On the relation between Rossi alpha and Feynman alpha methods

Degweker, S.B.; Rudra, Rashbihari

doi:10.1016/j.anucene.2016.04.001

Cited by 11 publications

(3 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The probability density function for the two-region Rossi-alpha distribution in Eqn. ( 1) can be integrated twice and algebraically manipulated [9,8,10] to obtain the two-region point kinetics model. Note that other methods of derivation exist in greater generality [7].…”

Section: Feynman-alpha Methodsmentioning

confidence: 99%

“…The histograms are fit by Eqn. (10) with a nonlinear least squares algorithm and weighting, with weights determined by the analytic method. The histograms were also fit with the one-exponential model in Eqn.…”

Section: Feynman-α Analysismentioning

confidence: 99%

“…Therefore, it is desirable to extend the traditional one-region point kinetic models to two-region point kinetics to account for the region introduced by reflector, which has been addressed in greater generality by existing literature [7,8]. This work simplifies the equations and follows a different derivation based on the double integration of the Rossi-alpha method [9,10]. The Rossi-alpha-integration approach is selected to utilize recent two-region point kinetic generalizations to the Rossi-alpha equations [11], which have been validated [12].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

On the Feynman-alpha Method for Reflected Fissile Assemblies

Hua¹,

Hutchinson²,

McKenzie³

et al. 2020

Preprint

View full text Add to dashboard Cite

The Feynman-alpha method is a neutron noise technique that is used to estimate the prompt neutron period of fissile assemblies. The method and quantity are of widespread interest including in applications such as nuclear criticality safety, safeguards and nonproliferation, and stockpile stewardship; the prompt neutron period may also be used to infer the k eff multiplication factor. The Feynman-alpha method is predicated on time-correlated neutron detections that deviate from a Poisson random variable due to multiplication. Traditionally, such measurements are diagnosed with one-region point kinetics, but two-region models are required when the fissile assembly is reflected. This paper presents a derivation of the two-region point kinetics Feynman-alpha equations based on a double integration of the Rossi-alpha equations, develops novel propagation of measurement uncertainty, and validates the theory. Validation is achieved with organic scintillator measurements of weapons-grade plutonium reflected by various amounts of copper to achieve k eff values of 0.83-0.94 and prompt periods of 5-75 ns. The results demonstrate that Feynman-alpha measurements should use the two-region model instead of the one-region model. The simplified one-region model deviates from the validated two-region models by as much as 10% in the estimate of the prompt neutron period, and the two-region model reduces to the one-region model for small amounts of reflector. The Feynman-alpha estimates of the prompt neutron period are compared to those of the Rossi-alpha approach. The comparative results demonstrate that the Feynman-alpha method is more precise than the Rossi-alpha method and more accurate for k eff < 0.92, whereas the Rossi-alpha method is generally more accurate for higher multiplications. The uncertainty propagation developed in this work should be used for all Feynman-alpha measurements and will therein improve fitting accuracy and appropriate precision estimates.

show abstract

Section: Feynman-alpha Methodsmentioning

confidence: 99%

Section: Feynman-α Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

On the Feynman-alpha Method for Reflected Fissile Assemblies

Hua¹,

Hutchinson²,

McKenzie³

et al. 2020

Preprint

View full text Add to dashboard Cite

show abstract

Principles of Neutron Coincidence Counting

Swinhoe,

Ensslin,

Hutchinson

et al. 2024

Nondestructive Assay of Nuclear Materials for Safeguards and Security

View full text Add to dashboard Cite

This chapter describes the principles involved with using neutron coincidences that obtain more information about a measured sample than through singles counting alone. The chapter describes the origin of neutron correlations and how they manifest themselves in the neutron pulse train from a detector. The Rossi-α distribution is presented. The chapter then describes measurement and analysis methods used to extract and analyze correlated counting rates, such as the Feynman variance to mean method and the shift register coincidence circuit. These methods can be used to estimate fission rate and neutron multiplication. Dead time corrections, multiple pulsing and the uncertainties resulting from counting statistics are presented. Several passive methods for the determination of 240Pueffective mass are presented in detail: ‘passive calibration curve’, ‘known alpha’ and ‘known multiplication’. This is followed by a description of active coincidence methods, in which an external neutron source is used to induce fission in the item of interest. This section includes a discussion of the selection of the external source, the use of fast and thermal interrogation modes and a presentation of measurement uncertainties. One example is given of an active technique to measure uranium linear density and burnable poison simultaneously.

show abstract