arXiv subjects

Moshe Gai

Publications and source records attributed to Moshe Gai.

At least 19 recordsLinked to original sources

arXiv2019

Gai Reply to Comment by Schumann et al. (arXiv:1904.03023v1)

Statements included in the comment published by Schumann et al. (arXiv:1904.03023v1) are contradicted by documents that were communicated to one of the co-authors of the comment (Dr. Koester). These documents are reviewed but cannot be disclosed here due to copyright (they are available on request). A summary of the scientific dispute between the collaboration and Dr. Schumann, was submitted on September 24, 2018, to the Directorate Support of the Paul Scherrer Institute (PSI) and can be provided on request.

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arXiv2019

Comment on N. Rijal et al. "Measurement of d + 7Be Cross Sections for Big-Bang Nucleosynthesis"

Rijal, et al. in their recent publication [Phys. Rev. Lett {\bf 122}, 182701 (2019), arXiv:1808.07893], on "Measurement of d + $^7$Be Cross Sections for Big-Bang Nucleosynthesis (BBN)", misrepresent their result, they misrepresent previous work of Parker (72) and of Caughlan and Fowler (88), and quite possibly, contradicts the very BBN theory that has been established over the last few decades. This comment is intended to correct these misrepresentations and critically review their claims on BBN.

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arXiv2018

The Interaction of Neutrons With 7Be: Lack of Standard Nuclear Physics Solution to the "Primordial 7Li Problem"

The destruction of 7Be with neutrons represents the last possible standard avenue to reduce the predicted abundance of the primordial 7Li and in this way to attempt to solve the Cosmological 7Li problem. We discuss the results of an experiment performed at the Soreq Applied Research Accelerator Facility (SARAF) in Israel where we measured the Maxwellian Averaged Cross Sections (MACS) of the 7Be(n,p), 7Be(n,a), and 7Be(n,ga) reactions. Our MACS measured at 49.5 keV in the window of the Big Bang Nucleosynthesis (BBN), indicate the lack of standard nuclear physics solution to the "Primordial 7Li Problem".

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arXiv2018

The Soreq Applied Research Accelerator Facility (SARAF) - Overview, Research Programs and Future Plans

The Soreq Applied Research Accelerator Facility (SARAF) is under construction in the Soreq Nuclear Research Center at Yavne, Israel. When completed at the beginning of the next decade, SARAF will be a user facility for basic and applied nuclear physics, based on a 40 MeV, 5 mA CW proton/deuteron superconducting linear accelerator. Phase I of SARAF (SARAF-I, 4 MeV, 2 mA CW protons, 5 MeV 1 mA CW deuterons) is already in operation, generating scientific results in several fields of interest. The main ongoing program at SARAF-I is the production of 30 keV neutrons and measurement of Maxwellian Averaged Cross Sections (MACS), important for the astrophysical s-process. The world leading Maxwellian epithermal neutron yield at SARAF-I ($5\times 10^{10}$ epithermal neutrons/sec), generated by a novel Liquid-Lithium Target (LiLiT), enables improved precision of known MACSs, and new measurements of low-abundance and radioactive isotopes. Research plans for SARAF-II span several disciplines: Precision studies of beyond-Standard-Model effects by trapping light exotic radioisotopes, such as $^6$He, $^8$Li and $^{18,19,23}$Ne, in unprecedented amounts (including meaningful studies already at SARAF-I); extended nuclear astrophysics research with higher energy neutrons, including generation and studies of exotic neutron-rich isotopes relevant to the rapid (r-) process; nuclear structure of exotic isotopes; high energy neutron cross sections for basic nuclear physics and material science research, including neutron induced radiation damage; neutron based imaging and therapy; and novel radiopharmaceuticals development and production. In this paper we present a technical overview of SARAF-I and II, including a description of the accelerator and its irradiation targets; a survey of existing research programs at SARAF-I; and the research potential at the completed facility (SARAF-II).

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arXiv2015

On the sensitivity of extracting the astrophysical cross section factor of the 12C(a,g) reaction from existing data [Comment on Schuermann et al. Phys. Lett. B711(2012)35]

