D. Chren

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.

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.

Study of PIN diode energy traps created by neutrons

Characterization of radiation defects is still ongoing and finds greater application in the increasing radiation doses on semiconductor detectors in experiments. Studying the changes of silicon PIN diode for high doses of radiation is the fundamental motivation for our measurements. In this article we describe the behavior of the PIN diode and development of the disorder caused by neutrons from a 252Cf and doses up to 8 Gy. The calibration curve for PIN diode shows the effect of disorders as the changes of the voltampere characteristics depending on the dose of neutron irradiation. The measured values for defects are in good agreement with created energy traps.

Relativistic hypernuclei at Dubna

At the Laboratory of High Energies (JINR, Dubna) a unique approach was elaborated with hypernuclei produced by the excitation of the beam nuclei and their decays observed at a distance of tens of cm behind the production target. While the very first experiments were carried out in the Synchrophasotron beams, more extensive hypernuclei research programme is planned for the Nuclotron accelerator and the new spectrometer created by the authors. At the time of the conference the first test run in the Nuclotron beam was in progress. Investigation of hydrogen hypernuclei isotopes is in the first line of the experimental research plans. Namely, lifetimes and production cross sections of Λ 4 H and Λ 3 H will be measured. Search for Λ 6 H is also among the tasks.

Study of the development of defects in Si PIN diodes exposed to 23 GeV/c protons

Studying the development of crystallographic defects in PIN diodes is the focus of the RD-50 (CERN) research project. The study was carried out on Si PIN diodes manufactured and used in the Czech Republic. The Si PIN diodes were irradiated with 23 GeV/c protons at doses ranging from 0.5 to 43 Gy. The Si PIN diodes were calibrated in a 23 GeV/c proton source [1], and the energy traps of the defects produced were measured by the DLTS method. The IV characteristics and the parameters of the defects were studied. The 23 GeV/c protons produce typical crystallographic defects and, at higher doses, bring about their regrouping thus giving rise to a new generation of defects. Defects are classified by their energy levels in the forbidden band from the conduction band. The mechanism influencing the parameters of the defects is discussed. The study of defects in silicon is important for silicon-based electronic elements used in cosmic research because of their effects on the operability and reliability of electronic equipment installed in satellites. Another application is the dosimetry measurements involving various types of particle accelerators.

Single photon avalanche diode on Ge-Si, dreams, objectives and first results

We are presenting the design, technology development and tuning of the Single Photon Avalanche Diode fabricated on the germanium - silicon epitaxial layer. The ultimate goal is to develop a solid state photon detector with picosecond timing resolution and stability and an increased spectral sensitivity beyond 1100 nanometres in comparison to detectors based on silicon. The technology development steps on the Ge-Si epitaxial layer are presented together with the first results of the preparation of the shallow junction and its parameters. The diffusion and annealing models have been tuned for GeSi epitaxial layer and implantation. The resulting concentration profiles have been verified by two independent diagnostics methods. The first avalanche diode structures on the basis of the Ge0.4Si0.6, epitaxial layer on Silicon have been prepared and tested. The ability of the avalanche structure to operate in a Geiger mode has been demonstrated for the first time, the dark count rate has been measured. The serial resistance of the structure above its breakdown voltage has been measured. The detection sensitivity in the wavelength range of 500 to 1600 nanometres has been measured.

Avalanche Photodiode Structure for Photon Counting on Si0.6Ge0.4 Epitaxial Layer

We are presenting the results of the research and development of an avalanche photodiode structure, on the basis of SiGe epitaxial layer on Si wafer. The ultimate goal is to develop a solid state photon counting detector with picosecond timing resolution and stability and a spectral sensitivity beyond 1100 nanometers. The technology development steps on the Si0.6Ge0.4 epitaxial layer are presented together with the first results of the preparation of the shallow junction and its parameters. The ability of the avalanche structure to operate in a Geiger mode has been demonstrated for the first time. The serial resistance of the structure above its breakdown voltage has been measured. The diffusion and annealing model has been tuned for GeSi epitaxial layer and implantation. The resulting concentration profiles have been verified by two independent diagnostics methods. The rapidity of avalanche grow was compared with Si photon counting diode.

Λ10Be and Λ10B hypernuclei on the Nuclotron

Recently, the Nuclotron accelerator at the Laboratory of High Energy has supplied the first extracted beam of medium energy ions. This opens up possibilities to perform hypernuclear experiments. Dedicated detector set up, including as main parts a silicon strip vertex detector, Cherenkov detectors and a magnetic spectrometer, opens possibilities to continue experiments performed on the Dubna synchrophasotron ion beams and, at the same time, to test a new method of identification of some hypernuclei using the αα decay of the 8Be residual nucleus as a trigger.