For a basic description of these experiments and their theoretical significance see Phys. Rev. Lett., vol.33, p.316 (1974). The authors report experiments, with close control of detector pulse height distribution, on /sup 6/Li, /sup 3/He, /sup 12/C and /sup 14/N.
Deutsch, J., Favart, D., Prieels, R., Van Oystaeyen, B., Argan, P., Audit, G., Blomquist, I., de Botton, N., Faure, J. L., Schuhl, Cl., Stoler, P., Tamas, G., & Tzara, C. (1975). Preliminary results of recent threshold pion photoproduction experiments on nuclei. AIP Conference Proceedings, p. 445-447.