[en] Recently, a new ²⁵²Cf neutron source was installed at the Soreq Nuclear Research Center neutron calibration facility. Absolute calibration of the neutron emission rate of the source was carried out using the manganese sulfate bath method which is a well-known method for absolute determination of radionuclide neutron sources. In this method the neutron source is placed at the center of a large spherical or cylindrical bath filled with a concentrated aqueous solution of MnS0₄. Fast neutrons emitted isotropically from the source will slow down in the hydrogenous medium and will be captured by the components of the aqueous solution, mainly by ^5:Mn atoms to produce radioactive ⁵⁶Mn (Ti.<₂ = 2.5789 h). Thus, from the measurement of ⁵⁶Mn, combined with the neutron capture cross section and atoms concentrations, it is possible to determine the neutron emission rate {B) of the ^2:>2Cf neutron source: B = j^*j*R where / is the fraction of neutrons captured by Mn, R is the production rate of ⁶Mn by the neutron capture reaction, and /''is a coefficient factor which contains eg., the fraction of neutrons that escape from the bath and the fraction of neutrons self-absorbed in the source. / Can be expressed as: N^Mn -⁰M_n +N_H -o_H +N_s-a_s+N₀ -a_Q where N_Mn,N_h,N_s and N_G are the number of nuclei of manganese, hydrogen, sulfur and oxygen in the solution, respectively and <_JMn,a_Nicr_s and o_Cj are their thermal neutron capture cross sections, 13.3, 0.33, 0.53 and 0.00019 barn, respectively