1. A derivation can be found in many articles, e.g. T. de Forest, Jr. and J.D. Walecka, Adv. in Physics 12 (1966)
2. E. Spamer, Z. Physik 191 (1966) 24
3. D.R. Isabelle and G.R. Bishop, Nuclear Phys. 45 (1963) 209
4. R.S. Willey, Nuclear Phys. 40 (1963) 529
5. F.H. Lewis, Jr., J.D. Walecka, I. Goldemberg and W.C. Barber, Phys. Rev. Letters 10 (1963) 493