Unexpected 13N concentrations in ISIS synchrotron room air.

The specific activity of air in the large open room housing the 800-MeV proton synchrotron of the ISIS Spallation Neutron and Muon Source has been measured. Air from several positions within the ISIS synchrotron room was sucked through a long flexible tube, and run past a shielded HPGe gamma-ray detector outside the synchrotron room. In spite of an expectation that 13N should be the largest component of the overall activity in the air, the results of the measurements are consistent with the presence in the air of 11C and 41Ar only, and suggest that the activity in the air is mostly created not in the synchrotron room itself but in the massive shielding monoliths around the neutron-producing targets, monoliths through which ventilation air is drawn into the synchrotron room. Typical specific activities of 11C and 41Ar in the air in the synchrotron room are ∼0.10 and ∼0.03 Bq cm-3 respectively, the upper limit for 13N being at most ∼0.01 Bq cm-3.

Cascade of Magnetic-Field-Induced Lifshitz Transitions in the Ferromagnetic Kondo Lattice Material YbNi_{4}P_{2}.

A ferromagnetic quantum critical point is thought not to exist in two- and three-dimensional metallic systems yet is realized in the Kondo lattice compound YbNi_{4}(P,As)_{2}, possibly due to its one-dimensionality. It is crucial to investigate the dimensionality of the Fermi surface of YbNi_{4}P_{2} experimentally, but common probes such as angle-resolved photoemission spectroscopy and quantum oscillation measurements are lacking. Here, we study the magnetic-field dependence of transport and thermodynamic properties of YbNi_{4}P_{2}. The Kondo effect is continuously suppressed, and additionally we identify nine Lifshitz transitions between 0.4 and 18 T. We analyze the transport coefficients in detail and identify the type of Lifshitz transitions as neck or void type to gain information on the Fermi surface of YbNi_{4}P_{2}. The large number of Lifshitz transitions observed within this small energy window is unprecedented and results from the particular flat renormalized band structure with strong 4f-electron character shaped by the Kondo lattice effect.