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Gadolinium oxyorthosilicate (GSO) with its high density, high effective Z, fast decay time and good performance at high temperature, is the scintillation detector of choice for a new generation of neutron-induced, inelastic gamma-ray spectroscopy tools for borehole measurements, specifically aimed at measuring the carbon and oxygen content from the region surrounding the borehole. The ratio of the carbon and oxygen gamma-ray yields are transformed into formation oil saturation. To get the maximum benefit from GSO, the data acquisition, choice of materials, and measurement geometry were optimized for a small diameter tool at elevated temperatures and crystal characteristics. The large neutron cross section of the gadolinium in the scintillation crystal, its second decay constant, and the desired precision of the oil saturation measurement had important consequences in the tool design. >

Even-A Pd nuclei were studied using the reactions /sup 92/,/sup 94/,/sup 96/Zr(/sup 13/C,3n..gamma..)/sup 102/,/sup 104/,/sup 106/Pd. The experiments included ..gamma..-ray yield as a function of energy, ..gamma..-ray angular distributions, ..gamma..-ray linear polarizations, and ..gamma..-..gamma.. coincidence measurements. A new treatment of ..gamma..-..gamma.. directional correlation from oriented nuclei, which combines data from all appropriate coincidence pairs to reduce uncertainties, has aided in determining multipolarities for 49 contaminated transitions. Extensive decay schemes are presented which include many high-angular-momentum, positive- and negative-parity states. In addition to the ground-state band, there appear to be three collective bands built on excited two-quasiparticle states. The measurements favor a slightly deformed rotor description of these nuclei over an interpretation in terms of a vibrational (interacting boson) model. (AIP)

Levels in 108Cd were studied using the reaction 96 Zr ( 16 O , 4nγ) 108 Cd with a bombarding energy of 56 MeV. The experiments included γ-ray yields as a function of bombarding energy, γ-ray angular distributions, γ-ray linear polarizations and γ-γ coincidence measurements. The decay scheme which includes 48 γ-ray transitions is very similar to those reported for even-even Pd isotopes. In addition to the ground-state band, there appear to be four collective bands built on two-quasiparticle states. The results are in excellent agreement with a slightly deformed rotor description of the 108Cd nucleus.

States excited by the $^{99}\mathrm{Ru}(\ensuremath{\alpha},2n\ensuremath{\gamma})^{101}\mathrm{Pd}$, $^{88}\mathrm{Sr}(^{16}\mathrm{O},3n\ensuremath{\gamma})^{101}\mathrm{Pd}$, and $^{92}\mathrm{Zr}(^{12}\mathrm{C},3n\ensuremath{\gamma})^{101}\mathrm{Pd}$ reactions have been studied by measuring the $\ensuremath{\gamma}$-ray yield as a function of incident projectile energy, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidences, $\ensuremath{\gamma}$-ray angular distributions, and $\ensuremath{\gamma}$-ray linear polarizations. Three intense $\ensuremath{\gamma}$-ray cascades were observed. These cascades are produced by quasirotational bands built on the 5/${2}^{+}$, 7/${2}^{+}$, and 11/${2}^{\ensuremath{-}}$ intrinsic states of the nucleus. A decay scheme is given which includes states with energy up to 6488 keV and angular momentum up to 35/2. The quasirotational bands seen in $^{101}\mathrm{Pd}$ are similar to the bands in the adjacent even-even nuclei which suggests that this odd-$A$ nucleus can be described as a particle decoupled from an even-even core. A cascade of seven $\ensuremath{\gamma}$ rays in $^{102}\mathrm{Rh}$ was also observed following the $^{92}\mathrm{Zr}(^{12}\mathrm{C},p n)^{102}\mathrm{Rh}$ reaction.[NUCLEAR REACTION $^{99}\mathrm{Ru}(\ensuremath{\alpha},2n\ensuremath{\gamma})$, $E=16\ensuremath{-}24$ MeV; $^{92}\mathrm{Zr}(^{12}\mathrm{C},3n\ensuremath{\gamma})$, $E=45\ensuremath{-}56$ MeV; $^{88}\mathrm{Sr}(^{16}\mathrm{O},3n\ensuremath{\gamma})$, $E=56\ensuremath{-}64$ MeV; measured $\ensuremath{\sigma}(E)\ensuremath{\gamma}$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coin, $\ensuremath{\sigma}(\ensuremath{\theta})\ensuremath{\gamma}$, linear $P$; deduced decay scheme, $J$, $\ensuremath{\pi}$.]

