Resolution of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>Σ</mml:mi></mml:mrow><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>-Mass Anomaly

Barkas, Walter H.; Dyer, John N.; Heckman, H. H.

doi:10.1103/physrevlett.11.26

Cited by 288 publications

(81 citation statements)

References 7 publications

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“…The short-ranged initial excitation can be rationalized in terms of the electronic localization length scale relevant to dielectric response [33], which is expected to be very short for LiF. Similar locality in the energy loss mechanism has been recently found in jellium clusters, however [34]. involve transitions between states in a possibly extremely sparse eigenspectrum.…”

Section: Time-dependent Density Functional Theorymentioning

confidence: 55%

The treatment of electronic excitations in atomistic models of radiation damage in metals

Race¹,

Mason²,

Finnis³

et al. 2010

Rep. Prog. Phys.

135

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Abstract. Atomistic simulations are a primary means of understanding the damage done to metallic materials by high energy particulate radiation. In many situations the electrons in a target material are known to exert a strong influence on the rate and type of damage. The dynamic exchange of energy between electrons and ions can act to damp the ionic motion, to inhibit the production of defects or to quench in damage, depending on the situation. Finding ways to incorporate these electronic effects into atomistic simulations of radiation damage is a topic of current major interest, driven by materials science challenges in diverse areas such as energy production and device manufacture.In this review, we discuss the range of approaches that have been used to tackle these challenges. We compare augmented classical models of various kinds and consider recent work applying semi-classical techniques to allow the explicit incorporation of quantum mechanical electrons within atomistic simulations of radiation damage. We also outline the body of theoretical work on stopping power and electron-phonon coupling used to inform efforts to incorporate electronic effects in atomistic simulations and to evaluate their performance.

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Section: Time-dependent Density Functional Theorymentioning

confidence: 55%

The treatment of electronic excitations in atomistic models of radiation damage in metals

Race¹,

Mason²,

Finnis³

et al. 2010

Rep. Prog. Phys.

135

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show abstract

“…It corresponds to an enhanced electron density around positive ions and to a reduction around negatively charged particles. This effect yields a Z 3 contribution to the stopping power at high velocities (Z is the projectile charge), and thus, it depends on the sign of the projectile charge.This so-called Barkas effect has first been observed by Barkas and collaborators [1] who found that the range of negative pions exceeds the one of positive pions with equal incident velocity. A direct determination of a relatively small Barkas effect has recently been performed using antiprotons and protons [2,3].…”

mentioning

confidence: 80%

“…This so-called Barkas effect has first been observed by Barkas and collaborators [1] who found that the range of negative pions exceeds the one of positive pions with equal incident velocity. A direct determination of a relatively small Barkas effect has recently been performed using antiprotons and protons [2,3].…”

mentioning

confidence: 80%

Giant Barkas Effect Observed for Light Ions Channeling in Si

et al. 2001

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Measurements of the electronic energy loss are presented for 4 He and 7 Li ions channeling along the Si main axial directions at intermediate to high projectile energies. The Barkas effect, an energy-loss enhancement proportional to the third power of the projectile charge at high energies, is clearly separated from other processes. It reaches about 50% for Li ions channeling along the Si ͗110͘ direction. The observed Barkas contribution from the valence-electron gas is in fair agreement with the Lindhard model. DOI: 10.1103/PhysRevLett.86.1482 The energy loss of ions slowing down in matter has been investigated for many years because of its relevance for ion beam analysis, materials modification, and nuclear physics. Moreover, there exist fundamental issues concerning the underlying physical processes of the energy loss at low and intermediate projectile energies. At high velocities, the main energy-loss mechanisms (ionization and excitation) are qualitatively well understood. But important points related to energy loss in the polarization field are still unclear. For the weakly interacting fast light ions, the polarization field is given by the dielectric function of the medium. It corresponds to an enhanced electron density around positive ions and to a reduction around negatively charged particles. This effect yields a Z 3 contribution to the stopping power at high velocities (Z is the projectile charge), and thus, it depends on the sign of the projectile charge.This so-called Barkas effect has first been observed by Barkas and collaborators [1] who found that the range of negative pions exceeds the one of positive pions with equal incident velocity. A direct determination of a relatively small Barkas effect has recently been performed using antiprotons and protons [2,3]. For heavier projectiles, other higher-order effects as well as shell corrections compete equally with the Barkas effect, and thus a clear and unequivocal separation of this effect from the others has not been achieved successfully yet [4]. Previously, channeling measurements of the Barkas effect [5,6] were performed under conditions where the so-called Bloch correction [7] is of comparable magnitude but of opposite sign as the Barkas contribution. The leading term of the Bloch correction is proportional to Z 4 , and it is closely related to the restriction of reaction probabilities to a maximum of 1 per target electron. To overcome these problems, it is therefore essential to determine the magnitude of the Barkas effect in an alternative way, where sources of errors are minimized.All theoretical models of the Barkas effect (reviewed by Basbas [8]) agree about the importance of the polarization of the medium in distant collisions, where ions act similar to photons. However, the importance of close collisions has been a subject of controversy in the literature [8]. Lindhard [9] stated that the close collisions may contribute nearly equally to the Barkas effect, because of the influence of the dynamical screening potential on electron-scatteri...

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“…The Barkas effect, in particular, accounts for the difference in the stopping powers of particles and their respective antiparticles and was first observed by Barkas when studying hyperon masses [2]. Barkas himself suggested that this difference might stem from higher-order terms relative to the Bethe theory [3] (namely, from the interference between the first-and second-order terms).…”

Section: Introductionmentioning

confidence: 99%

“…Initially, the observation of the Barkas effect relied upon indirect measurements only, where the ranges of positively charged particles in emulsions were observed to be smaller than those of negatively charged ones [2]. Later on, with the advent of antiproton beams, a direct measurement of the Barkas effect was possible using both proton and antiprotons beams [7,8].…”

Section: Introductionmentioning

confidence: 99%

Electronic energy loss of channeled ions: The giant Barkas effect

et al. 2004

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In this work we have measured the electronic energy loss of 9 Be and 11 B ions for the ͗100͘ and ͗110͘ directions in Si as a function of the incident ion energy. The channeling measurements cover a wide energy range between 100 keV/ amu and 1 MeV/ amu. The Rutherford backscattering technique has been employed in the present experiments. An overall compilation of channeling energy loss values for several ions, including those for He, Li, and O measured previously, provides a clear picture of the Barkas contribution to the stopping power due to valence electrons in the present energy regime. A maximum of the relative contribution occurs for Be ions around 250 keV/ amu while a saturation effect is observed for heavier ions. These results are interpreted in terms of a self-consistent nonlinear calculation based on the transport cross-section approach together with the unitary convolution approximation model, which describe the present data reasonably well at high projectile energies.

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Resolution of theΣ−-Mass Anomaly

Cited by 288 publications

References 7 publications

The treatment of electronic excitations in atomistic models of radiation damage in metals

The treatment of electronic excitations in atomistic models of radiation damage in metals

Giant Barkas Effect Observed for Light Ions Channeling in Si

Electronic energy loss of channeled ions: The giant Barkas effect

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