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Phonons and phase transitions in finite nuclei
No full textThe nature and evolution of collectivity and coherence in nuclei is one of the most fundamental issues in nuclear structure and its evolution with N and Z. Despite many experiments, the nature of nuclear vibrational modes in deformed nuclei and the nature of nuclear phase/shape transitions are not at all understood. We discuss new experiments on phonon and multi-phonon states in the rare earth nuclei and on new evidence for phase coexistence in Sm that relates to the possible existence of phase transitional behavior in finite nuclei
Current topics in gamma-ray astrophysics
No full textThis paper reports on recent progress toward unraveling the origin of gamma-ray bursts. It is concluded that neutron-star binaries are one of the few remaining candidates. A model is proposed based upon general relativistic hydrodynamic studies which indicate a new physical. process by which to power a gamma-ray burst. Relativistically driven compression, heating, and collapse of the individual neutron stars can occur many seconds before inspiral and merger. This compression may produce a neutrino burst of similar to 10(53) ergs lasting several seconds. The associated thermal neutrino emission produces an e(+)-e(-) pair plasma by annihilation. We show first results of a simulated burst which produces similar to 10(51) erg in gamma rays of the correct spectral and temporal properties
Neutrino induced Doppler broadening
No full textWhen a nucleus undergoes beta decay via the electron capture reaction, it emits an electron neutrino. The neutrino emission gives a small recoil to the atom, which can be experimentally observed as a Doppler broadening on subsequently emitted gamma rays. Using the two-axis flat-crystal spectrometer GAMS4 and the electron capture reaction in Eu-152, th, motion of atoms having an excess kinetic energy of 3 eV in the solid state was studied. It is shown how the motion of the atom during the first hundreds of femtoseconds can be reconstructed. The relevance of this knowledge for a new neutrino helicity experiment is discussed
Thermal conductivity of saturated liquid toluene by use of anodized tantalum hot wires at high temperatures
No full textAbsolute measurements of the thermal conductivity of a distilled and dried sample of toluene near saturation are reported. The transient hot-wire technique with an anodized tantalum hot wire was used. The thermal conductivities were measured at temperatures from 300 K to 550 K at different applied power levels to assess the uncertainty with which it is possible to measure liquid thermal conductivity over wide temperature ranges with an anodized tantalum wire. The wire resistance versus temperature was monitored throughout the measurements to study the stability of the wire calibration. The relative expanded uncertainty of the resulting data at the level of 2 standard deviations (coverage factor k = 2) is 0.5 % up to 480 K and 1.5 % between 480 K and 550 K, and is limited by drift in the wire calibration at temperatures above 450 K. Significant thermal-radiation effects are observed at the highest temperatures. The radiation-corrected results agree well with data from transient hot-wire measurements with bare platinum hot wires as well as with data derived from thermal diffusivities obtained using light-scattering techniques
Radiative calibration of heat-flux sensors at NIST: Facilities and techniques
No full textWe present an overview of the National institute of Standards and Technology high temperature blackbodies, both in operation and in development, suitable for heat-flux sensor calibration. Typical results of calibrations using the transfer technique in the 25 mm Variable-Temperature Blackbody are presented to demonstrate the long-term repeatability of the calibration technique. A comparative study of the absolute and transfer calibrations of a Garden gage in a spherical blackbody with a cooled enclosure surrounding the gage housing was conducted. Results of this study demonstrated the influence of convection associated with absolute calibration of sensors in a cooled enclosure. Plans for further development of the transfer technique to higher heat-flux levels and the associated technical issues are discussed
Thermal-conductivity apparatus for steady-state, comparative measurement of ceramic coatings
No full textAn apparatus has been developed to measure the thermal conductivity of ceramic coatings. Since the method uses an infrared microscope for temperature measurement, coatings as thin as 20 micro-m can, in principle, be measured using this technique. This steady-state, comparative measurement method uses the known thermal conductivity of the substrate material as the reference material for heat-flow measurement. The experimental method is validated by measuring a plasma-sprayed coating that has been previously measured using an absolute, steady-state measurement method. The new measurement method has a relative standard uncertainty of about 10 %. The measurement of the plasma-sprayed coating gives 0.58 W.m(-1).K-1 which compares well with the 0.62 W.m(-1).K-1 measured using the absolute method
Nuclear structure - The future with radioactive beams
No full textSome examples of new phenomena expected at extreme Values of neutron and proton number are discussed, including soft dipole modes and neutron-proton pairing. First results on the N = Z nucleus Ga-62 are presented in the context of the competition between T = 0 and 1 states in odd-odd, self-conjugate nuclei
Study of interatomic potentials in ZnS - Crystal-GRID experiments versus ab initio calculations
No full textCrystal-GRID measurements have been performed with ZnS single crystals. For the first time, an asymmetric Crystal-GRID line shape could be observed. The preliminary data evaluation indicates that the reported lifetime of the 3221 keV level in S-33 is too short. A value of about 60 fs has been found. Due to this ""long"" lifetime the line shape is much less structured than calculated with the reported lifetime
