Direct Correlation Method Research Articles

Level spin-parities and γ-ray transition multipolarities in140Ce

The gamma gamma directional correlation method was used to determine the spins of levels in 140Ce populated following the beta decay of 140La. The multipolarities of gamma -ray transitions were measured and, on the basis of the dominant multiple and published ICC data parity assignments were made. Past ambiguities in the decay have been removed, and from the present measurements the authors make unique spin-parity assignments to the following levels: 2350.0 keV, 5+; 2516.1 keV, 3+; 2548.0 keV, 1+. The structure is well accounted for by the shell-model calculation of B.H. Wildenthal, (1969). The level systematics of nuclei in this region are examined and it is found that the change from a vibrational- to a rotational-like structure is not so well defined as in heavier isotopes such as Sm or Gd. The behaviour of the 3- level energy as a function of Z value is examined for a ground of isotones in this mass region and is found to be linear.

Levels and transitions in142,144Ce populated following the βdecay of142,144La

The levels populated in 142,144Ce and the gamma -ray transitions between these levels have been studied by the gamma gamma directional correlation method following the beta decay of 142,144La. The lanthanum activities were produced by the decay of the corresponding caesium fission products. These were selected by the on-line mass separator OSTIS and the measurements were made in an off-line position. Coincidences were recorded in the event-by-event mode by a pair of Ge(Li) detectors and the correlations were measured at six angles. The coincidence data were analysed for a selection of gates to produce extensive decay schemes and transition intensities were also determined. The correlation data provide firm spin assignments to most levels and yielded multipole mixing ratios for many transitions in each isotope. Parity assignments to levels were made on the basis of dominant multipolarities. The experimental results provide extensive data on these transitional nuclei.

Eddy flux measurements over the ocean and related transfer coefficients

Eddy correlation measurements of vertical turbulent fluxes made during AMTEX 1975 are used to assess the reliability of flux prediction from established bulk transfer relations, using both surface-layer and planetary boundary-layer formulations. The surface-layer formulae predict momentum and latent heat fluxes to an accuracy comparable to the direct eddy correlation method, using transfer coefficients of CDN (at 10m and in neutral conditions) increasing with wind speed, and a constant CEN ∼- 1.5 × 10−3. The data suggest CCHN, for sensible heat, increases significantly with wind speed and is on average 30% lower than CCEN The boundary-layer drag coefficient, CGD, agrees within about 40% of recently published values using a vertically averaged geostrophic wind to the height of the lowest temperature inversion, corrected for trajectory curvature. Values of θ*/δθ from which CCGH is derived, are in excellent agreement if the published values are modified to account for inappropriate surface temperatures used in their derivation. Preliminary values of CGE are also presented.

Mixing of the transitions from the 3 + quasi γ-band level in 152Gd

The directional correlation method was used to determine the multipole mixing ratios of some γ-transitions in 152Gd. The 678.6 and 1089.8 keV γ-rays from the 3 + quasi γ-band level were observed to be almost pure E2 transitions, which is in disagreement with earlier results. The B(E2) ratios of the transitions from this level are consistent with theoretical calculations.

The E2/M1 mixing of the transitions from the Kπ = 2 + bands in 190, 192Os and 192Pt

The directional correlation method was used to determine multipole mixing ratios of several γ-transitions in 190, 192Os and 192Pt. A new level at 1406.4 keV has been established in 192Pt. The experimental E2/M1 mixing ratios of the transitions from the γ-bands have been compared with theoretical predictions of the Greiner model also including the rotation-vibration interaction, the Kumar-Baranger model and the Zackrevsky model.

Spins of levels in 194Pt

Selected cascades in the level scheme of the 194Pt nucleus have been studied by the γ-γ directional correlation method and the spins of the 924, 1513, 1623, 1672 and 1798 keV levels determined to be 3, 2, 2, 2 and 1 respectively. The multipole mixing ratios of the 301, 594, 1184 and 1295 keV γ-transitions have been determined and a number of B(E2) ratios are compared with theory.

E2/M1 mixing ratios of γ-transitions from the γ-vibrational band to the ground state band in 152Sm, 154Gd and 168Er

Abstract Using the γγ directional correlation method we have determined the E2/M1 mixing ratios of collective γ-transitions from the γ-vibrational band to the ground state rotational band for the deformed doubly even nuclei: 152 Sm: δ 22 = 11.0±1.0, δ 32 = 8.9±1.0, 154 Gd: δ 22 = 10.2±1.0, δ 32 = 6.6±0.7, 168 Er : δ 22 = -65 ± 26 135 For these measurements we used Nal(Tl) detectors as well as Ge(Li) detectors. The mixing ratios of the 2 + -2 + transitions for the nuclei at the beginning of the deformed region are in agreement with the predictions of the theories of Greiner and Bes et al., while for 168 Er it differs by nearly an order of magnitude. The ratios δ 32 δ 22 for Sm and Gd are in fair agreement with the theoretical predictions corrected for band mixing.

A Proper Wind-stress Drag CoefficientFormulation For Computer ModellingOf Seas And Coastal Regions

On the basis of the aerodynamic roughness parameterization formulated by Donelan et al in 1993 an overwater shear velocity equation is proposed which is a function of wind and wave information available routinely (i.e., wind speed, significant wave height, and spectral peak wave period) This proposed wind-wave interaction method is then compared to the direct eddy correlation method using the North Sea dataset provided by Geernaert et al in 1987. It is found that in the North Sea (where the JONSWAP wave formulation is valid) the composite RMSE between these two methods was 6.5 cm/sec when the wind speed was between 3 and 25 m/sec and the significant wave height between 1 and 8 m. Application of this wind-wave interaction method under both cyclogenesis and hurricane conditions show that the agreement between this method and others is within 95%. Therefore, for a site specific sea and coastal region, the proper drag coefficient formulation must incorporate the wave characteristics of that region Since the method proposed in this study is able to handle this requirement, it is recommended for general use.

Decay of Ce144

Level structure of Pr 144 was investigated by gamma-gamma coincidence measurements and the spins of the levels were determined using the gamma-gamma directional correlation method. The 166 keV level proposed by Freeman has been confirmed. A new 92 keV gamma ray coincident with the 41 keV gamma ray has been found. A decay scheme containing the new level is proposed. Interpretations of the levels are discussed in terms of the shell model.

Decay of Eu148

The level structure of Sm–148, which is near the neutron closed shell 82, has been studied by the analyses of the radiations from the decay of Eu–148 (54 days) with various scintillation spectrometers. The single and the coincidence measurements were made by means of 3''×3'' and 2''×2'' NaI(T1) crystals, and the 5''×4'' well type NaI(T1) crystal was also used for searching the level population in the Sm–148 nucleus. Spins of the levels were determined using the gamma-gamma directional correlation method. The following levels has been proposed for Sm–148; 555(2+), 1183(4+), 1470(1), 1598(3), 1735(4+), 1911(3 or 4), 2148, 2220, 2460, 2500, 2740, 2830, 3100 and 3370 keV. The results are compared with the predictions of various models of even-even nuclei.