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The availability at the Paul Scherrer Institute (PSI) of a spot-scanning technique with an isocentric beam delivery system (gantry) allows the realization of intensity-modulated proton therapy (IMPT). The development of 3D dosimetry is an important tool for the verification of IMPT therapy plans based on inhomogeneous 3D conformal dose distributions. For that purpose new dosimeters are being developed. The concept is to use a system of many millimetre sized scintillating volumes distributed in a polyethylene block, which are read on a CCD camera over a bundle of optical fibres and which can be irradiated from any direction orthogonal to the fibre axis. The purpose of this work is to investigate the composition of such small sensitive volumes. A mixture of inorganic phosphors and optical cement allows an optimal coupling between the scintillating volume and the optical fibre. Five different inorganic phosphors, available as powder, have been examined by considering their response along the Bragg curve. In particular, two phosphors have shown interesting behaviours: Gd 2 O 2 S:Tb and (Zn, Cd)S:Ag. Both phosphors have a high emission efficiency but contrasting behaviour in the Bragg peak region. The efficiency of Gd 2 O 2 S:Tb decreases with increasing stopping power (quenching of luminescence) while that of (Zn, Cd)S:Ag increases. Because of these contrasting behaviours it is possible to prepare a mixture of the two scintillating powders in a certain ratio in order to modulate the height of the measured Bragg peak relative to the entrance value so that it is in agreement with the ionization chamber measurements. We propose to use a mixture for the sensitive volume consisting of the following weight fractions: 48% Gd 2 O 2 S:Tb, 12% (Zn, Cd)S:Ag and 40% optical cement.

Bei der Umsetzung von w‐Dialkylamino‐carbonsäuren (I) mit phosphoriger Säure und Phosphortrichlorid in Chlorbenzol bei 100°C entstehen die w‐Dialkylamino‐hydroxyalkyliden‐bisphosphonsäuren (II) als amorphe Pulver, die sich beim Stehen an der Luft zu farblosen Ölen verflüssigen und in Wasser löslich sind.

Organophosphorus complexones represent a new class of multidentate reagents. The paper gives a broad survey of methods for the preparation of aminoalkylphosphonic acids, which include the organophosphorus complexones, and their complexing and biological properties are described. The specific characteristics of these complexones are revealed with respect both to certain elements-beryllium, the rare-earth metals, heavy elements, etc.-and with respect to extending the pH range of complex formation. The mode of reaction of organophosphorus complexones is discussed. The bibliography contains two hundred references. CONTENTS