Positron Annihilation Lineshape Research Articles

Positron annihilation characteristics in mesostructural silica films with various porosities

Porous silica films with various porosities were prepared via a sol-gel method using a nonionic amphiphilic triblock copolymer F127 as the structure-directing agent. Doppler broadening of positron annihilation radiation (DBAR) spectra were collected for the prepared films using a variable energy slow positron beam. Different linear relationships between positron annihilation line shape parameters S and W are found for the as-deposited films and calcined ones, indicative of the decomposition of the copolymer porogen in the as-deposited films upon calcination. This also reveals the variation of positron annihilation sites as a function of F127 loading or porosity. Strong correlations between positronium 3γ annihilation fraction, S parameter and porosity of the mesoporous silica films with isolated pores are obtained, which may provide a complementary method to determine closed porosities of mesoporous silica films by DBAR.

Mesoporosity in silica films studied by a slow positron beam and ellipsometry

Abstract Porous silica films were synthesized via a sol–gel method using a nonionic amphiphilic triblock copolymer F127 as the structural template. Mesoporosities of the prepared silica films were investigated by Doppler broadening of positron annihilation radiation (DBAR) spectroscopy, positron annihilation gamma-ray energy spectroscopy based on a slow positron beam, and ellipsometry. For the mesoporous silica films, the variation of positron annihilation line shape parameter reveals that the porosity of the silica films increases with loading more F127, which is also confirmed by a decrease of refractive index n. Little variation in positron 3γ-annihilation fraction is found for the silica films prepared with F127 loading less than 15 wt%, whereas a remarkable increment is seen for the films with higher loading. This indicates the pore percolation in porous silica films occurs around a loading of F127 with 15 wt%.

Void swelling in ion irradiated (15Ni–14Cr), Ti-modified stainless steel: A study using positron annihilation and step height measurements

The void swelling behaviour of (15Ni–14Cr) Ti-modified steels simulated by heavy ion irradiation, has been investigated using step height measurements and positron annihilation spectroscopy. 18% cold-worked samples were pre-implanted with helium at 170 keV and 275 keV energies so as to create a uniform helium concentration of 100 appm around the 588 nm depth region. This was followed by a 2.5 MeV Ni ion irradiation to create a peak damage of ~ 84 dpa (displacement per atom) at various irradiation temperatures between 700 and 970 K. The gross swelling which has occurred throughout the ion range is determined by step height measurements. Defect-sensitive positron annihilation lineshape S-parameter measurements show clear changes consequently to void formation as a function of sample depth. From the variation of the average S-parameter as a function of irradiation temperature, the peak swelling temperature has been deduced. The changes observed in step height measurements are compared with positron annihilation measurements and the results are discussed.

Microstructural Aspects of Irradiation Damage in A508 Gr 4N Forging Steel: Composition and Flux Effects

Abstract Neutron irradiation can promote significant changes in the microstructure and associated mechanical properties of low alloy steels. In particular, irradiation can induce the formation of non-equilibrium phases and segregation, which may lead to a degradation in toughness. In this study, the microstructural changes caused by neutron irradiation have been characterized in A508 Grade (Gr) 4N-type steels (∼3.5% Ni) using a variety of state-of-the-art analytical techniques including 3D-Atom Probe Field-Ion Microscopy and Small Angle Neutron Scattering, along with post-irradiation annealing studies combining Positron Annihilation Lineshape Analysis and hardness measurements. Important differences between conventional and “superclean” A508 Gr 4N steel have been identified in this investigation. The data indicate that Ni is not the controlling factor in the irradiation damage behavior of these materials; rather, the Mn content of the steel is a dominant factor in the irradiation-induced microstructural development of solute-related hardening features.

EXISTENCE OF A THIRD CRYSTALLINE PHASE IN TBBA

Positron annihilation lineshape (S-parameter) measurements and small angle X-ray scattering (SAXS) using synchrotron X-rays on liquid crystalline terepthal-bis-butylaniline (TBBA) are reported at cryogenic temperatures. The crystalline ↔ crystalline transition at 231 K deviates from the first order nature, as evidenced by the observation of a pronounced hysteresis in the layer spacing and the S-Parameter during the heating and cooling cycles. Presence of a possible third crystalline phase at a still lower temperature of 180 K is identified from X-ray diffraction patterns in corroboration with the slope change in layer spacing and electron density variations reflecting on the lineshape parameter.

