Positron annihilation spectroscopy study of radiation-induced defects in W and Fe irradiated with neutrons with different spectra

Abstract

The paper presents new knowledge on primary defect formation in tungsten (W) and iron (Fe) irradiated by fission and high-energy neutrons at near-room temperature. Using a well-established method of positron-annihilation lifetime-spectroscopy (PALS), it was found that irradiation of W in the fission reactor and by high-energy neutrons from the p(35 MeV)-Be generator leads to the formation of small radiation-induced vacancy clusters with comparable mean size. In the case of Fe, smaller mean size of primary radiation-induced vacancy clusters was measured after irradiation with fission neutrons compared to irradiation with high-energy neutrons from the p(35 MeV)-Be generator. It was found that one of the reasons of the formation of the larger size of the defects with lower density in Fe is lower flux in the case of irradiation with high-energy neutrons from the p(35 MeV)-Be source. The second reason is enhanced defect agglomeration and recombination within the energetic displacement cascade at high energy primary knock-on-atoms (PKAs). This is consistent with the concept of the athermal recombination corrected (arc-dpa) model, although the measured dpa cross-section of both fission neutrons and wide-spectrum high-energy neutrons in W is between the conventional Norgett–Robinson–Torrens (NRT-dpa) and arc-dpa predictions. This means that the physics of the primary radiation effects in materials is still not fully known and requires further study through a combination of modeling and experimental efforts. The present data serve as a basis for the development of an improved concept of the displacement process.

A new approach to near-surface positron annihilation analysis of ion irradiated ferritic alloys

“…The introduction of new vacancy-type defects in solids can be characterised by positron annihilation spectroscopy either in terms of an introduction of a new defect component(s) in positron lifetime spectrum (PALS measurements) or in terms of an increase of the line shape S parameter (DBS measurements). 2 Positron lifetime is given by an overlap of the positron density and the local electron density at the annihilation site. S parameter characterises the Doppler broadening of the annihilation line due to the non-zero momentum of the annihilating electrons.…”

“…Irradiation of bulk specimens in neutron radiation environments of various nuclear reactors inevitably leads to an induced activity of the tested samples. To minimise the handling of "hot" radioactive materials, research studies are either aimed at small-scale (miniaturised) samples [1] or relatively low neutron fluencies [2,3]. To experimentally simulate the neutron environment without the induced activity, neutrons can be effectively replaced in irradiation experiments by charged particles such as protons [4], alphas [5] or self-ions [6], respectively.…”

“…To minimise the handling of “hot” radioactive materials, research studies are either aimed at small-scale (miniaturised) samples 1 or relatively low neutron fluencies. 2,3 To experimentally simulate the neutron environment without the induced activity, neutrons can be effectively replaced in irradiation experiments by charged particles such as protons, 4 alphas 5 or self-ions, 6 respectively. A standalone ion implantation experiment, or irradiations using a combination of two, 7 or three 8 different ions simultaneously, enables very efficient simulation of the environments of thermonuclear reactors, with high production rates of transmutation elements such as hydrogen or helium.…”

Extended Positron‐Trapping Defects in the Eu3+‐Doped BaGa2O4 Ceramics Studied by Positron Annihilation Lifetime Method

“…[28][29][30][31][32][33] Among the less conventional but promising methods to study the defect-related free volumes in solids of different structural types is positron annihilation lifetime (PAL) spectroscopy. [34,35] This technique has long been serving as a tool for structural analysis of such functional materials as ceramics, [36,37] glass, [38] polymers, [39] nanocomposites, [40] etc. Researchers in the field have presented a number of approaches to the analysis of PAL spectra of ceramic materials and to the proper decomposition of such spectra into different numbers of components.…”

Positron Annihilation Lifetime Spectroscopy Insight on Free Volume Conversion of Nanostructured MgAl2O4 Ceramics

“…Positron annihilation lifetime spectroscopy (PALS) technique is considered as one of the promising alternative methods to analyze free volume and defects in functional and other materials [1][2][3][4][5], including ceramics [6][7][8], glasses [9][10][11], polymers [12][13][14], nanocomposites [15][16][17], etc. There are already several attempts to develop a phenomenological model describing the processes of positron annihilation in metal powders that contain Cu-, W-, Ni- [18], some types of BaTiO 3 [19][20][21] and SrTiO 3 perovskites [22,23], nanocrystallite ferrites [24,25], Ni-Cr alloy [26], In 2 O 3 nanocrystals [27], irradiated W and Fe [28], water diffusivity transition in composites [29,30] and others. Different approaches to the analysis of annihilation spectra as well as decompositions with a different number of components were introduced.…”