We propose inelastic neutron scattering (INS) experiment on single crystal of the prototype topological insulator (TI), Bi2Se3, at MAPS to measure q-dependent joint-DOS, based on Cooke and Blackman's theoretical works (PRB, 26, 4410). We will, first, compare measured q-dependent joint-DOS with the calculated one and see how accurate the first principle calculation is. This is very important, since the first principle calculations have been pivotal in this field, and there is no other tools to measure q-dependent joint-DOS of bulk electronics structure of a TI. More importantly, this work will be first measurement of q-dependent joint-DOS of a single crystal and will push the envelope of capabilities of INS. We shall also investigate the symmetry of ground state wavefunction of Bi2Se3, which plays crucial role to determine whether it is topological insulator, through form factor analysis.