A sectorised ionisation chamber: The MEΩ detection system

A detection system consisting of a sectorised ionisation chamber coupled with parallel plate avalanche counters and plastic scintillator telescopes is described. The active area is 120 cm² corresponding to angular apertures of 30° in plane and ±1° out of plane (experimental configuration). The sectorisation allows both an improved counting rate capability of the detector and a great versatility in its use. The addition of plastic scintillators in the rear part of the detector permits to enlarge the dynamic range of the charge measurement up to energetic light charged particles. A radial grid (θ grid) gives a precise in plane localisation (0.1°) while drift time measurement allows the determination of the out of plane coordinate. The energy resolution of the ionisation chamber is 1% for 120 MeV ³²S and the energy loss resolution is 3–5% depending on the anode section considered. The charge resolution is therefore better than 1.8%.     

Timing properties of transmission avalanche counters at moderate specific ionization

The subject of investigation is a large-area parallel plate avalanche counter (PPAC). The counter timing properties when detecting α-particles of low energy are analyzed at n-heptane vapour pressures ranging from 5 to 30 Torr. Under typical measurement conditions, a time resolution of 380 ps has been achieved at these pressures; there is no evidence for further improvement at higher pressures. Considered are the TOF test setup efficiency and the electron drift velocity in n-heptane under relatively high electric fields. Besides, the variability of the basic physical processes contributing to the detection is evaluated and the effect of the fine energy structure of the divergently emitted α-particles upon the PPAC actual time resolution is investigated. A large dynamic range of the PPAC energy resolution was noticed; the contributions of individual side effects to the detector timing properties are evaluated.The empirical relations resulting from the investigation lead to a safe method of estimating the plateau width on the time resolution curve of transmission avalanche counters.     

The test measurements of TOF in small and large scintillation counters

We tested the time resolution of “small” scintillation counters (0.8 (height) × 2.6 (width) cm² and 0.7 (height) × 2.1 (width) cm², with 1.0 cm thickness) and of a “large” counter (21 (height) × 96 (width) cm² with 2 cm thickness). The time walk correction using software (off-line) was compared with that using hardware (constant fraction discriminator). It was found that the two methods gave nearly equal time resolution. Intrinsic time resolutions of 155 and 370 ps fwhm were obtained for the small and the large counters, respectively.     

The argus time-of-flight system

The time-of-flight system of the ARGUS detector at the DORIS e⁺e^? storage ring consists of 64 barrel scintillation counters covering 75% of 4π, and 2 × 48 end cap counters, covering 17% of 4π. The barrel counters are viewed by two phototubes each, while the end cap counters have one tube only. The time-of-flight system serves as a part of the fast trigger and identifies charged particles. The time resolution achieved during the first year of ARGUS operation is 210 ps for Bhabhas (which are used for the off-line monitoring of the system), and 220 ps for hadrons, both in barrel and end cap counters. This converts into a three standard deviation mass separation up to 700 MeV/c between pions and kaons and 1200 MeV/c between kaons and protons. Electrons can be separated from heavier particles up to 230 MeV/c.     

A detection system for energetic light heavy ions

A light heavy ion detection system which consists of a gas-filled ionization chamber (IC) connected to a scattering chamber via a time-of-flight (TOF) system has been constructed. The entrance window of the IC has an area of 14 × 40 cm², the active depth is 115 cm. Filled with CF₄ at a pressure of 350 Torr, the energy range for ¹²C and ⁴⁰Ar is 5–20 MeV/A and 6–30 MeV/A, respectively. The TOF system consists of two parallel plate avalanche counters with a flightpath of 70 cm in between. The IC has been tested with ¹²C ions at an energy of 39 MeV. The energy resolution of the IC (1.1%) is mainly determined by the energy straggling in the foils of the TOF system and the ionization chamber. The energy-loss resolution is 3.5%, the horizontal position resolution varies between 6 and 20 mm and the vertical position resolution is 2 mm. The time resolution of the TOF system ranges from 800 ps for ⁴He at 5.0 MeV, to 280 ps for ²⁸Si at 55 MeV.     

Photon number resolving in geiger mode avalanche photodiode photon counters

Abstract

The paper reports on research and development in the field of avalanche photodiodes operated as photon counters in a Geiger mode. A technique has been developed and tested that permits estimation of the photon number involved in a detection process. It can be applied in a time correlated photon counting experiment simultaneously with original required time interval estimation. A time walk compensation circuit provides uniform electrical pulses, and the time interval between them is related to the number of photons detected. Employing a picosecond event timing device, the photon number can be estimated within the dynamic range 1–1000 photons with resolution better than a factor of three.     

Development of a moderating type higher sensitive rem counter using 6Li glass scintillator

A moderating type higher sensitive neutron rem counter was constructed using grains of ⁶Li glass scintillator. The sensitivity of this counter is about 3.9 cps/(μSv/h), which is approximately 10 times higher than that of the commonly used rem counters and could be successfully applied for neutron monitoring both in the reactor room and the natural environment aided by the pulse-shape discrimination method.     

