B. G. Turrell

Planar array of superheated superconductors: An improved superheated superconducting granule detector

We have invented a new superheated superconducting granule detector which is a prime candidate for sensing dark matter and which could prove very useful for other applications. The sensor element is a planar array of spherical granules for which the spread in transition temperatures is nearly an order of magnitude smaller than that for a colloidal device. The detecting efficiency for low‐energy deposition is thereby significantly increased. Preliminary results are described.

Pulsed nuclear magnetic resonance of oriented nuclei in an insulating magnetic material:54Mn−MnCl2.4H2O

The first observation of pulsed nuclear magnetic resonance of oriented nuclei in an insulating magnetic material is reported. The system studied was the ordered antiferromagnet54Mn−MnCl2.4H2O. The response of the54Mn spins to a single pulse of variable length, the free induction decay, and Hahn spin-echo have all been observed. A discussion of the transverse decoherent relaxation timeT2 in MnCl2.4H2O is given.

Nuclear magnetic resonance of oriented54Mn nuclei in antiferromagnetic MnCl2 · 4H2O

Nuclear magnetic resonance of oriented54Mn nuclei in antiferromagnetic MnCl2 · 4H2O has been observed. The first two lines of the sextuplet split by quadrupole interaction are at frequencies 500.4 and 514.7 MHz, implying a hyperfine field of 643(5) kG. The stronger line at 500.4 MHz has a half-width at half maximum of 60 kHz and is shifted downward and split in frequency on application of a magnetic field. The nuclear spin-lattice relaxation time is dependent both on the applied field and the size and/or quality of the crystal.

First observation of double quantum nuclear magnetic resonance of oriented nuclei

Abstract Double quantum nuclear magnetic resonance of oriented nuclei has been observed for the first time. The systems studied were 54MnMnCl2·4H2O and 54MnMn (COOCH3)2·4H2O and rotation patterns, free induction decays and spin echoes all have been observed. The double quantum signal can be significantly larger than the single quantum signal.

Recent developments in superheated superconducting granular detectors

Abstract The operation of a superheated superconducting granular detector with a SQUID readout is described, and the advantages and limitations of the colloidal device discussed. A new sensor consisting of a planar array of granules is described and results demonstrating an order of magnitude decrease in the spread of transition temperatures are presented.

Neutron detection using a planar array of superheated superconductors

Abstract A new thermal neutron detector consisting of an indium/mylar PASS array with a filler of boron powder has been tested successfully. A boron nucleus captures a neutron and the α-particle emitted in this reaction nucleates the transition to the normal state in a neighbouring grain. A PASS with grain radius r = 12 μ m showed very low response to irradiation by 835 keV γ-rays. The same PASS responded to α-particles with high efficiency, and thermal neutrons were detected with good efficiency and very low background. Thermal neutrons were also counted with an R = 25 μ m PASS. The use of large granules will allow spatial resolution to a single grain to be obtained and a read-out based on conventional inductive coupling and fast electronics to be utilized.

Nuclear orientation and nuclear spin-lattice relaxation in insulating magnetically ordered crystals

The mechanism of nuclear spin-lattice relaxation in insulating magnetically ordered crystals at low temperatures is discussed. In 3-dimensional systems the relaxation time T1 is long, but in the lower dimensional systems it can be quite short making them possible candidates for hosts in on-line experiments. An experiment in 2-dimensional54Mn−Mn (COOCH3)2·4H2O is discussed with particular reference to the relatively short value of T1 in low applied fields. A preliminary experiment in the 1-dimensional system54Mn−(CH3)4NMnCl3 (TMMC) is also described. Pulsed NMRON measurements in54Mn−MnCl2·4H2O are outlined and the advant-systems with fast relaxation emphasized.

Progress in the Development of the Tin PASS Granule Detector

Progress in the development of a PASS granule detector is reported. Arrays with small tin spheres, with radius r⋍2µm, have been fabricated. The responses of tin PASS samples, with r⋍2 µm and r=8 µm, to low energy γ-radiation have been measured and analyzed. Also the performance of a multilayer PASS has been investigated.

Pulsed NMRON studies of insulating magnetic materials

The apparatus and instrumental techniques developed for pulsed NMRON studies of insulating ordered magnets are described. Experiments have been performed on two salts,54Mn-MnCl2·4H2O and54Mn-Mn(COOCH3)2·4H2O, and rotation patterns, free induction decays and spin echoes have been obtained for both single quantum and double quantum transitions. The pulsed technique can produce signals larger than those obtained in CW NMRON, and is well suited for the measurement of the very short spin-lattice relaxation times that can occur in these systems.

Nuclear spin-lattice relaxation in54Mn-MnCl2.4H2O and lower dimensional magnetic systems

We report on nuclear spin-lattice relaxation studies on54Mn-MnCl2.4H2O and 2-dimensional54Mn-Mn(COOCH3)2.4H2O. In the former crystal, we find that at the lowest temperatures a direct process, normally thought of as forbidden, becomes the mechanism for relaxation. In lower dimensional systems the relaxation might be expected to be relatively fast and indeed in the acetate the relaxation timeT1 is ≈1000 s in an applied field of 0.2 T for the Mn2 site and is much shorter at lower fields. In 1-dimensional54Mn-(CH3)4NMnCl3(TMMC) a significant γ-ray anisotropy is observed on cooling indicating thatT1 is also short in this system. The shortness ofT1 in the lower dimensional systems suggests that they may be suitable hosts for on-line experiments.