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Recently, we observed an anomalous internal pair creation for the M1 transition depopulating the 18.15 MeV isoscalar 1+ state in 8Be. The deviation from the theoretical prediction can be described by assuming the creation and subsequent decay of a new, light boson with a mass of 16.7 MeV/c². In order to clarify the interpretation, we re-investigated the 8Be anomaly with an improved and independent setup. We have confirmed the signal of the assumed X(17) particle and constrained its mass (m0c² = 17:01(16) MeV) and branching ratio compared to the γ-decay (Bx = 6(1)× 10-6). We investigated also the high-energy (21 MeV) Jπ = 0- ℥ 0+ transition in 4He and got a consistent result for the X(17) particle. [ABSTRACT FROM AUTHOR]