EXISTENCE OF A THIRD CRYSTALLINE PHASE IN TBBA

Positron annihilation lineshape (S-parameter) measurements and small angle X-ray scattering (SAXS) using synchrotron X-rays on liquid crystalline terepthal-bis-butylaniline (TBBA) are reported at cryogenic temperatures. The crystalline ↔ crystalline transition at 231 K deviates from the first order nature, as evidenced by the observation of a pronounced hysteresis in the layer spacing and the S-Parameter during the heating and cooling cycles. Presence of a possible third crystalline phase at a still lower temperature of 180 K is identified from X-ray diffraction patterns in corroboration with the slope change in layer spacing and electron density variations reflecting on the lineshape parameter.

Fatigue Evaluation of Type 316 Stainless Steel Using Positron Annihilation Lineshape Analysis and β+-γ Coincidence Positron Lifetime Measurement

In order to non-destructively evaluate the degree of fatigue damage in type 316 stainless steel, frequently used in the primary system of nuclear power plants, positron annihilation lineshape analysis and β+-γ coincidence positron lifetime measurement were applied. In positron annihilation lineshape analysis, an energy spread of annihilation gamma ray peak was measured and expressed as the S-parameter. In positron lifetime measurement, mean lifetime analysis and two-component analysis were conducted. As a result, the S-parameter and the mean lifetime increased monotonously with fatigue life ratio. Strain-controlled fatigue increased more at the early stage of fatigue than stress-controlled fatigue. The S-parameter in the both stress- and strain-controlled fatigue reached almost the same value at the end of fatigue, and also the mean lifetime in the both stress- and strain-controlled fatigue reached almost the same value at the end of fatigue. In two-component analysis of positron lifetime measurement, the positron lifetime of the defect component did not change during fatigue, and the relative intensity of the defect component increased with fatigue life ratio. At the early stage, the relative intensity of defect component in the strain-controlled fatigue was larger than in stress-controlled fatigue, and both intensities reached almost the same value at the end of fatigue.

Orientational ordering in polymorphic terepthal-bis-4-butylaniline (TBBA)

Individual molecular tilt angle behavior in the smectic C region is represented upon application of a molecular statistical model to the polymorphic terepthal-bis-butylaniline (TBBA) in conjunction with the experimental layer spacings from SAXS measurements using the synchrotron X-ray beam. In the smectic A and smectic H phases of the mesogen, the order parameter fluctuations and pre-transitional effects responsible for sharp changes in the layer spacing and scattered intensities near the phase transition temperature are corroborated with varying positron annihilation lineshapes as a result of electron density fluctuations.

Positron trapping in plastically deformed Cd

Positron measurements, both lifetime and annihilation lineshape, have been performed in Cd, plastically deformed at room temperature by 40 and 60% thickness reductions. Less change in lineshape parameter for 60% deformation is observed. The annealing of 40% deformed sample between 25 and 200 °C indicates the breaking up of dislocation network during recrystallisation process.

Non-Destructive Evaluation of Fatigue Damage in Type 316 Stainless Steel Using Positron Annihilation Lineshape Analysis

We applied positron annihilation lineshape analysis for non-destructive evaluation of fatigue stored in type 316 stainless steel, mainly used in primary water lines of pressurized water reactors (PWR). Using 68 Ge as a positron source, an energy spread of annihilation gamma ray peaks from stainless steel specimens was measured. After preparing stress- and strain-controlled fatigue specimens, we investigated the relation between fatigue life and a non-destructive parameter of lineshape analysis defined as the S-parameter and compared the microstructure of the fatigue specimens with the S-parameter. As a result, there was good correlation between the S-parameter and fatigue life; the S-parameter increased with dislocation density monotonically. The relation between the S-parameter and fatigue life in stress-controlled fatigue differed from that in strain-controlled fatigue. The S-parameter increased faster in early stage of the latter than in the former. In stress-controlled fatig ue, the change in the S-parameter did not depend on stress amplitude in the range of ratio to yield stress under 0.9. In the strain-controlled fatigue, the change in the S-parameter did not depend on strain amplitude in the range from 0.25 to 0.31%. However, when stress amplitude or strain amplitude became higher, the change in the S-parameter increased largely in the early stage of the fatigue life. We demonstrated systematic data to evaluate the fatigue damage in type 316 stainless steel. (Received January 11, 2002; Accepted February 26, 2002)