$\ensuremath{\gamma}$-ray linear polarization measurements have been used to locate negative parity states in the even-odd isotopes $^{99,101,103}\mathrm{Pd}$. A Compton polarimeter based on two Ge(Li) coaxial detectors was used. Collective bands ($I={\frac{11}{2}}^{\ensuremath{-}}, {\frac{15}{2}}^{\ensuremath{-}}, {\frac{19}{2}}^{\ensuremath{-}}, \dots{}$) built on ${\frac{11}{2}}^{\ensuremath{-}}$ states were observed in $^{101}\mathrm{Pd}$ and $^{103}\mathrm{Pd}$. Many negative parity states were also observed in $^{99}\mathrm{Pd}$, but they do not appear to be part of a similar collective band. These polarization measurements also confirm many angular momentum assignments which previously had been made using systematic arguments.NUCLEAR REACTIONS $^{90,92,94}\mathrm{Zr}(^{12}\mathrm{C}, 3n)$, $E=48\ensuremath{-}56$ MeV; measured linear polarization of $\ensuremath{\gamma}$ rays; parities and multipole mixing ratios in $^{99,101,103}\mathrm{Pd}$ transitions deduced.

The linear polarization of ..gamma.. rays from the deexcitation of Cd isotopes A = 105 through 109 following (/sup 16/O,xn) reactions were measured using a Ge(Li) Compton polarimeter. The linear polarizations are used with ..gamma..-ray angular distributions to make unique-parity assignments and to remove ambiguity in angular-momentum values. With these measurements it is possible to identify many states in /sup 105hyphen109/Cd which are similar to states in Pd nuclei that have been interpreted as having one, two, or three quasiparticles coupled to a slightly deformed rotating core.

Levels in $^{105,107}\mathrm{Ag}$ have been studied using heavy-ion reactions. The experiments included $\ensuremath{\gamma}$-ray yields as a function of bombarding energy, $\ensuremath{\gamma}$-ray angular distributions, and three-detector $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence measurements. The positive-parity band based on the unique-parity ${g}_{\frac{9}{2}}$ orbital in both nuclei exhibits a $\ensuremath{\Delta}I=1$ character, unlike its counterpart ${h}_{\frac{11}{2}}$ band in Pd nuclei. The energy levels, $\ensuremath{\gamma}$-ray mixing ratios, branching ratios, and lifetimes in this band as well as in the ground-state negative-parity band are shown to be in good agreement with calculations using a particle-plus-rotor model at a small, symmetric deformation ($\ensuremath{\delta}=0.12$). The Coriolis and recoil effects are explicitly included and a variable moment of inertia is used. The low-lying "anomalous" $\frac{7}{{2}^{+}}$ state is also readily reproduced by this model. The calculation also shows that the $\ensuremath{\Delta}I=1$ nature of the positive-parity band results primarily from the fact that the Fermi surface is far from the $K=\frac{1}{2}$ state, whereas the transition properties are governed by the Coriolis mixing of the strong-coupled bands. Two bands built on the $\frac{17}{{2}^{\ensuremath{-}}}$ and $\frac{21}{{2}^{+}}$ states with high bandhead energies are thought to have three-quasiparticle configurations.NUCLEAR STRUCTURE $^{92}\mathrm{Zr}$($^{16}\mathrm{O}$,$p2n$)$^{105}\mathrm{Ag}$ at 60 MeV, $^{96}\mathrm{Zr}$($^{14}\mathrm{N}$, $3n$)$^{107}\mathrm{Ag}$ at 49 MeV: measured ${I}_{\ensuremath{\gamma}}(E(^{16}\mathrm{O}))$, ${I}_{\ensuremath{\gamma}}(E(^{14}\mathrm{N}))$, ${I}_{\ensuremath{\gamma}}(\ensuremath{\theta})$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coin $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ DCOQ. $^{105,107}\mathrm{Ag}$ deduced levels, $J$, $\ensuremath{\pi}$, $\ensuremath{\gamma}$ mixing ratios. Rotational model calculations, Coriolis, calculated levels, mixing ratios, branching ratios, lifetimes. Ge(Li) detectors.

