Effect of continuous gamma-ray exposure on performance of learned tasks and effect of subsequent fractionated exposures on blood-forming tissue

Sixteen monkeys trained to perform continuous and discrete-avoidance and fixed-ratio tasks with visual and auditory cues were performance-tested before, during, and after 10-day gamma-ray exposures totaling 0, 500, 750, and 1000 rads. Approximately 14 months after the performance-test exposures, surviving animals were exposed to 100-rad gamma-ray fractions at 56-day intervals to observe injury and recovery patterns of blood-forming tissues. The fixed-ratio, food-reward task performance showed a transient decline in all dose groups within 24 hours of the start of gamma-ray exposure, followed by recovery to normal food-consumption levels within 48 to 72 hours. Avoidance tasks were performed successfully by all groups during the 10-day exposure, but reaction times of the two higher dose-rate groups in which animals received 3 and 4 rads per hour or total doses of 750 and 1000 rads, respectively, were somewhat slower

Twisted [(R3P)PdX] groups above dicarbaborane ligands: 4-dimethylsulfido-3-iodo-3-triphenylphosphine-closo-3-pallada-1,2-dicarbadodecaborane and 3-dimethylphenylphosphine-3-chloro-4-dimethylsulfido-closo-3-pallada-1,2-dicarbadodecaborane

The structural analyses of [3-(PPh₃)-3-I-4-(SMe₂)-closo-3,1,2-PdC₂B₉H₁₀] or [Pd(C₄H₁₆B₉S)I(C₁₈H₁₅P)], (I), and [3-(PPhMe₂)-3-Cl-4-(SMe₂)-closo-3,1,2-PdC₂B₉H₁₀] or [Pd(C₄H₁₆B₉S)Cl(C₈H₁₁P)], (II), show that in comparison with [3-(PR₃)2-closo-3,1,2-PdC₂B₉H₁₁] the presence of the 4-SMe₂ group causes the [PdX(PR₃)] unit (X = halogen) to twist about an axis passing through the Pd atom and the directly opposite B atom of the carbaborane ligand. The halogen atoms are located almost directly above a C atom in the C₂B₃ face, and the conformations of the [PdX(PR₃)] units above the C₂B₃ faces are not those predicted from molecular orbital calculations of the closo-3,1,2-PdC₂B₉ system. The fact that the variation from the predicted conformation is greater in the case of (I) than in (II) may be ascribed to the greater steric interactions induced by the I atom in (I) compared with the Cl atom in (II)

The isotopic composition of cosmic ray B, C, N, and O nuclei

We report new high resolution measurements of the elemental and isotopic composition of galactic cosmic ray B, C, N, and O nuclei with ~ 30 to ~ 130 MeV nucleon^(-1). These observations place limits on the isotopic composition of the cosmic ray source and restrict possible models of cosmic ray origin and propagation. In particular, we find that N is significantly depleted in the cosmic ray source with respect to the solar system and local interstellar medium, a result inconsistent with models in which a majority of cosmic rays are accelerated interstellar medium material

The isotopic composition of galactic cosmic-ray iron nuclei

We report high-resolution observations made in interplanetary space of 83-284 MeV per nucleon galactic cosmic-ray iron isotopes and directly establish that ^(56)Fe is the dominant cosmic-ray Fe isotope. We find the following percentage abundances for Fe at the cosmic-ray source: ^(54)Fe = 9(+8, -5)%, ^(55)Fe ≤ 7%, ^(56)Fe = 91(+5, -11)%, ^(57)Fe ≤ 8%, and ^(58)Fe ≤ 6%. When compared to calculated nucleosynthesis yields and other observations, these results place significant constraints on the neutron excess of the environment where cosmic-ray Fe originates

High-Resolution Measurements of Galactic Cosmic-Ray Neon, Magnesium and Silicon Isotopes

The individual isotopes of galactic cosmic-ray Ne, Mg, and Si at ~0.20 amu. Our results suggest that the cosmic ray source is enriched in ^(22)Ne, ^(25)Mg, and ^(26)Mg when compared to the solar system. In particular, we find (^(25)Mg + ^(26)Mg)/^(24)Mg = 0.49(+0.23, -0.14) compared with the solar system value of 0.27, suggesting that the cosmic-ray source and solar system material were synthesized under different conditions

The isotopic composition of solar flare accelerated magnesium

We report observations of energetic solar particles from the 1978 September 23 solar flare in which the three stable isotopes of magnesium are clearly resolved with a mass resolution of 0.23 amu. We find ^(25)Mg/^(24)Mg = 0.14 (+0.05, -0.02) and ^(26)Mg/^(24)Mg = 0.15 (+0.04, -0.03) in the energy interval 12-36 MeV per nucleon. These observations are consistent with terrestrial magnesium isotopic abundances

The Isotopic Composition of Low Energy Cosmic Rays

We report new high-resolution isotope measurements of B, C, N, 0, and Ne nuclei with ~ 5 to ~140 MeV/nuc. These observations extend the study of cosmic ray isotopes to lower energies than before, and provide new information on the isotopic composition of the anomalous cosmic ray component