Micro-magnetic susceptometer for the actinides

A d.c. magnetic susceptometer incorporating a S.Q.U.I.D. as a magnetic flux sensor has been constructed with sensitivity to measure the magnetic susceptibility of submicrogram actinide samples as a function of temperature. For a two microgram actinide sample the minimum measurable dimensionless susceptibility is approximately 10-7 CGS in a 2000 gauss field. The sensitivity has been determined in a series of calibration experiments using samples of lead spheres at 4.2 K. Pick-up coils insensitive to changes in spatially uniform fields and fields with a constant first derivative were used to reduce noise. The field was trapped in a niobium cylinder to produce a uniform stable applied field. The flux produced by the sample in the pick-up coils is proportional to the magnetic susceptibility of the sample and is a function of the sample position