Irreversibility fields and pinning potentials in U/n treated Bi2223/Ag tapes

The magnetoresistance R( T, B) of virgin and four 235U doped Bi2223/Ag tapes irradiated with thermal neutrons (U/n treated) has been measured in the temperature range T⩾50 K and magnetic field B⩽1 T. For B⩾20 mT the pinning potentials U 0 of U/n treated tapes were enhanced compared to that of virgin tape. The relative enhancement U 0( B,U/n)/ U 0( B, virg.) increased with matching field B φ and persisted to higher B at higher B φ . For U/n treated samples, U 0 showed universal variation with B/ B φ : U 0( B≲ B φ )∝( B φ / B) α with α≈0.5 and faster variation at higher B. The resistive irreversibility fields B irr( T) of all U/n treated samples for T≲100 K were also enhanced: B irr( T, U/ n)/ B irr( T, virg.) increased with B φ and the enhancement persisted to lower T for higher B φ . The maximum enhancements of B irr scale well with the corresponding enhancements of U 0( B).