Momentum widths in the fragmentation of 32 MeV/uB10

Momentum widths of fragments produced in the reactions of 320 MeV ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$ with ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ have been measured. At forward angles the energy spectra of light particles ($Z=1, 2$) exhibit energy peaks characterized by a reduced momentum width ${\sigma }_0=54\mathrm{}$ MeV/c, which is well below the values near 85 MeV/c observed in the reactions of 43 MeV/u ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ with ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ and in reactions induced by relativistic heavy ions. These results suggest a rapid increase in momentum widths, or apparent temperature, in the 32 to 43 MeV/u range.