RESUMEN
From detailed spectroscopy of ^{110}Cd and ^{112}Cd following the ß^{+}/electron-capture decay of ^{110,112}In and the ß^{-} decay of ^{112}Ag, very weak decay branches from nonyrast states are observed. The transition rates determined from the measured branching ratios and level lifetimes obtained with the Doppler-shift attenuation method following inelastic neutron scattering reveal collective enhancements that are suggestive of a series of rotational bands. In ^{110}Cd, a γ band built on the shape-coexisting intruder configuration is suggested. For ^{112}Cd, the 2^{+} and 3^{+} intruder γ-band members are suggested, the 0_{3}^{+} band is extended to spin 4^{+}, and the 0_{4}^{+} band is identified. The results are interpreted using beyond-mean-field calculations employing the symmetry conserving configuration mixing method with the Gogny D1S energy density functional and with the suggestion that the Cd isotopes exhibit multiple shape coexistence.
RESUMEN
A high-precision half-life measurement for the superallowed ß+ emitter 26Al(m) was performed at the TRIUMF-ISAC radioactive ion beam facility yielding T 1/2 6346.54 ± 0.46(stat) ± 0.60 (syst) ms, consistent with, but 2.5 times more precise than, the previous world average. The 26Al(m) half-life and ft value, 3037.53(61) s, are now the most precisely determined for any superallowed ß decay. Combined with recent theoretical corrections for isospin-symmetry-breaking and radiative effects, the corrected Ft value for (26)Al(m), 3073.0(12) s, sets a new benchmark for the high-precision superallowed Fermi ß-decay studies used to test the conserved vector current hypothesis and determine the V(ud) element of the Cabibbo-Kobayashi-Maskawa quark mixing matrix.
Asunto(s)
Aluminio/química , Partículas beta , Radioisótopos/química , SemividaRESUMEN
The branching ratio for the superallowed beta(+) decay of (38)K(m) was measured at TRIUMF's ISAC radioactive ion beam facility. The M3 internal transition between the isomer and the ground state of (38)K(m) was observed with a branching ratio of 330(43) ppm. A search for the nonanalogue beta-decay branch to the first excited 0(+) state in (38)Ar was also performed and yielded an upper limit of < or =12 ppm at 90% C.L. These measurements lead to a revised superallowed branching ratio for (38)K(m) of 99.967(4)%, and increase the (38)K(m) ft value by its entire quoted uncertainty to ft=3052.1(10) s. Implications for tests of the nuclear-structure dependent corrections in superallowed beta decays and the extraction of the Cabibbo-Kobayashi-Maskawa matrix element V(ud) are discussed.
RESUMEN
A high-precision branching ratio measurement for the superallowed beta+ decay of 62Ga was performed at the Isotope Separator and Accelerator radioactive ion beam facility. Nineteen gamma rays emitted following beta+ decay of 62Ga were identified, establishing the dominant superallowed branching ratio to be (99.861+/-0.011)%. Combined with recent half-life and Q-value measurements, this branching ratio yields a superallowed ft value of 3075.6+/-1.4 s for 62Ga decay. These results demonstrate the feasibility of high-precision superallowed branching ratio measurements in the A>or=62 mass region and provide the first stringent tests of the large isospin-symmetry-breaking effects predicted for these decays.
