Position-sensitive Si Detector Research Articles

GEANT4 simulation study of the response of a miniature radiation detector in Galactic Cosmic Rays and inside a spacecraft

The Miniaturized Detector for Application in Space (MIDAS) is a compact device with dimensions 5 × 5 × 1 cm3that combines position-sensitive Si detectors and a fast neutrons spectrometer. MIDAS is developed with the purpose of acting as a linear energy transfer (LET) spectrometer for the charged particles and measuring dose and dose equivalent from both charged particles and neutrons. It is based on fully depleted monolithic active Si pixel sensors for the charged track and energy deposition measurements, while a plastic scintillator read out by a silicon photomultiplier is used to determine energy depositions from fast neutrons. A simulation study of the detector response in galactic cosmic ray (GCR) radiation fields with the aid of GEANT4 has been performed. Energy depositions and hit pixel addresses have been used to reconstruct tracks and calculate LET spectra. A method to calculate LET∞in water from the measured LET has been elaborated. The dose rate in water and dose equivalent rate has been calculated. The energy and particle composition of the radiation field produced by the interaction of GCR with the Al walls of a spacecraft model has been determined, and the response of MIDAS in this radiation field has been investigated.

Direct evidence for Sb as a Zn site impurity in ZnO

The lattice location of ion implanted antimony in zinc oxide has been determined by means of β− emission channeling from the radioactive S124b isotope. Following 30 keV implantation of S124b into a single-crystalline ZnO sample to a fluence of 1×1014 cm−2, the angular-dependent emission rate of β− particles around several crystallographic directions was measured with a position-sensitive Si detector. The majority of Sb was found to occupy Zn sites, with the possible fraction on O sites being at maximum 5%–6%.

A neural network device for on-line particle identification in cosmic ray experiments

On-line particle identification is one of the main goals of many experiments in space both for rare event studies and for optimizing measurements along the orbital trajectory. Neural networks can be a useful tool for signal processing and real time data analysis in such experiments. In this document we report on the performances of a programmable neural device which was developed in VLSI analog/digital technology. Neurons and synapses were accomplished by making use of Operational Transconductance Amplifier (OTA) structures. In this paper we report on the results of measurements performed in order to verify the agreement of the characteristic curves of each elementary cell with simulations and on the device performances obtained by implementing simple neural structures on the VLSI chip. A feed-forward neural network (Multi-Layer Perceptron, MLP) was implemented on the VLSI chip and trained to identify particles by processing the signals of two-dimensional position-sensitive Si detectors. The radiation monitoring device consisted of three double-sided silicon strip detectors. From the analysis of a set of simulated data it was found that the MLP implemented on the neural device gave results comparable with those obtained with the standard method of analysis confirming that the implemented neural network could be employed for real time particle identification.

Fine structure in the α-decay of radium isotopes with mass numbers 209-212

Radium isotopes with mass numbers from 209 to 212 have been produced by heavy-ion fusion reactions 204Pb( 12C, xn) 216-Ra. Radioactive decay properties were investigated by means of α- and α-γ-spectroscopy after in-flight separation of the evaporation residues from the projectile beam by the velocity filter SHIP and implantation into a 16-strip position-sensitive Si detector. For the even-even nuclei 210,212Ra we identified α transitions into the first-excited 2+-state of the daughter nuclei 206,208Rn. Weak α transitions into excited levels of the odd-A daughter nuclei 205,207Rn were also observed.

Investigation of scintillation detectors for relativistic heavy ion calorimetry

The new Δ E/ E detection system, calorimeter telescope (CATE), for charge and mass determination of heavy ions at high energies (⩾100 MeV/n) has been designed. CATE, a calorimeter telescope will consist of position sensitive Si detectors for Δ E determination and scintillators, readout by either PIN diode or PMT, for total- E determination. Different scintillation detectors were tested with 130Sn, 186Pb, 197Au and 238U beams of (100–300) MeV/n ion energy. By properly selecting the beam species from the FRS and applying position corrections, an energy resolution of ≃0.5% FWHM was observed. The corresponding mass resolution of 1/200 is adequate for employment of CATE in the Fast Beam RISING campaign at GSI.

Synthesis and halflives of heavy nuclei relevant for the rp-process

Neutron deficient nuclei up to 100Sn were produced by fragmentation of a 1A·GeV 112Sn beam in a Be target. After isotopic separation by a fragment separator, the radionuclides were implanted in a stack of position sensitive Si-detectors acting as a microcalorimeter. The halflives and other decay properties were measured. Here we report halflives of rp-process waiting point nuclei between 80Zr and 92,93Pd. In addition the halflifes of the very short lived odd-odd NZ nuclei 90Rh, 94Ag and 98In were determined and attributed to superallowed Fermi transitions. Two new isotopes close to the p-dripline, 76Y and 78Zr, were identified for the first time.

Decay properties of neutron-deficient nuclei in the region Z = 86–92

Neutron deficient isotopes of elements Z = 86–92 have been produced by heavy-ion fusion reactions 12C + 208Pb, 209Bi, 22Ne + 208Pb, 51V + 170Er, and 50Ti + 170Er. The evaporation residues were investigated by means of α- and α-γ-spectroscopy after in-flight separation from the projectile beam by the velocity filter SHIP and implantation into a 16-strip position-sensitive Si-detector. New or improved decay data for 225,226U, 216,217m,218Pa, 215,216,217Th, 214,215,216,216mAc, 214Ra and 213Rn have been obtained.

