B. Sopko

Scanning of irradiated silicon detectors using alpha particles and low-energy protons

Abstract In a spectroscopic study of non-irradiated and proton-irradiated silicon diodes, the detectors were illuminated from the front side and from the rear side by various alpha particle sources (mainly ThC’) and by monoenergetic protons with energies from 1.0 to 2.5 MeV. Their response characteristics have been studied as a function of the incoming particle energy and the applied bias voltage. The charge collection efficiency was determined as a function of fluence.

Charge sharing studies with a Medipix1 pixel device

Abstract The Medipix1 chip is a prototype (digital) CMOS imaging chip that emerged from particle detection in high energy physics experiments. It was designed at CERN following specifications from the Medipix1 Collaboration. This contribution aims at demonstrating the applicability of Medipix1 Si and GaAs pixel devices for alpha and X-ray particle detection. A study of “charge sharing” between pixels and test of “spatial resolution” using narrow beam and “edge” image contrast was performed. For photons with energy

Studying of hypernuclei with nuclotron beams

A spectrometer is created to study relativistic hypernuclei produced with beams of accelerated nuclei from the Nuclotron facility (Dubna, JINR). Test runs have been carried out and the conclusion is drawn that the properties of the facility meet the requirements of the task of searching for unknown and studying poorly known neutron-rich hypernuclei.

Measurement of energy levels in a silicon detector damaged by neutrons

The level of defects in a semiconductor silicon detector diode made of high resistivity N type material and exposed to neutrons in a research nuclear reactor was examined by measuring the thermally stimulated current (TSC). A modified TSC method was employed where the released charge was measured in the reverse direction on a diode with zero bias voltage. Electrons captured in cooled traps due to the photoelectric effect are released when the material is heated. The detector was irradiated with an integral neutron flux of 7.63 × 1015 n/cm2.

Photon counting timing uniformity–unique feature of the silicon avalanche photodiodes K14

The paper reports on detailed tests of active area uniformity of three different single photon avalanche detectors (SPADs). Relative sensitivity, timing jitter, and relative detection delay have been measured for a series of points across the detection area; the resulting spatial profiles have been plotted and analysed. Unique features have been found in the case of silicon-based K14 SPADs: their active area is extremely uniform, especially with respect to the detection delay, in contrast to the remaining two SPADs, which exhibit significant fluctuations of the delay. The perfect uniformity of the K14 SPADs enables the detector to maintain its high temporal resolution of 40 ps FWHM even for large detection areas of 200 µm diameter.

Novel Contribution in Branch of Ultra-Fast Condensed Matter Spectroscopic Photon Counting System

We are reporting on the novel design of an all solid state photon counting package and its applications in ultrafast spectroscopy. Developing the new active gating and quenching circuit of the diode we achieved the short and precisely defined detector dead time, the fast gate response and simultaneously the circuit simplicity and compactness.

High-resolution imaging of biological and other objects with an X-ray digital camera.

A high-resolution CCD X-ray camera based on YAG:Ce or LuAG:Ce thin scintillators is presented. The high resolution in low energy X-ray radiation is quantified with several test objects. The achieved spatial resolution of the images is <1 microm. The objects used for imaging are grids and small animals with parts of several microns in extent. The high-resolution imaging system can be used with different types of ionizing radiation (X-ray, electron, UV, and VUV) and for non-destructive micro-radiography and synchrotron beam inspection.

Relativistic hypernuclei: old problems and new prospects

The first experiments with relativistic hypernuclei (Bowen; Khorozov and Lukstins) were done many years ago. They demonstrated not only that such extremely difficult experiments are manageable but also their great advantage, a possibility of observing and studying independently the production and weak decay of hypernuclei: the points of the production and decay of relativistic hypernuclei are separated by tens of centimeters instead of some microns in classical experiments. At the same time these first experiments revealed a huge problem with selection of the proper trigger.Recently we proposed to explore a unique feature of the 9Be nucleus: after removing a neutron from its ground state several groups of alpha-particles appear from different excited states of a residual nucleus 8Be. Detection of the correlated pair of α-particles produced in a vacuum volume at a distance of some 40 cm from target is an unambiguous signal of nonmesonic decay of hypernucleus 10ΛBe(→α+α+n+n) or 10ΛBe(→α+α+n+p). In this particular case it is possible to take exclusive decay rates (on different excited states of 8Be*). This open a way for a phenomenological analysis of matrix elements of the four-baryon weak interaction.The experiment is approved for new accelerator Nuclotron at JINR, Dubna.

Study of the characteristics of silicon MESA radiation detectors

Abstract The MESA process for building silicon diodes is described. I – V and C – V features of MESA detectors are given. Results of pulse-height spectra measurements with α particles incident on the front and back sides of a MESA diode establish the energy resolution of these detectors, show the evolution of their response as a function of applied bias voltage, and bring information about the influence of MESA structure on charge collection. The characteristics of MESA detectors as a function of fluence are investigated in view of their possible use in high particle fluence environment. Charge collection data obtained from the measurements of the current-pulse response induced by β and α particles are presented as a function of applied bias voltage and particle fluence. Some electrical characteristics of detector material, namely the effective impurity or dopant concentrations ( N eff ), the electron ( μ e ) and hole ( μ h ) mobilities, are studied as a function of fluence using a charge transport model. A comparison is made with the features of standard planar (SP) silicon detectors.

Space resolution of a silicon pixel detector as a function of the track angle

Abstract We measured the spatial resolution of a 300 μm thick 75 × 500 μ m silicon pixel detector as a function of the track angle using a 120 GeV pion beam. We observed that 13% of tracks perpendicular to the detector give a signal on two neighboring pixels; this fraction increases to 50% at an angle of 15° w.r.t. the normal incidence direction. The average spatial resolution is 28.2 μm at 0° and 14.6 μm at 15°. The detector efficiency is not affected by the charge sharing between pixels. Our data agree with the predictions of a simple geometrical model describing the charge sharing in the region between pixels. This model can be the basis for a full simulation of the behaviour of a pixel detector.