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When proportional counters are employed in charge integration mode to determine the magnitude of a radiation pulse, so intense that individual detection events take place in a time too short to produce individual output pulses, mostly in pulsed neutron sources, the strong build-up of positive space charge reduces the electric multiplication factor of the proportional detector. Under such conditions the ensuing measurement underestimates the amount of radiation that interacted with the detector. If the geometric characteristics, the filling gas pressure and the voltage applied to that detector are known, it becomes possible to apply an analytical correction method to the measurement. In this article we present a method that allows to determine the absolute value of the detected radiation burst without the need to know the characteristics of the employed detectors. It is necessary to employ more than one detector, taking advantage of the Influence Method. The “Influence Method” is conceived for the absolute determination of a nuclear particle flux in the absence of known detector efficiency and without the need to register coincidences of any kind. This method exploits the influence of the presence of one detector in the count rate of another detector, when they are placed one behind the other and define statistical estimators for the absolute number of incident particles and for the efficiency (Rios and Mayer, 2015 [1,2] ). Its practical implementation in the measurement of a moderated neutron flux arising from an isotopic neutron source was exemplified in (Rios and Mayer, 2016 [3] ) and the extension for multiple detectors in (Rios and Mayer 2016 [4] ). [ABSTRACT FROM AUTHOR]

The “Influence Method” is conceived for the absolute determination of a nuclear particle flux in the absence of known detector efficiency and without the need to register coincidences of any kind. This method exploits the influence of the presence of one detector in the count rate of another detector, when they are placed one behind the other and define statistical estimators for the absolute number of incident particles and for the efficiency ( Rios and Mayer, 2015a ). Its detailed mathematical description was recently published ( Rios and Mayer, 2015b ) and its practical implementation in the measurement of a moderated neutron flux arising from an isotopic neutron source was exemplified in ( Rios and Mayer, 2016 ). With the objective of further reducing the measurement uncertainties, in this article we extend the method for the case of multiple detectors placed one behind the other. The new estimators for the number of particles and the detection efficiency are herein derived. [ABSTRACT FROM AUTHOR]

The “Influence Method” is conceived for the absolute determination of a nuclear particle flux in the absence of known detector efficiency. This method exploits the influence of the presence of one detector, in the count rate of another detector when they are placed one behind the other and define statistical estimators for the absolute number of incident particles and for the efficiency. The method and its detailed mathematical description were recently published (Rios and Mayer, 2015 [1] ). In this article we apply it to the measurement of the moderated neutron flux produced by an 241 AmBe neutron source surrounded by a light water sphere, employing a pair of 3 He detectors. For this purpose, the method is extended for its application where particles arriving at the detector obey a Poisson distribution and also, for the case when efficiency is not constant over the energy spectrum of interest. Experimental distributions and derived parameters are compared with theoretical predictions of the method and implications concerning the potential application to the absolute calibration of neutron sources are considered. [ABSTRACT FROM AUTHOR]

A new method for the absolute determination of nuclear particle flux in the absence of known detector efficiency, the “Influence Method”, was recently published (I.J. Rios and R.E. Mayer, Nuclear Instruments & Methods in Physics Research A 775 (2015) 99–104). The method defines an estimator for the population and another estimator for the efficiency. In this article we present a detailed mathematical description which yields the conditions for its application, the probability distributions of the estimators and their characteristic parameters. An analysis of the different cases leads to expressions of the estimators and their uncertainties. [ABSTRACT FROM AUTHOR]

In this article we introduce a new method, which we call the “Influence Method”, to be employed in the absolute determination of a particle flux, most especially applicable to time-of-flight spectrum determination of a neutron beam. It yields not only the absolute number of particles but also an estimator of detectors efficiencies. It may be useful when no calibration standards are available. The different estimators are introduced along with some Monte Carlo simulations to further illustrate the method. [ABSTRACT FROM AUTHOR]