Mass resolution of recoil fragment detector telescopes for 0.05–0.5 A MeV heavy recoiling fragments

The factors governing the mass resolution for 0.05–0.5 A MeV recoil nuclei have been investigated for detector telescopes in which carbon-foil time zero detectors and ion-implanted silicon detectors are used to determine the time of flight and energy respectively. Experimentally determined second moments of the mass distribution have been compared with theoretical estimates based on literature data. The experimental mass resolution is in reasonably good absolute agreement with theoretical estimates. For low energy (< 0.3 A MeV) particles the mass resolution is dominated by the contribution from the silicon detector and thus largely independent of timed flight length. In fact for detection of very low energy (0.1 A MeV) recoil nuclei timed flight lengths of less than 0.22 m are sufficient.     

CHICSi—a compact ultra-high vacuum compatible detector system for nuclear reaction experiments at storage rings. I. General structure, mechanics and UHV compatibility

CELSIUS Heavy-Ion Collision Silicon detector system (CHICSi) is a large solid angle, barrel-shaped detector system, housing up to 600 detector telescopes arranged in rotational symmetry around the beam axis. CHICSi measures charged particles and fragments from nuclear reactions. It operates at internal targets of storage rings. In order to optimize space and momentum-space coverage and minimize the low-energy detection limits, CHICSi is designed for use in ultra-high vacuum (UHV, 10⁻⁸ Pa) inside a cluster-jet target chamber. This calls for materials in mechanical support, detectors, Very Large Scale Integrated (VLSI) electronics, connectors, cables and other signal transport devices with very low outgassing. Two auxiliary detector systems, which will operate in coincidence with CHICSi, a heavy-recoil, time-of-flight system (HR-TOF) also placed inside the target chamber and a projectile fragmentation wall (PF-WALL) located outside the chamber, have also been constructed. In total, this combined system registers more than 80% of all charged particles and fragments from typical heavy-ion reactions at energies of a few hundreds of MeV per nucleon.     

CD: A double sided silicon strip detector for radioactive nuclear beam experiments

A very compact double sided silicon strip detector array is described, designed for use in reaction studies involving radioactive nuclear beams. It is small enough to fit inside a large solid angle γ-detector array and will enable Doppler-shift corrections at energies in the vicinity of the Coulomb barrier. The detector provides sufficient energy and time-of-flight resolution for the identification of light reaction products and can be set up to cover a substantial part of the scattering angular distribution with good resolution.

The device is available in thicknesses of up to 500 μm to stop all interesting reaction products. Moreover, a very thin (35–40 μm) variant of this detector is described that can be used as an energy loss detector in a ΔE−E telescope geometry followed by a detector that measures the residual energy. This provides additional particle identification capabilities, e.g. in light exotic nuclei induced reactions. First results from a commissioning run using a post-accelerated radioactive beam are presented.     

Experimental results from a sandwich calorimeter using U absorbers and 0.25 m of Si active area

The electromagnetic section of a hadronic calorimeter, consisting of uranium absorbers and of silicon sampling units with an active area of 0.25 m², was investigated. The overall performance of the silicon detectors and especially developed associated electronics, seems to be stable and reliable. During a four-week run at the t₉, CERN-PS (Proton Synchrotron) electron beam (energies of 2 to 6 GeV), no variation of energy calibration of the calorimeter was observed. The energy resolution for electromagnetic showers was found to be about , where E is the energy of the incoming electron and τ is the number of radiation lengths of passive material interspaced between two active samplers, for a calorimeter depth of 15.6 X₀ (radiation lengths), with Si samplers depleted to 200 μm. The fiberglass supports of the silicon mosaics cause a reduction of energy response to electromagnetic showers. It can be exploited to equalize the response of a Si/U hadronic calorimeter to incoming electrons and hadrons.     