We address a conflicting report on the value and uncertainty of the astrophysical cross section factor of the 12C(a,g) reaction extracted from existing data. In sharp contrast to previously reported ambiguities (by up to a factor 8), Schuermann et al. suggest an accuracy of 12%. We demonstrate that the so claimed "rigorous data selection criteria" used by Schuermann et al. relies on the s-factors extracted by Assuncao et al. But these results were shown in a later analysis (by this author) to have large error bars (considerably larger than claimed by Assuncao em et al.) which render these data not appropriate for a rigorous analysis. When their "rigorous data selection" is adjusted to remove the results of Assuncao et al. the astrophysical cross section factor cannot be extracted with 12% accuracy, or even close to it. Such data on the S_E2 values at low energies deviate by up to a factor two from their fit and exhibit a sharper slope rising toward low energies, leading to strong doubt on their extrapolated S_E2(300) value and the quoted small error bar. Contrary to their claim the small value of S_E1(300) ~10 keVb cannot be ruled out by current data including the most modern gamma-ray data. As previously observed by several authors current data reveal ambiguities in the value of S_E1(300) ~10 keVb or ~80 keVb, and the new ambiguity that was recently revealed (by this author) of S_E2(300) ~60 keVb or ~154 keVb, appear to be a more reasonable evaluation the status of current data.

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arXiv2014

Nuclear Structure and the Fate of Core Collapse (Type II) Supernova

For a long time Gerry Brown and his collaborator Hans Bethe considered the question of the final fate of a core collapse (Type II) supernova. Recalling ideas from nuclear structure on Kaon condensate and a soft equation of state of the dense nuclear matter they concluded that progenitor stars with mass as low a 17-18M$_\odot$ (including supernova 1987A) could collapse to a small mass black hole with a mass just beyond 1.5M$_\odot$, the upper bound they derive for a neutron star. We discuss another nuclear structure effect that determines the carbon to oxygen ratio (C/O) at the end of helium burning. This ratio also determines the fate of a Type II supernova with a carbon rich progenitor star producing a neutron star and oxygen rich collapsing to a black hole. While the C/O ratio is one of the most important nuclear input to stellar evolution it is still not known with sufficient accuracy. We discuss future efforts to measure with gamma-beam and TPC detector the 12C(a,g)16O reaction that determines the C/O ratio in stellar helium burning.

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arXiv2013

Ambiguities of the Rate of Oxygen Formation During Stellar Helium Burning in the 12C(a,g) Reaction

The rate of oxygen formation determines the C/O ratio during stellar helium burning. It is the single most important nuclear input of stellar evolution theory including the evolution of Type II and Type Ia supernova. Yet the low energy cross section of the fusion of 4He + 12C denoted as the 12C(a,g)16O reaction still remains uncertain after forty years of extensive work. We analyze and critically review the most recent measurements of complete angular distributions of the outgoing gamma-rays at very low energies (Ecm > 1.0 MeV). Our analysis of the angular distribution measured with the EUROGAM/GANDI arrays lead us to conclude considerably larger error bars than published hence they are excluded from the current sample of "world data". We show that the current sample of "world data" of the measured E2 cross section factors below 1.7 MeV cluster to two distinct groups that lead to two distinct extrapolations of SE2(300) ~ 60 or ~ 154 keVb. We point to a much neglected discrepancy between the measured E1-E2 phase difference (phi_12) and unitarity as required by the Watson theorem, suggesting systematic problem(s) of some of the measured gamma-ray angular distributions. The ambiguity of the extrapolated SE2(300) together with a previously observed ambiguity of SE1(300) represent the current state of the art of the field and they must be resolved by future measurements of complete and detailed angular distributions of the 12C(a,g) reaction at very low energies (Ecm < 1.0 MeV).

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arXiv2007

The Dissociation of 8B in the Coulomb Field and the Validity of the CD Method

The GSI1, GSI2 (as well as the RIKEN2 and the corrected GSI2) measurements of the Coulomb Dissociation (CD) of 8B are in good agreement with the most recent Direct Capture (DC) 7Be(p,g)8B reaction measurement performed at Weizmann and in agreement with the Seattle result. Yet it was claimed that the CD and DC results are sufficiently different and need to be reconciled. We show that these statements arise from a misunderstanding (as well as misrepresentation) of CD experiments. We recall a similar strong statement questioning the validity of the CD method due to an invoked large E2 component that was also shown to arise from a misunderstanding of the CD method. In spite of the good agreement between DC and CD data the slope of the astrophysical cross section factor (S17) can not be extracted with high accuracy due to a discrepancy between the recent DC data as well as a discrepancy of the three reports of the GSI CD data. The slope is directly related to the d-wave component that dominates at higher energies and must be subtracted from measured data to extrapolate to zero energy. Hence the uncertainty of the measured slope leads to an additional uncertainty of the extrapolated zero energy cross section factor, S17(0). This uncertainty must be alleviated by future experiments to allow a precise determination of S17(0), a goal that so far has not be achieved in spite of strong statement(s) that appeared in the literature.

