Parallel Plate Avalanche Detector Research Articles

EMIL: Advanced emission Mössbauer spectrometer for measurements in versatile conditions

The current work presents a contemporary design of an advanced emission Mössbauer Spectrometer: eMIL equipped with a parallel-plate avalanche detector, which has been devised and built for the Mössbauer collaboration at ISOLDE/CERN. The setup is based on emission geometry, combined with on-line/off-line isotope implantation and provides numerous advantages over conversion electron, common emission (where isotope is deposited chemically on a sample) or transmission Mössbauer spectroscopy. eMIL is designed to measure hyperfine interactions in solids under various exposures. The implemented design overcomes limitations and improves performance and handling. In the current revision, the chamber is supplied with an UV extension — allowing to perform studies of photo-catalytic materials under external light exposure. A specifically designed motorized lid-samples-holder is fully automatized, and makes it possible to study up to 4 samples loaded in a magazine within a temperature range from RT up to 1100 K and to perform angular dependent measurements in high vacuum. This work additionally briefly describes data acquisition with additional electronic blocks, vacuum and data-acquisition system construction.

SOME CHARACTERISTICS AND APPLICATIONS OF PARALLEL PLATE AVALANCHE DETECTORS (A REVIEW)

Parallel plate avalanche detectors (PPADs) are new gas detectors and are being extensively used to detect heavy ions, fission fragments and minimum ionizing particles. Due to their excellent timing characteristics and low cost, they are being widely used in different areas of science and technology, particularly as start and stop detectors in different experiments. These detectors are ideal for coincidence measurements and for photofission studies. Different characteristics; construction operation, performance, time resolution, energy resolution and experimental techniques based on PPADs are reviewed in this paper.

Fiasco: a multidetector optimized for semiperipheral heavy ion collisions at Fermi energies

The Fiasco multidetector is a low-threshold apparatus, optimized for the investigation of peripheral to semi-central collisions in heavy ion reactions at Fermi energies. It consists of three types of detectors. The first detector layer is a shell of 24 position-sensitive Parallel Plate Avalanche Detectors (PPADs), covering about 70% of the forward hemisphere, which measure the velocity vectors of the heavy (Z≳10) reaction products. Below and around the grazing angle, behind the most forward PPADs, there are 96 ΔE–E silicon telescopes (with thickness of 200 and 500μm, respectively); they are mainly used to measure the energy of the projectile-like fragment and to identify its charge and, via the time-of-flight of the PPADs, also its mass. Finally, behind most of the PPADs there are 158 (or 182, depending on the configuration) scintillation detectors, mostly of the phoswich type, which cover 25–30% of the forward hemisphere; they identify both light charged particles (Z=1,2) and intermediate mass fragments (3⩽Z≲20), measuring also their time-of-flight.

Photofission of heavy nuclei from 0.2 to 3.8 GeV

Total photofission cross sections for ${}^{237}\mathrm{Np},$ ${}^{233}\mathrm{U},$ ${}^{235}\mathrm{U},$ ${}^{238}\mathrm{U},$ ${}^{232}\mathrm{Th},$ and ${}^{\mathrm{nat}}\mathrm{Pb}$ have been measured simultaneously, using tagged photons in the energy range ${E}_{\ensuremath{\gamma}}=0.17--3.84 \mathrm{GeV}$ in Hall B at Jefferson Lab. The fission fragments were detected using parallel-plate avalanche detectors. Our results show that, of these nuclei, ${}^{237}\mathrm{Np}$ has the largest photofission cross section per nucleon, and that the photofission cross section for ${}^{238}\mathrm{U}$ relative to that for ${}^{237}\mathrm{Np}$ is about 80% over the entire energy range. The relative photofission cross sections per nucleon increase with the fissility parameter ${Z}^{2}/A,$ approaching an apparent asymptote at the ${Z}^{2}/A$ value for ${}^{237}\mathrm{Np},$ and they do not depend strongly on the incident photon energy over this entire energy range. These results, together with a comparison of the ${}^{237}\mathrm{Np}$ photofission cross section per nucleon with total photoabsorption data, indicate that the photofission probability for ${}^{237}\mathrm{Np}$ is almost unity. If we make this assumption, we observe a significant shadowing of the interior nucleons starting below 1.5 GeV, so that the photoabsorption cross section decreases by 20% near 4 GeV.

