Photoneutron cross section of 29Si

The photoneutron cross section of ²⁹Si has been measured over the energy range 8 to 28 MeV using the bremsstrahlung yield curve technique. The giant dipole resonance is observed to be centered at 21.2 MeV and is 5.5 MeV wide. In addition, a pygmy resonance containing much fine structure is observed below 17 MeV. An attempt is made to interpret these observations in terms of the weak coupling of the extra neutron to a ²⁸Si core. However, detailed comparisons of the structure and relative strengths of the ²⁸Si and ²⁹Si cross sections reveal that the coupling of the extra-core nucleon is large and significantly modifies the core wave function.