Measurement coincidence

The arrangement for a single coincidence measurement can be expanded to a multiple detector arrangement. If, for example, it is necessary to measure coincidence rates over an angular range, detectors can be placed at the angles of... 

In 1967 G.N. Flerov reported that a Soviet team working at the Joint Institute for Nuclear Research at Dubna may have produced a few atoms of 260-105 and 261-105 by bombarding 243Am with 22Ne. The evidence was based on time-coincidence measurements of alpha energies. 

If one suspects such a coincidence, measurements should be taken at a third wavelength, not necessarily an absorption maximum. It is unlikely that the necessary relations between the ratios k /k2 and ei/eP will remain. Better yet, a method other than spectrophotometry should, if possible, be used for the next series of measurements. 

Many experiments (see Section I.B) require the energy analysis and detection of two or more particles with time correlation in other words, coincidence counting techniques must be used. Coincidence methods have long been used in nuclear physics because of the convenient fast detectors that have long been available. The more recent availability of fast, high-gain electron multipliers has created the possibility of coincidence measurements in electron spectroscopy. Various aspects of coincidence measurements have been discussed elsewhere.100 102... 

Recently the two-step mechanism (III.5) and scheme (III.6) have been proven correct in a direct way by coincidence measurements.90 The fragment ions H2+, HeH,+ and HeH were measured in coincidence with the Penning electrons. In this way separate electron spectra were obtained for the different fragment ions, from which branching ratios for the ion-molecule reaction as a function of the vibrational quantum number of the formed by Pgl can be obtained. It is found that HeH is, indeed, only formed from H2 (t) = 0), as proposed in (HI.6), and that the fraction of ionizations leading to initially bound He-H systems is 0.18, to be compared with 0.15 of (III.6). Further, it is found that HeH+ is only formed from (v>4) and that the average fraction of (t>>4) leading to HeH+ formation is 0.37. For unbound in systems and bound... 

It will be+very difficult to obtain further evidence for the rotational band on the J7r=0 state in 196Pb. A y-y coincidence measurement to establish the coincidence relations between the proposed intraband transitions seems... 

We have performed coincidence measurements to establish that the 38 ns half-life previously measured [Led78] belongs to the 27.4 keV level. The relevant portion of the Pa decay scheme is shown in Fig.3. The major alpha transitions populate the 29.9 and 46.4 keV levels very little intensity occurs at the 27.4 keV level. The 29.9 keV level decays to the ground state by a fast highly converted Ml transition and the 46.4 keV level decays via the 27.4 keV level. Both the 29.9 and 18.9 (46.4-27.4) keV transitions generates Ac L X-rays. 

In a double-coincidence measurement, then, only 2-4% of the events are good peak-peak values, and, in a triples measurement, much less than 1% are useful. The solution to this problem has been known for some time put... 

There is a large variety of processes which can be studied by the nuclear spectroscopist. Many instrumental methods can be used in each case, like singles and coincidence measurements, angular distributions and correlations. The complementarity of various approaches has been discussed by... 

The different emission products which are possible after photoionization with free atoms lead to different experimental methods being used for example, electron spectrometry, fluorescence spectrometry, ion spectrometry and combinations of these methods are used in coincidence measurements. Here only electron spectrometry will be considered. (See Section 6.2 for some reference data relevant to electron spectrometry.) Its importance stems from the rich structure of electron spectra observed for photoprocesses in the outermost shells of atoms which is due to strong electron correlation effects, including the dominance of non-radiative decay paths. (For deep inner-shell ionizations, radiative decay dominates (see Section 2.3).) In addition, the kinetic energy of the emitted electrons allows the selection of a specific photoprocess or subsequent Auger or autoionizing transition for study. 

Figure 4.48 Typical spectrum of electron-electron coincidences recorded with a TDC. The data refer to a situation in which the photon beam has no time structure. True coincidences are collected in the peak while accidental coincidences give a flat and smooth background. At indicates the coincidence resolving time and dt the time resolution of the time-measuring device. The two shaded areas represent accidental coincidences, measured on the left-hand side together with the desired true coincidences, but on the right-hand side separately (and simultaneously) in the full time spectrum.

For a correct analysis of photoionization processes studied by electron spectrometry, convolution procedures are essential because of the combined influence of several distinct energy distribution functions which enter the response signal of the electron spectrometer. In the following such a convolution procedure will be formulated for the general case of photon-induced two-electron emission needed for electron-electron coincidence measurements. As a special application, the convolution results for the non-coincident observation of photoelectrons or Auger electrons, and for photoelectrons in coincidence with subsequent Auger electrons are worked out. Finally, the convolutions of two Gaussian and of two Lorentzian functions are treated. 

For electron-electron coincidence measurements both spectrometer functions have to be taken into account, giving as the response function for selected pass... 

ESc96] Eland JHD and Schmidt V 1996 Coincidence measurements on ions and electrons, in VUV and soft X-ray photoionization studies, eds. U Becker and DA Shirley (Plenum, New York). [Fan35] Fano U 1935 Nuovo dm. 12 154. 

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