetite thin films on both type of substrates. Both, MOKE and XMCD measurements show in-plane easy magnetization with a reduced magnetic moment in case of the films on ZnO.

cond-mat.mtrl-sci↗

arXiv2009

Determination of the stellar (n,gamma) cross section of 40Ca with accelerator mass spectrometry

The stellar (n,gamma) cross section of 40Ca at kT=25 keV has been measured with a combination of the activation technique and accelerator mass spectrometry (AMS). This combination is required when direct off-line counting of the produced activity is compromised by the long half-life and/or missing gamma-ray transitions. The neutron activations were performed at the Karlsruhe Van de Graaff accelerator using the quasistellar neutron spectrum of kT=25 keV produced by the 7Li(p,n)7Be reaction. The subsequent AMS measurements were carried out at the Vienna Environmental Research Accelerator (VERA) with a 3 MV tandem accelerator. The doubly magic 40Ca is a bottle-neck isotope in incomplete silicon burning, and its neutron capture cross section determines the amount of leakage, thus impacting on the eventual production of iron group elements. Because of its high abundance, 40Ca can also play a secondary role as "neutron poison" for the s-process. Previous determinations of this value at stellar energies were based on time-of-flight measurements. Our method uses an independent approach, and yields for the Maxwellian-averaged cross section at kT=30 keV a value of 30 keV= 5.73+/-0.34 mb.

astro-ph.SR↗