The energy level structure of 103 Pd was studied using the reactions 100 Ru(α, nγ) 103 Pd and 94 Zr( 12 C, 3nγ) 103 Pd. The experiments included the measurement of γ-ray yield as a function of incident projectile energy, γ-γ coincidence measurements, γ-ray angular distributions, and γ-ray linear polarization measurements. Two ΔI = 2 bands built on the 7 2 + and 11 1 − intrinsic states were observed. The ( 12 C, 3n) reaction was found to be much more effective than the (α, n) reaction in exciting these bands. A decay scheme is presented showing energies up to 6049 keV and spins up to 35 2 . Additional information relating to the coupling between the odd particle and the core is presented. A cascade of six γ-rays in 103 Rh was observed following the reaction 94 Zr( 12 C, p2nγ) 103 Rh.

Colson, J.L., Schlumberger Well Services; Grau, J.A., Herron, M.M., Herron, S.L., and Schweitzer, J.S., Schlumberger-Doll Research; Hertzog, R.C.* and Preeg, W.E.,* Schlumberger Well Services; Nurmi, R.D.,* Schlumberger Middle East ; and Johnston, J.,* Schlumberger Overseas Abstract Elemental logs can be combined with mineral models to provide significant information for geological description provide significant information for geological description and evaluation of downhole formations. Mineral compositions from geochemical logs can be applied to a variety of lithologies, stratigraphic settings, and geological ages including those of the Middle East. The most abundant element concentrations in the rock forming minerals are obtained from the Geochemical Logging Tool (GLT). This tool measures natural, activation, and prompt neutron capture gamma-ray spectra. In addition to the traditional potassium, thorium, and uranium from natural gamma-ray spectrometry, a direct measurement of aluminum concentration is provided. A geochemically-based closure model is used to derive silicon, calcium, iron, sulfur, gadolinium, and titanium concentrations. The concentration of these elements, expressed in weight percent, significantly improves identification of mineral percent, significantly improves identification of mineral composition, and allows the estimation of important formation properties — an excellent basis for a broad range of applications useful to petroleum engineers, geologists, and petrophysicists. Introduction Three gamma-ray spectrometers have recently been combined into a single logging tool string to obtain elemental concentrations as a continuous function of depth for ten elements: Si, Ca, Fe, S, Ti, Gd, Al, Th, U, and K. This suite of elements has been shown to provide valuable information on the nature of the rock matrix, such as a detailed mineralogical description, sandstone classification, source rock evaluation, better porosity determination from logs, cation exchange capacity, grain-size distribution, and permeability. Much of this information could only be obtained previously through discrete core analyses. The Geochemical Logging Tool (GLT) includes measurements of natural activity for determining Th, U, and K concentrations, measurements of delayed activity induced by thermal neutron capture for determining Al concentration, and measurements of prompt gamma-rays following thermal neutron capture for determining Si, Ca, Fe, S, Gd, and Ti concentrations. While a fairly complete overall description of this tool has been presented previously, this paper provides a focus on the potential applications of geochemical logging in typical Middle East oil fields. Three examples are included to illustrate the broad range of geochemical applications:our first example of geochemical elemental concentration logging in the Middle East, taken from a clastic environment in south Oman;a second clastic example from sediments in California, similar to the problem shales that run from Egypt through the Arabian Platform into Oman and Yemen, that demonstrates detailed applications which can be derived from elemental concentration logs; anda third example from a major oil producing carbonate formation in North America that is typical of many carbonate reservoirs in the world containing a complex mixture of minerals such as those of the Arab, Khuff, Eocene of the Arabian Platform and the Kirkuk field of Northern Iraq. P. 365