RESUMEN
Maize (Zea mays L.) and pearl millet (Pennisetum americanum (L.) Leeke) seedlings were exposed to [(15)N]nitrate for 1-h periods at eight times during a 24-h period (16-8 h light-dark for maize; 14-10 h for millet). Influx of [(15)N]nitrate as well as its reduction and translocation were determined during each period. The efflux of previously absorbed [(14)N]nitrate to the uptake solution was also estimated. No marked diurnal changes in [(14)N]nitrate efflux or [(15)N]nitrate influx were evident in maize. In contrast, [(14)N]nitrate efflux from millet increased and eventually exceeded [(15)N]nitrate influx during the late dark and early light periods, resulting in net nitrate efflux from the roots. The dissimilarity of their diurnal patterns indicates that influx and efflux are independently regulated. In both species, [(15)N]nitrate reduction and (15)N translocation to shoots were curtailed more by darkness than was [(15)N]nitrate influx. In the light, maize reduced 15% and millet 24% of the incoming [(15)N]nitrate. In darkness, reduction dropped to 11 and 17%, respectively. Since the accumulation of reduced-(15)N in shoots declined abruptly in darkness, whereas that in roots was little affected, it is suggested that in darkness [(15)N]nitrate reduction occurred primarily in roots. The decrease in nitrate uptake and reduction in darkness was not related to efflux, which remained constant in maize and did not respond immediately to darkness in pearl millet.
RESUMEN
The diurnal pattern of nitrate uptake by Capsicum annuum L. cv. California Wonder in a constant environment is described by a Fourier harmonic, with the maximum uptake in the middle of the photoperiod and the minimum in the middle of the dark period. Comparison of the uptake pattern with that of nitrate reductase (EC 1.6.6.1.) activity suggests against a direct control of one process by the other. This was confirmed by the observation that the pattern of nitrate reductase activity was not altered by restricting nitrate uptake to one hour per day. Translocation of (15)N from the roots is much greater in the lightperiod than in the dark period. Reduction of (15)N in the leaves occurs in the lightperiod but very little is reduced in the dark period. Amino acid levels showed marked daily fluctuations but in the roots neither amino acids, sucrose, fructose, glucose nor malate showed fluctuations. The amino acid composition of roots and leaves differed: glutamine+glutamate were relatively more important in leaves than in roots whereas alanine was a more important constituent of roots than of leaves.
RESUMEN
When waterlogged over a period of 80 days plants of Eucalyptus robusta Sm. showed symptoms of leaf chlorosis, epinasty and premature abscission, reduction of stem elongation, stem hypertrophy and formation of adventitious shoots; chlorophyll content was reduced and soluble protein content of the upper leaves increased. Waterlogging doubled the rate of release of ethylene from roots and stems within 6 days, but had no effect on the ethylene concentration of leaves.
RESUMEN
The leaves of Capsicum annuum L. cv. California Wonder function as efficient carbon exporting organs for a large part of their life span. Young and old leaves export the same percentage of fixed carbon (74% within 24 hours) although fixation rates per unit area of young leaves may be three times that of old leaves. A constant feature of translocate distribution is a supply to the roots and to the terminal fruit of the main axis from both the main axis leaves and branch leaves. Carbon supply to branch fruit is flexible in that main axis leaves supply carbon to the very small fruit, but the subtending branch leaves supply more as the fruit grows and the branch node becomes more self-sufficient. Fruit are capable of carbon fixation but translocation to terminal fruit from main axis leaves supplies about 7.5 times as much carbon as direct fixation.
RESUMEN
Net carbon-dioxide exchange and loss of photosynthate-(14)C from leaves of Vicia faba L. were estimated throughout a day (16/8 h light/dark periods) by infrared gas analysis and Geiger-Müller-tube monitoring, respectively. Net photosynthesis reached 95% of the mean maximum rate within 1 h of the start of the photoperiod, and thereafter remained relatively constant before declining during the last 2-4 h of the photoperiod. Respiration was highest at the start of the dark period. The loss of photosynthate-(14)C from leaves exhibited two phases: a rapid phase which was fastest but shortest following (14)C incorporation in the middle of the photoperiod, and a slower phase of much longer duration. Absolute rates of (14)C loss exhibited diurnal trends reaching 95% of the maximum 6 h after the start of the photoperiod and remaining high until darkness, and then declined markedly. Of the total carbon fixed in one 24 h period, about 50% was lost during the current photoperiod, 14% during the dark period and 5% during the next photoperiod. The estimated amount of carbohydrate remaining within the leaf followed a diurnal pattern of accumulation and depletion. The daily course of translocation was not closely related to that of net photosynthesis or carbohydrate concentration.