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    STP1608

    Rigorous Uncertainty Propagation Using a Dosimetry Transfer Calibration

    Published: 2018


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    Abstract

    The process of determining the uncertainty in the neutron fluence from the measured activity of a dosimetry monitor is reviewed and the importance of treating the energy-dependent correlation is illustrated using several representative neutron fields. The process of determining the uncertainty in the neutron fluence when a transfer calibration is used is then detailed. The conversion factor, when a transfer calibration is used, has a term that has an integral over the cross section appearing in both the numerator and the denominator. This term introduces a nonlinear dependence on the cross section within the conversion factor and an explicit correlation between the terms appearing in the numerator and denominator of the conversion factor. A method for rigorously treating this nonlinear uncertainty propagation is presented. This method is based upon utilizing the covariance matrix for the cross section and utilizing a statistical sampling approach based on a Cholesky transformation of this covariance matrix. This methodology is then applied to the determination of the uncertainty from a transfer calibration for a set of nine neutron spectra based upon using the 32S(n,p)32P reaction and a transfer calibration in a 252Cf standard benchmark neutron field. A very strong correlation is found in the cross-section terms as they appear in the numerator and in the denominator. When a rigorous treatment is used to propagate the uncertainty due to the cross section for the dosimetry monitor, the uncertainty in the conversion factor is reduced by a factor of more than ten times from a worst-case approach that treats the uncertainty components in the numerator and denominator as uncorrelated. This ten times difference is also seen when the comparison is made between a rigorous treatment and a treatment of the cross-section contributions where the numerator and denominator are treated as uncorrelated (i.e., when compared to a root-mean-square approach).

    Keywords:

    uncertainty, covariance, transfer calibration, dosimetry, sulfur, activation, neutron fluence, error propagation


    Author Information:

    Griffin, Patrick J.
    Sandia National Laboratories, Radiation and Electrical Sciences Center, Albuquerque, NM

    Vehar, David W.
    Sandia National Laboratories, Applied Nuclear Technologies, Albuquerque, NM

    Parma, Edward J.
    Sandia National Laboratories, Applied Nuclear Technologies, Albuquerque, NM

    Hahn, Kelly D.
    Sandia National Laboratories, Neutron and Particle Diagnostics, Albuquerque, NM


    Committee/Subcommittee: E10.05

    DOI: 10.1520/STP160820170043