http://apo-prod.ansto.gov.au:80/dspace The APO digital repository system captures, stores, indexes, preserves, and distributes digital research material. 2013-05-20T20:07:43Z http://apo.ansto.gov.au/dspace/handle/10238/4616 Title: The magnetocaloric effect and critical behaviour of the Mn0.94Ti0.06CoGe alloy Authors: Shamba, P; Lwang, J; Debnath, JC; Kennedy, SJ; Zeng, R; Din, MFM; Hong, F; Cheng, ZX; Studer, AJ; Dou, SX Abstract: Structural, magnetic and magnetocaloric properties of the Mn(0.94)Ti(0.06)CoGe alloy have been investigated using x-ray diffraction, DC magnetization and neutron diffraction measurements. Two phase transitions have been detected, at T(str) = 235 K and T(C) = 270 K. A giant magnetocaloric effect has been obtained at around Tstr associated with a structural phase transition from the low temperature orthorhombic TiNiSi-type structure to the high temperature hexagonal Ni(2)In-type structure, which is confirmed by neutron study. In the vicinity of the structural transition, at T(str), the magnetic entropy change, -Delta S(M) reached a maximum value of 14.8 J kg(-1) K(-1) under a magnetic field of 5 T, which is much higher than that previously reported for the parent compound MnCoGe. To investigate the nature of the magnetic phase transition around T(C) = 270 K from the ferromagnetic to the paramagnetic state, we performed a detailed critical exponent study. The critical components gamma, beta and delta determined using the Kouvel-Fisher method, the modified Arrott plot and the critical isotherm analysis agree well. The values deduced for the critical exponents are close to the theoretical prediction from the mean-field model, indicating that the magnetic interactions are long range. On the basis of these critical exponents, the magnetization, field and temperature data around T(C) collapse onto two curves obeying the single scaling equation M(H, epsilon) = epsilon(beta)f +/- (H/epsilon(beta+gamma)). © 2013 IOP Publishing LTD 2013-02-05T13:00:00Z http://apo.ansto.gov.au/dspace/handle/10238/4597 Title: Reprocessing of B-10-contaminated Be-10 AMS targets. Authors: Simon, KJ; Pedro, JB; Smith, AM; Child, DP; Fink, D Abstract: Be-10 accelerator mass spectrometry (AMS) is an increasingly important tool in studies ranging from exposure age dating and palaeo-geomagnetism to the impact of solar variability on the Earth's climate. High levels of boron in BeO AMS targets can adversely impact the quality of Be-10 measurements through interference from the isobar B-10. Numerous methods in chemical sample preparation and AMS measurement have been employed in order to reduce the impact of excessive boron rates. We present details of a method developed to chemically reprocess a set of forty boron-contaminated BeO targets derived from modern Antarctic ice. Previously, the excessive boron levels in these samples, as measured in an argon-filled absorber cell preceding the ionisation detector, had precluded routine AMS measurement. The procedure involved removing the BeO + Nb mixture from the target holders and dissolving the BeO in hot concentrated H2SO4. The solution was then heated with HF to remove the boron as volatile BF3 before re-precipitating as Be(OH)(2) and calcining to BeO. This was again mixed with niobium and pressed into fresh target holders. Following reprocessing, the samples gave boron rates reduced by 10-100x, which were sufficiently low and similar to previous successful batches of ice core, snow and associated blank samples, thus allowing a successful Be-10 measurement in the absence of any boron correction. Overall recovery of the BeO for this process averaged 40%. Extensive testing of relevant processing equipment and reagents failed to determine the source of the boron. As a precautionary measure, a similar H2SO4 + HF step has been subsequently added to the standard ice processing method. © 2013, Elsevier Ltd. 2012-12-31T13:00:00Z http://apo.ansto.gov.au/dspace/handle/10238/4596 Title: Nuclear tools for characterising radiological dispersion in complex terrain: evaluation of regulatory and emergency response models Authors: Williams, Alistair G; Clark, Geoffrey H; Dyer, Leisa L; Barton, R Abstract: Routine operations of a nuclear research reactor and its facilities offer opportunities for collection of rare environmental tracer datasets which can be used for atmospheric dispersion model evaluation studies. The HIFAR reactor near Sydney, Australia, routinely emits the radioactive noble gas Ar-41, and other radionuclides such as Xe-133 and Xe-135 are also emitted from nearby radiopharmaceutical production facilities. Despite extremely low emission levels of these gases, they are nevertheless detectable using state-of-the-art technology, and sensitive detectors have been placed at four locations in the surrounding region which features complex terrain. The high research potential of this unique dataset is illustrated in the current study, in which predictions from two atmospheric dispersion models used for emergency response are compared with Ar-41 peak observations from the detector network under a range of stability conditions, and long-term integrated data is also compared with a routine impact assessment model. © 2005, Inderscience Enterprises Ltd. 2005-06-30T14:00:00Z http://apo.ansto.gov.au/dspace/handle/10238/4595 Title: Magnetization reversal in Nd-Fe-B based nanocomposites as seen by magnetic small-angle neutron scattering Authors: Bick, J-P; Honecker, D; Dobrich, F; Suzuki, K; Gilbert, EP; Frielinghaus, H; Kohlbrecher, J; Gavilano, J; Forgan, EM; Schweins, R; Lindner, P; Birringer, R; Michels, A Abstract: We have studied the magnetization-reversal process of a Nd2Fe14B/Fe3B nanocomposite using small-angle neutron scattering. Based on the computation of the autocorrelation function of the spin misalignment, we have estimated the characteristic size l(C) of spin inhomogeneities around the Nd2Fe14B nanoparticles. The quantity l(C) approaches a constant value of about 12.5 nm (similar to average Nd2Fe14B particle radius) at 14 T and takes on a maximum value of about 18.5 nm at the coercive field of -0.55 T. The field dependence of l(C) can be described by a model that takes into account the convolution relationship between the nuclear and the magnetic microstructure. © 2013, American Institute of Physics 2013-01-13T13:00:00Z