Parallel-plate avalanche detectors with anode wire grids

A fission-fragment detection system was designed and built at The George Washington University, to be used in photofission experiments at the Saskatchewan Accelerator Laboratory and the Jefferson Laboratory. The fission fragments were detected using parallel-plate avalanche detectors with anode wire grids. An array of several target–detector pairs was mounted inside a low-pressure reaction chamber. The results of calibrations of the detectors using a 252Cf source and their performance with a bremsstrahlung photon beam during the experiments are presented.

Photofission of actinide nuclei in the quasideuteron and lower part of theΔenergy region

The total photofission cross sections for the actinide nuclei ${}^{232}\mathrm{Th},$ ${}^{233}\mathrm{U},$ ${}^{235}\mathrm{U},$ ${}^{238}\mathrm{U},$ and ${}^{237}\mathrm{Np}$ have been measured from 68 to 264 MeV using tagged photons at the Saskatchewan Accelerator Laboratory. The fission fragments were detected using parallel-plate avalanche detectors. The results show that the fission probability for ${}^{238}\mathrm{U}$ is 20% lower than that for ${}^{237}\mathrm{Np}$ and 40% higher than that for ${}^{232}\mathrm{Th}.$ Less significant differences were also found among the individual uranium isotopes. These results contradict the assumption that the fission probability for ${}^{238}\mathrm{U}$ is approximately equal to unity in this energy range. It has also been observed that the fission probability as a function of energy for all these isotopes is constant, with the exception of that for ${}^{232}\mathrm{Th},$ which increases with energy, although it seems to be reaching a saturation value. Comparison between the total photofission cross section for ${}^{237}\mathrm{Np}$ and the photoabsorption cross sections for lighter nuclei shows a behavior consistent with a broadening of the $\ensuremath{\Delta}$ resonance with increasing atomic mass.

Photofissility of 232Th measured with tagged photons from 250 to 1200 MeV.

The photofission cross section of [sup 232]Th was measured in the energy range 250--1200 MeV using a monochromatic tagged photon beam and a parallel-plate avalanche detector. The [sup 232]Th nuclear photofissility was obtained by measuring simultaneously and in the same energy range the photofission cross section of [sup 238]U and assuming a photofissility equal to one for [sup 238]U. It was found that, contrary to the case for heavier actinides, the [sup 232]Th photofissility value does not saturate up to 1200 MeV. Rather, it lies between 0.6 and 0.8, and shows a weak energy dependence: it increases by about 15% over an interval of 1 GeV. A comparison of these experimental findings with the predictions of an intranuclear-cascade Monte Carlo calculation is given.

X-ray-absorption studies of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O films at oxygen K edge by means of fluorescence and total electron yield: A comparison of two techniques.

X-ray fluorescence and total electron yield around the oxygen K edge of high-${\mathit{T}}_{\mathit{c}}$ Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O superconductor films were measured. The oxygen fluorescence spectra in these materials were obtained by using a new parallel-plate avalanche detector and a high-resolution soft-x-ray spectrometer. Comparison of the fluorescence results with total electron yield and with other data indicates that the fluorescence method is free from spurious features caused by contaminants and oxygen-depletion layers, as usually found in the electron-spectroscopy measurements, and that meaningful information on photoexcitation of core electrons at the oxygen sites can be readily obtained by these bulk-sensitive measurements.

A novel type of depth-selective Auger electron Mössbauer spectroscopy

The utility of parallel-plate avalanche detectors for depth-selective Auger electron Mossbauer spectroscopy is demonstrated for the 24 keV transition of119Sn. Possible developments and applications of this technique to other Mossbauer isotopes are discussed.

Muon capture rates in233U,234U,235U,236U,238U, and237Np

The time spectra for muon induced fission of233U,234U,235U,236U,238U, and237Np were measured simultaneously, detecting both fragments in coincidence in a fast multi parallel plate avalanche detector. The observed mean lifetimes τ are 68.9 ± 0.3 ns, 70.6 ± 0.2 ns, 72.2 ±0.2 ns, 74.3 ± 0.3 ns, 77.0 ±0.4 ns, and 69.8 ±0.2 ns for the above isotopes, respectively. No second time component, tentatively ascribed to a possible fission isomer, was observed. The deduced total capture rates are compared with theoretical predictions.

