Solid state microdosimetry of a 148 MeV proton spread-out Bragg peak with a pixelated silicon telescope

A constant value of the Relative Biological Effectiveness (RBE), equal to 1.1, to weight the physical dose of proton therapy treatment planning collides with the experimental evidence of an increase of effectiveness along the depth dose profile, especially at the end of the particle range. In this context, it is desirable to develop new optimized treatment planning systems that account for a variable RBE when weighting the physical dose. In particular, due to the increasing interest on microdosimetry as a possible methodology for measuring physical quantities correlated with the biological effectiveness of the therapeutic beam, the development of new Tissue-Equivalent Proportional Counters (TEPCs) specifically designed for the clinical environment are in progress. In this framework, the silicon technology allows to produce solid state detectors of real micrometric dimensions. This is a valid alternative to the TEPC from a practical point of view, being simple, easy-of-use and more versatile. The feasibility of a solid state microdosimeter based on a monolithic double stage silicon telescope has been previously proposed and deeply investigated by comparing its response to the one obtained by reference TEPCs in various radiation fields. The device is constituted by a matrix of cylindrical elements, 2 μm in thickness and 9 μm in diameter, coupled to a single E stage, 500 μm in thickness. Each segmented ΔE stage acts as a solid state microdosimeter, while the E stage gives information on the energy of the impinging proton up to about 8 MeV. This work is dedicated to the description of the microdosimetric characterization of the 148 MeV energy-modulated proton beam at the radiobiological research line of the Trento Proton Therapy Centre by means of a pixelated silicon microdosimeter. All measurements were carried out at different positions across the spread-out Bragg peak (SOBP) and the corresponding microdosimetric distributions were derived by applying a novel extrapolation algorithm. Finally, microdosimetric assessment of Relative Biological Effectiveness was carried out by weighting the dose distribution of the lineal energy with the Loncol's biological weighting function. Benefits and possible limitations of this approach are discussed

A telescope detection system for direct and high resolution spectrometry of intense neutron fields

A high energy- and spatial-resolution telescope detector was designed and constructed for neutron spectrometry of intense neutron fields. The detector is constituted by a plastic scintillator coupled to a monolithic silicon telescope (MST), in turn consisting of a DE and an E stage. The scintillator behaves as an “active” recoil-proton converter, since it measures the deposited energy of the recoil-protons generated across. The MST measures the residual energy of recoil-protons downstream of the converter and also discriminates recoil-protons from photons associated to the neutron field. The lay-out of the scintillator/MST system was optimized through an analytical model for selecting the angular range of the scattered protons. The use of unfolding techniques for reconstructing the neutron energy distribution was thus avoided with reasonable uncertainty (about 1.6% in neutron energy) and efficiency (of the order of 106 counts per unit neutron fluence). A semi-empirical procedure was also developed for correcting the non-linearity in light emission from the organic scintillator. The spectrometer was characterized with quasi-monoenergetic and continuous fields of neutrons generated at the CN Van De Graaff accelerator of the INFN-Legnaro National Laboratory, Italy, showing satisfactory agreement with literature data

Preliminary results of an aging test of RPC chambers for the LHCb Muon System

The preliminary results of an aging test performed at the CERN Gamma Irradiation Facility on a single--gap RPC prototype developed for the LHCb Muon System are presented. The results are based on an accumulated charge density of 0.42 C/cm^2, corresponding to about 4 years of LHCb running at the highest background rate. We observe a rise in the dark current and noise measured with source off. The current drawn with source on steadily decreased, possibly indicating an increase of resistivity of the chamber plates. The performance of the chamber, studied with a muon beam under several photon flux values, is found to still fulfill the LHCb operation requirements.Comment: 4 pages, 6 figures, presented at RPC2001, VIth Workshop on Resistive Plate Chambers and Related Detectors, November 26-27 2001, Coimbra, Portuga

First results from an aging test of a prototype RPC for the LHCb Muon System

Recent results of an aging test performed at the CERN Gamma Irradiation Facility on a single--gap RPC prototype developed for the LHCb Muon System are presented. The results are based on an accumulated charge of about 0.45 C/cm$^2$, corresponding to about 4 years of LHCb running at the highest background rate. The performance of the chamber has been studied under several photon flux values exploiting a muon beam. A degradation of the rate capability above 1 kHz/cm$^2$ is observed, which can be correlated to a sizeable increase of resistivity of the chamber plates. An increase of the chamber dark current is also observed. The chamber performance is found to fulfill the LHCb operation requirements.Comment: 6 pages, 9 figures, presented at the International Workshop on Aging Phenomena in Gaseous Detectors'', DESY-Hamburg (Germany), October 200

First evaluation of neutron induced single event effects on the CMS barrel muon electronics

Neutron irradiation tests of the currently available electronics for the CMS barrel muon detector were performed using Thermal and fast neutrons at E< 11MeV. The Single Event Upset rate on the Static RAM was measured, while upper limits are derived for events having experienced no failure. The results are used to guess the upper limits on the mean time between failures in the whole barrel muon detector

New results from an extensive aging test on bakelite Resistive Plate Chambers

We present recent results of an extensive aging test, performed at the CERN Gamma Irradiation Facility on two single--gap RPC prototypes, developed for the LHCb Muon System. With a method based on a model describing the behaviour of an RPC under high particle flux conditions, we have periodically measured the electrode resistance R of the two RPC prototypes over three years: we observe a large spontaneous increase of R with time, from the initial value of about 2 MOhm to more than 250 MOhm. A corresponding degradation of the RPC rate capabilities, from more than 3 kHz/cm2 to less than 0.15 kHz/cm2 is also found.Comment: 6 pages, 7 figures, presented at Siena 2002, 8th Topical Seminar on Innovative Particle and Radiation Detectors 21-24 October 2002, Siena, Ital