1517roughly the order of 1.5 Mev. The (gg/2) 2 state is depressed by somewhat more than the \p112) 2 state from the diagonal energy contribution, but the extra effects of configuration interaction should act principally in the (P112) 2 state, 6 adding the order of 0.5 Mev to its depression. The two states of the pi/2g9/2 configuration are depressed by a much smaller amount due to the poor overlap of the single particle states, perhaps by a few tenths of an Mev. In the limit of short-range forces, the 4-state is not shifted, 5 and the 5-is shifted downward by a small amount. One concludes that the occurrence of the 5-isomeric state (below the 4-) and its excitation energy are in accord with simple shell theory. Also, one expects that the spin 0 state of the (gQ/2) 2 configuration might lie below the 5-state, because of the much greater mutual interaction of two equivalent than of two inequivalent particles.A hypothetical level diagram is presented in the right side of Fig. 1, adjusted to fit what is now known experimentally. In addition to the 5-state discussed above, 2 and the new 0+ state just discovered, 3 there has been observed in the decay of 4 iNb 90 -• > 4oZr 90 a level at 2.23 Mev, 7 which appears not to be the 5state because of its rapid decay to the ground state and because the energy difference is outside experimental error. This state could be interpreted as the 2+ state of the (gg/2) 2 configuration. The small 0-2 separation (^0.5 Mev) of this configuration must then be attributed to the configuration interaction of the 0+ state. In a usual even-even nucleus, the 0-2 spacing is substantially increased by configuration interaction. In this nucleus it may be decreased because of the unusual circumstance that there is another 0+ state below the one of interest. According to the semiempirical formulas of Moszkowski, 8 the 5-to 2+ 70-kev E3 transition should be slower by a factor of about 100 than the 5-to 0+ 2.3-Mev E5 transition. The observation of the ground-state transition only is therefore reasonable.Regarding other nuclei in the neighborhood, we make two remarks. First, the nucleus 38Sr 50 88 does not show a double closed shell character. This may be attributed to the ease of exciting the pi/2 state and/or a substantial ^3/2-^1/2 mixing. Second, most odd-even nuclei in the region show a gwpi/2 energy difference small compared to the 0.9 Mev in 39Y50 89 . This is not necessarily in contradiction to a simple shell picture, since the other nuclei have multiparticle configurations. For example, in 4 iNb 5 o 91 the "£1/2" and "#9/2" states should more correctly be called g9/2 2 pi/2 and pi/2 2 g9/2, and these three-particle configurations should not have the same spacing as the single-particle levels.Aside from its interest as a double closed shell nucleus, Zr 90 calls to attention the way in which the beta-and gamma-decay selection rules can cause lowlying levels to go unobserved in conventional experiments. Shell theory predicts many low-lying states which have not been observed (see, e.g., reference ...

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Scintillation measurements were made of the beta and gamma radiation from high-purity natural silicon targets after bombardment with fast neutrons produced by the Li 7 (

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Wavelength-shifting fiber readout of scintillator crystals permits efficient discrete event localization over large scintillator areas, by flexibly interfacing position-sensitive photosensors or photosensor arrays to scintillator crystal surfaces. We describe techniques for localizing gamma-ray interactions within large crystals, and for determining the crystal of interaction within multicrystal arrays. Measurements carried out with NaI(T1) coupled through fibers to photomultipliers c o n f m the technique's expected light yield, and measurements with BGO coupled through fibers to avalanche photodiodes demonstrate the usefulness of this method for crystal-of-interaction determination. We use a block detector geometry, combining fiber localization with direct energy measurement by large photomultipliers. Potential applications for gamma cameras and for high resolution PET systems are discussed.

PHYSICAL REVIEW LETTERS 16APRIL1979nals was estimated from single-particle inclusive data in which one arm was used as the trigger, and the other (untriggered) arm recorded the relative frequency of Cherenkov signals. 4 The original configuration of the apparatus is described by Bintinger et al. (Ref. 2), and the rearranged configuration (for which one of the Cherenkov counters was relocated behind the magnet) is described in Ditzler et al. (Ref. 2).Several unexpected results have recently raised interest in hadron production on heavy nuclei. The multiplicity of hadron-nucleus collisions grows with nuclear size much less rapidly than a simple cascade model would predict. 1 On the other hand, the inclusive production of high-/> x particles rises as A a with a significantly greater than l. 2 " 4 Theoretical models which attempt to describe this behavior include multiple scattering, nucleon clusters, and decay of high-mass states. 5 We report here the results of an experiment on the A dependence of dihadron production. 6 Only charged particles were detected, and for the purposes of this paper no distinction is made between 7T, K, and/>. The quantum-number correlations observed in lead and beryllium have been reported separately. 7 This experiment was performed at the Fermi National Accelerator Laboratory in a 400-GeV/c proton beam, with a typical intensity of 4x 10 7 sec" 1 . Other results and a detailed description 5 Our kinematic correlation results are reported in D. A. Finley etal., Phys. Rev. Lett. 42, 1031 (1979) (this issue). 6 M. G. Albrowet al. 9 Phys. Lett. 65B, 295 (1976). 7 R. J. Fisk et al. t Phys" Rev. Lett. 40, 984 (1978). 8 The observation that heavier nuclei reduce quantumnumber correlations as well as kinematic correlations (see Finley et al. t Ref. 2) is consistent with an inelastic multiple-scattering process.of the apparatus have been published previously. 8 The apparatus consisted of two identical magnetic spectrometers placed at 100 mrad on opposite sides of the beam. In the proton-nucleon centerof-mass system, each spectrometer was centered at 6 = 110° and subtended about ± 10° in polar angle, and ± 17° in azimuth. The trigger required each hadron to have£ ±^ 1 GeV/c.Measurements of the A dependence were made with a target of nine 1.3-mm lead segments followed by three 6.1-mm beryllium segments, all 3.8 mm wide. Data were taken on both nuclei simultaneously with targets of equal width in order to eliminate uncertainties arising from beam normalization or changes in experimental conditions. The good spatial resolution of the spectrometer drift chambers allowed unambiguous identification of the target element, as shown in Fig. 1. The acceptance of the spectrometer was uniform over the length of the target. The data were corrected for beam attenuation in the tar-We have measured the nucleon-number (A) dependence of hadron-pair production in 400-GeV/c proton-nucleus collisions, using Pb and Be targets. Charged-hadron pairs were observed near rapidity y Ca mr~ -0.4 with Acp s 180°. The A-dependenc...

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