Capture Cross Sections for Slow Neutrons

A method for measuring capture cross section for slow neutrons has been developed. Neutrons from a $\mathrm{Ra}-\alpha -\mathrm{Be}$ source are slowed down in a paraffin block containing a cylindrical cavity. A B${\mathrm{F}}_3$ detector in the center of the cavity measures the reduction in neutron intensity which results when an element or compound under investigation "suspended" in graphite powder is introduced into the cavity. The arrangement is calibrated with boron. The method has been used to measure the capture cross section of 19 elements. The results are tabulated at the end of the paper.