The γ-to-charge multiplicity ratio 〈Mγ〉〈Mch〉 in N¯N annihilations is restricted by I-spin conservation. In deuterium, the ratio is constrained by I-spin conservation to be equal to 1, while an experiment reported a value of 1.24±0.03; this measurement was based on missing and γ energies. The experiment reported in this paper measures the rate of conversion of γ's as a function of converter thickness and obtains 〈Mγ〉〈Mch〉=1.26±0.03 for p¯p annihilations, which is in agreement with the large γ excess observed in deuterium. Statistical models which ignore I-spin conservation predict such a γ excess, while those taking into account I-spin conservation predict values near 1.
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