Chapter 18, Problem 77PP

A helium ion (He⁺⁺) that comes within about 10 fm of the center of the nucleus of an atom in the sample may induce a nuclear reaction instead of simply scattering. Imagine a helium ion with a kinetic energy of 3.0 MeV heading straight toward an atom at rest in the sample. Assume that the atom stays fixed. What minimum charge can the nucleus of the atom have such that the helium ion gets no closer than 10 fm from the center of the atomic nucleus? (1 fm = 1 × 10⁻¹⁵ m, and e is the magnitude of the charge of an electron or a proton.)

1. A.    2e
2. B.     11e
3. C.     20e
4. D.    22e