Search

We have designed and built a new hodoscope for heavy ion beams consisting of two tracking stations equipped with silicon microstrip detectors operated at 130 K. Preliminary results from tests performed in the high intensity CERN-SPS Pb ion beam show that we were able to detect and identify each incoming ion up to a beam intensity of ∼107 ions/s. The beam profile could be monitored on-line with 50 μm resolution. The detector performed satisfactory even after a dose of 90±40 Grad. [Copyright &y& Elsevier]

It has been recently observed that heavily irradiated silicon detectors, no longer functional at room temperature, “resuscitate” when operated at temperatures below 130 K. This is often referred to as the “Lazarus effect”. The results presented here show that cryogenic operation represents a new and reliable solution to the problem of radiation tolerance of silicon detectors. [Copyright &y& Elsevier]

The cryogenic silicon Beam Tracker of NA60 is the first detector based on the Lazarus effect used in a high-energy physics experiment. It employs single-sided silicon strip sensors of 50 μm pitch operated at a temperature of 130 K. Two tracking stations determine the transverse coordinates of the interaction point at the target with 20 μm resolution, to improve the determination of the offset of secondary vertices. This impact parameter measurement allows NA60 to distinguish between prompt dimuons and muon pairs from D-meson decays. The detector concept and technical feasibility have been demonstrated in beam time periods between 1999 and 2002. [Copyright &y& Elsevier]

Abstract: We report measurements in a high-energy pion beam of the sensitivity of the edge region in “edgeless” planar silicon pad diode detectors diced through their contact implants. A large surface current on such an edge prevents the normal reverse biasing of the device, but the current can be sufficiently reduced by the use of a suitable cutting method, followed by edge treatment, and by operating the detector at low temperature. The depth of the dead layer at the diced edge is measured to be (12.5±8stat..±6syst.)μm. [Copyright &y& Elsevier]

Abstract: We report measurements in a high-energy beam of the sensitivity of the edge region in “edgeless” planar silicon pad diode detectors. The edgeless side of these rectangular diodes is formed by a cut and break through the contact implants. A large surface current on such an edge prevents the normal reverse biasing of this device above the full depletion voltage, but we have shown that the current can be sufficiently reduced by the use of a suitable cutting method, followed by edge treatment, and by operating the detector at a low temperature. A pair of these edgeless silicon diode pad sensors was exposed to the X5 high-energy pion beam at CERN, to determine the edge sensitivity. The signal of the detector pair triggered a reference telescope made of silicon microstrip detector modules. The gap width between the edgeless sensors, determined using the tracks measured by the reference telescope, was then compared with the results of precision metrology. It was concluded that the depth of the dead layer at the diced edge is compatible with zero within the statistical precision of ±8μm and systematic error of ±6μm. [Copyright &y& Elsevier]

Silicon microstrip detectors will provide the forward tracking in the TOTEM experiment at the LHC. To allow efficient tracking closest to the beam (≈1 mm) these detectors should be sensitive up to their physical edge (i.e. edgeless). Edgeless (without guard rings) microstrip planar detectors can be operated at cryogenic temperatures (about 130° K) where leakage currents due to the active edge are drastically reduced. A silicon microstrip prototype, cut perpendicular to the strips, has been tested with a pion beam at CERN to study its efficiency close to the edge by using reference tracks from a simple silicon telescope. Results indicate that the detector measures tracks with good efficiency up to the physical edge of the silicon. [Copyright &y& Elsevier]

The recovery of the charge collection efficiency (CCE) at low temperatures, the so-called ”Lazarus effect”, was studied in Si detectors irradiated by fast reactor neutrons, by protons of medium and high energy, by pions and by gamma-rays. The experimental results show that the Lazarus effect is observed: (a) after all types of irradiation; (b) before and after space charge sign inversion; (c) only in detectors that are biased at voltages resulting in partial depletion at room temperature. The experimental temperature dependence of the CCE for proton-irradiated detectors shows non-monotonic behaviour with a maximum at a temperature defined as the CCE recovery temperature. The model of the effect for proton-irradiated detectors agrees well with that developed earlier for detectors irradiated by neutrons. The same midgap acceptor-type and donor-type levels are responsible for the Lazarus effect in detectors irradiated by neutrons and by protons. A new, abnormal “zigzag”-shaped temperature dependence of the CCE was observed for detectors irradiated by all particles (neutrons, protons and pions) and by an ultra-high dose of γ-rays, when operating at low bias voltages. This effect is explained in the framework of the double-peak electric field distribution model for heavily irradiated detectors. The redistribution of the space charge region depth between the depleted regions adjacent to p+ and n+ contacts is responsible for the “zigzag”- shaped curves. It is shown that the CCE recovery temperature increases with reverse bias in all detectors, regardless of the type of radiation. [Copyright &y& Elsevier]

This paper describes a novel technique to monitor high-intensity particle beams by means of a semiconductor detector. It consists of cooling a semiconductor detector down to cryogenic temperature to suppress the thermally generated leakage current and to precisely measure the integrated ionization signal. It will be shown that such a device provides very good linearity and a dynamic range wider than is possible with existing techniques. Moreover, thanks to the Lazarus effect, extreme radiation hardness can be achieved providing in turn absolute intensity measurements against precise calibration of the device at low beam flux. [Copyright &y& Elsevier]