Results 1 - 10 of 2119
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[en] Highlights: • Dead-time correction formulae for superimposed non-homogeneous Poisson processes. • Live-timed counting method extended using the time stamps of live-time intervals. • Implementation on instruments equipped with digital signal processing systems. • Application to the measurement of short-lived radionuclides with background. - Abstract: Dead-time correction formulae are established in the general case of superimposed non-homogeneous Poisson processes. Based on the same principles as conventional live-timed counting, this method exploits the additional information made available using digital signal processing systems, and especially the possibility to store the time stamps of live-time intervals. No approximation needs to be made to obtain those formulae. Estimates of the variances of corrected rates are also presented. This method is applied to the activity measurement of short-lived radionuclides.
[en] This paper extends analysis given by Larsen and Kostinski (Meas. Sci. Technol. 20 (2009) 095101) for the measurement of the rate of a Poisson process using a counter with dead time. It is shown that when there is dead time after each event, and not merely after each observation of an event, there are two rates that are consistent with the result of any measurement. In this case, extra information is needed if the true rate, λ, is to be recovered unambiguously. Explicit confidence intervals for λ are given for the two types of dead time in the practical situation where the period of observation is finite. The result that two true rates correspond to any rate obtained with the second form of dead time holds with many other processes and with counters in which the dead time is a random variable
[en] Counting statistics with an extended variable dead-time is reviewed. The three unusual counting processes are considered and expressions for the interval distribution of the first event are given. Two sets of asymptotic formulae for mean and variance of the number of counted events in a given measuring time are derived. The first one is obtained without any approximation on the dead-time distribution; the second one includes all the approximations required in the corresponding case of a non-extended variable dead-time. The two are respectively consistent with expressions given previously for the case of a constant dead-time and with their developments as functions of the dead-time. (Auth.)
[en] Counting statistics modified by introducing two dead times in series under a Poisson input distribution are discussed. A previous study examined the two cases of series combinations of nonextended-extended (NE-E) and extended-extended (EE) dead times. The present study investigated the remaining two cases of extended-nonextended (E-NE) and nonextended-nonextended (NE-NE) dead times. For the three time origins of the counting processes - ordinary, equilibrium, and shifted processes - a set of formulae was newly developed from a general formulation and presented for the event time interval densities, total densities, and exact mean and variance of the counts in a given counting duration. The asymptotic expressions for the mean and variance of the counts, which are most convenient for applications, were fully listed. The equilibrium mean count rates distorted by the three dead times in series were newly derived from the information obtained in these studies. An application of the derived formulae is briefly discussed
[en] The linearity of gamma camera counting is an essential feature for users engaged in quantitative dynamic studies. Instead of defining this quality by the usual dead time, the disadvantages of which are reported, it is proposed to use the experimental count rate giving 10% loss. It is shown that by proceeding in this way all ambiguity would be abolished, where both the counting linearity itself and its relation to sensitivity are concerned
[fr]La linearite de comptage d'une gamma camera apparait comme une qualite essentielle pour l'utilisateur qui s'interesse aux etudes dynamiques quantitatives. Au lieu de la definir par l'habituel temps mort, dont on expose les inconvenients, on propose de le faire a l'aide du taux de comptage experimental donnant 10% de perte. On souligne qu'en agissant ainsi, on eliminerait toute ambiguite portant d'une part sur la linearite de comptage elle-meme et d'autre part sur sa relation avec la sensibilite
[en] The security of quantum key distribution (QKD) can easily be obscured if the eavesdropper can utilize technical imperfections in the actual implementation. Here, we describe and experimentally demonstrate a very simple but highly effective attack that does not need to intercept the quantum channel at all. Only by exploiting the dead time effect of single-photon detectors is the eavesdropper able to gain (asymptotically) full information about the generated keys without being detected by state-of-the-art QKD protocols. In our experiment, the eavesdropper inferred up to 98.8% of the key correctly, without increasing the bit error rate between Alice and Bob significantly. However, we find an even simpler and more effective countermeasure to inhibit this and similar attacks.
[en] A controlled delay circuit of nanosecond range (0 - 200 nsec) is designed so as to reduce dimensions, zero and dead time. Control of a delay time is ensured through variation of the initial level of the capacity charge by negative control voltage. Zero delay time is less than 9 nsec with dead delay time being 15 nsec. In case high-frequency transistors are used, zero delay time may be reduced to 5-6 nsec
[en] Dead-time effects for coincident pulses are known to be a very difficult subject. Apart from some trivial cases, no rigorous results are yet known. For all practical applications, approximate solutions are used, the quality of which is difficult to judge. Whereas in general they seem to be sufficiently reliable, their deficiency begins to show up clearly for very high count rates. Unfortunately, the present small note will not really improve this situation. It may, however, provide some guideline for the credibility of the various approaches which have been suggested