Absorption of Slow Neutrons in Silver

Fermi and his collaborators [1] have measured the absorption of slow neutrons in a variety of elements using as a detector of the neutrons usually rhodium, and sometimes silver. Wide differences are found among the various elements tested, and the removal of neutrons from the beam by absorbing layers has been shown to be due to the mechanisms of capture (with emission of a gamma-ray or of a heavy particle) and elastic scattering. Of these two mechanisms, the first seems to be predominately important in those elements exhibiting the largest cross sections for slow neutrons [2]. It seemed desirable to measure the absorption of neutrons in a single element, using a variety of detectors, and this letter is a preliminary report of investigations of that sort. While this work was in progress, other investigators have noted [3] that the cross section measured for an absorber depends strongly on the reaction whereby the slow neutrons are detected.