Measurements on a GaAs microstrip detector with 50 GeV/c electrons

A microstrip gallium arsenide detector (thickness 508 μm, strip width 100 μm, strip pitch and readout pitch 200 μm) has been tested in a 50 GeV/c electron beam at CERN. Using the low noise Viking preamplifier chip (shaping time 1.5 μs) signal to noise ratios up to 25 were measured depending on bias voltage and angle of incidence. Applying the so-called η-algorithm (using the impact position-sensitive charge sharing between adjacent strips) a resolution down to σ 20 μm could be obtained.     

A 5 in. Si(Li)/Pb sampling calorimeter telescope for observation of cosmic gamma rays in the GeV region

A 5 in. diameter Si(Li)/Pb sampling calorimeter with a depth of 28 radiation lengths (30 unit cells × 0.93 radiation lengths) has been constructed. The energy and angular resolutions of the calorimeter have been investigated using CERN SPS positron beams with energies of 10 to 147.8 GeV. The calorimeter shows good linearity over this energy region and the energy resolution is expressed well by σ_E (rms)/E = (16.9 ± 0.9)%/ √E[GeV], where E represents the incident beam energy. The angular resolution of the calorimeter for a single event is 0.3° (rms) at 80 GeV/c. The agreement between these results and Monte Carlo simulations is good.

We are showing a new design of the Si(Li)/Pb sampling calorimeter telescope (SSCT) with an angular resolution (point source localization capability) of about 0.04° (rms) for bright galactic gamma-ray sources. We believe that this telescope is a suitable detector for future observations of cosmic gamma rays in the GeV region, especially when used to search for point sources.     

Performance of a three-element thin film detector

A nuclear charged particle detector has been designed and fabricated at the University of Florida for use in identifying the nuclear charge Z and mass number A of low energy (1 MeV/amu) heavy mass ions. The detector consists of a stack of three sequential thin film detectors (made from NE-102A plastic scintillator) for three successive measurements of the specific luminescence ΔL/Δx and velocity of a transiting ion and a terminal surface barrier detector for measuring the ion residual energy. This detector assembly was tested by measuring its response to various isotopes of germanium and selenium ions accelerated to selected energies between 53 and 169 MeV and then scattered from a thin gold target foil. The tests were performed to obtain quantitative information on the ability of the detector system to identify the nuclear Z of an impinging ion and to test the 0810 1076 V 3 advantage of having three successive measurements of ΔL/Δx from three sequential and independent thin film detectors. It was determined that below 2 MeV/amu the detector response was dependent on particle velocity but independent of particle mass and below about 0.9 MeV/amu the detector was not able to distinguish between ions having two units difference in Z, probably due to similarities in ionic charge state distributions. It was also determined that the use of three detectors reduced the FWHM of the TFD response by 54%.     

Ion-implanted capacitively coupled silicon strip detectors with integrated polysilicon bias resistors processed on a 100 mm wafer

Double-sided silicon strip detectors with integrated coupling capacitors and polysilicon resistors have been processed on a 100 mm wafer. A detector with an active area of 19 × 19 mm² was connected to LSI readout electronics and tested. The strip pitch of the detector is 25 μm on the p-side and 50 μm on the n-side. The readout pitch is 50 μm on both sides. The number of readout strips is 774 and the total number of strips is 1161. On the p-side a signal-to-noise of 35 has been measured using a ⁹⁰Sr β-source. The n-side has been studied using a laser.     

A high resolution silicon beam telescope

We describe the design and present the performances of a charged particle telescope used for high resolution silicon pixel developments. A telescope made of four x and four y single-sided silicon microstrip layers was built, providing an r.m.s. position resolution of 1 μm for high energy charged particles. A signal over noise ratio of 130 was achieved with minimum ionizing particles.     

