X-rays from Proton Bremsstrahlung: Evidence from Fusion Reactors and Its Implication in Astrophysics (original) (raw)
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Proton bremsstrahlung and its radiation effects in fusion reactors
Fusion Engineering and Design, 2010
Protons and neutrons are emitted in many fusion processes of light nuclei. In a fusion reactor, a proton and a neutron thus generated may again fuse with each other. Or they can in turn fuse with or be captured by an un-reacted nuclear fuel, for example deuterium. The average center-of-mass energy for such reaction is around 10 keV in a typical fusion reactor. At this low energy, the reacting nucleons are in an s-wave state in terms of their relative angular momentum. The single-gamma radiation process is thus strongly suppressed due to conservation laws. Instead the gamma ray released is likely to be accompanied by soft X-ray photons from a nuclear bremsstrahlung process. The generated soft X-ray has a continuous spectrum and peaks around a few hundred eV to a few keV. The average photon energy and spectrum properties of such a process are calculated with a semi-classical approach, with the explicit example of proton-neutron capture. This phenomenon may have been observed in some prior tokamak discharge experiments, and its interpretation is complicated by the presence of electron bremsstrahlung. However, it also opens up the possibility of new plasma diagnostics which are more sensitive to the ionic or nuclear degree of freedom.
Nuclear and High-Energy Astrophysics
Structure and Interaction of Hadronics Systems - Proceedings of the VIII International Workshop on Hadron Physics 2002, 2003
There has never been a more exciting time in the overlapping areas of nuclear physics, particle physics and relativistic astrophysics than today. Orbiting observatories such as the Hubble Space Telescope, Rossi X-ray Timing Explorer (RXTE), Chandra X-ray satellite, and the X-ray Multi Mirror Mission (XMM) have extended our vision tremendously, allowing us to see vistas with an unprecedented clarity and angular resolution that previously were only imagined, enabling astrophysicists for the first time ever to perform detailed studies of large samples of galactic and extragalactic objects. On the Earth, radio telescopes (e.g., Arecibo, Green Bank, Parkes, VLA) and instruments using adaptive optics and other revolutionary techniques have exceeded previous expectations of what can be accomplished from the ground. The gravitational wave detectors LIGO, LISA VIRGO, and Geo-600 are opening up a window for the detection of gravitational waves emitted from compact stellar objects such as neutron stars and black holes. Together with new experimental forefront facilities like ISAC, ORLaND and RIA, these detectors provide direct, quantitative physical insight into nucleosynthesis, supernova dynamics, accreting compact objects, cosmic-ray acceleration, and pairproduction in high energy sources which reinforce the urgent need for a strong and continuous feedback from nuclear and particle theory and theoretical astrophysics. In my lectures, I shall concentrate on three selected topics, which range from the behavior of superdense stellar matter, to general relativistic stellar models, to strange quark stars and possible signals of quark matter in neutron stars.
Small effects in astrophysical fusion reactions
Nuclear Physics A, 1997
We study the combined effects of vacuum polarization, relativity, Bremsstrahlung, and atomic polarization in nuclear reactions of astrophysical interest. It is shown that these effects do not solve the longstanding differences between the experimental data of astrophysical nuclear reactions at very low energies and the theoretical calculations which aim to include electron screening.
N-P Bremsstrahlung Interpretation of High Energy Gamma Rays from Heavy-Ion Collisions
Physical Review C, 1987
A model based upon nucleon-nucleon (n-p) bremsstrahlung is presented as a possible explanation of high energy y rays produced in heavy-ion collisions. A semiclassical bremsstrahlung formula is "calibrated" to p+ d bremsstrahlung data, then incorporated into the Boltzrnann master equation as a means for following the nucleon-nucleon collisions. The input parameters to the master equation are taken from previous studies of preequilibrium nucleon spectra, eliminating all free parameters from our calculation. The results of this calculation are compared to the available high energy y-ray data, with generally excellent agreement. Data taken with lead glass detectors are generally underestimated in our model calculation.
Photoneutron Reactions in Nuclear Astrophysics
Journal of Physics: Conference Series, 2015
Highly-monochromatic γ-ray beams are produced at the NewSUBARU synchrotron radiation facility by the inverse Compton scattering of laser photons from relativistic electrons. The latest s-process study in nuclear astrophysics with the γ-ray beam is presented.
Very high energy γ-ray emission from X-ray transients during major outbursts
Astronomy and Astrophysics, 2007
Context. Some high mass X-ray binaries (HMXB) have been recently confirmed as γ-ray sources by ground based Cherenkov telescopes. In this work, we discuss the γ-ray emission from X-ray transient sources formed by a Be star and a highly magnetized neutron star. This kind of systems can produce variable hadronic γ-ray emission through the mechanism proposed by Cheng and Ruderman, where a proton beam accelerated in the pulsar magnetosphere impacts the transient accretion disk. We choose as case of study the best known system of this class: A0535+26. Aims. We aim at making quantitative predictions about the very high-energy radiation generated in Be-X ray binary systems with strongly magnetized neutron stars. Methods. We study the gamma-ray emission generated during a major X-ray outburst of a HMXB adopting for the model the parameters of A0535+26. The emerging photon signal from the disk is determined by the grammage of the disk that modulates the optical depth. The electromagnetic cascades initiated by photons absorbed in the disk are explored, making use of the so-called "Approximation A" to solve the cascade equations. Very high energy photons induce Inverse Compton cascades in the photon field of the massive star. We implemented Monte Carlo simulations of these cascades, in order to estimate the characteristics of the resulting spectrum. Results. TeV emission should be detectable by Cherenkov telescopes during a major X-ray outburst of a binary formed by a Be star and a highly magnetized neutron star. The γ-ray light curve is found to evolve in anti-correlation with the X-ray signal.
