H.W. Kraner

The use of the signal current pulse shape to study the internal electric field profile and trapping effects in neutron damaged silicon detectors

The induced current pulse from ionizing events occurring near contacts on each side of a p+−n−n+ silicon junction detector may be used to map the electric field present in the detector. It is of interest to define the operative effects of fast neutron-induced displacement damage in detectors destined for high radiation environments in SSC or LHC. The hole current shape, in particular, has been useful to determine that the field maximum moves to the “rear” n+ contact as the material apparently changes to p-type at 8 × 1012 1 MeV n/cm2. Trapping times for both holes and electrons have been measured as a function of neutron fluence using the current pulse width to measure charge collection time as well as using calculated charge collection times. A clear linear relationship is found for the trapping probability (l/τ) versus neutron fluence. Current pulse shapes have been calculated for representative detector fields and mobility relationships and comparison with measured shapes is reasonable.

Fast neutron damage in silicon detectors

Radiation effects of fast neutrons have been measured in silicon detectors of varying resistivity irradiated to approx. 10/sup 11/ n/cm/sup 2/ over periods of weeks. The principal damage effect is increased leakage current due to generation of carriers from defect levels in the depletion region. Damage and leakage current constants have been established for detector resistivities between 10 and 27,000 ohm-cm and lie in the range of 0.7 /minus/ 2 /times/ 10E7 sec/cm/sup 2/ (K) for PuBe neutrons. A slight increase in K was observed for higher resistivities which translates into somewhat improved radiation hardness. A fit of this data was attempted to a two-level recombination formulation of the damage constant. 13 refs., 6 figs., 1 tab.

Effects of fast neutron radiation on the electrical properties of silicon detectors

Effects of neutron radiation on electrical properties of Si detectors have been studied. At high neutron fluence (φn ≥ 1012 n/cm2), C-V characteristics of detectors with high resistivities (ρ ≥ 1 kΩ cm) become frequency dependent. A two-trap level model describing this frequency dependent effect is proposed. Room temperature anneal of neutron damaged (at LN2 temperature) detectors shows three anneal stages, while two anneal stages were observed in elevated temperature anneal.

Development of large linear silicon drift detectors for the STAR experiment at RHIC

Abstract Large area linear Silicon Drift Detectors (SDD) are being developed for high energy and relativistic heavy ion collider experiments. SDDs have been proposed for the inner tracking detector in the STAR experiment at the BNL relativistic heavy ion collider to become operational in 1999. The Silicon Vertex Tracker (SVT) will consist of a three layer barrel structure composed of 216 individual detectors, each 6.3 × 6.3 cm 2 . Prototypes, including one-way drift detectors (4.5 × 4.5 cm 2 ) and bi-directional drift detectors (6 × 6 cm 2 ) have been manufactured,and their properties have been studied. Design considerations, as well as test results, are presented in this article. Recent work has focused on minimizing the inactive guard structure area in order to optimize tracking efficiency. Particular attention is given to discussion of parameters that are sensitive to the reduced guard structure area, such as leakage current, maximum voltage and drift non-linearities.

First results from CERES/NA45 on low-mass electron pair production in PbAu collisions

We report preliminary results of the first measurement of low-mass electron pairs in 160 GeV/nucleon PbAu collisions at central rapidities in a wide multiplicity range. This work is the continuation of our systematic studies on pair production in p-Be, p-Au and SAu interactions. The motivation for this effort derives from a new source of lowmass dileptons recently observed in SAu and S-W collisions by CERES and HELIOS/3, respectively. The results obtained in the analysis of the PbAu data confirm our previous finding that pair production in the mass range 0.2 < mee < 1.5 GeV/c2 is enhanced over the contributions from hadron decays while no significant excess could be observed for mee ≲ 2mπ. A comparison of the results for different multiplicity bins favours a non-linear dependence of the e+e−-yield on the accompanying charged particle densities.