Search for electromagnetic transitions between12C-12C cluster states in24Mg

The superdeformed states in heavy nuclei withA≳60 are characterized by their gamma decay pattern. In light nuclei, this signature is still missing especially for the cluster states formed in light heavy-ion reactions. The aim of the present experiment was thus to search for γ-ray transitions between 10+ and 8+ resonant states formed in the12C +12C reaction. A bombarding energy ofElab = 32.9 MeV has been chosen to populate a known and isolated 10+ resonance. The experiment has been carried out in a triple coincident mode (fragment-fragment-g) with the outgoing binary fragments detected in two position-sensitive Si detectors and the γ rays in the 4π array Château de Cristal. A few events have been observed which we attributed to the γ-ray transitions we searched for. This would be the first time that such transitions have been seen and, under certain assumptions, a radiative partial width of (1.2 ± 0.4) 3 1025 has been deduced for the 10+ resonant state.

Improvement of mass resolution of cosmic ray nuclei using a ΔE × E Si detector telescope

Abstract Using 5-in.-diameter Si(Li) detectors with a detector thickness of 1, 2 and 3 mm combined with 62 mm × 62 mm position-sensitive Si detectors, an excellent isotope telescope has been constructed for the Geotail mission. The performance of the telescope and the individual detectors has been investigated using 56Fe beams with energies between 430 and 696 MeV/n. The nonuniformity of the detector thickness as measured by exposing the detectors to a monochromatic Fe beam is 0.44% for 1 mm thick detectors, 0.54% for 2 mm thick detectors and 0.15% for 3 mm thick detectors. The secondary isotopes of Al through Fe produced by 430 MeV/n 56Fe in a polyethylene target were clearly resolved by the telescope. The measured mass resolution for Si, Ca and Mn were 0.36 amu, 0.42 amu and 0.44 amu in FWHM, respectively. The telescope has the following two key features: an excellent resolution (better than 0.5 amu) and an exceptionally high sensitivity ( SΩ = 43 cm 2 sr ) for a broad range of species from He through Ni with energies between 2.4 and 210 MeV/n.

Measurement of the 6Li + natSi reaction cross section at 18 to 28 MeV with a magnetic spectrograph and position-sensitive Si detector

Abstract The average reaction cross section σ R for 6 Li in nat Si was determined from the 6 Li energy spectrum in a two-dimensional position-sensitive Si detector in the focal plane of a magnetic spectrograph. The average σ R for 18 to 28 MeV 6 Li, 1490±80 mb, is compared with specific optical and strong absorption model calculations. Good agreement is obtained for certain models. This method for measuring σ R may be particularly useful when only small particle fluxes (≤100/s) are available; e.g., for radioactive nuclear beams.

Lattice site changes of ion implanted 8Li in InP studied by alpha emission channeling

The lattice sites of implanted radioactive 8Li atoms in si-InP:Fe have been investigated with the α-emission channeling method using a position-sensitive Si-detector. It is shown that after room temperature implantation the major part of the Li atoms is located on tetrahedral interstitial sites with four P atoms as nearest neighbours, whereas after implantation at a temperature of about 450 K almost only substitutional In-sites are occupied.

Direct transfer and two-step processes in the 42Ca(α, 3He)43Ca reaction

Abstract The 42 Ca(α, 3 He) 43 Ca reaction has been studied at 36 MeV incident energy. Angular distributions have been measured from 4° to 42° using a split-pole spectrometer and position sensitive Si detectors, for about 40 levels located up to 6 MeV excitation energy. A local zero-range DWBA analysis has been carried out; l = 3 and 4 assignments are tentatively proposed for levels located above 4 MeV excitation energy, indicating a strong fragmentation of the 1 f 5 2 strength between 4 and 6 MeV and the location of the main component of the 1 g 9 2 strength above 6 MeV. A number of weakly excited levels cannot be reproduced by DWBA analysis. Their angular distributions have been compared with the results of coupled-reaction-channel calculations assuming two-step excitation of weak coupling states with a [ 42 Ca ∗ ⊗ f 7 2 structure. A reasonable agreement has been obtained, confirming that the two-step process cannot be neglected in the analysis of the (α, 3 he) reaction.

Thin, circular, two-dimensional position sensitive Si detectors for trajectory determination

Thin (∼ 50 mu;m) two-dimensional position sensitive Si detectors have been developed for spacefliht which have circular sensitive areas of ∼ 2.5 cm 2. Gold and aluminum strips are evaporated onto the front and back surfaces, respectively, of an n-type silicon wafer, and are then connected to external resistor networks. The position response characteristics of a detector with 86 strips on each side are demonstrated using a pulsed light source. Measurements with both light pulses and 56Fe nuclei show that a position resolution of ∼ 150 μm fwhm is achieved for ∼ 60 MeV energy deposits. The trajectory determination capability for heavy ions of a pair of these detectors depends upon accurate mechanical alignment. Their long-term stability, excellent thermal-vacuum characteristics, and precise position indication for heavy ions make these detectors well suited as the trajectory determining elements in a telescope designed for isotopic studies of low energy heavy cosmic rays.

A large area circular position sensitive Si detector

Circular position sensitive detectors with sensitive areas of 17 cm 2 have been constructed by connecting gold strips on the front surface of a Li-drifted silicon detector to an external resistor network. Detector responses to alpha-particle sources and pulsed-light sources are presented which demonstrate the position and energy response characteristics of the detectors. Measurements with a pulsed-light source equivalent of 140 MeV show that a resolution (fwhm) of 0.19 mm (the width of the gold strips) can be achieved for energy deposits of ∼ 40 MeV. The position resolution (fwhm) obtained from these detectors mounted in a telescope exposed to 95–350 MeV/nucleon 40Ar nuclei is 0.82 mm for a single detector.