Errors in evaluated neutron cross sections

The underestimation of the errors in the recommended neutron cross sections calculated on the basis of an analysis of measurement results using strict statistical methods is discussed. The basic reasons for the underestimation of the errors in the cross sections are described. A statistical model is proposed - a constant bias model -for taking into account effectively the component of the measurement error that is unknown to the experimentor The results of a statistical analysis of the measurements of the ratio of the fission cross sections of 238 U and 235 U on the basis of the constant bias inodel are presented. It is noted that the experimental errors are much higher (on the average by a factor of 2) than the declared errors. The consequences of using the generally accepted method for correcting the errors in the evaluated cross sections are examined for an exactly solvable inodel example. It is shown that such a procedure does reconstruct the real errors in the evaluated cross sections.