Low Temp Physics: Why He (3) Needs Higher Pressure to Solidify

[pleasehelpmeno]

Homework Statement

Why at absolute zero does He (three) have a larger molar volume and require a higher pressure to solidify than He(four)?

The Attempt at a Solution

I feel the answer lies in the Pauli exclusion principle, at low temps the ferions are nopt as easily confined as the bosons so they will have a larger molar volume, but i can't explain why this would then require a higher pressure to solidify:

Pv = nRT

where if v is increased surely P must decrease?

 

[mfb]

I think I saw some pairing process for He3 - so you have to consider "molecules" (those are bosons again) instead of atoms.