R. Henderson

Gamow-Teller strength observed in the 48Ti(n, p)48Sc reaction: Implications for the double beta decay of 48Ca

Abstract Cross sections for the 48 Ti(n, p) reaction have been measured at angles of 0°, 6°, and 12° at an energy of 200 MeV. The measurements are compared with results of DWIA calculations to obtain estimates of transition strengths for L = 0, 1, and ⩾2 up to an excitation energy of 25 MeV. Gamow-Teller strength ( L = 0) is peaked between 3 and 4 MeV excitation energy, with a significant distribution extending to about 12 MeV. The L = 1 strength is found mainly between 6 and 20 MeV while the cross section for transitions with L ⩾2 increases from 10 MeV to the upper limit of the measurements. The distribution of Gamow-Teller strength is in poor agreement with theoretical distributions used to calculate the lifetime for double beta decay of 48 Ca.

Etching of anode wire deposits with CF4/isobutane (80:20) avalanches

Abstract An ionization exposure of 0.5 C per cm of wire in a gas mixture of CF 4 /isobutane (80:20) is shown to reverse anode wire damage in single-wire chamb

The T2K fine-grained detectors

T2K is a long-baseline neutrino oscillation experiment searching for νe appearance in a νμ beam. The beam is produced at the J-PARC accelerator complex in Tokai, Japan, and the neutrinos are detected by the SuperKamiokande detector located 295 km away in Kamioka. A suite of near detectors (ND280) located 280 m downstream of the production target is used to characterize the components of the beam before they have had a chance to oscillate and to better understand various neutrino interactions on several nuclei. This paper describes the design and construction of two massive fine-grained detectors (FGDs) that serve as active targets in the ND280 tracker. One FGD is composed solely of scintillator bars while the other is partly scintillator and partly water. Each element of the FGDs is described, including the wavelength shifting fiber and Multi-Pixel Photon Counter used to collect the light signals, the readout electronics, and the calibration system. Initial tests and in situ results of the FGDs’ performance are also presented.

Measuring the (d,He-2) reaction with the focal-plane detection system of the BBS magnetic spectrometer at AGOR

At intermediate energies, the (d, He-2) charge-exchange reaction can be used to observe Gamow-Teller strength in the direction. He-2 denotes the two-proton system being in the singlet S-1(0) state. In the present experiment the two protons, which in the laboratory frame are emitted into the forward direction, have been momentum analyzed and detected in coincidence by the same spectrometer and detector. Protons from deuteron breakup processes can induce a large accidental coincidence background because of the much larger breakup cross-section as compared to the (d, He-2) cross-section. Nevertheless, background-free He-2 spectra with a resolution of 145 keV at an incident energy of 170 MeV are obtained, allowing the identification of many levels with high precision in the residual nuclei. The essential features of the detection system and the data-acquisition and analysis techniques which make our (d 2 He) experiments possible are described. Two nuclei, C-12 and Mg-24, have been used as a test case

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. >

A highly efficient polarimeter for the medium resolution spectrometer at TRIUMF

Abstract A polarimeter which uses inclusive scattering from carbon has been mounted after the focal plane of the TRIUMF medium resolution spectrometer. Four drift chambers measure scatterings at all azimuthal angles out to 20° in polar angle over a spectrometer momentum acceptance of ± 5%. A microprocessor rejects events with small scattering angles. The efficiency for 400 MeV protons is 4%, and for 295 MeV deuterons is 1.5%. Analyzing powers for protons are similar to those previously reported for polarimeters of this type.

Apparatus for a search for T-violating muon polarization in stopped-kaon decays

Abstract The detector built at KEK to search for T-violating transverse muon polarization in K + → π 0 μ + ν μ ( K μ 3 ) decay of stopped kaons is described. Sensitivity to the transverse polarization component is obtained from reconstruction of the decay plane by tracking the μ+ through a toroidal spectrometer and detecting the π0 in a segmented CsI(Tl) photon calorimeter. The muon polarization was obtained from the decay positron asymmetry of muons stopped in a polarimeter. The detector included features which minimized systematic errors while maintaining high acceptance.

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. >

A segmented target chamber for (n, p) studies at TRIUMF☆

Abstract We have developed an (n, p) target chamber consisting of six target layers sandwiched between seven gas detector layers. This target chamber is now commonly used with the new (n, p) facility at TRIUMF. With this arrangement, large total (n, p) target thicknesses (> 1 g/cm 2 ) can be used and yet the target contribution to overall energy resolution is moderate, typically less than 500 keV. The simultaneous accumulation of data from six target layers has proven to be highly advantageous with a number of applications, such as; (1) using multiple thicknesses of one target material, (2) including a target of known cross-section in the target stack for normalization, (3) adding a target to obtain simultaneous spectra for later subtraction of contamination lines and (4) the use of several target materials at once.

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.