[en] Using several identical test cells, the authors investigated the aging characteristics of CF/sub 4//Isobutane (80:20) and Argon/Ethane (50:50). The gas gain and gas flow rate were varied and the measurements extended beyond 6 Coulomb/cm of wire (C/cm). 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 an excellent candidate for a high rate chamber. A small area MWPC using this mixture has been evaluated in a pion beam with particle fluxes up to 3x10/sup 7/ particles/cm/sup 2/-sec

[en] Gas mixtures with high specific ionization allow the use of small interelectrode distances while still maintaining full efficiency. With the short electron drift distances the timing resolution is also improved. The authors have built and operated two 25 cm/sup 2/ chambers with small interelectrode distances. Also single wire detector cells have been built to test gas mixture lifetimes. Various admixtures of CF/sub 4/, DME, Isobutane, Ethane and Argon have been tested. Possible applications of such chambers are as beam profile monitors, position tagging of rare events and front end chambers in spectrometers

[en] Published in summary form only

[en] We have measured analyzing powers in d(rvec p,π^-pp)p at a beam energy of 400 MeV and laboratory pion detector angles of 35 degree and 43 degree. The π^- and two of the outgoing protons were detected in coincidence in a geometry which selected the quasifree two-body reaction pn→π^-pp(¹S₀). The analyzing-power data combined with ³He(π^-,pn)n differential cross sections allow determination of the transition amplitudes. The results indicate a significant contribution from a very short-range part of the nucleon-nucleon interaction

[en] In a series of parallel tests the aging characteristics of CF/sub 4//Isobutane (80:20), 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 aging performance of the Ar/Et/CF/sub 4/ cells

[en] The total inclusive (p,xn) charge exchange reaction cross section on bismuth from 62 to 800 MeV was measured using activation and radiochemical techniques. These data for products with as many as 14 neutrons removed from the coherent product display the simple E^-1 dependence of the total cross section with incident projectile energy. The distribution of charge exchange products is discussed in terms of quasifree processes in (p,n) reactions. A model comparison between the data and an intranuclear cascade calculation was satisfactory as evidenced by reproducing the energy dependence, cross section magnitude, and mass yields for products up to 14 neutrons removed. Better agreement between the model and data were obtained with mean-free paths of nucleons in nuclear matter twice as long as the one derived from nucleon-nucleon scattering

[en] The energy dependence of the total angle-integrated cross section for the production of astatine isotopes from (p,π^-xn) double charge exchange reactions on bismuth (²⁰⁹Bi) was measured from 120 to 800 MeV using activation and radiochemical techniques. Chemical yields were estimated by direct radioassaying of ²¹¹At activity in thin (approx.1 mg/cm²), irradiated bismuth targets. Calculations of the contributions of secondary (two-step) reactions to these measured astatine yields were performed, based partially upon the observed ²¹¹At activity although even at the highest energies, the contribution to products lighter than ²⁰⁷At was negligible. These data for products with as many as seven neutrons removed from the doubly coherent product (²¹⁰At) display nearly Gaussian shapes for the mass distributions of the astatine residues, with the maximum occurring for about ²⁰⁴At. The most probable momentum transfer deduced from these distributions for the initial π^- production step was 335 MeV/c. The observed excitation functions display a behavior similar to that observed for the yield of ²¹⁰Po from a (p,π⁰) reaction on ²⁰⁹Bi, but radically different from that observed for inclusive π^- reactions on a heavy nucleus. These data are discussed in terms of recent theoretical approaches to negative pion production from bismuth. In addition, a simple, schematic model is developed to treat the rapidly decreasing percentage of the total inclusive π^- emission which is observed for this double charge exchange reaction. This model reflects the opacity of a nucleus to a source of internal energetic protons

[en] The excitation function for the combined ²⁰⁹Bi(p,γ)²¹⁰Po and ²⁰⁹Bi(p,π⁰)²¹⁰Po reactions was measured for proton energies from 62 to 480 MeV. The measurements were made using standard radiochemical and residual α-counting techniques. Below pion-production threshold the radiative proton-capture cross section was observed to decrease with increasing proton energy. Above threshold the combined cross section increases to about 10 μb at 170 MeV. From a smooth extrapolation of the (p,γ) cross section to energies above pion-production threshold, an estimate of a cross section for the (p,π⁰) process is obtained. A theoretical fit of the summed total cross section into all particle bound states was made using a density of states factor, a two nucleon t matrix, and by taking into account the initial state (proton) and final state (pion) distortions using optical potentials

[en] 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 beam (>10⁷ particles/s). (orig.)

[en] TACTIC is a new detector for low-energy nuclear reactions currently under development at TRIUMF. The cylindrical ionization chamber allows three-dimensional reconstruction of particle tracks by means of a two-dimensional anode array combined with a TOF measurement of the drift electrons. In addition, the integrated charge for each pulse provides information about the energy loss of the particle and therefore allows a better identification of the nuclear species producing the track. The geometry of TACTIC covers a large angular range permitting the measurement of differential cross-sections over a large solid angle. It will be ideal for investigations of nuclear processes pertinent to the field of nuclear astrophysics. (orig.)