  The energy loss and energy loss straggling widths have been measured in
transmission for MeV protons traversing a thin kapton polyimide foil. In a
prior step, the thickness and non-uniformity of the target foil were carefully
investigated. The overall relative uncertainties in the stopping power and
energy loss straggling variance data amount, respectively, to less than 2% and
8%. The experimental data show to be in excellent agreement with available
previous ones and with those compiled in the ICRU-49 report. They are fully
consistent with the predictions of Sigmund-Schinner's binary collision theory
of electronic stopping over the whole proton energy range explored. An average
deviation of ~2.5% relative to values calculated by the SRIM-2008 code, likely
due to effects of valence electrons involving the , and bonds, is however
observed at low proton velocities. The measured energy loss straggling data,
which are unique to our knowledge, are found to be in good agreement with
values derived by the classical Bohr formula for keV but they significantly
exceed Bohr's collisional energy loss straggling at lower proton velocities
where target electrons can no longer be considered as free. They also show to
be consistent with the predictions of the Bethe-Livingston and Sigmund-Schinner
theories over the low proton velocity region ( keV). However, they are
significantly overestimated by these theories over the intermediate and high
proton velocity regions, which may be due to bunching effect by inner shell
electrons of the polymer target. Besides, our energy loss straggling data are
in better overall consistency with the Yang, O'Connor and Wang empirical
formula for keV, while deviations above the latter amounting up to ~18% are
observed at lower proton velocities.
  Keywords: Swift protons; Kapton polyimide; Stopping power; Energy loss
straggling; Binary collision theory.
