Do molecular bounded systems shield or reduce neutron cross-sections? When talking about neutron cross-sections, literature is usually investigating isolated cases of Neutron + Atom. Here, the abundance of hydrogen is dominating neutron fluxes through material.
I wonder whether the reflection or capture propability of neutron radiation changes when the flux is penetrating a system of (organic) molecules. I can imagine two effects potentially reducing the neutron cross-section for bounded hydrogen:


*

*The dense grid of organic material (folded proteins etc, imagine thick tree or a croud of humans) could be able to shield their hydrogen atoms from beeing struck by neutrons. Assuming organic material to be much denser (nuclei/volume) then other material like soil, rocks.

*Neutrons are not able to transfer their whole energy to the hydrogen nucleus when it is electrically bounded (p is bounded to its electron, which is bounded to the electrons of the molecular system, which introduces inertia to the protons ability to move). Concluding that the capability of slowing down neutrons is reduced compared to free hydrogen.
Is this complete non-sense or could there be a measurable influence to neutron fluxes when using (a) non-organic or (b) organic material, containing the same amount of hydrogen?
 A: Essentially no.
Being neutral the neutron interacts with electrons only magnetically and constraints on bound electrons suppress this very strongly. So, to a neutron an atom mostly looks like a nucleus sitting in space.
Likewise the neutron's electromagnetic interaction with the nucleus is strongly suppressed.
That leaves the strong nuclear interaction which has a range on order of $\approx 10^{-15}\,\mathrm{m}$.
Now, compare the size of atoms ($\approx 10^{-10}\,\mathrm{m}$) with that of nuclei ($\approx 10^{-14}\,\mathrm{m}$). Now notice that the cross-sectional area goes by the square of that ratio.
The result is that even in a very large and complicated molecule like a protein the "outer" atoms provide very, very little shielding for the "inner" ones.
A: From an energy perspective, a free neutron sees a nucleus as a three-dimensional square well with a depth of a 5--10 MeV. The presence or absence of milli-eV thermal oscillations or eV-scale molecular bonds may change the details of the shape of that potential well, but in general the change is much less important than the uncertainty in the neutron's energy or momentum.
There are a few exceptions. Neutron diffraction from a crystal is very different from neutron scattering by a gas of the same material; for the same reasons, neutron diffraction from solid hydrogen or solid oxygen would be very different from neutron diffraction by water ice. In a few systems with very low density of states (most famously, parahydrogen) very cold neutrons don't have enough energy to excite molecular transitions, and therefore have a much lower scattering cross section than higher-energy neutrons.  Absorption cross sections, however, are generally (and reasonably) treated as being completely independent of the environment of the absorbing nucleus.
I suppose it's likely that a nuclear isomer (that is, a long-lived nuclear excited state)  would have a different neutron capture cross section than the ground state of the same nucleus.
A: http://www.ncnr.nist.gov/resources/activation/ 
Running the numbers suggests composition, density, and pathlength account for real world observations 
http://www.sbfisica.org.br/bjp/files/v35_850.pdf 
with a foonote 
http://en.wikipedia.org/wiki/Small-angle_neutron_scattering 
or two, all consistent with only nuclei being important for hot neutrons. 
http://www.fys.ku.dk/~willend/Neutron1_4.pdf
http://en.wikipedia.org/wiki/Atomic_form_factor#Magnetic_scattering 
Neutron magnetic lattice scattering has low energies uncovering small footnotes in kind, especially atomic form factors from outer electron envelopes.  If you wish to experiment, contrast C_nH_2n: high density polyethylene d = 0.97 g/cm^3 versus TPX polymethylpentene d = 0.83 g/cm^3.
