Martoff, C. J., Schaad, M., Straumann, U., Truoel, P., Crowe, K. M., Joseph, C., Perroud, J. P., Rugger, D., Tran, M. T., Gregoire, G., Dahme, W., van Elmbt, L., Lebrun, M., Deutsch, J., & Prieels, R. (1984). NO PRECRITICAL ENHANCEMENT OBSERVED IN C-13 (PI+, GAMMA) N-13 (G.S.) AT Q = (approximately) 2 M (PI). Nuclear Physics, Section A, A430, 557-572. https://doi.org/10.1016/0375-9474(84)90094-0 (Original work published 1984)