E. Gatti

Silicon drift detectors for high resolution room temperature X-ray spectroscopy

New cylindrical silicon drift detectors have been designed, fabricated and tested. They comprise an integrated on-chip amplifier system with continuous reset, on-chip voltage divider, electron accumulation layer stabilizer, large area, homogeneous radiation entrance window and a drain for surface generated leakage current. The test of the 3.5 mm2 large individual devices, which have also been grouped together to form a sensitive area up to 21 mm2 have shown the following spectroscopic results: at room temperature (300 K) the devices have shown a full width at half maximum at the MnKα line of a radioactive 55 Fe source of 225 eV with shaping times of 250 to 500 ns. At −20°C the resolution improves to 152 eV at 2 μs Gaussian shaping. At temperatures below 200 K the energy resolution is below 140 eV. With the implementation of a digital filtering system the resolution approaches 130 eV. The system was operated with count rates up to 800 000 counts per second and per readout node, still conserving the spectroscopic qualities of the detector system.

Suboptimal filtering of 1/ƒ-noise in detector charge measurements☆

Processing of 1tf-noise by suboptimal filters in detector charge measurements is considered. The achievable values of equivalent noise charge are compared to those provided by the optimum filter. Some aspects of filters processing 1tf-noise, like the degradation in the accuracy of charge measurements due to a bipolar or to a unipolar, flat-topped weighting function are described. Several conclusions are expected to be useful in the design of analog processors for radiation detectors when the front-end 1tf-noise is not negligible.

Low-mass e+e− pair production in 158 A GeV Pb-Au collisions at the CERN SPS, its dependence on multiplicity and transverse momentum

We report a measurement of low-mass electron pairs observed in 158 GeV/nucleon Pb-Au collisions. The pair yield integrated over the range of invariant masses 0.2<m<2.0 GeV is enhanced by a factor of 3.5 +/- 0.4 (stat) +/- 0.9 (syst) over the expectation from neutral meson decays. As observed previously in S-Au collisions, the enhancement is most pronounced in the invariant-mass region 300-700 MeV. For Pb-Au we find evidence for a strong increase of the enhancement with centrality. In addition, we show that the enhancement covers a wide range in transverse momentum, but is largest at the lowest observed pt.We report a measurement of low-mass electron pairs observed in 158 GeV/nucleon Pb-Au collisions. The pair yield integrated over the range of invariant masses 0.2 < m < 2.0 GeV is enhanced by a factor of 3.5 +/- 0.4 (stat) +/- 0.9 (syst) over the expectation from neutral meson decays. As observed previously in S-Au collisions, the enhancement is most pronounced in the invariant-mass region 300-700 MeV. For Pb-Au we find evidence for a strong increase of the enhancement with centrality. In addition, we show that the enhancement covers a wide range in transverse momentum, but is largest at the lowest observed pt.Abstract We report a measurement of low-mass electron pairs observed in 158 GeV/nucleon Pb-Au collisions. The pair yield integrated over the range of invariant masses 0.2 ≤ m ≤ 2.0 GeV/c 2 is enhanced by a factor of 3.5 ± 0.4 (stat) ± 0.9 (syst) over the expectation from neutral meson decays. As observed previously in S-Au collisions, the enhancement is most pronounced in the invariant-mass region 300-700 MeV/c 2 . For Pb-Au we find evidence for a strong increase of the enhancement with centrality. In addition, we show that the enhancement covers a wide range in transverse momentum, but is largest at the lowest observed p ⊥ .

A NEW METHOD FOR ANALOG TO DIGITAL CONVERSION

A method is suggested to improve the differential linearity of analog-to- digital converters for multichannel pulse height analyzers. The method is explained for a feedback coding system. (C.E.S.)

Extension of Ramo's theorem as applied to induced charge in semiconductor detectors☆

Abstract Extension of Ramos theorem to the case of presence of fixed space charge has been questioned in the past and very recently. It is here shown that the authors who criticized its application, fell into some errors, which are here discussed. A proof of the extended Ramos theorem is given. Further on, in order to clarify the matter, the simple case of a unidimensional problem relevant to semiconductor detectors is fully discussed.

Semiconductor drift chambers for position and energy measurements

Abstract Semiconductor drift chambers have been recently suggested and feasibility tests performed. This paper presents the first operative silicon drift detectors for position and energy measurements. Design criteria and experimental results in the laboratory and on an accelerator beam are reported.

Electrical properties and performances of natural diamond nuclear radiation detectors

Abstract Hole and electron drift velocities and mean free drift time have been measured with a time-of-flight technique as functions of electric field in crystals of natural diamond. The performances of diamond nuclear radiation detectors have been investigated using alpha and beta particles. An energy for electron-hole pair creation of 13.19 eV has been determined for alpha particles in the 5–6 MeV energy range. Spectral lines of alpha particles within this energy range have shown a resolution of 82 keV at room temperature.

Implanted silicon JFET on completely depleted high-resistivity devices

To satisfy the increasing interest in the integration of electronics onto optical and ionizing particle fully depleted detectors, a nonconventional JFET (junction field-effect transistor), designed to operate on a completely depleted, 2-k Omega -cm resistivity silicon substrate, has been designed, fabricated, and tested at room temperature. The devices show very low gate leakage current, low output conductance, a transconductance per unit gate width of 3 mS/mm, and a pinch-off voltage of -1.5 V. The integration of the devices onto the detectors makes possible the matching of the input capacitance of the JFET to the detectors output capacitance, which is of the order of few hundreds of femtorads. The measured gate capacitance of 200 fF is shown to correspond to an expected resolution in charge measurements, at room temperature, of less than 40 electrons rms. The fabrication constraints, imposed by the limited number of production steps of the detectors, are reported.<<ETX>>

On the induced charge in semiconductor detectors

The induced charge in an ionization chamber is usually represented by DELTA q = e DELTA x/d (1) or DELTA q = e DELTA V/V (2), where V = voltage across the device, d = spacing between electrodes, and DELTA V = potential difference between two points spaced DELTA x along the path of the charge e. Equation (1) is shown to be valid in the presence of a fixed space charge (depletion layer), while equation (2) is not. (D.L.C.)

SILICON DRIFT CHAMBERS - FIRST RESULTS AND OPTIMUM PROCESSING OF SIGNALS

Abstract A Semiconductor Drift Chamber was produced and tested. The paper describes: 1. 1)|principle of the chamber operation; 2. 2)|the performance of the test chamber; 3. 3)|the signal processing to obtain the best position resolution.