Application of synchrotron radiation to elemental analysis

Abstract The use of a synchrotron storage ring as a high brightness source for production of monoenergetic variable energy, and highly polarized X-ray beams promises to revolutionize the field of elemental analysis. The results of exploratory work using the Cornell synchrotron facility, CHESS, will be described. Design considerations and features of the new X-ray microprobe facility now under construction at the Brookhaven National Synchrotron Light Source will be presented. This facility will be used for bulk analysis and for microanalysis with an initial spatial resolution of the order of 30 μm.

Performance of the multianode cylindrical silicon drift detector in the CERES NA45 experiment: first results☆

Abstract A silicon drift detector of circular geometry giving unambiguously the radial and azimuthal coordinates of particles interaction point for events with high multiplicity is part of the experimental set up of the NA45 experiment at CERN SPS. The paper reviews the characteristics of the detector and of its assembly among the other detectors of the experiment. The first experimental results showing the performance of the detector in term of resolution and its effectiveness in reconstructing the position of the event are reported.

Microscopic analysis of defects in a high resistivity silicon detector irradiated to 1.7x10(15)n/cm(2)

Current-based microscopic defect analysis methods with optical filling techniques, namely current deep level transient spectroscopy (I-DLTS) and thermally stimulated current (TSC), have been used to study defect levels in a high resistivity silicon detector (p(+)-n-n(+)) induced by very high fluence neutron (VHFN) irradiation (1.7x10(15) n/cm(2)). As many as fourteen deep levels have been detected by I-DLTS. Arrhenius plots of the I-DLTS data have shown defects with energy levels ranging from 0.03 eV to 0.5 eV in the energy band gap. Defect concentrations of relatively shallow levels (E(t) 0.33 eV) are in the order of 10(14) cm(-3). TSC data have shown similar defect spectra. A full depletion voltage of about 27,000 volts has been estimated by C-V measurements for the as-irradiated detector, which corresponds to an effective space charge density (N-eff) in the order of 2x10(14) cm(-3). Both detector leakage current and full depletion voltage have been observed to increase with elevated temperature annealing (ETA). The increase of the full depletion voltage corresponds to the increase of some deep levels, especially the 0.39 eV level. Results of positron annihilation spectroscopy have shown a decrease of total concentration of vacancy related defects including vacancy clusters with ETA, suggesting the breaking up of vacancy clusters as possible source of vacancies for the formation of single defects during the reverse anneal.

Fast neutron radiation effects in silicon detectors fabricated by different thermal oxidation processes

High resistivity silicon detectors along with MOS capacitors made on five silicon dioxides with different thermal conditions (975 degrees C to 1200 degrees C) have been exposed to fast neutron irradiation up to the fluence of a few times 10/sup 14/ n/cm/sup 2/. New measurement techniques such as capacitance-voltage of MOS capacitors and current-voltage and back-to-back diodes (p/sup +/-n/sup -/-p/sup +/ if n/sup -/ is not inverted to p) or resistors (p/sup +/-p-p/sup +/ if inverted) have been introduced in this study in monitoring the possible type-inversion (n to p) under high neutron fluence. No type-inversion in the material underneath SiO/sub 2/ and the p/sup +/ contact has been observed for detectors made on the five oxides up to the neutron fluence of a few times 10/sup 13/ n/cm/sup 2/. However, it has been found that detectors made on higher temperature oxides (>or=1100 degrees C) exhibited less leakage current increase at high neutron fluence. >

Silicon drift detectors for the STAR/SVT experiment at RHIC

Large area linear Silicon Drift Detectors (SDD) were developed to be used in the Silicon Vertex Tracker (SVT) of the STAR experiment at the BNL relativistic heavy ion collider (RHIC). The SDD is in its final design and has been submitted for large scale production. Test results show that the detector exhibits excellent position resolution and low noise. A special characterization procedure was developed to test detector wafers in order to select good detectors for the SVT. Recently, 15 STAR/SVT SDDs were assembled as a tracking device in a BNL-AGS heavy ion experiment (E896). It is the first tracking application of these detectors and their corresponding front-end electronics in an experimental environment. Preliminary results indicating good detector performance are shown and discussed in this paper.