Deceleration of neutrons to ultracold

Hello, dear experts! Please, can I suggest, is it correct to use NeutronHPphysics to model the process of neutron slowing down to 10^(-7) eV? I have considered the UCN example, but there we are talking about ultracold neutrons and their reflection. My question is more about the process of neutron energy loss and correct consideration of all physical processes.
In addition, there is a question about helium for neutron deceleration. In simulations for neutron deceleration, how is it correct to define superfluid helium? Is it the same as specifying ordinary helium at cryogenic temperature?

This is the first time I am asking a question on the forum,
I would be very grateful for your advice!