Measuring the moderation length of fission neutrons in sintered beryllium oxide at energies of 1.44 and 0.3 eV

Abstract

We have measured the density distribution of neutron moderation at energies Er equal to 1.44 and 0.3 eV for a point source of fission neutrons in beryllium oxide and we have determined the squares of the moderation length L f 1.44 → 0.3 2 up to energies of 1.44 and 0.3 eV; they were 92±1.5 and 104.5±2 cm2 (with a beryllium oxide density of 2.79 g/cm3). We found that the experimentally obtained quantity L ℕ 2 (12.5±2.5 cm2) is much larger than that calculated on the assumption of moderation at free beryllium and oxygen atoms. We have chosen synthetic functions of the effect for the moderation density in the form $$P(r_1 E_r ) = K_{n, 2n} \sum\limits_{i = 1}^3 { \frac{{pi}}{{(4\pi \tau _i )^{{\raise0.5ex\hbox{$\scriptstyle 3$}\kern-0.1em/\kern-0.15em\lower0.25ex\hbox{$\scriptstyle 2$}}} }} e^{ - r^{2/4\tau _i } } ,} $$ agreeing satisfactorily with the experimental data.