K. Hinode

Recovery study of copper electron irradiated at 130 K by positron lifetime

Abstract The annealing behavior of election irradiated copper was studied by means of positron lifetime. In Stage III recovery, the long-lived component appeared in the lifetime spectrum. It was attributed to the formation of three-dimensional micro voids. Therefore it is concluded that vacancies are migrating in this temperature range. The lifetime component corresponding to micro voids remains up to a rather high temperature annealing. In addition to micro voids, the existence of other kinds of defects was concluded from the detailed analysis of the lifetime data. The defects formed in Stage III disappeared at high temperature but below the temperature of annealing out of micro voids. These defects were attributed to vacancy loops. Vacancy loops were also formed through the vacancy clustering in Stage III.

Positron study of the martensitic transformation in Fe-29.5at.%Ni

Precision measurements of positron lifetime spectra in Fe-29.5at.%Ni alloy specimens were performed to clarify the nature of the martensitic transformation in this alloy. The forward transformation did not introduce any defects which behave as strong trapping sites for positrons. On the other hand, the reverse transformation accompanied the production of defects, to which the positron lifetime is sensitive, maybe dislocations. From the present results, the nature of the transformation was discussed.

Positron annihilation in glassy metals

Glassy Ni-P and Co-P alloys are studied by positron annihilation. The angular correlation of the glassy state is not so different from that of the crystalline state of the alloys. This shows that the alloys do not consist of very fine crystals but a supercooled uniform glassy state. This result also supports the fact that positrons push neighbouring atoms in the liquid metals.

Effect of doping and thermal vacancies on positron annihilation in semiconductors

The effect of lattice defects on positron annihilation in semiconductors was studied. In silicon, any detectable doping effect could not be found. In germanium, the thermal equilibrium measurements of annihilation lineshapes showed no vacancy effect. From these experimental facts, the interaction of positrons with lattice defects was discussed.

Effect of gaseous impurity atoms on the formation of microvoids studied by positron annihilation

Abstract Positron annihilation techniques have been applied to study the nucleation, growth and annealing of voids and gas bubbles. This technique is extremely powerful for the study of microvoids and microbubbles which are too small to be observed by electron microscopy. The lifetime of a component of positron lifetime spectra determines the size of the voids and the intensity of the component determines the density of voids. From the results of irradiation damage in nickel, copper, aluminum, platinum, Cu-Ni alloy, Cu-B alloy, A1-Li alloy, iron, molybdenum and tantalum, it is concluded that gaseous impurity plays a quite important role for selecting whether bubbles and voids or collapsed vacancy loops are formed. This selection will be probably made at a fairly early stage, i.e., when several vacancies coagulate in a cluster.

Positron lifetime measurement in NaNO2

Positron lifetimes in NaNO2 were measured as a function of temperature. The lifetime spectra consisted of one component, and could not be resolved into two component. The positron trapping model is not applicable in this case. Observed changes of lifetimes around the transition temperature could not be understood only by the volume dilatation, but they must be affected by the ferro-para electric phase transition

Preparation of48V source for measurements of lineshapes of annihilation radiations and positron lifetimes

The preparation of the48V positron source induced in a 1 μm thick Ti foil by (3He, pxn) reaction with a cyclotron is described. This source is very convenient for measurements of lineshapes of annihilation radiations and positron lifetimes at low or high temperatures, in a vacuum or for liquid metals. The absence of the mixing of long lifetime components is also convenient for the study of defects.