Neutron beam damage

Simulation of the neutron-induced damages using triple ion beams is schematically shown in Fig. 7. A proton and a helium ion are provided by the ion implanter and the single-ended accelerator, respectively. Heavy ions, such as iron or silicon, accelerated by the tandem accelerator, are injected into the target simultaneously. For example, the SiC/SiC composite was tested under triple ion beam irradiation consisting of a 380-keV proton, a 1.2-MeV helium ion, and a 7.8-MeV Si " ion. The triple irradiation system is equipped with an energy degrader and a beam scanner for uniform three-dimensional (3-D) irradiation. 

Figure 7 Schematic drawing of the damage in reactor materials induced by neutrons, and its simulation by the triple-ion-beam irradiation.

Probably the most important of these is the diffraction of waves from the film. X-ray diffraction, neutron diffraction and electron diffraction have all been employed and examples of their use will be discussed below. For films less than a few micrometres thick, X-rays and neutrons can only be used in the low angle mode as the diffracting power of such films is not sufficient to obtain useful results if the incident beam is directed normally at the film. Electron diffraction can be used with relatively thin films but the destructive effect of the high energy beam often damages the film before an image can be recorded. 

Ion implantation is often recommended as an efficient tool to enhance electrocatalysis either by disrupting the surface structure of the catalyst or by placing active atoms on an inactive (or less active) matrix. The latter possibility (which links this section with Section 3.3 devoted to adatoms) offers also a way to the use of extremely small amounts of active but expensive materials. In order to investigate the effect of surface damages, self-implantation or ion beam bombardment is the most appropriate approach. Implantation of Ni on Ni has led to a modest enhancement of the surface area, but not to electrocatalytic effects [279]. On the other hand, Pt bombarded with neutrons has shown an increase in the activity for hydrogen evolution [280]. However, it has been suggested that this is not related to the formation of surface defects, but rather to the effect of the radioactivity induced on the electrode and on the electrolyte. 

The rate at which electron radiation damage occurred in neutron-irradiated specimens also varied from one variety of quartz to another. Whereas synthetic quartz (dose Dq) became amorphous after a few seconds of exposure to a focused electron beam, amethyst quartz (dose < Do) was more stable in the electron beam than the sample before neutron irradiation. 

Thermal neutrons have a low energy (0.025 eV) compared to X-rays (10000 eV) and they are a non-ionising radiation. This means that protein crystals are not damaged by neutrons as they are by X-rays or electrons. Hence, a crystal can remain in the beam for extremely long periods (even years) without suffering radiation damage. This offers a partial compensation for the low flux of neutron sources. 

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