A parallel plate avalanche detector system for the localization of relativistic heavy ions

Parallel plate avalanche counters have been designed and used for localization of relativistic heavy ions. They have been tested alpha particles from a 241Am source. They have been used with the heavy-ion beams from Saturne in conjunction with the 4 π detector Diogene. They provide an accurate measurement of the vertex position with eficiency.

Absolute photofission cross sections for 232Th and 235,238U measured with monochromatic tagged photons (20 Mev < Eγ < 110 Mev)

Abstract The absolute photofission cross sections for 232 Th and 235, 238 U has been studied from 20 to 110 MeV using the photon tagging technique at the Saclay linear electron accelerator (ALS). The fission fragments were directly detected using a parallel plate avalanche detector (PPAD). The basic experimental results are a set of data giving σ ( E γ , fission). These results are compared with the few other measurements performed with monochromatic photons. From a comparison of the present fission data with the total absorption cross section, the total fission probability was deduced. The behaviour of this probability was discussed in terms of a cascade model for fission-evaporation competition. Quite good agreement is found with a calculation based on the hybrid model of pre-equilibrium reactions.

Relaxation of the mass-asymmetry degree of freedom in heavy-ion reactions.

The $^{58}\mathrm{Ni}$+$^{165}\mathrm{Ho}$ reaction has been studied at 5.9 and 6.5 MeV per nucleon (reverse kinematics). Coincident reaction fragments were detected with two position-sensitive parallel plate avalanche detectors. Correlations between energy, mass, and angle show that a small fraction of the events have fully relaxed kinetic energies, masses intermediate between those of the projectile (target) and symmetric fragmentation, and angular distributions with a marked forward-backward asymmetry.

A position-sensitive particle detector with a meander-type delay line

A position-sensitive parallel plate avalanche detector with delay-line readout is described. The delay line is formed by two mutually shifted bent meanders. The characteristics of the operation are discussed. The position resolution is found to be 2 mm in accordance with the chosen geometry and the energy resolution is about 25%. Possible applications and ways for further developments are presented.

Measurement of the total cross section for 235U and 238U photofission in the δ-resonance region

The total cross section for the photoemission of fission fragments σ(γ, F) has been measured for 235U and 238U using tagged bremsstrahlung photons in the energy range 120–460 MeV. The fission fragments were detected in parallel plate avalanche detectors. The results are compared with other information on the photonuclear absorption cross section.

Arrangements of parallel plate avalanche detectors for electrofission and photofission experiments

The construction and performance of several arrangements of parallel plate avalanche detectors are described. The set ups can be used for the measurement of: fragment time of flight, photofission cross sections, out of plane angular distributions, inclusive and exclusive electrofission cross sections. First results are discussed, demonstrating the wide field of applicabilities of these detectors.

Test and performance of position sensitive parallel plate avalanche detectors in heavy-ion kinematic coincidence measurements

Two-dimensional position sensitive parallel plate avalanche counters (PPAC) with an active area of 6 × 16 cm 2 were built and used in particle-particle-gamma coincidence experiments with heavy ions. The performance of the detector and of a kinematical coincidence set-up with two detectors is described. The position resolution in the x and y coordinates is Δx=1 mm and Δy=5 mm. A time resolution of Δt=150 ps has been achieved in the case of elastic scattering of 5–10 MeV/u 86Kr from different targets.

The use of large area-detectors in heavy ion collisions at intermediate energies

For the exclusive investigation of 12C and 18O induced reactions at 84 MeV/u a set of three large area detectors has been developed, which allows to detect light particles and nuclear fragments over a large range in masses and energies. For this purpose a new type of parallel-plate avalanche detector has been constructed. Results on the determination of the average impact parameters for different event types and on the angular correlations between projectile fragments and light particles emitted from the target will be presented.

The preparation of large area uranium target layers for a multiple parallel plate fission detector

Abstract The preparation of large area uranium layers (diameter 65 mm) with a thickness of 2–3 mg/cm 2 by electrolysis on Al foils is described. The layers are used in a multiple parallel plate avalanche detector with 30 counter gaps for photofission experiments. The performances and applications of this detector set-up are discussed.

A position sensitive parallel plate avalanche fission detector for use in particle induced fission coincidence measurements

A parallel plate avalanche detector developed for the detection of fission fragments in particle induced fission reactions is described. The active area is 6 × 10 cm 2; it is position sensitive in one dimension with a resolution of 2.5 mm. The detector can withstand a count rate of 25 000 fission fragments s −1.