G. Sheffer

Tests of wire chamber ageing with CF/sub 4//isobutane (80.20), argon/ethane (50:50), and argon/ethane/CF/sub 4/ (48:48:4)

In a series of parallel tests the ageing characteristics of CF/sub 4/ isobutane (80:20), argon ethane (50:50), and argon ethane/CF/sub 4/ (48:48:4), have been investigated. Parameters such as flow rate, gas gain, anode wire current density and materials in contact with the gas stream have been varied. Some tests have been extended beyond 8 Coulomb/cm of wire. The Ar/Et chambers have shown a high incidence of pulse height degradation, dark currents, cathode foil etching, and deposits on the electrodes. A strong correlation between anode wire current density and rate of damage (%/C/cm) is indicated for Ar/Et chambers. The CF/sub 4//Iso chambers have shown effectively zero pulse height degradation and few other problems to accumulated charges exceeding 5 C/cm, except for one low-flow chamber with some cathode etching and cathode related pulse height degradation. The addition of 4% CF/sub 4/ to the Ar/Et mixture has dramatically improved the ageing performance of the Ar/Et/CF/sub 4/ cells. >

Wire chamber ageing with CF/sub 4//isobutane and argon/ethane mixtures

The ageing characteristics of CF/sub 4//isobutane (80:20) and argon/ethane (50:50) in identical test cells have been investigated. The gas gain and gas flow rate were varied and the measurements extended beyond 6 C/cm of wire. Study of a third gas mixture Ar/eth/CF/sub 4/ (48:48:4) is at an early stage. The Ar/eth mixture has shown a variety of problems including cathode foil etching, anode deposits, dark currents, and pulse-height degradation. In contrast the CF/sub 4//iso mixture produced some cathode etching for low flow velocities and only very minor anode deposits. With very little pulse-height degradation or dark current this mixture is a considered excellent candidate for a high-rate chamber. A small-area multiwire proportional chamber using this mixture has been evaluated in a pion beam with particle fluxes up to 3*10/sup 7/ particles/cm/sup 2/-s. >

Precision planar drift chambers and cradle for the TWIST muon decay spectrometer

To measure the muon decay parameters with high accuracy, we require an array of precision drift detector layers whose relative position is known with very high accuracy. This article describes the design, construction and performance of these detectors in the TWIST (TRIUMF Weak Interaction Symmetry Test) spectrometer.

Time expansion chamber system for characterization of TWIST low energy muon beams

A low-mass time expansion chamber (TEC) has been developed to measure distributions of position and angle of the TRIUMF low-energy surface muon beam used for the TRIUMF Weak Interaction Symmetry Test (TWIST) experiment. The experiment is a high-precision measurement of muon decay and is dominated by systematic uncertainties, including the stability, reproducibility, and characterization of the beam. The distributions measured by two TEC modules are one essential ingredient of an accurate simulation of TWIST. The uncertainties, which are extracted through comparisons of data and simulation, must be known to assess potential systematic uncertainties of the TWIST results. The design criteria, construction, alignment, calibration, and operation of the TEC system are discussed, including experiences from initial beam studies. A brief description of the use of TEC data in the TWIST simulation is also included.

Analysis of the readout of a high rate MWPC

Abstract An analytical method to reduce the raw data supplied by a high-speed multiwire proportional chamber (MWPC) is presented. The results obtained with the MWPC and the associated readout system, LeCroy PCOS III, when monitoring a high-intensity flux of positive pions delivered by the M11 channel at TRIUMF are discussed. The method allows the flux intensity, the beam envelope and the detector efficiency to be determined with little uncertainty (few %) at intense particle beams ( > 10 7 particles/s).

Drift chambers for a precision measurement of the Michel parameters in muon decay

Planar drift chambers will be used in a solenoidal magnetic field to measure the Michel parameters in muon decay. The chamber manufacture procedure uses flat glass tables and precise ceramic glass spacers to provide precise anode– cathode spacing. Results of bench and beam tests of the prototype chambers are discussed. # 2001 Elsevier Science B.V. All rights reserved.

Apparatus for a measurement of charge symmetry breaking in np→dπ0☆

Abstract TRIUMF experiment E704 is a study of Charge Symmetry Breaking in the reaction np→dπ 0 . The observable is the forward–backward asymmetry in the centre-of-mass differential cross-section, predicted to be −0.0035 at 5 MeV above threshold. As a check on the understanding of certain systematic effects the reaction pp→dπ + , which cannot have an asymmetry, is measured also. Similarly, neutron–proton elastic scattering is used to verify spectrometer acceptance. We describe the beams, target, and detectors developed for this experiment.

NEURAL - A tracking detector for neutron-induced reactions of astrophysical importance

Observations from gamma ray telescopes indicate that most of the galactic 26Al originates in massive stars. Several sites have been discussed for its production, including proton burning in the winds of very massive stars, and the later, explosive burning stages of these stars. Observations from the RHESSI and INTEGRAL missions currently seem to point to the latter scenario. In the advanced burning stages of massive stars the presence of neutrons becomes an important factor in nuclear reaction networks, so in addition to the 26Al(p,γ)27Si reaction the neutron capture reactions 26Al(n,p)26Mg and 26Al(n,α)23Na can lead to the destruction of 26Al, and thus alter the observed 26Al abundance. NEURAL is a detector design to measure the excitation functions of these reactions over a wide range of energies. 26Al targets implanted at TRIUMF will be exposed to a pulsed neutron beam at the neutron time-of-flight facility at LANSCE (Los Alamos Neutron Science CEnter). NEURAL is designed to detect all charged reaction products, combining a time projection chamber for the heavy ions, and Si detectors for the light particles mounted around the target. A first prototype has been built and partially tested at TRIUMF and LANSCE in December 2009.

The CF 4 /isobutane (80:20) gas mixture and high rate proportional chambers

In several laboratories there is considerable interest in developing proportional chambers that are able to operate at high rate and suffer minimal degradation over an extended period of operation. However, the causes of damage and degradation in these devices are still poorly understood. At TRIUMF we have a continuing program to study ageing effects. Using several identical single wire test cells, we have investigated the ageing characteristics of CF4/Isobutane (80:20), Argon/Ethane (80:20), and Argon/Ethane/CF4 (48:48:4) [1–3]. With our early results [1] showing a superior ageing performance of the CF4/Iso mixture, we decided to test a small admixture (4%) of CF4 to Ar/Et to see if it would inhibit damage. Parameters such as flow rate, gas gain, anode wire current density, and materials in contact with the gas stream have been varied. Some tests have been extended beyond 8 Coulomb/cm of wire. The Ar/Et chambers have shown a high incidence of pulse height degradation, dark currents, cathode foil etching, and deposits on the electrodes. A strong correlation between anode wire current density and rate of damage (%/C/cm) is indicated for Ar/Et chambers. The CF4/Iso chambers have shown effectively zero pulse height degradation and few other problems to accumulated charges exceeding 5 C/cm. The addition of 4% CF4 to the Ar/Et mixture has dramatically improved the ageing performance of the Ar/Et/CF4 cells.