Application of air proportional counters to a tritium-in-air monitor

A tritium-in-air monitor using air proportional counters as a detector has been devised. The detector consists of two layers of identical multiwire counters, and it operates without using any counting gas other than sampled air. The background due to internal α-rays was eliminated by pulse-height discrimination, and that due to external, penetrating γ-rays and cosmic rays was evaluated from the coincidence counting rate of the two counters. The counting rate by tritium β-rays was obtained from the anticoincidence counting rate N_a by subtracting the product of the coincidence counting rate N_c and a constant ratio k = N_a/N_c for the background. The ratio k was verified to be independent of the intensity, energy and incident direction of the γ-rays, though it varied with pressure and humidity of the sampled air. A detection efficiency of about 14% was obtained for tritium β-rays, and a detection limit of less than 1 pCi/cm³ was obtained with a normal background level and a counting time of 30 s.     

Dopant concentration dependence of the response of SiC Schottky diodes to light ions

The responses of Silicon Carbide (SiC) Schottky diodes of different dopant concentration to ¹²C ions at 14.2, 28.1 and 37.6 MeV incident energies are compared. The relation between the applied reverse bias and the thickness of the depleted epitaxial region is studied for different dopant concentrations. The experimental data show that SiC diodes with lower dopant concentration need lower reverse bias to be depleted. Moreover it has been observed that the energy resolution, measured as a function of the applied reverse bias and of the ions incident energies, does not depend on the dopant concentration. The radiation damage, produced by irradiating SiC diodes of different dopant concentration with ¹⁶O ions at 35.2 MeV, was evaluated by measuring the degradation of both the signal pulse-height and the energy resolution as a function of the ¹⁶O fluence. Diodes having a factor 20 lower dopant concentration exhibit a radiation hardness reduced by 60%. No inversion in the signal at the breakdown fluence was observed for ¹⁶O ions stopped inside the diode epitaxial region.     

14 MHz rate photon counting with room temperature InGaAs/InP avalanche photodiodes

Abstract

We have developed high speed gated-mode single-photon counters based on InGaAs/InP avalanche photodiodes for use at 1.55 μm wavelength. Operation at room temperature allows afterpulse probability to be below 0.2% for gate rates up to 14 MHz. We obtained optimum noise-equivalent power of 2.2 ×s; 10^?15 W Hz^?1/2 at 14% quantum efficiency with dark-count probability of 0.2%. We propose a metric (noise-equivalent power divided by gate frequency) for comparing high speed photon counters and show that for this metric our system outperforms previously reported counters at 1.55 μm wavelength. We demonstrate that for gate widths of a nanosecond or below, the differing amplitude distributions of dark versus light counts allow an optimal decision threshold to be set for a given bias voltage.     

Detector physics and simulation of resistive plate chambers

We present a simulation model suited to study efficiency, timing and pulse-height spectra of Resistive Plate Chambers. After discussing the details of primary ionisation, avalanche multiplication, signal induction and frontend electronics, we apply the model to timing RPCs with time resolution down to 50 ps and trigger RPCs with time resolution of about 1 ns.     

High speed quantitative digital beta autoradiography using a multistep avalanche detector and an Apple II microcomputer

The development of an electronic, digital beta autoradiography system is described. Using a multistep avalanche/multiwire proportional counter (MSA/MWPC) detector system fitted with delay line readout, high speed digital imaging is demonstrated with submillimeter spatial resolution. In the case of autoradiography with a tritium label, image acquisition requires about one hour compared with several weeks for conventional film techniques. Good proportionality of observed counting rate relative to the known tritium activity is demonstrated. The application of the system to autoradiography in immunoelectrophoresis, histopathology and DNA sequencing is described (using ¹²⁵I, ¹⁴C and ³⁵S labels in addition to ³H).     

A three dimensionally position sensitive large area detector

A large area detector consisting of a parallel plate avalanche counter (PPAC) and a trapezohedral ionization chamber (TIC) is described. Its active area is 184 cm². The time resolution of the PPAC is 175 ps. The energy resolution of the TIC is 0.4%, the energy loss resolution 2.8%, the nuclear charge resolution 2.3%. The TIC is position sensitive in three dimensions. The position x is measured via a saw-tooth anode with a resolution of 0.7 mm; the drift time coordinate shows a resolution of δy ? mm. The range z is determined by a new technique, a graded density Frisch grid. It enlarges the dynamic range of the charge measurement down to the Bragg maximum at E/A ～ 1 MeV. The resolution is δZ/Z ? 3.5%     

Counting rate plateau of transmission proportional counters at low organic vapour pressure

The slope and width of the counting rate plateau of large-area transmission proportional counters filled with organic vapours commonly used in avalanche counters are the subject of an experimental analysis. The investigation was performed at vapour pressures ranging from 5 to 150 Torr, using low-energy α-particles and simple electronic systems. The results which were obtained with n-heptane over 5 to 30 Torr are compared to the performance of parallel plate avalanche counters used as elementary detecting devices for charged particles [1].     

