Role Of Electron Capture Research Articles

Aspects of linear energy transfer (LET) and relative biological effectiveness (RBE) in radiation therapy with positively charged particles and the role of electron capture

In radiotherapy, dose-effect relations induced by Co60 serve as a reference of the LET and RBE in normal and tumor tissue, which are usually handled by the linear-quadratic model S (LQ) with the parameters α and β, i.e. S = exp (-α·D-β·D2), working excellently up to the shoulder domain. In particle therapy, we have strictly to differ between RBE in the initial plateau and environment of the Bragg peak. Thus for protons LET and RBE of the initial plateau agree with Co60, whereas in the Bragg peak domain both properties are increased, but RBE of SOBP (spread out Bragg peak) only varies between 1.1 and 1.17; the RBE of carbon ions is increased once again. Their dose-effect curves are much steeper with a rather small shoulder domain due to dense ionizing radiation. Protons are also dense ionizing in the Bragg peak region, but their magnitude is rather smaller compared to carbon ions. A generalization of the LQ-model based on the nonlinear reaction-diffusion model is proposed to include LET and RBE of dense ionizing particles, which accounts for intra-cellular properties, too. The linear term of the reaction diffusion formula describes destroy of cells, the nonlinear term is related to repair. The diffusion term accounts for the density of the radiation damages. Based on dose-effect properties of Co60 the parameters of dense ionizing particles can be determined and compared with measurement data. However, a rigorously theoretical access starting with neglect of energy straggling and lateral scatter must account for electron capture of positively charged particles. By mathematical descriptions local dense of radiation effects and their consequences in dose-effect curves are interpreted providing a key to understanding modern therapy planning with different modalities and properties of intracellular processes.

Considerations about projectile and target X-rays induced during heavy ion bombardment

Abstract In this work we present some results concerning the X-rays emitted by heavy ions during target bombardment. In this case, Cl4+ and Cl5+ ions with energies from 4 MeV to 10 MeV were employed to irradiate vitreous carbon planchets. Moreover, total X-ray production cross sections of titanium X-rays induced by chlorine ions were obtained as well for the same energy range. Only inner shell transitions were considered in the present work. The titanium target consisted of a thin film deposited over vitreous carbon planchets. The results indicate that the projectile X-ray yields increase as a function of the bombarding energy for the present energy range. Effects due to projectile charge state appears to be of minor importance at these low ion velocities. It is shown that a simple exponential function can represent the continuum background of such complex spectra. The chlorine transition rates Kβ/Kα obtained from chlorine acting as a projectile interacting with a carbon target are about half the value when compared to the chlorine Kβ/Kα ratios obtained when a LiCl target is bombarded with C+ and C3+ ions with energies from 2 MeV to 6 MeV. As far as the total X-ray production cross sections of Ti induced by chlorine ions are concerned, the ECPSSR theory underestimates the Ti total X-rays production cross sections by several orders of magnitude. The role of electron capture and possible mechanisms responsible for these effects are discussed.

The role of electron capture in core-collapse supernovae

Abstract Electron captures on nuclei play an important role in the dynamics of the collapsing core of a massive star that leads to a supernova explosion. After the discovery of the importance of this mode by Bethe, Brown, Applegate and Lattimer and the pioneering work to derive individual nuclear capture rates by Fuller and collaborators, more recent calculations of these capture rates were based on microscopic models which account for relevant degrees of freedom and agree well with the relevant experimental data. Incorporated into supernova simulations the modern capture rates lead to important changes in the collapse dynamics. In particular, it became clear that electron capture on nuclei dominates over the one on free protons during the entire collapse until neutrino trapping.

