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Neutron Capture Measurements on Unstable Nuclei at LANSCE

Description: Although neutron capture by stable isotopes has been extensively measured, there are very few measurements on unstable isotopes. The intense neutron flux at the Manual Lujan Jr. Neutron Scattering Center at LANSCE enables us to measure capture on targets with masses of about 1 mg over the energy range from 1 eV to 100 keV. These measurements are important not only for understanding the basic physics, but also for calculations of stellar nucleosynthesis and Science-Based Stockpile Stewardship. Preliminary measurements on {sup 169}Tm and {sup 171}Tm have been made with deuterated benzene detectors. A new detector array at the Lujan center and a new radioactive isotope separator will combine to give Los Alamos a unique capability for making these measurements.
Date: November 4, 1998
Creator: Ullmann, J.; Haight, R.; Wilhelmy, J.; Fowler, M.; Rundberg, R. & Miller, G.
Partner: UNT Libraries Government Documents Department

Thulium oxide irradiation

Description: Thulium oxide can be irradiated to meet the desired specific heat generation of 1.5 watts per gram as part of a flux amplification test, which will be conducted the early part of FY-1965. To obtain the heat generation level, is calculated that a 120-day irradiation will be required at a flux of 1.1 {times} 10{sup 14} neutrons/cm{sup 2}-sec. if the proposed target element is modified by reducing the thulium oxide wafer thickness from 0.080 to 0.050 inch. Also, the length of the target element should be reduced to not more than 20 inches to minimize the possibility of sticking in the process tube. This would require four targets rather than a single element as proposed. Prior to undertaking this irradiation, it would be desirable to place a prototype target element in the Hanford Test Reactor to determine the approximate rise factor (change in neutron flux level between the target element and adjacent tubes of fuel elements) in order to more precise data for planning the loading pattern in the production test.
Date: April 17, 1964
Creator: Kusler, L. E.
Partner: UNT Libraries Government Documents Department

High power 2 {mu}m diode-pumped Tm:YAG laser

Description: Using a scaleable diode end-pumping technology developed at LLNL, we have demonstrated a compact Tm:YAG laser capable of generating more than 50 W of cw 2 {mu}m laser output power. The design and operational characteristics of this laser, which was built originally for use in assessing laser surgical techniques, are discussed.
Date: January 1, 1996
Creator: Beach, R.J.; Sutton, S.B.; Honea, E.C.; Skidmore, J.A. & Emanuel, M.A.
Partner: UNT Libraries Government Documents Department

{mu}{sup +}SR studies of magnetic properties of boron carbide superconductors

Description: Positive-muon spin relaxation ({mu}{sup +}SR) has been carried out in the recently-discovered rare-earth boron carbide superconductors RNi{sub 2}B{sub 2}C, R = Ho, Er and Tm. For R = Ho and Er zero-field {mu}{sup +}SR measurements showed a well-defined internal field below the Neel temperatures of 5.5 K coexisting with the superconducting state down to 0.1 K. The observed temperature dependence of the order parameter for Ho is consistent with a 2-dimensional Ising model. For R = Tm a spontaneous internal field appears above 30 K, whose magnitude saturates below about 3 K at a value corresponding to a rare earth moment much smaller than for Ho and Er. Transverse-field {micro}{sup {minus}}SR measurements in R = Tm showed a superconducting penetration depth {lambda}, = 1,200 {angstrom}. The temperature dependence of {lambda} is consistent with conventional s-wave pairing.
Date: June 8, 1994
Creator: Le , L.P.; Heffner, R.H. & Nieuwenhuys, G.J.
Partner: UNT Libraries Government Documents Department

Proton radioactivity studies at the FMA

Description: A double sided silicon strip (DSSD) setup is installed at the Argonne National Laboratory recoil separator FMA. Ground state proton emitters {sup 146,147}Tm, {sup 160}Re, {sup 156}Ta, {sup 150,151}Lu were produced in a series of test experiments. Improved T{sub 1/2} values were obtained for {sup 147}Tm, {sup 160}Re, and {sup 156}Ta. Improved alpha T{sub 1/2} value of (13.2 {plus_minus} 1.1) ms was obtained for {sup 161}Re. In a search of new proton radioactivities a (5 {plus_minus} 2)% proton decay branch with E{sub p} = (1345 {plus_minus} 13) keV for {sup 161}Re was found.
Date: December 31, 1995
Creator: Penttila, H.; Davids, C.N. & Woods, P.J.
Partner: UNT Libraries Government Documents Department

