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Study of Neutron Induced Defects in Ceramics using positron lifetime measurements


  Sharon May-Tal Beck [1]  ,  Aharon Ocherashvili [1]  ,  Maik Butterling [2]  ,  Wolfgang Anwand [2]  ,  Arie Beck [1]  ,  Andreas Wagner [2]  ,  Gerhard Brauer [2]  ,  Itamar Israelashvili [1]  ,  Or Hen [3]  
 [1] Physics department, NRCN,P.O.Box 9001, Beer-Sheva, Israel
[2] Institut für Strahlenphysik, Helmholtz-Zentrum Dresden-Rossendorf, 01314 Dresden, Germany
[3] School of Physics and Astronomy, Tel-Aviv university, Tel-Aviv 69978, Israel

There has been an increased interest in defects within structural materials motivated by future fission and fusion reactor needs. While reactor steels are extensively studied, much more research effort is needed in order to understand radiation damage in ceramic materials and its effect on their macroscopic characteristics [1].

Sapphire – the single crystal of Al2O3, is a candidate material to serve in diagnostic systems for burning plasma experiments [2], due to its transparency to a wide range of wavelengths (200-5000 nm), high melting temperature (~2300K) and hardness close to that of a diamond. Its optical and electronic properties are expected to be affected by the harsh radiation environment.

 

The family of ceramics that contains Boron is another interesting group of materials for the nuclear industry, mainly due to high cross sections for thermal neutron capture in Boron, which produce helium inside the material. The much higher neutron flux expected in future reactors can cause swelling of materials and macroscopic cracks formation. Helium is also considered to be one of the most interesting challenges for fusion reactors, due to alpha particles production in the D-T reaction. Materials that will be used as first wall, matrices for Li, or coating materials, will suffer from high radiation damage.

The sensitivity of Positron Annihilation Spectroscopy (PAS) methods to point defects makes them perfect tools to study radiation damage in its first stages of creation. Especially, Positron Annihilation Lifetime Spectroscopy (PALS) is sensitive to size and concentration of the point defects.

We present results of Sapphire and Boron Carbide (B4C) samples investigated by PALS at the Gamma Induced Positron Spectroscopy (GiPS) facility at the HZDR [3]. Un-irradiated Sapphire and B4C samples were measured, as well as neutron irradiated samples, to a fluence of 6*1018 n/cm2 and ~1015 n/cm2 for the Sapphire and B4C samples, respectively. Also presented are results of PALS meaureents, performed at the NRCN PAL system, of Sapphire samples, previously irradiated to a range of neutron fluences: 1-6*1018 n/cm2.

References

[1]  Workshop on Advanced Computational Materials Science: Application to Fusion and Generation IV Fission Reactors, Washington, D.C. 31 March – 2 April 2004.

[2] D.M. Duffy, Phil. Trans. R. Soc. A 368 (2010) 3315-3328.

[3] M. Butterling et al., Phys. Status Solidi A 207 (2010) 334-337.