UNCORRECTED PROOF Radiation Physics and Chemistry xxx (xxxx) 109740 Contents lists available at ScienceDirect Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem Radiations hardness of nanocrystalline nickel under 450 keV protons M. Salhi a, bd, e , S.E.K. Abaidia a, b, d , S. Mammeri a, b, c , A. Sari c, d, e , D. Kpeglo a, b , M. Maaza a, b, ∗ a UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology, College of Science, Engineering and Technology, University of South Africa, Muckleneukridge, PO Box 392, Pretoria-South Africa b Nanosciences African Network (NANOAFNET), Materials Research Department, iThemba LABS-National ResearchFoundation of South Africa, Old Faure Road, PO Box 722, Somerset West 7129,Western Cape - South Africa c Centre de Recherche Nucléaire de Birine, B.P. 180, Ain Oussera, Djelfa, Algeria d Unité de Recherche MPE, Faculté des Sciences de l’Ingénieur, Université M'hamedBougarra de Boumerdes, Algeria e Centre de Recherche Nucléaire d’Alger, CRNA, B.P. 399, 02 Bd. Frantz Fanon, Alger-Gare, Algiers, Algeria ARTICLE INFO Keyswords: Radiations hardness Proton irradiation Nanostructured Ni thin Films Defects Neutron optics ABSTRACT This contribution reports on the effects of 450 keV proton irradiation within the 10 15 –10 17 H + /cm 2 fluence range on nano-crystalline Ni thin films. The surface and in-volume induced damages were investigated by grazing inci- dence X-rays diffraction, atomic force microscopy, Rutherford backscattering as well as four-point probe resistiv- ity measurements. Within such a type of H + irradiation, a significant surface roughening and amorphization of the external parts of the Ni crystallites for the lowest fluence (10 15 H + /cm 2 and a re-crystalization for higher flu- ences (10 16 –10 17 H + /cm 2 ) was observed. 1. Inroduction Due to its high positive coherent nuclear scattering length (b Ni = 10.31Fm) as well as that of its several isotopes especially 58 Ni (b 58Ni = 14.41Fm), Nickel is the reflecting material of choice in neu- tron optics in general & for neutron guides in all modern neutron re- search reactors especially. It is used for the design of neutron guides as an effective reflectors, monochromators, polarizers & supermirrors (Jiang et al., 1992; Chernenko et al., 1994; Farnoux et al., 1993; Sella et al.,1992; Sella et al.,1993; Spegel et al., 1999; Chauvineau et al., 1999; Pardo, 1993,1995, 1996; Bridou et al.; Maaza et al., 1993,1994; 1993; Sella et al., 19,941; Menelle et al., 1997;Hamidi et al., 2012; Matiwane et al., 2018). Because such Ni based thin film optical coatings operate at grazing incidence geometry <1.5 Deg), hence the smoothness of their surface is of a pivotal importance. Unfortunately, such reflecting optical surfaces experience a severe roughening& hence a significant degrada- tion of their neutron optical properties. In view of quantifying the life- time of Ni based neutron optics, Ni resistance to various radiations, in- cluding gamma rays, neutrons as well as protons is to be considered. In- deed, one should expect that above a certain threshold of fluence, such radiations would induce a significant interfacial degradation which would provoke, in its turn, a severe decrease of their optical properties. The advantage of protons radiations is their relative availability within the bulk of accelerators in addition of the non activation phenomenon related to neutron irradiation. Hence, this contribution reports on the effects of 450 KeV protons radiations at various fluences on Ni thin films. More specifically, it reports on the effect of such radiations on their surface & their crystallographic properties. From the published literature on the subject, yet limited, one should point out the net discrepancy on the reported results so far (Hudson et al., 1997; Iwase et al., 2000; Iwata and Iwase, 2001; Jones et al., 1983; Yao et al., 2003). In addition, most of them have specifically focused on the modification of the mechanical properties (Fabritsiev et al., 2011; Matsuoka et al., 1970) Voegli et al. (Voegli et al., 2003) reported that ion-induced grain growth can take place only if the thermal spike vol- ume is larger than the grain volume or if it overlaps the grain bound- aries area. In such cases, it was observed that vacancies and vacancy clusters are formed while interstitials are accommodated by the grain boundaries [Nita et al., 2005]. In addition, Nita et al. [Nita et al., 2005] reported that there was no variation in the grain size in electro- deposited Ni nanostructures irradiated while establishing a change in the microstructure leading to an effective mechanical hardening. This latter consists of stacking fault tetrahedra with densities much lower than coarse Ni grains. Likewise, Sharma et al. [Sharma et al., 2011] re- ported similar hardening effect on nanocrystalline Ni but with a domi- nance of dislocations. Equally, Samaras et al. [Samaras et al., 2002] ∗ Corresponding author. UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology, College of Science, Engineering and Technology, University of South Africa, Muckleneukridge, PO Box 392, Pretoria-South Africa. E-mail address: Maaza@tlabs.ac.za (M. Maaza). https://doi.org/10.1016/j.radphyschem.2021.109740 Received 29 September 2020; Received in revised form 5 August 2021; Accepted 8 August 2021 0969-806/© 2021