Application of nuclear reaction geometry for 3He depth profiling in nuclear ceramics

Direct observation of nuclear reactions leading to the emission of charged particles (p or α) allows to determine specifically the spatial distribution of isotopes of light elements from 1H to 23Na and despite low cross section values some heavier isotopes from 24Mg to 68Zn. After a brief overview of the analytical capabilities offered by μNRA, this contribution is focussed on the measurement of the thermal diffusion coefficient of 3He in crystalline ceramics. The experimental method is based on the observation of the 3He(d, p)α reaction. Due to the severe energy loss along the outgoing path, the choice of the detection of the high energy proton or recoil α nucleus depends on the average depth of the 3He distribution. For near surface distributions (<2 μm), the detection of the α-particle gives a good depth resolution (50 nm). For larger depths (5<x<10 μm), the detection of the 12-14 MeV proton limits the depth resolution around 100 nm. After temperature-controlled annealing, the thermal diffusion coefficient can be deduced from the broadening of the helium-3 depth profile according to the classical Fick's law formalism by using the computing code SIMNRA. Several examples concerning simple oxides and more complex ceramics considered as potential nuclear waste forms or transmutation targets are then presented and discussed