94 research outputs found
An instrument to measure Hall voltages in low-mobility, high-resistivity irregularly shaped samples
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B-RAD: a radiation survey meter for operation in intense magnetic fields
No full textB-RAD is a hand-held radiation survey meter, specifically designed for operation in regions of strong magnetic field. The instrument has been jointly developed by CERN Radiation Protection group and the Department of Energy of the Polytechnic of Milan (POLIMI), originally to perform measurements of the residual radioactivity (radiation surveys) in the experimental areas of CERN Large Hadron Collider (LHC) and inside the ATLAS detector without switching the magnetic field off. B-RAD is based on a scintillating crystal coupled to Silicon Photomultipliers, and its operation is unaffected by magnetic field intensity up to 3 T. Five engineered prototype units were built and made available for routine use at CERN. The design of the instrument has subsequently been licenced to a company in order to industrialise it. This paper describes the CERN-POLIMI engineered version of the instrument, discusses its characterization in details and provides an overview of the commercial unit
Automatic trimming technique for multipolar magnets
No full textThe paper presents a technique for identifying and removing unwanted terms in the field power expansion of multipolar magnets. The technique is based on the measurement of the radial field at the poles of the magnet. The field terms are derived by analytical formulas and used to evaluate the current corrections. This trimming procedure has been tested for a 16-pole magnet designed for electron paramagnetic resonance imaging and permits a continuous control of the field configuration
Optimisation of axial RF field distribution of inductively coupled low frequency EPR loop-gap resonator
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Gamma irradiation of polyester films
No full textIrradiation in air of several thermoplastic aromatic polyesters was carried out in order to investigate changes in characteristic
properties. Polymers are irradiated at high doses, until 1 MGy, and no drastic changes seem to emerge. Dielectric and resistance
measurements are carried out in order to evaluate changes in electrical insulation property; moreover, nanoholes dimensions, analyzed by positron spectroscopy, are measured in pristine and irradiated polyesters. The study shows good durability of this kind of polyesters, due to the aromatic rings able to stabilize the polymeric chains towards ionizing radiations and able to preserve the original structural, electrical and permeability properties
A micrometric thickness silicon diode proposed as a microdosimeter
No full textA thin silicon diode formed by a deep p+ implantation under a shallow n+ one is proposed as a solid state microdosimeter. The thickness of the sensitive layer of the tested device is about two micrometers and the active area is about 10 mm(2). Due to the very large electric capacitance of the diode (about 1 nF) a low noise read-out circuit based on a discrete JFET has been developed. The noise due to the parasitic resistance of the detector itself dominates and fixes the lower threshold of the energy spectrum. A prototype of the proposed microdosimeter covered with a polyethylene converter has been irradiated with fast monoenergetic neutrons at the INFN-Legnaro Labs (1). The first experimental spectra are in good agreement with the simulated ones. The effect of direct interactions of thermal neutrons in silicon has been measured
Pulse discrimination between recoil protons and secondary electrons for a silicon diode based neutron spectrometer
No full textThe feasibility of the discrimination between protons and secondary electrons was investigated in order to decrease the lower limit of a recoil-proton spectrometer for neutrons based on a silicon p-i-n diode. The simulation of the ionization generated in the detector by protons and electrons and the simulation of the relevant induced currents show that such discrimination is feasible provided that the "rear side injection" configuration and a low noise setup are adopted. The difference between the collecting times of the two pulses is maximized and used for the rising time based discrimination. The neutron spectrometer consists of a 3 mm(2) area, 300 mum-thick silicon p-i-n diode covered with a polyethylene foil on the n-side. The ENC is 720 rms electrons at 20 ns shaping time. Experimental results on monoenergetic neutrons show the effectiveness of this discrimination in decreasing the lower limit of the recoil proton energy spectrum from 1.1 to 0.6 MeV
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