[en] The measured space point resolution of a D0 Muon Chamber is /+-/0.31 mm perpendicular to the anode wire and 2.7 mm parallel to the wire. A voltage change of 1 kV, which changes the gas gain by a factor of 50, only causes a change of drift velocity of 12%. Tracks inclined of 45/degree/ have a resolution worse than those of 0/degree/ by a factor 3 /+-/ 2. A change in gas composition from CO₂(10%) to CO₂(11%) decreases the gas gain by 17 /+-/ 5%, and decreases drift velocity by 0.2 /+-/ 0.2%. The effect of an oxygen contamination of 3200 ppM is to change the mean pulse height by 45% over the 5 cm width of the cell. 4 refs., 15 figs

[en] Typical gases which are stock at Fermilab are Ar:C₂H₆(50:50) and Ar:CO₂ (80:20). Argon:Ethane has the virtue of high gas gain and a saturated drift velocity. In fact, parametrizing the drift velocity as a function of electric field we find v/sub d/(E) = v/sub o/(1/minus/e/sup -E/E/o) with v/sub o/ ≅ 5.4 cm/μsec and E/sub o/ = 160 V/cm. However, safety considerations make this gas somewhat inconvenient. The addition of alcohol as quencher also raises the saturation field to, for example, E/sub o/ ≅ 500 V/cm for 1.5% added alcohol. This gas also tends to break up in a high-beam flux environment and leave carbon deposits. The addition of alcohol to avoid such aging often takes a unit cell out of saturation over its entire volume. Finally, for collider applications it is useful to exclude free protons from the gas in order to reduce the sensitivity to the sea of slow neutrons which are present in the collider environment. In contrast, Ar:CO₂ (80:20) is a gas with more moderate gas gain. The drift velocity at high field is v/sub d/(E > 1.5 kV/cm) ≅ 5.8 cm/μsec. For most field configurations this gas does not saturate, causing a long tail in the drift time distrubtion due to low field regions in the unit cell. The virtues of this gas mixture are that it is cheap, not flammable, and stable under high-beam flux. However as the Collider Upgrade progresses, we wish to find a gas which is faster than 5.0 cm/μsec since the time separation between collisions will at some point be less than drift time of 1μsec for drift distance of 5 cm. 3 refs., 5 figs

[en] Short communication

No abstract available

[en] To analyze the surface of polymers using positron-annihilation lifetime spectroscopy (PALS), a pulsed slow-positron beam system having both a high pulsing efficiency and a good time resolution is now under development. The time resolution, which is defined by the full width at half maximum (FWHM), and the pulsing efficiency of this system were achieved to be 0.54 ns and 50%, respectively. The lifetime of ortho-positronium (o-Ps) in low-density polyethylene (LDPE), obtained by PALS using our new pulsing system, agreed with that obtained by a conventional PALS.

[en] A system consisting of a superconducting solenoid, a multi-ring trap and a slow positron source has been built to prepare a cold highly charged ion (HCI) beam, which will be applied to study interactions with solids or gases, e.g. potential energy deposition scheme during interaction of slow HCIs with a surface. An electron plasma with density more than 10¹⁰ cm^-3 has already been prepared to trap positrons

[en] We report on the current status of a project to develop a dedicated superconducting accelerator for slow positron production at AIST. Two 500 MHz 5 cell cavities will form the basis of the new accelerator. Initial set-up and preliminary design activities are reported. (author)

[en] Positron annihilation techniques including the positron annihilation lifetime spectroscopy (PALS) and Doppler broadening of the positron annihilation radiation (DBPR) have been applied to study characteristics of various materials. For example, PALS has been applied to the detection of free volumes in polymers. The positron source commonly used for PALS is ²²Na. γ-rays of 1.275 MeV are emitted from ²²Na almost simultaneously with positrons. These γ-rays indicate the emission of positrons and are used as start signals in PALS. The positron annihilation γ-rays of 0.511 MeV are used for stop signals. The time interval between these two γ-rays is considered to be the positron lifetime. The positrons emitted from ²²Na have continuous energy distribution from 0 to 0.54 MeV (the average energy is ∼0.22 MeV) , and if they are used directly for PALS, only the bulk information of a specimen is obtained (this PALS is referred to conventional method). In order to study depth-dependent characteristics near the surface of polymers using PALS, a system for pulsing slow positrons is under development in our group. Since the energy of the slow positrons can be varied, material characterization become possible by PALS at an arbitrary depth near the surface, e.g. 10 nm to 0.7 μm at energy regions from 0.2 to 10 keV for polymer. The present paper reports the status of our pulsing system and the preliminary experimental results using the slow-positron beam for a 50 nm iron deposited on polytetrafluoroethylene (PTFE) substrate. (author)

[en] Silicon-oxide-backboned hybrid thin films with thicknesses around 600 nm were fabricated through plasma enhanced chemical vapor deposition from tetraethyl orthosilicate mixed with hexamethyldisiloxane as precursors, and their subnano-scaled holes, generated by annealing at 560 °C, were investigated by means of the positron lifetime technique with a pulsed, low-energy positron beam. The hole dimension was quantified from the ortho-positronium lifetime for the as-prepared and annealed films with different compositions. The effect of the heat treatment and the precursor composition on the subnano holes was discussed.

[en] Positron annihilation with a slow positron beam was applied to the characterization of composite reverse osmosis membranes. The results, obtained at different positron incident energies, indicated that the membranes are asymmetric with respect to the pore structure, consisting of a thin top layer with little porosity and an underlying thick porous layer. A relationship between the longest positron lifetime near the membrane surface and the salt rejection rate was discussed in terms of the free-volume hole size for the thin top layer.