Measurement of the Transport Mean Free Path of Thermal Neutrons inD2O by a Boron Poisoning Method

The transport mean free path of thermal neutrons in ${\mathrm{D}}_2$O was experimentally determined by measuring the change in the relaxation length upon the introduction of known amounts of ${\mathrm{B}}_2$ ${\mathrm{O}}_3$. The value found for 99.7 percent pure ${\mathrm{D}}_2$O was 2.49±0.04 cm. Upon correcting for the small hydrogen impurity, a value of 2.52±0.04 cm was obtained for ${\lambda }_{\mathrm{tr}}$ in pure ${\mathrm{D}}_2$O.