The Compact Muon Solenoid (CMS) detector is described. The detector operates at the Large Hadron Collider (LHC) at CERN. It was conceived to study proton-proton (and lead-lead) collisions at a centre-of-mass energy of 14 TeV (5.5 TeV nucleon-nucleon) and at luminosities up to 10(34)cm(-2)s(-1) (10(27)cm(-2)s(-1)). At the core of the CMS detector sits a high-magnetic-field and large-bore superconducting solenoid surrounding an all-silicon pixel and strip tracker, a lead-tungstate scintillating-crystals electromagnetic calorimeter, and a brass-scintillator sampling hadron calorimeter. The iron yoke of the flux-return is instrumented with four stations of muon detectors covering most of the 4 pi solid angle. Forward sampling calorimeters extend the pseudo-rapidity coverage to high values (vertical bar eta vertical bar <= 5) assuring very good hermeticity. The overall dimensions of the CMS detector are a length of 21.6 m, a diameter of 14.6 m and a total weight of 12500 t.

/pdf/the-cms-experiment-at-the-cern-lhc-4d2umuzboo.pdf

The CMS experiment at the CERN LHC

Particle detectors were made using semiconductor epitaxial 4H–SiC as the detection medium. The investigated detectors are formed by Schottky contact (Au) on the epitaxial layer and an ohmic contact on the back side of 4H–SiC substrates with different micropipe densities from CREE. For radiation hardness studies, the detectors have been irradiated with protons ( 24 GeV /c ) at a fluence of about 10 14 cm −2 and with electrons (8.2 MeV ) and gamma-rays ( 60 Co source) at doses ranging from 0 to 40 Mrad . We present experimental data on the charge collection properties by using 5.48, 4.14 and 2.00 MeV α-particles impinging on the Schottky contact. Hundred percent charge collection efficiency (CCE) is demonstrated for reverse voltages higher than the one needed to have a depletion region equal to the α-particle projected range, even after the irradiation at the highest dose. By comparing measured CCE values with the outcomes of drift–diffusion simulations, values are inferred for the hole lifetime, τp, within the neutral region of the charge carrier generation layer. τp was found to decrease with increasing radiation levels, ranging from 300 ns in non-irradiated detectors to 3 ns in the most irradiated ones. The diffusion contribution of the minority charge carriers to CCE is pointed out.

/pdf/radiation-tolerance-of-epitaxial-silicon-carbide-detectors-3hkxmoqm1w.pdf

Radiation tolerance of epitaxial silicon carbide detectors for electrons, protons and gamma-rays

The current models for bulk damage in high resistivity silicon have been reviewed. The damage constants were obtained from a global data survey. On this basis the degradation of the silicon counters in the ATLAS Inner Detector during a 10 year LHC operation is forecasted.

Radiation studies and operational projections for silicon in the ATLAS inner detector

This work presents an overview of the most important mechanisms of radiation damage in silicon detectors to be used for high energy experiments in LHC. The changes in the shallow concentration have been studied by thermally stimulated currents (TSC) after proton and neutron irradiation with fluences up to 10/sup 15/ cm/sup -2/ to investigate the role of thermal donors and the donor-removal effect in standard and oxygen enriched silicon with different resistivities. Deep defects in irradiated silicon have been analysed by deep level transient spectroscopy (DLTS) and photo induced current transient spectroscopy (PICTS) in the same materials. The radiation-induced microscopic disorder has been related with the carrier transport properties of irradiated silicon measured by the Hall effect, by capacitance and current vs. voltage characteristics and with charge collection efficiency. The dependence of the irradiated silicon detectors performances on crystal orientation, on incident particle type and on the initial concentration of oxygen and carbon is also discussed.

Radiation damage in silicon detectors

The subject of radiation damage to Si detectors induced by 24-GeV/c protons and nuclear reactor neutrons has been studied. Detectors fabricated on single-crystal silicon enriched with various impurities have been tested. Significant differences in electrically active defects have been found between the various types of material. The results of the study suggest for the first time that the widely used nonionizing energy loss (NIEL) factors are insufficient for normalization of the electrically active damage in case of oxygen- and carbon-enriched silicon detectors. It has been found that a deliberate introduction of impurities into the semiconductor can affect the radiation hardness of silicon detectors.

/pdf/comparison-of-radiation-damage-in-silicon-induced-by-proton-1zw62bsknf.pdf

Comparison of radiation damage in silicon induced by proton and neutron irradiation

Systematic investigations of the reverse annealing effect after radiation damage have been performed in particular for the change of the effective impurity concentration. The pronounced long term anneal observed at room temperature was further investigated by isochronal and isothermal studies. In order to demonstrate the radiation hardness of silicon detectors during 10 years of LHC operation an experiment was started at a higher temperature which compressed the real operational scenario to about 10 months.

/pdf/reverse-annealing-of-the-effective-impurity-concentration-54ppym7pix.pdf

Reverse annealing of the effective impurity concentration and long term operational scenario for silicon detectors in future collider experiments

Future high-energy hadron colliders (LHC, SSC) will generate a high flux of hadronic and electromagnetic particles in the experimental areas which has to be sustained by the detectors. The performance and electrical characteristics of silicon detectors evolve with time, during and after irradiations with 1 MeV neutrons up to 1.1/spl times/10/sup 14/ n cm/sup -2/, with 24 GeV protons up to 9.5/spl times/10/sup 13/ p cm/sup -2/, and with /sup 60/Co gammas up to 10 Mrad. Ion-implanted single-diode silicon detectors with an area of 1 cm/sup 2/ have been used for these studies. >

/pdf/neutron-proton-and-gamma-irradiations-of-silicon-detectors-3pdgdc631a.pdf

Neutron, proton and gamma irradiations of silicon detectors

Charge transport in silicon detectors

High resistivity ion-implanted silicon pad detectors have been irradiated at +20°C, +10°C, 0°C and −20°C with 24 GeV/c protons at a flux of ∼ 5 × 109cm−2s−1, up to fluences of ∼ 1.1 × 1014cm−2, and maintained at these temperatures during several months after the end of irradiation. The change of the diode reverse current, full depletion voltage and collection efficiency of the charge, deposited by relativistic electrons, are presented as a function of the proton fluence and of annealing time. It is found that operating the detectors below +10°C limits the diode reverse current and the bias voltage necessary to achieve full depletion. Moreover, at these temperatures, the charge collection efficiency for an integration time of 20 ns (typical of LHC operation) is better than 90% for 300 μm detectors irradiated to a fluence of 1014 cm−2 and biased at 160 V.

Study of characteristics of silicon detectors irradiated with 24 GeV/c protons between −20°C and +20°C

High-resistivity, ion-implanted silicon detectors have been irradiated with positive and negative pions up to fluences of 10 14 cm ‐2 and 10 13 cm ‐2 , respectively. The energy dependence of the leakage-current damage constant around the Δ resonance is presented. Studies of the leakagecurrent damage constants (corrected for self-annealing and the long-term value) and the evolution of the depletion voltage with time show pions of momentum 350 MeV/c to be 20‐25% more damaging than 1 MeV neutrons. Charge-collection measurements are also presented that show no more degradation in efficiency than previously measured for 1 MeV neutrons and 24 GeV/c protons.

/pdf/damage-induced-by-pions-in-silicon-detectors-26zt0k7e67.pdf

Damage induced by pions in silicon detectors

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