# Calgary Neutron Monitor Efficiency Factor Estimation After Major Renovation

*C.J. Bland and A.F. Kouznetsov,
Dept. of Physics and Astronomy, University of Calgary, Canada*

Most Neutron Monitors (NMs) have been in operation for many years, if not decades. When components such as tubes, electronics, etc., are changed, average count rates can be altered. If, after modifications, the NM is promptly put back into operation, any changes in the average count rates can be readily tracked. The NMDB thus includes data corrected for “efficiency.” In the case of the Calgary NM, we have ~30 years of reliable data (1979-2009) covering three solar cycles. After an extensive renovation, we have collected another ~5 years of data (2017 -present) during solar minimum, but quantitative estimating the change in “efficiency” is not straightforward. Our solution is based on a multiple regression analysis performed on the two sets of data, assuming that, to a first approximation, pressure-corrected count rates depend on solar activity and elapsed time. The linear coefficients and variances are contained in the matrix solution of the least-squares procedure. Thus, the constant level and variance for each data set is obtained, whence the “efficiency factor” may be estimated.

**Oral**