The Role of Electron Capture and Energy Exchange of Positively Charged Particles Passing Through Matter

The conventional treatment of the Bethe-Bloch equation for protons accounts for electron capture at the end of the projectile track by the small Barkas correction. This is only a possible way for protons, whereas for light and heavier charged nuclei the exchange of energy and charge along the track has to be accounted for by regarding the projectile charge q as a function of the residual energy. This leads to a significant modification of the Bethe-Bloch equation, otherwise the range in a medium is incorrectly determined. The linear energy transfer (LET) in the Bragg peak domain and at the distal end is significantly influenced by the electron capture: Thus the stepwise filling operation of the electron shells along the particle track is treated by the Fermi energy EF of Fermi-Dirac statistics and leads to the conversion of carbon ions from C6+ at the beginning of the track to C1+ at the Bragg peak region. A rather significant consequence is that in the domain of the Bragg peak the superiority of carbon ions is reduced compared to protons.

Role of electron capture in ion-induced electronic sputtering of insulators

Measurements of the sputtering yield of solid ${\mathrm{O}}_{2}$ by $25--240\text{\ensuremath{-}}\mathrm{keV}$ ${\mathrm{H}}^{+}$ show that it is double valued in its dependence on electronic stopping power. We propose that this is because the electronic sputtering yield is dominated by repulsion of ions in the ionization track of the projectile which, at low velocities, is augmented near the surface due to the additional ionization resulting from electron captures. This process may also be responsible for enhanced radiation damage in insulators, in particular in the production of fission tracks.

Proton-induced damage in p+– n InP solar cells: the role of electron capture at high fluences

Through the technique of electron beam induced current (EBIC), the effects of proton irradiation on InP solar cells of p +– n polarity have been investigated. InP cells of the opposite polarity ( n +– p) have been shown to collapse under heavy proton irradiation, due to carrier removal that first depletes and eventually type converts the base region. In contrast, we show that for cells of p +– n polarity, electron capture plays the dominant role in the cell radiation response at high damage levels.

Relevance of thermally populated first excited state of 44Ti to the abundance problem of cassiopiea A: A model study

We examine the possible role of electron-capture on the thermally populated first 2+ excited state of 44Ti in hot astrophysical environments pertaining to post explosive nucleosynthesis supernova debris. We find in a simple schematic model that the astrophysical weak interaction rate for electron-capture decay of 44Ti can depend considerably on temperature and hence on time. We propose a time varying decay rate for the evolving supernova debris and demonstrate its consequence for the 44Ti mass yield of the supernova Cas A, observed through the measured 1.157 MeV γ-ray flux from the electron-capture decay of 44Ti.

The vibrational spectra of molecular ions isolated in solid neon. VII. CO+, C2O+2, and C2O−2

When a Ne:CO=100 mixture is codeposited at approximately 5 K with a beam of neon atoms that have been excited in a microwave discharge, several new infrared absorptions appear in the resulting sample deposit. Detailed isotopic substitution experiments support the assignment of these absorptions to CO+, trans-OCCO+, and trans-OCCO−. Analysis of the infrared data has permitted determination of the CO-stretching force constants of the dimer cation and anion and has yielded a preliminary estimate of the valence angles for trans-OCCO−. The role of electron capture in the ‘‘photobleaching’’ of trans-OCCO+ by visible radiation is considered.

On the role of electron capture in the inner-shell alignment of atoms in ion-atom collisions

Abstract The alignment of the 2p 3 2 vacancy in Mg resulting from collisions with protons is calculated. Two possible mechanisms of ionisation are considered: direct Coulomb ionisation and electron capture by protons. The inclusion of electron capture leads to a marked improvement of the agreement between theory and experiment.

Electron capture and loss in collisions of H + and H with Pb vapors

Cross sections for single and double electron capture by protons and electron capture and loss from hydrogen atoms in lead vapors have been measured in the energy range 7.5–40 keV. Our results on Pb are compared with those on Mg reported by other workers. Analysis of electron capture collisions is complicated by the presence of multiple pseudocrossings of potential energy curves, though it may be inferred that the role of electron capture from inner shells becomes increasingly important at velocities larger than 2×10 8 cm/s. The double electron-capture processes are best described assuming the validity of the rule of conservation of electronic spin in the collisions.