Composition Charges of Test Materials: Neutron Fraction, Binding and Coulomb Levers for Equivalence and Fifth-Force Tests

An equivalence or fifth-force experiment constrains a coupling only through the difference in charge-to-mass ratio between its two test materials. For a force coupled to baryon-minus-lepton number, that charge per unit mass is the neutron fraction, which runs from 0.556 for beryllium to 0.600 for platinum. The MICROSCOPE pair, titanium against platinum, carries a neutron-fraction lever of 0.058; the classic beryllium-titanium pair carries 0.014; aluminium against platinum would carry 0.081. This paper tabulates the levers for the standard materials and pairs, together with a Coulomb-energy proxy, so that any proposed coupling can be priced against any published experiment in one multiplication. Computed from nuclear data, not measured.