Delayed coincidence

Rather sophisticated applications of Mossbauer spectroscopy have been developed for measurements of lifetimes. Adler et al. [37] determined the relaxation times for LS -HS fluctuation in a SCO compound by analysing the line shape of the Mossbauer spectra using a relaxation theory proposed by Blume [38]. A delayed coincidence technique was used to construct a special Mossbauer spectrometer for time-differential measurements as discussed in Chap. 19. 

W. Fichtner and W. Hacker, Time-resolution of Ge avalanche photodiodes operating as photon counters in delayed coincidence, Rev. Sci. Instrum. 47, 314-ill (1976). 

The second method uses pulsed lasers and the laser-induced fluorescence is detected by telescope. If the telescope and the laser source have a definite base distance, the crossing of laser beam and the acceptance angle of the telescope define the height of the atmospheric layer at which fluorescence is detected. There is also the technique of delayed coincidence, where the time interval between laser pulse and detected fluorescence pulse determines the distance of the observed molecules from the observer (Lidar)... 

Smith, A.J., Read, F.H. and Imhof, R.E. (1975). Measurement of the lifetimes of ionic excited states using the inelastic electron-photon delayed coincidence technique. J. Phys. B At. Mol. Phys. 8 2869-2879. 

Lifetimes of levels in Ra, Ac, and Ac have been measured by delayed coincidence techniques and these have been used to determine the El gamma-ray transition probabilities. The reduced El transition probabilities in Z25Ra and 225Ac are about two orders of magnitude larger than the values in mid-actinide nuclei. On the other hand, the El rate in 2 7Ac is similar to those measured in heavier actinides. Previous studies suggest the presence of octupole deformation in all the three nuclei. The present investigation indicates that fast El transitions occur for nuclei with octupole deformation. However, the studies also show that there is no one-to-one correspondence between El rate and octupole deformation. 

API 14 MeV neutrons in coincidence with the associated a-particles (n, n y) Like FNA in delayed coincidence with a (d,T) O.C,N, metals... 

The techniques used in the three measurements of the 23S —23Pj, J = 0,1,2 intervals are summarized in Figure 8. In all of these experiments the initial state is the 23S i state formed from positrons striking a metal target with about 100 eV kinetic energy. The first two measurements [15] [16] detected the transition as a 243 nm Lyman-a photon in delayed coincidence with a detected 7 ray from the annihilation of orthopositronium. The most recent and most precise experiment [17], which we detail below, uses only the Lyman-a detection. 

Given that the implanted nuclei are radioactive, the positions measured for the implantation and all subsequent decay processes are the same. This is the case because the recoil effects are small compared with the range of implanted nuclei, emitted a particles or fission products, and detector resolution. Recording the data event by event allows for the analysis of delayed coincidences with variable position and time windows for the identification of the decay chains [14],... 

In photoion—photoelectron coincidence (PIPECO), an ion M+ formed by PI is detected in delayed coincidence with the electron emitted [264, 266, 323, 324], If the energy of the emitted electron is measured and the photon energy is known, the internal energy of the ion M+ is known. Thus the reactions of ions with selected internal energies, E, can be studied by this technique. The statement that ions with selected internal energy states are studied , which appears often in the literature, seems too strong in the context of polyatomic ions. The total energy is selected, but further information about the states would have to be obtained by other means. 

Delayed coincidence method used to determine radiative lifetime of F(2p 3p)... 

Parent ions of internal energy equal to the nominal photon energy or their ionic reaction products are selectively detected in delayed coincidence with threshold electrons. For this purpose the threshold electron signal is used to trigger an electric pulse producing a 10 V/cm electric field for 15 ps i.e., longer than the total ion TOF. The primary ions are thus accelerated over 0.3 cm of the ionization chamber and refocused by a 3 element electrostatic immersion lens. onto an effusive jet of... 

A more direct method for lifetime measurements is the delayed coincidence technique [6] in which the time between an initiation event and the emission of a decay product is measured. A schematic diagram of an apparatus used for the measurement of atomic lifetimes is shown in figure BLIP.5. The slope of the graph of the natural log of the number of decay events as a function of time delay gives the lifetime directly. The... 

The half-life of the 82-3-keV excited state as determined by two delayed coincidence methods and from the Mossbauer linewidth is = 3-8(3) ns... 

A Au/Pt source and a Pt absorber at 15 K were found to give a very weak effect (0-16%). The linewidth gave an excited-state half-life (lower limit) of 0-49 0-05 ns, compared to the value of 0-62 + 0-07 ns from delayed coincidence measurements. Theoretical calculations of the recoilless fraction for both transitions have been made [87]. 

The 7 s emitted are of different energy the 7 is 0.51 MeV, but 73 much higher. There is also a time lag between the 7 s because of the time required for the fast neutrons to be slowed down to thermal energy. The detection system allowed a delay time to ascertain a relation between 7j and 72 (delayed coincidence arrangemmit). When the reactor was on, 0.2 cpm were observed, while it was practically zero a short time after the reactor had been turned off thereby demonstrating the formation of neutrinos during reactor operation. 

O.M. Williams, W.J. Sandle, A pile-up gate generator for removing distortion in multichannel delayed coincidence experiments, Phys. Sci. Instrum. 3, 741-743 (1970)... 

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