= Solution
The annealed sample initially has relatively few obstacles to <dislocation glide>. After its elastic response it yields, undergoes appreciable plastic deformation and develops <strain hardening>. Irradiation produces <dislocation loops> and defect clusters that obstruct gliding <dislocations>, usually raising the <yield strength>. In a simple dispersed-obstacle model the strengthening scales as $\Delta\sigma\sim M\alpha Gb\sqrt{Nd}$, with obstacle density $N$ and diameter $d$.
Irradiated material often has less uniform plastic elongation and weaker subsequent hardening because slip localizes into channels that have cleared irradiation obstacles. Earlier <necking> or fracture can then reduce ductility. The elastic slope is much less affected than the yield <stress> in this schematic comparison; the exact strength and elongation depend on dose and <temperature>.
\Image[/past-exam-of-the-materials-science-course-of-the-university-of-cambridge/2019/paper-1-irradiation-mechanics.png]
{title=Irradiation hardening and convergence toward a dose-dependent dislocation steady state}
{description=Original illustrative curves. Stress, strain and dose scales are schematic rather than measured stainless-steel data; the dose model uses fixed irradiation conditions.}
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