A large area liquid scintillation multiphoton detector

A 60 layer lead-liquid scintillator shower detector, which we call the SLIC, has been used for multiphoton detection in the Fermilab tagged photon spectrometer. The detector has an unimpeded active area which is 2.44 m by 4.88 m and is segmented, by means of teflon coated channels, into 3.17 cm wide strips. The 60 layers in depth are broken into three directions of alternating readouts so that three position coordinates are determined for each shower. At present the readouts are made by 334 photomultiplier tubes coupled to BBQ doped wavelength shifter bars which integrate the entire depth of the detector. It is relatively straightforward to increase the number of readouts to include longitudinal segmentation and to increase the segmentation of the outer region which are at present read out two strips to a readout. The energy and position resolutions of isolated showers are about and 3 mm., respectively. The SLIC has been used to study the K⁻π⁺π⁰ decay of the D⁰ [1], as well as for electron and muon identification in ψ → e⁺e⁻ and ψ → μ⁺μ⁻ plus π⁰ identification in γp → ψχ [8].     

An electron diffraction study of the ZnIn2Se4 crystal structure: A novel phase

A novel layered-structure ZnIn₂Se₄ phase has been obtained. Texture electron diffraction patterns aid in the identification of a crystal structure with lattice parameters a = 4.045 Å and c = 52.29 Å, space group R m, and z = 4.5. Crystal electron diffraction patterns displayed superstructural reflection, thus indicating a √3-fold increase in the a parameter. The similirity of reflection locations and intensities both on the crystal rotation electron diffraction pattern and on texture electron diffraction patterns showed that no phase transition occurred on specimen pounding. Electrophysical and optical parameters (E_g = 1.68 eV; N = 8 × 10²² m^-3; = 0.1Ωm) are studied at 300 K. The Hall coefficient is constant (R_H = 7.2 × 10^-5m³C^-1, mobility μ = 8 × 10^-3m²V^-1s^-1 at 200–300 K.     

The Indiana silicon sphere 4π charged-particle detector array

A low threshold charged particle detector array for the study of fragmentation processes in light-ion-induced reactions has been constructed and successfully implemented at the IUCF and Saturne II accelerators. The array consists of 162-triple-element detector telescopes mounted in a spherical geometry and covering 74% of 4π in solid angle. Telescope elements are composed of (1) an axial-field gas ionization chamber operated with C₃F₈ gas; (2) a 0.5 mm thick passivated silicon detector, and (3) a 2.8 cm thick CsI(Tl) scintillation crystal with photodiode readout. Discrete element identification is obtained for ejectiles up to Z 16 over the dynamic range 0.7 ≤ E/A ≤ 95 MeV/nucleon. Isotopes are also distinguished for H, He, Li and Be ejectiles with 8 E/A 95 MeV. Custom-designed electronics are employed for bias supplies and linear signal processing. Data are acquired via a CAMAC/VME/Ethernet system.     

Development of a momentum determined electron beam in the 1–45 GeV range

A beam line for electrons with energies in the range of 1–45 GeV, low contamination of hadrons and muons and high intensity up to 10⁶ per accelerator spill at 27 GeV was setup at U70 accelerator in Protvino, Russia. A beam tagging system based on drift chambers with 160 μm resolution was able to measure relative electron beam momentum precisely. The resolution σ_p/p was 0.13% at 45 GeV where multiple scattering is negligible. This test beam setup provided a possibility to study properties of lead tungstate crystals (PbWO₄) for the BTeV experiment at Fermilab.     

High concentration erbium doping of silicon-rich SiO2 thin films on silicon

In this work, high concentration erbium doping in silicon-rich SiO₂ thin films is demonstrated. Si plus Er dual-implanted thermal SiO₂ thin films on Si substrates have been fabricated by using a new method, the metal vapor vacuum arc ion source implantation with relatively low ion energy, strong flux and very high dose. X-Ray photoelectron spectroscopy measurement shows that very high Er concentrations on the surfaces of the samples, corresponding to 10 at.% or the doping level of 10²¹ atoms cm⁻³, are achieved. This value is much higher than that obtained by using other fabrication methods such as the high-energy ion implantation and molecular beam epitaxy. Reflective high-energy electron diffraction, atomic force microscopy and cross-section high-resolution transmission electron microscopy observations show that the excess Si atoms in SiO₂ matrix accumulate to form Si clusters and then crystallize gradually into Si nanoparticles embedded in SiO₂ films during dual-ion implantation followed by rapid thermal annealing. Er segregation and precipitates are not formed. Photoluminescence at the wavelength of 1.54 μm exhibits very weak temperature dependence due to the introduction of Si nanocrystals into the SiO₂ matrix. The 1.54-μm light emission signals from annealed samples decrease by less than a factor of 2 when the measuring temperature increases from 77 K to room temperature.     

