  The experimental thermal neutron cross sections of the twenty proteinogenic
amino acids have been measured over the incident-neutron energy range spanning
from 1 meV to 10 keV and data have been interpreted using the multi-phonon
expansion based on first-principles calculations. The scattering cross section,
dominated by the incoherent inelastic contribution from the hydrogen atoms, can
be rationalised in terms of the average contributions of different functional
groups, thus neglecting their correlation. These results can be used for
modelling the total neutron cross sections of complex organic systems like
proteins, muscles, or human tissues from a limited number of starting input
functions. This simplification is of crucial importance for fine-tuning of
transport simulations used in medical applications, including boron neutron
capture therapy as well as secondary neutrons-emission induced during proton
therapy. Moreover, the parametrized neutron cross sections allow a better
treatment of neutron scattering experiments, providing detailed sample
self-attenuation corrections for a variety of biological and soft-matter
systems.
