H. de Waard

Damage studies on the system\(^{111} \mathop {In}\limits^ \to \underline {Ni}\)

Lattice damage after implantation of111In in Ni has been studied applying the DPAC technique to the 171–245 keV γ-ray cascade in the daughter nucleus111Cd. Implantations were carried out at 10 K and at 300 K. The low temperature implantation yields a higher regular substitutional fraction (80%) than the room temperature implantation (40%). The annealing behaviour of both implants above RT is the same. In addition, two distinct defect-associated sites were observed in isochronal annealing sequences. A microscopic model for these defects is presented, which takes into account magnetic and electric hyperfine interaction strengths, binding energies and site populations as a functions of temperature.

Unraveling protein stabilization mechanisms: Vitrification and water replacement in a glass transition temperature controlled system

The aim of this study was to elucidate the role of the two main mechanisms used to explain the stabilization of proteins by sugar glasses during drying and subsequent storage: the vitrification and the water replacement theory. Although in literature protein stability is often attributed to either vitrification or water replacement, both mechanisms could play a role and they should be considered simultaneously. A model protein, alkaline phosphatase, was incorporated in either inulin or trehalose by spray drying. To study the storage stability at different glass transition temperatures, a buffer which acts as a plasticizer, ammediol, was incorporated in the sugar glasses. At low glass transition temperatures (<50°C), the enzymatic activity of the protein strongly decreased during storage at 60°C. Protein stability increased when the glass transition temperature was raised considerably above the storage temperature. This increased stability could be attributed to vitrification. A further increase of the glass transition temperature did not further improve stability. In conclusion, vitrification plays a dominant role in stabilization at glass transition temperatures up to 10 to 20°C above storage temperature, depending on whether trehalose or inulin is used. On the other hand, the water replacement mechanism predominantly determines stability at higher glass transition temperatures.

The Investigation of Radiation Damage and Lattice Location by Nuclear Hyperfine Interaction Techniques

Nuclear hyperfine interaction investigations of radiation damage are reviewed. Emphasis is laid on implantation experiments, where nuclear radiation emitted by the implanted probes conveys information about defect structure and its annealing. Various nuclear hfi techniques are briefly discussed and their merits and limitations for radiation damage studies are compared. It is pointed out how defect rearrangements that occur in various annealing stages can be recognized from their influence on hyperfine interactions. Recent experiments that provide more than qualitative information about radiation damage are discussed in some detail. Where possible, hfi and channeling results are compared. The importance of extending the implantation dose range to lower doses so as to avoid overlap effects of damage cascades is emphasized.

STRUCTURE OF LATTICE-DEFECTS TRAPPED AT IN IMPURITIES IN HE-DOPED NI AND CU CRYSTALS DERIVED FROM PERTURBED ANGULAR-CORRELATION MEASUREMENTS

Abstract “Helium decorated” defects, trapped by 111 In impuriteis implanted in Ni and Cu crystals doped with He, have been observed. This new type of defect possesses a three-fold axis of symmetry along the 〈111〉 direction and is characterized by a strong electric quadrupole interaction and a remarkably high trapping probability: almost 100%.

Shape of the 962 keV beta spectrum of 198Au

Abstract The shape of the 962 keV beta spectrum of 198Au has been measured by many investigators but the results do not agree very well. We have remeasured this shape in the energy range 420–940 keV with some improvements in the experimental arrangement and with a careful analysis of the results. Using the NBS-Fermi function, the coefficient a in the expression k(1 + aW) of the shape factor is found to be −0.050±0.010. The dependence of a on the value chosen for the maximum energy is discussed. The performance of the spectrometer was checked with a 24Na source, giving a = +0.002±0.010.

ANISOTROPIC RECOILLESS FRACTION AND TEMPERATURE-DEPENDENT QUADRUPOLE INTERACTION OF SUBSTITUTIONAL I-129 IN SI DUE TO JAHN-TELLER DISTORTION

Abstract A dope concentration dependent quadrupole relaxation and a large anisotropy of the recoilles fraction are observed for substitutional iodine impurities in silicon, using 129 I Mossbauer spectroscopy. The results are interpreted in terms of a transition from a static to a dynamic Jahn-Teller distortion.

Shape factors of the beta spectra of 170Tm, 186Re and 188Re

Abstract The beta spectra of 170 Tm, 186 Re and 188 Re have been investigated with an intermediate image spectrometer. In all three cases, the shape factors of the 1 − → 2 + and 1 − → 0 + transitions have been found to be approximately the same.

A new system for depth-selective conversion electron mössbauer spectroscopy

Abstract A conversion electron Mossbauer spectrometer has been constructed in which a mini-orange magnetic filter focuses conversion electrons emitted by a moving absorber onto a thin window silicon surface barrier detector. This detector serves as an electron spectrometer. A special multi-scaler is used to record a number of Mossbauer spectra, corresponding to different conversion electron energy groups, simultaneously. A large reduction in counting time compared to other methods of energy differential conversion electron Mossbauer spectroscopy is achieved by the relatively high transmission of the mini-orange (∼2%), the high efficiency of the detector and the feature of simultaneous recording. Depth selectivity is mainly limited by the resolution (600–900 eV) of the Si-detector. The system has been tested with a sandwich absorber of 57Fe evaporated onto stainless steel enriched in 57Fe irradiated by a 57Co Rh source.

The beta decay of 147Nd

The beta components with maximum energies of 806 and 364 keV in the decay of 147Nd have been studied. The coefficient a in the expression C(W) = k(1+aW) for the shape factor is found to be −0.07±0.01 for the 806 keV transition and −0.20±0.15 for the 364 keV transition. The previously reported degree of longitudinal polarization, measured for an electron energy of 261 keV, is −(1.000±0.025) v/c yielding b = 0.00±0.05 for the 806 keV component and b = 0.00±0.16 for the 364 keV component in the expression P = −(v/c)(1−b/W). The coefficients Rand e in the expression ϵ = (p2/W)(R+eW)/C′(W) for the β-γ angular correlation are R = −0.008±0.006, e = 0.002±0.003 for the (806β, 91γ) cascade and R = +0.06±0.05, e = −0.04±0.03 for the (364β, 531γ) cascade. The very low intensity of the beta component to the ground state of 147Pm (<0.2% of the 806 keV component) is briefly discussed.

Excited states of 166Er

Abstract The level scheme of 166Er has been studied from the decays of 166 Ho ∗ (> 30 y ) and 166Tm(7.7h) by means of scintillation and β-spectroscopic coincidence techniques. A discussion is given about the character of the excited states of 166Er.