Annealing studies combined with low temperature emission Mössbauer spectroscopy of short-lived parent isotopes: Determination of local Debye-Waller factors.

An extension of the online implantation chamber used for emission Mössbauer Spectroscopy (eMS) at ISOLDE/CERN that allows for quick removal of samples for offline low temperature studies is briefly described. We demonstrate how online eMS data obtained during implantation at temperatures between 300 K and 650 K of short-lived parent isotopes combined with rapid cooling and offline eMS measurements during the decay of the parent isotope can give detailed information on the binding properties of the Mössbauer probe in the lattice. This approach has been applied to study the properties of Sn impurities in ZnO following implantation of 119In (T½ = 2.4 min). Sn in the 4+ and 2+ charge states is observed. Above T > 600 K, Sn2+ is observed and is ascribed to Sn on regular Zn sites, while Sn2+ detected at T < 600 K is due to Sn in local amorphous regions. A new annealing stage is reported at T ≈ 550 K, characterized by changes in the Sn4+ emission profile, and is attributed to the annihilation of close Frenkel pairs.

Local increase of the Curie temperature in Mn/Fe implanted Y3Fe5O12 (YIG).

The change in the Curie temperature of single crystalline garnet Y3Fe5O12 (YIG) sample due to lattice damage induced by ion implantation has been investigated in 57Fe emission Mössbauer Spectroscopy (eMS) following implantation of 57Mn (T½ = 1.5 min). The Mössbauer spectra analysis reveal high spin Fe3+ ions substituted on both the octahedral and the tetrahedral sites. Measurements in the temperature range 298 K-798 K show that average values of the magnetic hyperfine field are decreased by the implantation-induced damage on the local lattice structure of the YIG. The Curie temperature, however, is determined to be 651 ± 5 K, considerably higher than the value of bulk YIG (559 K). This is most likely due to lattice damage-induced changes on the spin configurations of YIG through a FeA-O-FeD distortion scheme.

Charge states and lattice sites of dilute implanted Sn in ZnO.

The common charge states of Sn are 2+ and 4+. While charge neutrality considerations favour 2+ to be the natural charge state of Sn in ZnO, there are several reports suggesting the 4+ state instead. In order to investigate the charge states, lattice sites, and the effect of the ion implantation process of dilute Sn atoms in ZnO, we have performed 119Sn emission Mössbauer spectroscopy on ZnO single crystal samples following ion implantation of radioactive 119In (T ½ = 2.4 min) at temperatures between 96 K and 762 K. Complementary perturbed angular correlation measurements on 111mCd implanted ZnO were also conducted. Our results show that the 2+ state is the natural charge state for Sn in defect free ZnO and that the 4+ charge state is stabilized by acceptor defects created in the implantation process.

Spectroscopy of double-beta and inverse-beta decays from 100Mo for neutrinos.

Spectroscopic studies of two beta rays from 100Mo are shown to be of potential interest for investigating both the Majorana nu mass by neutrinoless double beta decay (0nubetabeta) and low energy solar nu's by inverse beta decay. With a multiton 100Mo detector, coincidence studies of correlated betabeta from 0nubetabeta, together with the large Q value ( Q(betabeta)), permit identification of the nu-mass term with a sensitivity of approximately 0.03 eV. Correlation studies of the inverse beta decay and the successive beta decay of 100Tc, together with the large capture rates for low energy solar nu's, make it possible to detect, in real time, individual low energy solar nu in the same detector.