The analysis of parity nonconservation (PNC) measurements performed on Th-232 by the TRIPLE Collaboration has been extended to include the neutron energy range of 250 to 1900 eV. Below 250 eV all ten statistically significant parity violations have the same sign. However, at higher energies PNC effects of both signs were observed in the transmission of longitudinally polarized neutrons through a thick thorium target. Although the limited experimental energy resolution precluded analysis in terms of the longitudinal asymmetry, parity violations were observed and the cross section differences for positive and negative neutron helicities were obtained. For comparison, a similar analysis was performed on the data below 250 eV, for which longitudinal asymmetries were obtained previously. For energies below 250 eV, the p-wave neutron strength functions for the J = 1/2 and J = 3/2 states were extracted: S-1/2(1) = (1.68 +/-i 0.61) x 10(-4) and S-3/2(1) = (0.75 +/- 0.18) x 10(-4). The data provide constraints on the properties of local doorway states proposed to explain the PNC sign effect in thorium.

Several species of higher plants and mushrooms have been surveyed growing under the canopy of old stands of hemlock surrounding Clear Lake near Minden, Ontario. Some of the hemlock seedlings growing on fallen trunks together with debris in which they were growing were brought to a greenhouse in pots, and some of them were transferred into sandy soil. The conditions of growth involved a gradient of shading. As an analysis of the debris revealed a low pH, the soil in all pots was kept at a pH of 5.5. The best growing seedlings were in the most shaded areas in pots filled with plant debris and the worst growth was in sandy soil in full sunlight. We have measured the concentration of phenolic compounds, which was found to be highest in dying plants in sandy soils in full sunlight, and lowest in shaded areas in pots filled with debris.

Single event upsets (SEU) result when modem microelectronic circuits are exposed to energetic charged particles in space, around accelerators and in the various natural or manmade radiation environments encountered by computers on earth. Estimating a circuit's SEU sensitivity at an early stage of system design requires detailed understanding of the physical phenomena through which upsets are induced, the localized generation of charge, its collection at the SEU-sensitive junction and the circuit's response. The amount of charge collected depends on the contribution from drift, field tunneling and diffusion as well the removal of charge through recombination. Decreasing the area of the junction through improvements in lithography increases the complexity of the charge collection in a way which significantly complicates modeling.

Irradiation of MOS SRAMs by energetic heavy ions results in pulses on the power lines of the device. Pulse-height analysis shows a series of peaks when the irradiation consists of identical particles incident in the same direction. Analysis through a microbeam shows that the pulses are generated by traversals of the p-n junctions making up the transistors of the device. Junctions in the memory array were found to dominate the spectrum from a CMOS device while those of the support circuitry dominate the spectrum from a DRAM.< >

Charge collection was measured across the base-emitter heterojunction to test certain assumptions of the standard sensitive-volume models for calculating SEU (single-event-upset) rates. The observed dependence of charge collection on the LET (linear energy transfer) and the angle of incidence of 4.4-MeV on oxygen ions is consistent with the hypothesis that the charge collected equals the product o...

Charge-collection measurements were carried out on HI/sup 2/L transistors in GaAs in order to determine the thickness of the equivalent sensitive volume to be used in calculating single-event-upset (SEU) rates for this technology and to set a lower limit to the critical charge. The measurements were in the form of pulse-height spectra measured between the base-emitter and collector-emitter contact...

Single event upsets in microelectronic circuits follow the collection of more than some critical amount of charge at certain reverse-biased junctions. Reducing charge collection at the junctions lowers the upset rate without requiring performance tradeoff. Three mechanisms for reducing the fraction of charge collected at a junction can be incorporated in the use of CMOS-type wells. For illustration the CHMOS-III-D process used in Intel's P51C256 is shown to lower the error rate to be expected in deep space by an order of magnitude from that calculated for an equivalent dRAM of standard design.

Simulations of the diffusion contribution to charge collection in SEU events are carried out under the simple assumption of random walk. The results of the simulation are combined with calculations of the funneling length for the field-assisted drift components to determine the effective thickness of the sensitive volume element to be used in calculations of soft-error rates for heavy-ion-induced ...

Careful measurements of the SEU cross section versus the LET of the incident heavy ion were carried out on a single Intel 64K dRAM for which proton SEU data had been recently obtained in order to test whether a single set of modeling assumptions could provide fits to both data sets. The Intel 2164A 64k dRAM exhibited consistent cross-section measurements among devices tested, a high total-dose tolerance, and a proton SEU cross section that was unaffected by accumulated dose, making the device very suited for extended radiation studies. The heavy-ion cross section versus LET data was used as input to the CUPID code predictions of the proton-upset cross section versus incident proton energy. Observed agreement is consistent with the hypothesis that proton-induced upsets, even in alpha sensitive devices, are the result of recoiling nuclear fragments from inelastic nuclear interactions and the same basic mechanism is reponsible for both heavy ion and proton-induced upsets.