REACCELERATION OF ION BEAMS FOR PARTICLE THERAPY

Abstract At the Heidelberg Ion-Beam Therapy Centre (HIT) more than 2000 cancer patients have been treated with ions using the raster-scanning method since 2009. The synchrotron provides pencil beams in therapy quality for more than 250 energy steps for each ion species allowing to vary the penetration depth and thus to irradiate the tumour slice-by-slice. So far, changing the beam energy necessitates a new synchrotron cycle, including all phases without beam extraction. As the number of ions that can be accelerated in the synchrotron usually exceeds the required number of ions for one energy slice, the duty cycle could be significantly reduced by reaccelerating or decelerating the remaining ions to the adjacent energy level. By alternating acceleration and extraction phases several slices could be irradiated with only short interruptions. This leads to a better duty cycle and a larger number of patients that can be treated in the same time. Therefore the behaviour of a reaccelerated but transversally blown up beam -due to the use of RF-knockout extraction -must be investigated in detail, beam losses have to be minimised. To estimate the potential benefit of such an operation mode, treatment time has been simulated and compared to the time achieved in the past. A reduction of more than 50 % is possible

Tunneling Spectra of Individual Magnetic Endofullerene Molecules

The manipulation of single magnetic molecules may enable new strategies for high-density information storage and quantum-state control. However, progress in these areas depends on developing techniques for addressing individual molecules and controlling their spin. Here we report success in making electrical contact to individual magnetic N@C60 molecules and measuring spin excitations in their electron tunneling spectra. We verify that the molecules remain magnetic by observing a transition as a function of magnetic field which changes the spin quantum number and also the existence of nonequilibrium tunneling originating from low-energy excited states. From the tunneling spectra, we identify the charge and spin states of the molecule. The measured spectra can be reproduced theoretically by accounting for the exchange interaction between the nitrogen spin and electron(s) on the C60 cage.Comment: 7 pages, 4 figures. Typeset in LaTeX, updated text of previous versio

BIOPIXE: A new PIXE-data software package to analyse quantitative elemental distributions of inhomogeneous samples

A new software package "BIOPIXE" with emphasis on biological samples inhomogeneous in mass is presented. PIXE and STIM measurements were carried out on pixel-by-pixel basis. The elemental concentrations are evaluated using GUPIX. Main features of BIOPIXE are correction of thermal shifts during long time measurements (72 h), offline evaluation of elemental concentrations of arbitrary regions and, especially, true elemental maps of samples inhomogeneous in mass. (C) 2002 Published by Elsevier Science B.V

BIOPIXE: A new PIXE-data software package to analyse quantitative elemental distributions of inhomogeneous samples

A new software package "BIOPIXE" with emphasis on biological samples inhomogeneous in mass is presented. PIXE and STIM measurements were carried out on pixel-by-pixel basis. The elemental concentrations are evaluated using GUPIX. Main features of BIOPIXE are correction of thermal shifts during long time measurements (72 h), offline evaluation of elemental concentrations of arbitrary regions and, especially, true elemental maps of samples inhomogeneous in mass. (C) 2002 Published by Elsevier Science B.V

Micro-PIXE investigations of apoplastic iron in freeze-dried root cross-sections of soil grown barley

Freeze-dried cryo-sections of barley roots (Hordeum vulgare L. cv. Alexis) were used to investigate the possible role of the root apoplast as an iron-storage pool for plants; this possibility has been a matter of controversy. Micro-PIXE analyzes in pixel mode were complemented by the STIM technique. Data were analyzed using the new Heidelberg software package BIOPIXE, which provides true elemental maps of inhomogeneous samples such as freeze-dried cross-sections of roots. The maps clearly show a high heterogeneity of the iron distribution in roots between adjacent cell layers. Accumulations of iron were observed in the cell walls of the outermost cell layers of the roots and at the endodermis. Based on the correlation between iron and soil related elements like titanium, aluminum and silicon, most of the iron located at the root surface could be attributed to soil contamination. It could also be shown that these soil contaminations lead to an overestimation of the apoplastic iron concentrations determined by methods commonly used in the botanical field. Besides this, low accumulations of iron were observed in the cell walls of the outmost cell layers of the roots. This may indicate that the root apoplast may have a minor function in iron nutrition. (C) 2002 Published by Elsevier Science B.V

Element distribution in mycorrhizal and nonmycorrhizal roots of the halophyte Aster tripolium determined by proton induced X-ray emission

The salt aster (Aster tripolium L.) colonized by the arbuscular mycorrhizal fungus Glomus intraradices Sy167 and noncolonized control plants were grown in a greenhouse for nine months with regular fertilization by Hoagland nutrient solution supplemented with 2% NaCl. Mycorrhizal roots showed a high degree of mycorrhizal colonization of 60–70% and formed approximately 25% more dry weight and much less aerenchyma than the nonmycorrhizal controls. Cryosectioning essentially preserved the root cell structures and apparently did not cause significant ion movements within the roots during cuttings. The experimental conditions, however, did not allow to discriminate between fungal and plant structures within the roots. Quantification of proton-induced X-ray emission (PIXE) data revealed that in control roots, Na+ was mainly concentrated in the outer epidermal and exodermal cells, whereas the Cl– concentration was about the same in all cells of the roots. Cross sections of roots colonized by the mycorrhizal fungus did not show this Na1 gradient in the concentration from outside to inside but contained a much higher percentage of NaCl among the elements determined than the controls. PIXE images are also presented for the four other elements K, P, S, and Ca. Both in colonized and control roots, the concentration of potassium was high, probably for maintaining homoeostasis under salt stress. This is seemingly the first attempt to localize both Na+ and Cl– in a plant tissue by a biophysical method and also demonstrates the usefulness of PIXE analysis for such kind of investigation