TRASMA, a detector for γ-charged particle coincidences

An apparatus for detecting light and heavy fragments, in coincidence with γ-rays is described. Its use is foreseen for studying heavy ion complete and incomplete fusion reactions at low and intermediate energy.

The ΔE-E and TOF techniques are used for charged particle identification at small angles using a combination of Si strip detectors and CsI(Tl) crystals. The γ-ray detection is performed by using a coverage of 9 clusters, each consisting of 7 BaF₂ crystals, similar to the TAPS configuration, resulting in a large solid angle and a high granularity. We report on recent results about the charged particle discrimination and the time and energy resolution for the whole detector. Initial tests were performed using ¹²C, ¹⁹F and ²⁸Si beams accelerated by the 15 MV tandem of the Laboratorio Nazionale del Sud in Catania.     

Pulsed high energy density plasma processing silicon surface

Pulsed high energy density plasma (PHEDP) is a new material modification technique, which has the features of: high energy density (1–10 J/cm²), high plasma density (10¹⁴–10¹⁶ cm⁻³), high electron temperature (10–100 eV), high directed plasma velocity (10–100 km/s) and short pulse duration (10–100 μs). PHEDP interacting with material will result in rapid melting and re-solidification of surface layer with a quenching rate up to 10⁸ K/s; thus the material surface properties are modified. At the same time, PHEDP contains condensable ions or/and atoms, so a thin film layer can be formed on the modified surface and the deposited layer can be mixed with the substrate (or previous deposited layer) during following pulses. Therefore, this technique actually combines film deposition and mixing into one step. In this paper, we have reported the research results on the metallization of Si by PHEDP. The Ti---Si reactions under PHEDP are also discussed.     

High impedance discrete delay-line readout circuit for silicon strip detector

A prototype 16-tap high impedance discrete delay-line readout circuit has been designed and fabricated for Si-strip detectors suitable for nuclear physics experiments involving moderate count rate applications. The delay-line offers a delay of 30 ns per tap with very good linearity. The energy resolution for -particles from ²⁴¹Am²³⁹Pu source is found to be satisfactory, when 16 strips are connected through the above readout circuit of a 32-strip Si-strip detector having a dead layer of 5 μm. This readout system is very useful where a large number of detectors are integrated in a compact space and accommodating their readout electronics is a cumbersome task.     

Design, fabrication and optical characterization of cerium oxide-magnesium fluoride double layer antireflection coatings on monocrystalline silicon substrates

Theoretical and experimental studies of a double layer antireflection coating deposited onto silicon wafers have been carried out. Magnesium oxide and cerium oxide fabricated by physical vapor deposition method have been applied as low- and high-refractive index materials. MgF₂–CeO₂–Si structures exhibited the reflectivity below 3% in the wavelength window from 0.5 μm to 1.2 μm. Theoretical simulations of spectral characteristics of the reflectivity of these coatings have been performed. A good correlation between experimental data and theoretical curves has been observed with the assumption that a thin SiO₂ layer of a thickness of 16 nm is formed onto Si substrates.     

VIKING, a CMOS low noise monolithic 128 channel frontend for Si-strip detector readout

A low noise Si-strip detector readout chip has been designed and built in 1.5 μm CMOS technology. The chip is optimized w.r.t. noise. Measurements with this chip connected to several silicon strip detectors are presented. A noise performance of ENC = 135 e⁻ + 12 e⁻/pF and signal to noise ratios between 40–80, depending on the detector, for minimum ionizing particles traversing silicon has been achieved.