The inter atomic spacing in a crystal of table salt is 0.282 $\mathrm{nm}$ . This crystal is being studied in a neutron diffraction experiment, similar to the one that produced the photograph in Figure 29.12$a .$ How fast must a neutron (mass $=1.67 \times 10^{-27} \mathrm{kg} )$ be moving to have a de Broglie wavelength of 0.282 $\mathrm{nm}$ ?