Authors:E. Kuzmann, Z. Klencsár, Z. Homonnay, A Vértes, G. Braga, A. De Oliveira, V. Garg, M. Bódogh, I. Kotsis, and A. Nath
57Fe and 151Eu Mössbauer spectroscopy as well as RF susceptibility measurements were applied to study the effects of Pr substitution either into the rare earth or into the Ba site in Eu1–xPrxBa2Cu3O7– and EuBa2–xPrxCu3O7–, respectively. Site mixing of Pr between the rare earth and Ba sites could be excluded by the utilization of 57Fe Mössbauer spectroscopy. It was found that there exists a correlation between the 151Eu isomer shift and the onset temperature of the superconducting transition independent of the location of Pr. RF susceptibility measurements provide an evidence for a difference in the magnetic moment of Pr substituted for the Eu or Ba sites. The obtained results can be explained by hole filling as the dominant effect of Pr substitution.
Authors:M. Leitão, C. Nobre, J. Jesus, and J. Redinha
The study of trans- and cis-1,2-cyclohexanediol by infrared spectroscopy was performed. The variation of the maximum frequency and of the bandwidth of the OH stretching vibration give evidence of the role played by hydrogen bonding in the solid and liquid phases of both isomers and allows to follow the phase transitions. A solid rotator phase is shown for the cis compound.
A high-resolution high-rate ψ-spectroscopy system is essential or, respectively, useful in three groups of applications: (1)
measurement of nuclides with half-lives of less than one second; (2) Measurement of nuclides with half-lives in the second
range at high sample activity; (3) Measurement in the same counting geometry of sample series of highly different sample activities.
Examples are given for these applications.
The optimum condition for setting the single channel analyzer /SCA/ has been studied with respect to the time required for data acquisition in Mössbauer spectroscopy. It has been found that, regardless what the peak height to background ratio may be, for most practical purposes the best point to cut off the constant background is where the intensity of the Mössbauer peak drops to about 20% of its full height.
Authors:F. Ambe, Y. Ohkubo, S. Ambe, Y. Kobayashi, T. Okada, Y. Yanagida, J. Nakamura, K. Asai, Y. Kawase, and S. Uehara
The features of time-differential perturbed angular correlation (TDPAC) in studies on local chemical structures around impurity atoms are described in comparison with those of Mössbauer emission spectroscopy with four typical examples of recent applications to metal oxide systems, namely,99Rh
99Ru in -Fe2O3 and YBa2Cu3O7– and117Cd
117In in MO (M=Mn, Co, Ni) and BaRu2/3Cd1/3O3.
Authors:D. Barb, M. Morariu, O. Cozar, V. Znamirovschi, and R. semeniuc
Using Mössbauer spectroscopy the quinolinates of iron/II/ and iron/III/ have been studied. In iron/II/ quinolinate three sublattices were evidenced, two of them being attributed to Fe2+ ions and the third to Fe3+ impurities. In the iron/III/ quinolinate five structural sublattices were found, two of them containing Fe3+ ions, the other two Fe2+ ions and the fifth may be attributed to the interstitial Fe3+ ions.
Different iron hydroxide precipitation processes simulating radioactive waste, treatment have been investigated by Mössbauer spectroscopy at room temperature and at 80 K. Magnetic oxides (hematite or magnetite) partially affected by superparamagnetic relaxation have been observed. The crystallization degree and the particle size depend on the concentration and the addition order of chemicals. Much smaller particles were precipitated with Ca(OH)2 than with NaOH as neutralization reagent.
Utilizing a portable spectroscopy system, a quantitative method for analysis of samples containing a mixture of fission and
activation products in nonstandard geometries was developed. This method was not developed to replace other methods such as
Monte Carlo or Discrete Ordinates but rather to offer an alternative rapid solution. The method can be used with various sample
and shielding configurations where analysis on a laboratory based gamma-spectroscopy system is impractical. The portalle gamma-spectroscopy
method involves calibration of the detector and modeling of the sample and shielding to identify and quantify the radionuclides
present in the sample. The method utilizes the intrinsic efficiency of the detector and the unattenuated gamma fluence rate
at the detector surface per unit activity from the sample to calculate the nuclide activity and Minimum Detectable Activity
(MDA). For a complex geometry, a computer code written for shielding applications (MICROSHIELD) is utilized to determine the
unattenuated gamma fluence rate per unit activity at the detector surface. Lastly, the method is only applicable to nuclides
which emit gamma-rays and cannot be used for pure beta or alpha emitters. In addition, if sample self absorption and shielding
is significant, the attenuation will result in high MDA's for nuclides which solely emit low energy gamma-rays. The following
presents the analysis technique and presents verification results using actual experimental data, rather than comparisons
to other approximations such as Monte Carlo techniques, to demonstrate the accuracy of the method given a known geometry and
Authors:A. Weiss, G. Yang, J. Kim, A. Nangia, and N. Fazleev
Positron annihilation induced Auger Electron Spectroscopy (PAES), makes use a beam of low energy positrons to excite Auger transitions by annihilating core electrons. This novel mechanism provides PAES with a number of unique features which distinguishes it from other methods of surface analysis. In PAES the very large collisionally induced secondary electron background which is present under the low energy Auger peaks using conventional tecniques can be eliminated by using a positron beam whose energy is below the range of Auger electron energies. In addition, PAES is more surface selective than conventional Auger Spectroscopy because the PAES signal originates almost exclusively from the topmost atomic layer due to the fact that the positrons annihilating with the core electrons are trapped in an image correlation well just outside the surface. In this paper, recent applications of Positron Annihilation Induced Auger Electron Spectroscopy (PAES) to the study of surface structure and surface chemistry will be discussed including studies of the growth, alloying and inter-diffusion of ultrathin layers of metals, metals on semiconductors, and semiconductors on semiconductors. In addition, the possibilities for future application of PAES to the study of catalysis and surface chemistry will be outlined.
A neutron detector based on detection of the prompt gamma-radiation emitted as a result of neutron interaction with a suitable neutron absorber is described. Boron-10 loaded polyethylene is used as the neutron converter. Neutrons are thermalized in the polyethylene and are subsequently absorbed by 10B. The result of the neutron absorption is production of 7Li, in the excited state (7Li*) and an alpha-particle. This occurs for 94% of the absorbed neutrons. The 7Li* (T1/2 = 10-13 s) emits a 477.6 keV gamma-ray ("prompt" gamma-ray) after it is formed and may be detected in a gamma-ray spectroscopy system. Since the "prompt" gamma-ray peak is Doppler broadened – the recoiled 7Li* emits the gamma-ray on "fly" – it is easily distinguishable from other non-capture gamma-ray peaks. The neutron converter, 10B loaded into a polyethylene end cap placed on the standard gamma-ray spectroscopy detector, adds the neutron detection capability without impeding the system's gamma-ray spectroscopy characteristics. Results for detection of neutrons from a moderated 252Cf source are presented.