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arXiv2006

Production of Fast Neutron With Plasma Focus Device

Before its demise DIANA Hi-TECH, LLC, demonstrated the use of two 50 kJoule Plasma Focus devices for the copius production of fast neutrons, x-rays and radio-isotopes. Such a device is suitable for fast neutron non invasive interogation of contra-band materials including hidden nuclear materials. It could be particularly useful for a fast and fail safe interogation of large cargo containers, or in merchant marine port of entries. The performance and fast neutron production (2.5 or 14 MeV at 10^11 or 10^13 neutrons per pulse, respectively) of the two PF50 Plasma Focus devices produced by DIANA HiTECH, LLC, are discussed.

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arXiv2006

The Coulomb Dissociation of 8B; A Triumph of Good Science

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arXiv2006

Comment on Esbensen, Bertsch and Snover Concerning Reconciling Coulomb Dissociation and Radiative Capture Measurements

The RIKEN data on the Coulomb Dissociation (CD) of 8B were shown to be in good agreement with the Direct Capture (DC) data on the 7Be(p,g)8B reaction (that were known at that time) of Filippone {\em et al.} Yet recently it was claimed that the RIKEN2 CD data must be corrected in order to be reconciled with the slope of DC data. Considering the (correct) so called scale independent b-slope parameter of the RIKEN2 CD data, the resultant corrected b-slope parameter suggested by Esbensen, Bertsch and Snover is shown to be considerably smaller than the so called average b-slope parameter of DC data. The suggested corrections of the b-slope parameter lead to a large disagreement with DC data, in sharp contrast to the claim. The slope corrections are only significant for the RIKEN2 CD data. For the GSI kinematics, where in fact one may observe slope different than for DC (at least for the GSI1 data), they find a fortuitous cancellation that leads to a vanishingly small slope correction. Hence the validity of these correction based on the observed slopes can not be substantiated.

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arXiv2005

Status of the Standard Solar Model Prediction of Solar Neutrino Fluxes

The Standard Solar Model (BP04) predicts a total 8B neutrino flux that is 17.2% larger than measured in the salt phase of the SNO detector (and if it were significant it will indicate oscillation to sterile neutrinos). Hence it is important to examine in details uncertainties (and values) of inputs to the SSM. Currently, the largest fractional uncertainty is due to the new evaluation of the surface composition of the sun. We examine the nuclear input on the formation of solar 8B [S17(0)] and demonstrate that it is still quite uncertain due to ill known slope of the measured astrophysical cross section factor and thus ill defined extrapolation to zero energy. This yields an additional reasonably estimated uncertainty due to extrapolation of +0.0 -3.0 eV-b (+0% -14%). Since a large discrepancy exists among measured as well as among predicted slopes, the value of S17(0) is dependent on the choice of data and theory used to extrapolate S17(0). This situation must be alleviated by new measurement(s). The "world average" is driven by the Seattle result due to the very small quoted uncertainty, which we however demonstrate it to be an over-estimated accuracy. We propose more realistic error bars for the Seattle results based on the published Seattle data.

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arXiv2005

Is There a Significant Difference Between the Results of the Coulomb Dissociation of 8B and the Direct Capture 7Be(p,g)8B Reaction?

Recent claims of the Seattle group of evidence of "slope difference between CD [Coulomb Dissociation] and direct [capture] results" are based on wrong and selective data. When the RIKEN2 data are included correctly, and previously published Direct Capture (DC) data are also included, we observe only a 1.9 sigma difference in the extracted so called "scale independent slope (b)", considerably smaller than claimed by the Seattle group. The very parameterization used by the Seattle group to extract the so called b-slope parameter has no physical foundation. Considering the physical slope (S' = dS/dE), we observe a 1.0 sigma agreement between slopes (S') measured in CD and DC, refuting the need for new theoretical investigation. The claim that S17(0) values extracted from CD data are approximately 10% lower than DC results, is based on misunderstanding of the CD method. Considering all of the published CD S17(0) results, with adding back an unconfirmed E2 correction of the MSU data, yields very consistent S17(0) results that agree with recent DC measurements of the Seattle and Weizmann groups. The recent correction of the b-slope parameter (0.25 1/MeV) suggested by Esbensen, Bertsch and Snover was applied to the wrong b-slope parameter calculated by the Seattle group. When considering the correct slope of the RIKEN2 data, this correction in fact leads to a very small b-slope parameter (0.14 1/MeV), less than half the central value observed for DC data, refuting the need to correct the RIKEN2 data. In particular it confirms that the E2 contribution in the RIKEN2 data is negligible. The dispersion of measured S17(0) is mostly due to disagreement among individual DC experiments and not due to either experimental or theoretical aspects of CD.

