Search for Decay Rate Variation of ^7Be in Pt and Al

The decay rate variation of 7Be implanted into platinum and aluminum host materials has been measured via detecting the 478 keV ?-rays from the first excited state of 7Li populated in the electron capture decay of 7Be. The result (?Pt ? ?A1)/?0 = (?0.17 ? 0.13)% is obtained. It is smaller than the theoretical estimate from the TB-LMTO calculation (0.38%). This is quite different from our previous study which showed a larger decay rate variation ((0.8 ? 0.2)%) than the TB-LMTO calculation (0.30%) of 7Be in palladium and gold. It is suggested that the effective quasi-free electron density near the implanted ions in different metal host materials may play an important role in 7Be EC decay rate variation in addition to the electronic affinity and crystal structure of different host materials.