Fast Timing Detectors Research Articles

Heavy particle timing and imaging with low-pressure MWPCs

MWPCs operated at gas pressures around 1 Torr are shown to have excellent timing and position response for heavily ionizing particles. The avalanche growth process at such conditions is of a double-step nature and is characterized by fast collection times of electrons and positive ions. A substantial spatial distribution of the avalanche (1–2 mm fwhm) leads to an excellent position resolution even when interpolating between neighbouring wires. Very thin (100–200 φg/cm 2 of polypropylene), fast timing and position-sensitive detectors are providing time resolutions of the order of 100–130 ps (fwhm), and position resolutions, with delay-line read-out, of the order of 100 φm (fwhm). Various detectors of this type, with sizes reaching 80 cm 2, operating at counting rates up to 10 5 c/s·mm 2, are used as routine tools for timing and imaging of heavily ionizing particles.

Half-life measurements of excited levels in the nanosecond and microsecond region

The application of the delayed-coincidence technique to accurate half-life measurements of excited levels in the nanosecond and microsecond region is described. In order to achieve an overall uncertainty of ⩽ 1% on the final values of the half lives a series of precautions depending on the time region have to be taken. In the nanosecond time range the most serious sources of errors are jitter, walk and drift phenomena. To minimize those the time pickoff has to be defined carefully by means of modern fast timing detectors and electronics. In the microsecond time range the ratio of true delayed coincidences to chance coincidences influences considerably the final accuracy of the half-life measurements. It must be the aim to reduce the chance-coincidence rate as much as possible. In both cases the analysis of the experimental data is of critical importance. The choice of the analysis region will be discussed. Time calibration and a careful consideration of system linearity, short- and long-term stability of the entire experimental system, are of great importance. Regular checks of these quantities performed during the measurements cycles allow estimates of the systematic uncertainties. The successful application of the experimental procedures mentioned above yielded the following half-life values for the 37.1-keV level in 121Sb (3.46 ± 0.03) ns, the 81-keV level in 133Cs (6.23 ± 0.03)ns, the 482.18-keV level in 181Ta (6.05 ± .012) μs 23.87-keV level in 119Sn (18.03 ± 0.07)ns, the 6.21-keV levelin 181Ta (6.05 ± 0.12) μs and the 615.25-keV level in 181Ta (17.64 ± 0.14) μs.