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arXiv2005

Optical Readout Time Projection Chamber (O-TPC) for a Study of Oxygen Formation In Stellar Helium Burning

We are developing an Optical Readout Time Projection Chamber (O-TPC) detector for the study of the 12C(a,g)16O reaction that determines the ratio of carbon to oxygen in helium burning. This ratio is crucial for understanding the final fate of a progenitor star and the nucleosynthesis of elements prior to a Type II supernova; an oxygen rich star is predicted to collapse to a black hole, and a carbon rich star to a neutron star. Type Ia supernovae (SNeIa) are used as standard candles for measuring cosmological distances with the use of an empirical light curve-luminosity stretching factor. It is essential to understand helium burning that yields the carbon/oxygen white dwarf and thus the initial stage of SNeIa. The O-TPC is intended for use with high intensity photon beams extracted from the HIgS/TUNL facility at Duke University to study the 16O(g,a)12C reaction, and thus the direct reaction at energies as low as 0.7 MeV. We are conducting a systematical study of the best oxygen containing gas with light emitting admixture(s) for use in such an O-TPC. Preliminary results with CO_2 + TEA mixture were obtained

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arXiv2004

Do We Accurately Know the Formation of Solar 8B?

A detailed examination of current data on S_17 (as opposed to an examination of S_17(0) only) excludes quoting S_17(0) with sufficiently small uncertainty. In contrast to suggestions that S_17(0) is now known with the accuracy of \pm 3%, the exact value of S_17(0) is dependent on the choice of the data and the choice of theory used for extrapolation. In addition recent high precision results (including the Seattle data) on S_17 which are in good agreement, still differ on the measured slopes, as do theoretical models that predict different d-wave contribution, precluding an accurate extrapolation to zero energy of the consistent data. Using a common extrapolation of only the consistent high precision data, suggests a value of S_17(0) = 21.2 \pm 0.5 eV-b, but a value equal to or smaller than 19.0 eV-b can not be excluded due to the uncertainty in the extrapolation, leading to an additional error of +0.0 -3.0 eV-b. This (unacceptable) situation must be cleared by future experiments.

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arXiv2004

Comment on B. Davids et al.; Proton-Decaying States in 22Mg and the Nucleosynthesis of 22Na in Novae

B.S. Davids {\em et al.} make the explicit assumption that radiative widths of analog states in \ne22 and \mg22 are equal. We demonstrate that this misapplication of iso-spin symmetry leads to very wrong results. Considerations of elementary nuclear structure suggests that such an assumption can be inaccurate by a large factor (in \mg22), as is evident from a comparison with recent measurements of radiative width in \mg22. Estimates of radiative widths from analog transitions are common but often wrong (e.g. in \mg22) and should not be considered a useful tool in nuclear astrophysics.

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arXiv2004

(Two) Open Questions in Stellar Nuclear Physics

No doubt, among the most exciting discoveries of the third millennium thus far are {\bf Oscillations of Massive Neutrinos} and {\bf Dark Energy} that leads to an accelerated expansion of the Universe. Accordingly, Nuclear Physics is presented with two extraordinary challenges: the need for precise (5% or better) prediction of solar neutrino fluxes within the Standard Solar Model, and the need for an accurate (5% or better) understanding of stellar evolution and in particular of Type Ia super nova that are used as cosmological standard candle. In contrast, much confusion is found in the field with contradicting data and strong statements of accuracy that can not be supported by current data. We discuss an experimental program to address these challenges and disagreements.

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arXiv2004

The Coulomb Dissociation of 8B and a Critical Assessment of the Seattle S17(0) Result

The Coulomb dissociation of 8B, measured with high precision by the GSI group, is in excellent agreement with the astrophysical cross section factor (S17) measured by the Weizmann group with a 7Be target. The GSI and Weizmann data are in good agreement with the Seattle data at high energies, but at low energies we observe a slight systematic (up to 2sigma) deviation, yet the Seattle group repeatedly rejects the CD method. We show that when plotting the slopes, they mis plotted one CD data point and exclude measured slopes that contradict their claim. Indeed the measured slope is essential to elucidate the d-wave correction to S17(0) that could be as large as 15%, and is the last open question that needs to be resolved before S17(0) can be quoted with an accuracy of 5% or better. We show that this goal has not been achieved (in spite of the strong claim of the Seattle group), since currently there is no agreement among experiments as well as among theoretical models on the value of the slope. In addition, currently there is no theoretical framework within which (for example the Seattle) data can be analyzed and S17(0) extrapolated with the claimed high precision of 2.5%. This (last) issue of the slope and the d-wave correction must be resolved (by future measurements) so as to allow quoting S17(0) with an accuracy of 5% or better.

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