The ${\mathrm{He}}^3$ neutron cross section was measured for neutron energies from 0.0003 to 11 eV. In this energy region no deviation from the $\frac{1}{v}$ law can be found from the data. The cross section at 2200 m/sec was found to be $\sigma \left({\mathrm{He}}^3\right)={{5327}_{-9\mathrm{}}}^{+10\mathrm{}}$. As an instrumental check the cross sections of natural boron and of gold were also measured and the results agree with the most accurate existing data. The absorption cross sections at 2200 m/sec were found to be ${\sigma }_a\left(\mathrm{B}\right)=759.1\mathrm{}\pm 2.0 \mathrm{b}$ and ${\sigma }_a\left(\mathrm{Au}\right)=98.6\mathrm{}\pm 0.2 \mathrm{b}$.

• Received 20 September 1963

DOI:https://doi.org/10.1103/PhysRev.133.B925