Triple-coincidence technique

Frasinski et al. [15] devised a triple coincidence technique to study double ionization in the single photon regime. In these photoelectron-photoion-photoion coincidence experiments, the photoelectron provides the start pulse to an analogue-to-digital converter and the two ions the stop pulses and it was an easy matter to ensure that there was less than one molecular ion in the interaction region for the period of measurement of the ion energies, about 10 fis. In the multiphoton case, however, may ions are produced per laser pulse and this conventional approach cannot be employed. 

In 1989, Frasinski et al. [16] introduced a new triple coincidence technique called covariance mapping. A brief explanation of the technique can be given by considering again the process [N2 ]-+Nb and denoting by ti and... 

Dupre C, Lahmam-Bennani A and Duguet A 1991 About some experimental aspects of double and triple coincidence techniques to study electron Impact double Ionizing processes Meas. Sci. Technol. 2 327... 

Recent studies of SF of Cf with large y-ray detector arrays, Gammasphere (Lee 1990), revealed a new fission mode, cold fission with no neutron emission in the pair fragments of Zr-Ce and Mo-Ba (Ter-Akopian et al. 1994 Hamilton et al. 1995). Cold ternary SF, as Cf Ba + Sr -l- °Be, has also been identified by measuring the various y-transitions of these nuclei in coincidence (Ramayya et al. 1998). The use of the high-resolution triple y-coincidence technique can provide important information on very rare events in fission. 

Several approaches have been considered so far in order to tackle this problem where the Co prompt-peak interferes with the physical part of the positron lifetime spectrum [145-147]. Aside from the PLEPS technique, one acceptable solution seems to be a triple-coincidence method using a Na source [145,147]. In this case, three y rays - one with an energy of 1274keV and two with energies of 511 keV - accompany each event of positron annihilation, while only two y-rays result from the °Co decay. However, compared to conventional two-detector systems, the requirement for triple coincidence drastically reduces the rate of accumulation of positron lifetime spectra [145,148]. In comparison, PLEPS reduces the measuring time by a factor of 500 and also enables the estimation of the defect concentration. 

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