High Energy Gamma-Ray Production in Nuclear Reactions
High energy gamma-ray production in heavy ion collisions has been the object of a number of recent studies between 15 and 86 MeV/Nucleon incident energies (Grosse,1985; Grosse,1986; Stevenson,l986; Stevenson.1987; Alamanos,l986; Hingmann,1987; Berthollet,l986, Berthollet,l987; Kwato Njock,1986). Photons have attracted attention since they are not as seriously affected by absorption phenomena as pions, for example ; they can serve as unambiguous probes to study the reaction dynamics in the early stage of the collision. The main drawback of hard photon studies is the smallness of the -r-cross sections. Several models have been proposed to predict the photon production yields. Some of them suggest that incoherent nucleon-nucleon bremsstrahlung is the main source of the -r-emission. These collisions can take place either in the initial stage of the reaction (Cassing,1986; Nakayama.1986; 8auer,1986; Bauer,1987; Che min Ko,1987; Remington.1986; Randrup,l988) or within an equilibrated hot participant zone (Nifenecker,l985; Prakash,1987). Other models suppose that photons are produced by coherent bremsstrahlung where both nuclei or substantial parts of them act as a whole (Vasak,1985; Vasak,1986; Stah1,1987) In the following, after a short overview of the experimental techniques involved we first present the experimental results. Our main emphasis will be with the inclusive measurements of differential production cross-sections. These include the shape of the spectra, the angular distributions and the absolute cross-sections. We shall show, on qualitative grounds, that these inclusive experiments tend to favor a picture where the photons are produced in first nucleon-nucleon collisions. Results from exclusive reactions which display the impact parameter dependence of the multiplicity and spectra of the gamma-rays will be presented. After summarizing the experimental status, we give a first, semi-classical, approach of a theoretical account of the photon production in many nucleon systems. The main aim of this presentation is to show how, and in what limits. it mav be justified to schematized Nucleus- Nucleus reactions into an incoherent sum of independent nucleon-nucleon contributions. It will clearly appear that the understandino of the Nucleus-Nucleus reactions reauires both knowledge and-understanding of the simple; nucleon-nucleon and nucleon-Nucleus cases. We shall, therefore, review the experimental and theoretical aspects of these simpler reactions insofar as they relate to our main subject. Doina so we are conscious that we mav omit important deveiopments, both experimental or theoretical, but it would have been out of scope of this review to give a full account of such an extended field. It will appear that the contribution of charged pion exchange currents to photon production is probably very important. Finally, we present an overview of the available theoretical approaches, and try to balance these different approaches with the experimental results, as well as with our knowledge of the more elementary processes.
2022
We have measured the -ray line production cross sections in proton-induced nuclear reactions on various target nuclei (12 C, 16 O, 24 Mg, 28 Si, 56 Fe) of chemical elements abundant in astrophysical sites (solar flares, the interstellar medium, cosmic compact objects) over the incident energy range of Ep = 30-200 MeV. We carried out experimental campaigns in joint collaboration at the K = 200 separated sectors cyclotron of iThemba LABS using a highenergy resolution, high-efficiency detection array composed of 8 Compton-suppressed clover detectors comprising 32 HP-Ge crystals for recording the -ray spectra. In the current paper, we focus on -ray de-excitation lines produced in proton irradiations of nat C and Mylar targets, in particular, on the prominent 4.439 and 6.129 MeV lines of 12 C and 16 O which are among the strongest lines emitted in solar flares and in interactions of low-energy cosmic rays (LECRs) with the gas and dust of the inner galaxy. We report new -ray production experimental cross section data for ten nuclear -ray lines that we compare to previous lowenergy data sets from the literature, to the predictions of the TALYS code of nuclear reactions and to a semi-empirical compilation. In the first approach, performing calculations with default input parameters of TALYS we observed substantial deviations between the predicted cross sections and experimental data. Then, using modified optical model potential (OMP) and nuclear level deformation parameters as input data we generated theoretical excitation functions for the above two main lines fully consistent with experimental data. In contrast, the experimental data sets for the other eight analyzed lines from the two proton-irradiated targets exhibit significant deviations with the predicted cross section values. We also report line-shape experimental data for the line complex observed at E = 4.44 MeV in irradiations of the two targets. Finally, we emphasize the astrophysical implications of our results.
Further direct approaches to the nuclear reactions in the Sun
Nuclear Physics A, 1997
Nuclear fusion reactions play a key role in the understanding of energy production, neutrino emission and nucleosynthesis of the elements in stars. The direct measurement of the cross section of these reactions at the relevant energies is usually hampered by cosmic radiation, beam induced background and/or the radioactivity of the nuclei involved. *Supported in part by INFN, BMBF, DFG, DAAD-VIGONI and NSF/NATO. 0375-9474/97/$17.00 © 1997 -Elsevier Science B.V. All rights reserved. PII: S0375-9474(97)00312-6 604c U Greife et al./Nuclear Physics A621 (1997) 603c-606c