Measurement of electromagnetic shower position and size with a saturated avalanche tube hodoscope and a fine grained scintillation hodoscope

A hodoscope has been constructed from 100 μm diameter wires and brass tubes (1.2 × 0.7 cm² cross section) filled with a mixture of argon, ethane and ethyl alcohol. It has been tested in the saturated avalanche mode in an SCG1-C electromagnetic shower detector to determine its properties for the measurement of the position and size of electromagnetic showers. Two of these tube hodoscopes were positioned 3.5 radiation lengths deep in the detector and the profiles of 1–25 GeV electromagnetic showers were measured. Simultaneous measurements were performed using a plane of twenty, 0.5 cm wide scintillation counters positioned immediately behind the gas tube hodoscope. In addition the transition between saturated avalanche and limited streamer modes was observed for the tube hodoscopes.     

Observation of the 3He(n,tp) Reaction by Detection of Far-Ultraviolet Radiation

We have detected Lyman alpha radiation, 121.6 nm light produced from the n = 2 to n = 1 transition in atomic hydrogen, as a product of the ³He(n, tp) nuclear reaction occurring in a cell of ³He gas. The predominant source of this radiation appears to be decay of the 2p state of tritium produced by charge transfer and excitation collisions with the background ³He gas. Under the experimental conditions reported here we find yields of tens of Lyman alpha photons for every neutron reaction. These results suggest a method of cold neutron detection that is complementary to existing technologies that use proportional counters. In particular, this approach may provide single neutron sensitivity with wide dynamic range capability, and a class of neutron detectors that are compact and operate at relatively low voltages.     

The endcap shower counters for the MARK III detector

We describe below the design, construction and performance of the end cap shower counters of the MARK III detector. These counters, made up of layers of aluminum proportional tubes sandwiched between lead sheets, achieve a position resolution for electrons or photons of about 7 mm × 9 mm using charge division for the position measurement along the wire direction. The energy resolution for fully contained electron and photon showers is $\text{σ}{}_{\mathrm{<mtext>E</mtext>}}\text{E}\text{=}\text{17\%}\text{√E}$. The counters are segmented into twelve individual readouts in depth, allowing the very good pattern recognition needed for the separation of nearby showers. The total depth of the counter, twelve radiation lengths, is adequate for the SPEAR energy range. Good photon detection efficiency extends to energies below 100 MeV.     

He and BF3 neutron detector pressure effect and model comparison

Radiation detection systems for homeland security applications must possess the capability of detecting both gamma rays and neutrons. The radiation portal monitor systems that are currently deployed use a plastic scintillator for detecting gamma rays and ³He gas-filled proportional counters for detecting neutrons. Proportional counters filled with ³He are the preferred neutron detectors for use in radiation portal monitor systems because ³He has a large neutron cross-section, is relatively insensitive to gamma-rays, is neither toxic nor corrosive, can withstand extreme environments, and can be operated at a lower voltage than some of the alternative proportional counters. The amount of ³He required for homeland security and science applications has depleted the world supply and there is no longer enough available to fill the demand. Thus, alternative neutron detectors are being explored.Two possible temporary solutions that could be utilized while a more permanent solution is being identified are reducing the ³He pressure in the proportional counters and using boron trifluoride gas-filled proportional counters. Reducing the amount of ³He required in each of the proportional counters would decrease the rate at which ³He is being used; not enough to solve the shortage, but perhaps enough to increase the amount of time available to find a working replacement. Boron trifluoride is not appropriate for all situations as these detectors are less sensitive than ³He, boron trifluoride gas is corrosive, and a much higher voltage is required than what is used with ³He detectors. Measurements of the neutron detection efficiency of ³He and boron trifluoride as a function of tube pressure were made. The experimental results were also used to validate models of the radiation portal monitor systems.     

Modeling of the signals of an optical particle counter for real nonspherical particles

An optical particle counter (OPC) was exposed to atmospheric particles of diameters of 200, 300, and 400 nm. The OPC data were combined with the results of single-particle analysis with a transmission electron microscope (TEM) on samples taken in parallel with the OPC measurements. With a T-matrix-based optical model the measured OPC spectra of scattered light pulses could be approximated with good precision. With an algorithm that simulated the response of the OPC to a given population of model particles derived from the TEM results, average absorption properties of different particle types were retrieved. For mobility sizes of 400 nm, higher light absorption was retrieved with the optical model for soot aggregates than for the rest of the morphological particle types. At smaller mobility sizes no compositional information could be derived from the model particles derived from the TEM data. Despite the limited success of the new methodology applied to the present experiment the results encourage the use of OPCs in combination with electrical mobility analyzers to derive more than aerosol-size distributions. With state-of-the-art pulse-height analysis the light-scattering pulses could be resolved with much finer resolution than in the instrument used.     

Test of a ring imaging Cherenkov counter

We have tested a ring imaging Cherenkov counter with readout of the projection chamber type. A specific detector response of N₀ = 80 cm^?1 was measured which corresponds to 8 photoelectrons per event in 1.60 m long nitrogen radiator. The resolution of the ring radius was measured to be Δr/r = 3.6%. The crosstalk between neighboring wires due to photons generated in the avalanche process was estimated to contribute up to 50% per hit. It was reduced considerably by inserting shielding walls between the wires and by adding C₂H₆ or iC₄H₁₀ to the CH₄-TMAE gas mixture.