Experiments have been performed on the formation of bromine and rhodium isomers, by thermal as well as resonance neutrons, in order to study capture levels. With slow neutrons of variable energies obtained from a Ra-Be source in a slowing-down medium of paraffin, we have studied: (a) the relative formation of the isomeric pairs as a function of the distance from the source and (b) the migration distances for each isomer.

The experimental results show that for bromine isomers produced by resonance neutrons as well as for rhodium isomers produced by resonance and $C$-neutrons, the ratio of the activities of the fundamental state to the metastable state is a function of the distance from the source. Moreover, at each point this ratio is different for resonance and for $C$-neutrons. The migration distances corresponding to each of the isomers formed by resonance neutrons on bromine, or by $C$-neutrons on rhodium, are found to be different.

This leads to the assumption of the existence of more than one capture level in the formation of the bromine and rhodium isomers. It may be suggested that for rhodium the resonance levels extend within the region defined by the $C$-neutrons.

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