Effects of neutron irradiation on polycrystalline Mg11B2

TL;DR

This study investigates how neutron irradiation affects the structural and superconducting properties of polycrystalline MgB2, revealing that thermal neutrons cause main damage and that irradiation can enhance critical fields and current densities at certain levels.

Contribution

It provides new insights into the damage mechanisms and property enhancements in MgB2 due to neutron irradiation, especially considering isotopic enrichment to isolate effects.

Findings

Thermal neutrons are the primary damage source despite low 10B content.

Irradiation at certain fluences improves critical current density and upper critical field.

Higher fluences depress superconducting properties.

Abstract

We studied the influence of the disorder introduced in polycrystalline MgB2 samples by neutron irradiation. To circumvent self shielding effects due to the strong interaction between thermal neutrons and 10B we employed isotopically enriched 11B which contains 40 times less 10B than natural B. The comparison of electrical and structural properties of different series of samples irradiated in different neutron sources, also using Cd shields, allowed us to conclude that, despite the low 10B content, the main damage mechanisms are caused by thermal neutrons, whereas fast neutrons play a minor role. Irradiation leads to an improvement in both upper critical field and critical current density for an exposure level in the range 1-2x1018 cm-2. With increasing fluence the superconducting properties are depressed. An in-depth analysis of the critical field and current density behaviour has been carried out to identify what scattering and pinning mechanisms come into play. Finally the correlation between some characteristic lengths and the transition widths is analysed.