This proposal seeks to perform high resolution grazing incidence diffraction (GI-XRD) at BM20 to determine the variable structural response and tendency to amorphize in the monazite solid solutions, La1-xLnPO4 for Ln = Pr, Nd and Sm, which were subject to ion irradiations with 10MeV Au ions. Monazite is touted as a waste form candidate material for the immobilisation of high level active nuclear waste (HLW), due to its favourable radiation damage tolerance properties. We recently demonstrated using GI-XRD at BM20 [1] for La1-xCexPO4, where Ce is a surrogate for Pu+3, the tendency to amorphize is dependent on the mixing of La and Ce, i.e. uneven solid solution mixing leads to lowered tolerance. What is unclear is how variation of the solid solution constituents, heavy vs. light lanthanides, affects radiation tolerance. To this end, we have irradiated La1-xLnPO4 for Ln = Pr, Nd and Sm at varying x values and accordingly wish to determine their tendency to amorphize via GI-XRD at BM20.