1. R. L. Walker, B. L. Berman, R. C. Der, T. M. Kavanagh, and J. M. Khan, Phys. Rev. Lett. 25:5 (1970). This experiment was essentially duplicated, with 1-GeV poistrons and electrons, by V. L. Morikhovskii, G. D. Kovalenko, I. A. Grishaev, A. N. Fisun, V. I. Kasilov, B. I. Shramenko, and A. N. Krinitsyn, Pis’ma Zh. Eksp. Teor. Fiz. 16:162 (1972) [English translation: JETP Lett. 16:112 (1972)]. They too, observed channeling radiation, but this fact has not been recognized until now.
2. R. L. Walker, B. L. Berman, and S. D. Bloom, Phys. Rev. A 11:736 (1975). Low-energy enhancement like that seen in this experiment also has been seen with 800-MeV electrons by S. A. Vorobiev, B. N. Kalinin, V. V. Kaplin, and A. P. Potylitsin, Pis’ma Zh. Tekh. Fiz. 4:1340 (1978) [English translation: Soy. Phys.-Tech. Phys. Lett. 4:539 (1978)], and with 1.2-GeV positrons by B. I. Shramenko, V. I. Vit’ko, and I. A. Grishaev, Pis’ma Zh. Tekh. Fiz. 4:1423 (1978) [English translation: Soy. Phys.-Tech. Phys. Lett. 4:576 (1978)].
3. T. F. Godlove and M. E. Toms, private communication (1969); U.S. Naval Research Laboratory, Nuclear Physics Division, Annual Report (1969), p. 96.
4. R. W. Terhune and R. H. Pantell, Appl. Phys. Lett. 30: 265 (1977);
5. R. H. Pantell, private communication (1975).