Upconversion-pumped luminescence efficiency of rare-earth-doped hosts sensitized with trivalent ytterbium

Description: We discuss the upconversion luminescence efficiencies of phosphors that generate red, green, and blue light. The phosphors studied are single crystals and powders co-doped with Er{sup 3+} and Yb{sup 3+}, and with Tm{sup 3+} and Yb{sup 3+}. The Yb ions are pumped near 980 nm; transfers of two or three quanta to the co-doped rare earth ion generate visible luminescence. The main contribution embodied in this work is the quantitative measurement of this upconversion efficiency, based on the use of a calibrated integrating sphere, determination of the fraction of pump light absorbed, and careful control of the pump laser beam profile. The green phosphors are the most efficient, yielding efficiency values as high as 4 %, with the red and blue materials giving 1 - 2 %. Saturation was observed in all cases, suggesting that populations of upconversion steps of the ions are maximized at higher power. Quasi-CW modeling of the intensity- dependent upconversion efficiency was attempted; input data included level lifetimes, transition cross sections, and cross-relaxation rate coefficients. The saturation of the Yb,Er:fluoride media is explained as the pumping of Er{sup 3+} ions into a bottleneck (long-lived state)- the {sup 4}I{sub 13/2} metastable level, making them unavailable for further excitation transfer. 32 refs., 5 figs., 3 tabs.
Date: July 26, 1997
Creator: Page, R.H.; Schaffers, K.I.; Waide, P.A.; Tassano, J.B.; Payne, S.A.; Kruplce, W.F. et al.
Partner: UNT Libraries Government Documents Department

Neutron and resonant x-ray scattering studies of RNi{sub 2}B{sub 2}C (R = rare earth) single crystals

Description: This family of intermetallic compounds is ideal for the study of the interplay between superconductivity and magnetism since, in several of these compounds (Ho, Er, Tm, Dy), superconductivity coexists with magnetic ordering. The most important findings of the scattering studies are (a) in the Ho-compound, a complex magnetic structure characterized by two incommensurate wave vectors, {rvec k}{sub a} = 0.585 {rvec a}* and {rvec k}{sub c} = 0.915 {rvec c}*, exists in the vicinity of 5 K, where the almost reentrant behavior of this compound occurs; (b) an incommensurate magnetic structure with wave vector along {rvec a}*, close to the zone boundary, is observed in several of these compounds; and (c) pronounced soft-phonon behavior was observed for both the acoustic and first optical {Delta}{sub 4}[{xi}00] branches in the superconducting Lu and Ho compounds, a behavior characteristic of strongly coupled conventional superconductors. Furthermore, these phonon anomalies occur at wave vectors close to those of the incommensurate magnetically ordered structures observed in the magnetic compounds of this family. This observation suggests that both the magnetic ordering and phonon softening originate from common nesting features of the Fermi surfaces of these compounds. Band theoretical calculations are in qualitative agreement with these results.
Date: June 1, 1996
Creator: Stassis, C. & Goldman, A.I.
Partner: UNT Libraries Government Documents Department

Upconversion processes in Yb-sensitized Tm:ZBLAN

Description: A spectroscopic study of 22 rare-earth-ion doped ZBLAN (fluorozirconate) glass was done to study feasibility of sensitizing Tm:ZBLAN with Yb to facilitate development of an efficient, conveniently pumped blue upconversion fiber laser. it was found that, under single-color pumping, 480 nm emission from Tm{sup 3+} was strongest when Yb,Tm:ZBLAN is excited at 975 nm; the strongest blue blue emission was obtained from a glass sample with 2.0 wt% Yb + 0.3 wt% Tm. Also, for weak 975 nm pump intensities, strength of blue upconversion emission can be greatly enhanced by simultaneously pumping at 785 nm. This increased upconversion efficiency is due to reduced number of energy transfer steps needed to populate the Tm{sup 3+} {sup 1}G{sub 4} energy level. Measurements of fluorescence lifetimes vs dopant concentration were also made for Yb{sup 3+}, Tm{sup 3+}, and Pr{sup 3+} transitions in ZBLAN in order to better characterize concentration quenching effects. Energy transfer between Tm{sup 3+} and Pr{sup 3+} in ZBLAN is also described.
Date: October 1, 1996
Creator: Carrig, T.J. & Cockroft, N.J.
Partner: UNT Libraries Government Documents Department