陽電子消滅法による原子力発電所ステンレス鋼配管の疲労評価

Since positron annihilation lineshape analysis can evaluate the degree of fatigue damage, detecting defects such as dislocations in metals, we used the method to evaluate the degree of fatigue damage in a type 316 stainless steel pipe, which is used in the primary system of a nuclear power plant. Using 68Ge as a positron source, an energy spread of annihilation gamma ray peak from the material was measured and expressed as the S-parameter.Actual plant material cut from a surge line pipe of a pressurizer in a pressurized water type nuclear power plant was measured by positron annihilation lineshape analysis and the S-parameter was found. Comparing the S-parameter with a relationship between the S-parameter and fatigue life ratio of the type 316 stainless steel, we evaluated the degree of fatigue damage of the actual material. Furthermore, to verify the evaluation, microstructures of the actual material were investigated by TEM (transmission electron microscope) to observe dislocation densities. As a result, a change in the S-parameter of the actual material from standard as-received material (type 316 stainless steel) was in the range from −0.0013 to 0.0014, while variations in the S-parameter of the standard as-received material were about ±0.002; differences between the actual material and the as-received material were not significant. Moreover, the dislocation density of the actual plant material observed by TEM was almost the same as that of the as-received material. In conclusion, we could verify the evaluation of the positron annihilation lineshape analysis for fatigue damage.

ドップラー幅広がり測定を用いた陽電子消滅法によるSUS316鋼の非破壊的疲労評価

Aiming at non-destructive evaluation of fatigue stored in type 316 stainless steel which is mostly used in the primary water line of pressurized water reactor (PWR), we tried to apply positron annihilation lineshape analysis to fatigue damage. By making use of 68Ge as a positron source, an energy spread of annihilation gamma ray peak from stainless steel specimens was measured. We prepared stress controlled fatigue specimens and strain controlled fatigue specimens, and then we investigated the relation between fatigue life and a non-destructive parameter of lineshape analysis defined as S-parameter and compared the microstructure of the fatigue specimens with the S-parameter. As a result, it is seen that there exists a good correlation between the S-parameter and the fatigue life; the S-parameter increases with dislocation density monotonically. The relation between the S-parameter and the fatigue life in the stress controlled fatigue is different from that in strain controlled fatigue. The S-parameter in the latter increases faster in early stage than that in the former. In the case of stress controlled fatigue, the change in the S-parameter does not depend on stress amplitude in the range from 200 to 250 MPa. In the case of strain controlled fatigue, the change in the S-parameter does not depend on strain amplitude in the range from 0.25 to 0.31%. Finally we succeeded in demonstrating systematic data to evaluate the fatigue damage in type 316 stainless steel.

Positron annihilation study of defects in boron implanted silicon

Defects and their annealing behavior in boron implanted silicon have been studied using positron annihilation spectroscopy (PAS), ion channeling, nuclear reaction analysis, and transmission electron microscopy. Silicon wafers were implanted with 80 keV boron ions to fluences from 1012 to 1015 cm−2. Furnace annealing or rapid thermal annealing (RTA) of the implanted Si samples was conducted to temperatures in the range 750–950 °C in a N2 ambient. For as-implanted samples, the defect profiles extracted from PAS spectra were found to extend beyond the implanted boron distribution given by TRIM calculations. The Sdefect/Sbulk values increased monotonically with increasing boron fluences. For boron fluences ⩾1013 cm−2,Sdefect/Sbulk was found to be >1.04 (the characteristic value for divacancy), while Sdefect/Sbulk was found to be <1.04 for a boron fluence of 1012 cm−2. After annealing at 750 °C, all B-implanted samples had similar S-parameter values in the near-surface region, while in the deep region the S values for high B fluences (φ⩾1014 cm−2) were found to be lower than those for low B fluences (φ⩽1013 cm−2). Annealing at 950 °C did not change the S-parameter data for the lowest boron fluence (1012 cm−2), but caused a slight increase of the S parameters in the deep region for other boron fluences. RTA at 750 °C shows that major defects in B-implanted Si are annealed out within the first 3 s. An interesting transient annealing behavior is observed in which the S value decreases in the initial annealing stage, and then increases to a saturating value after prolonged annealing. Possible effects of electric fields resulting from the electrical activation of implanted boron on the behavior of positron annihilation line shapes after annealing are discussed.

