A new format for the elastic scattering differential cross section covariance of charged particles

For the elastic scattering of charged particles, there is no clear format in the ENDF-6 document to publish the covariance data of the differential cross sections. Since the covariance data is a function of both energy and angle, the publication of the raw data will make the data file extremely large and is difficult to be used in the nuclear data processing programs. In this paper, we proposed a new format for publishing this data. The angular distributions of correlation coefficients are fitted using a superposition equation and the fitting parameter values along with the standard deviation data are published, which can be used to reconstruct the covariance matrix. Based on the Generalized Reduced R-matrix theory, the RAC program (R-matrix analysis code) was employed to evaluate the experimental data of all nuclear reaction channels associated with the  ⁷Be system. The  ⁶Li(p, p)⁶Li reaction of the  ⁷Be system were selected as an example for testing the proposed data format. The calculated results show that the amount of released data with the new format is only 1/10 of the original covariance raw data and the accuracy is reduced by only 5.21%, which indicates the proposed new format is effective and reliable.