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A dosimetry experiment used to measure the neutron flux and spectrum of a D-T neutron generator is presented. The D-T generator at Pacific Northwest National Laboratory is installed in the middle of a large room to minimize scatter of neutrons back to the sample. The efficacy of maintaining a pure fast neutron field for the sample is investigated. Twenty-one positions within 13 cm of the neutron source contained foils or wires of Fe, Ni, and Al with additional Au, and in monitors at some locations. Spectral adjustment of the neutron flux at each position based on the measured reaction rates and theoretical Monte Carlo calculations show that at least 99.1% of the spectrum lies above 110 keV for all measured positions, and neutrons above 14 MeV can account for as much as 91% at locations along the axis of the generator and close to the source. The 14 MeV component drops to 77% in radial positions far from the source. The largest total flux observed was 8.29E+08 n/cm 2 s (±1.4%) in the center of the cooling cap, although additional experiments have shown this value could be as high as 1.20E+09 n/cm 2 s.

We present an overview of a process-based modelling approach for predicting how change in flow affects drift density, net rate of energy intake (NREI) and numbers of drift-feeding salmonids. It involves linking an existing two-dimensional flow model (River2D) with models of invertebrate drift transport and drift-foraging which we have developed. We describe, demonstrate and partially test our models in an application on a 80 m × 20 m pool on a New Zealand river. We show how these models realistically capture hydraulic, drift dispersion and bioenergetics drift-foraging processes to predict the relationship between stream flow, habitat quality and quantity (in terms of NREI), and carrying capacity for drift-feeding salmonids. Overall, the 2D hydraulic model made good predictions of water levels, depths and water velocity at the calibration flow and a lower (validation) flow. The drift transport model made good predictions of the spatial distribution of invertebrate drift density throughout the pool at low flow after it was calibrated against observed drift density at the higher flow. The model correctly predicted that drift density would decline downstream and into the margins due to the process of settling dominating over entry from the stream bed, and that drift would be carried further downstream and laterally as flow increased. The foraging model made a reasonable prediction (6–7) of the numbers of 0.5 m adult brown trout observed (5) in the pool. It accurately predicted that trout should be distributed down the thalweg where net rate of energy intake (NREI) was highest, but when NREI was adjusted for depletion by feeding fish the predicted drift-feeding locations were more closely spaced (bunched) than observed fish locations. Our process-based modelling approach has important implications for improving biological realism in predictions of the response of drift-feeding fishes to flow change within the context of the IFIM.

Summary A theoretical and experimental study is presented for the small amplitude fundamental harmonic a.c. polarographic response with systems involving dimerization following the charge transfer step. The theoretical derivation invokes the procedure recently presented for the disproportionation case, which combines numerical methods with conventional functional analysis procedures. Computer programs were developed which provide the option of calculating the a.c. polarographic response on the basis of various commonly-used models for the DME, including the expanding sphere model. The electrode reduction of benzaldehyde in alkaline aqueous ethanol is employed as a model system in an experimental evaluation of the theoretical equations. Excellent agreement is obtained between predictions of the theoretical a.c. polarographic rate law and experimental results.

AC polarographic data are presented in which the applied dc potential scan utilizes a pulse program of the normal pulse polarographic type. AC data were obtained using the FFT faradaic admittance measurement protocol. These data indicated that the FFT-FAM procedure is applicable when the relatively short, large-amplitude pulses characterizing the normal pulse polarographic waveform are invoked as the de scan. The results also support conjecture regarding appropriate theoretical rate laws for such measurements.

Summary A study is presented of faradaic admittance versus frequency measurements based on Fourier analysis of the response to multiple-frequency test signal waveforms. The waveform types employed encompass both the discrete frequency and broadband categories, including stochastic and deterministic examples of the latter. More specifically, data are acquired using: (a) complex periodic signals; (b) almost periodic signals; (c) transient inputs; and (d) bandwidth-limited white noise. Data analysis is based on the highly-efficient fast Fourier transform algorithm which is implemented by an on-line minicomputer. An instrumental configuration is described which yields valid faradaic admittance data, regardless of the type of test signal waveform employed. Results are examined with regard to the effect of test signal properties on measurement efficiency, where measurement efficiency is defined in terms of the data dispersion observed after a particular number of replicate measurements. In this context the data show that a complex periodic waveform composed of a fundamental harmonic and a sufficient number of odd harmonics is superior to the others which were examined. This result, together with the overall empirical ordering of waveform types versus measurement efficiency, is rationalized in terms of the influences of extraneous noise, faradaic non-linearity, waveform frequency spectrum, and special measurement system characteristics.