Application of positron annihilation lineshape analysis to fatigue damage and thermal embrittlement for nuclear plant materials: Uchida, M., Ohta, Y., Nakamura, N. and Yoshida, K. 13th International Conference on NDE in the Nuclear and Pressure Vessel industries, Kyoto, Japan (22–25 May 1995) 349–353

Fatigue crack growth (FCG) threshold has been determined on Ti6A14V, Al 7475-T7351, quenched and tempered steel 24CrMo4 as well as on the Ni-base alloys Inconel 617 and Nicrofer 5219 Nb. The main objective of the studies was to prove the transferability of the experimentally determined FCG threshold to service type fatigue loading. For FCG threshold testing, the following requirements must be fulfilled: 1.(A) a FCG threshold has to be entirely above Kop;2.(B) a FCG threshold has to exist and has to be measured over the fatigue loading range Kmax, i.e. K∗max< Kmax<KIc;3.(C) a FCG threshold has to be the upper bound amplitude of cycles at a given Kmax, the action of which does not produce FCG no matter how these threshold amplitudes are applied:4.(D) a FCG threshold must be a material parameter useful for material characterization and FCG design methodology under all fatigue loading conditions.It was shown that all the experimental procedures, i.e. type I, III and IV tests, furnished ΔK T values for Al 7475-T7351, Ti6A14V and the quenched and tempered steel 42CrMo4. The results suggest that this might be true for all Al alloys, Ti alloys and steels. Therefore, any one test method can be used to determine ΔKT for these materials. The ASTM E 647 recommended procedure for threshold testing furnishes ΔKT values for these materials as well, if the R -ratio is equal to or higher than Rc.For the Ni-base alloys (Inconel 617 and Nicrofer 5219 Nb) only type III and IV tests can be used to determine a FCG threshold ΔKT. This is due to the different behaviour of Ni-base alloys with respect to Kop.

Defect annealing and the formation of Li-rich clusters in Al-Li alloys

Positron annihilation lineshape measurements are conducted on pure Al, Al-1.9 at.% Li and Al-(12.0-12.5) at.% Li alloys. The recovery of each sample following quench and/or cold-work treatments is discussed in terms of vacancy migration and clustering, dislocation annealing and precipitation. The results indicate precipitation in both alloy concentrations but no positron trapping at dislocations. All cold-worked alloys show large vacancy clustering effects, providing strong evidence of vacancy agglomeration at precipitates.

Deconvolution of Doppler-broadened positron annihilation lineshapes by the generalised least-squares method

Deconvolution of the Doppler-broadened annihilation radiation lineshape has been carried out using the generalised least-squares method. The nondashlinear background subtraction is examined through tail stripping and step function fitting procedures. Spurious oscillations of the residual instrumental function are found not to produce an efficient inverse transformation. For this reason least-squares solutions are subjected to a nondashnegativity constraint in order to reduce the oscillations in the deconvoluted spectrum. This procedure improves the results dramatically and shows promise as regards quantitative studies of the local momentum distributions and defect characterisation at various depths of solids in future positron beam experiments.

Positron Annihilation for the Non-Destructive Assessment of the Early Stages of Damage

Positron annihilation γ-ray lineshape analysis is one of the few techniques which can provide an early warning of incipient materials degradation in metallic components. The National NDT Centre at AEA Technology Harwell has developed a portable NDT system, the Positron Annihilation Lineshape Analysis (PALA) System, which can be used to carry out measurements both in the laboratory and at external sites. The system utilises the narrowing of the annihilation gamma ray lineshape, which occurs if the annihilation event occurs near vacancies in the lattice of a metal, to give information on the early stages of damage. A brief description of the PALA system is given, and its use to measure plastic damage in a number of cases illustrated

Surface acidity by positron annihilation lineshapes

An alternative new method to measure the specific acidity of catalytic materials with large internal surface areas by using positron annihilation spectroscopy was introduced. Results of lineshape parameter evaluations from two-dimensional angular correlation and Doppler broadened annihilation radiation measurements for a zeolite ZSM-5 were presented.

Experimental studies of positron stopping in matter: the binary sample method

The measurement of implantation profiles and median implantation depths for keV positrons in solids is described. Details of the experimental technique, which is based on the difference between positron annihilation lineshape parameters in two materials that otherwise appear similar to the incident positrons, are presented, using the examples of aluminium-glass and gold-tungsten. Criteria for the suitability of the two elements of the binary sample are discussed, as are limiting factors such as post-implantation diffusion and trapping at interfaces.

Temperature Dependence of Positron Trapping to Dislocations in Deformed Zinc

Doppler-broadened lineshapes of positron annihilation in zinc have been measured as a function of temperature between 4.2 and 270 K after deformation and annealing up to various temperatures. The experimental results are well described in terms of a generalized trapping model where positrons become trapped in deep traps ( e.g. , jogs) via shallow traps (dislocation lines). It has been found that the positron trapping rate to the dislocation line decreases rapidly with increasing temperature up to about 80 K, whereas above 80 K the trapping rate is basically constant. The binding energy between a positron and a dislocation line has been shown to be about 50 meV.