Existence problem of proton semi-bubble structure in the 21 + state of 34Si Feng Wu, C. L. Bai, J. M. Yao, H. Q. Zhang and X. Z. Zhang Eur. Phys. J. A, 53 9 (2017) 183 Published online: 21 September 2017 DOI: 10.1140/epja/i2017-12375-5