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We have measured the complete crystalline electric field (CEF) spectrum of Nd 3+ in superconducting Nd 1.85 Ce 0.15 CuO 4 and in the non-superconducting parent compound, Nd 2 CuO 4 , by neutron inelastic scattering. The best description of the ground state excitations for both compounds is achieved by the addition of a molecular field parameter to the CEF Hamiltonian that takes account of exchange interactions from Nd or Cu spin ordering. This model predicts a small splitting of each of the five crystal field doublets, and the Schottky anomaly associated with the splitting of the ground state is consistent with earlier observations of peaks in the specific heat at low temperatures. The agreement between existing specific heat data and the Schottky anomaly calculated with the assumption of a temperature independent molecular field splitting is very good for Nd 1.85 Ce 0.15 CuO 4 , but for Nd 2 CuO 4 there are differences which may be due to magnetic ordering of the Nd ions and to the change in the molecular field splitting with temperature.

We present the results of a detailed theoretical analysis of neutron inelastic scattering measurements of the crystal-field excitations in PrBa 2 Cu 3 O 7 . Using a scaling procedure we estimate the crystal-field parameters for Pr 3+ from those of Ho 3+ determined from neutron spectra of HoBa 2 Cu 3 O 7 . With the scaled parameters as a starting point and guide we refine a model which is able to account for the main features of the crystal-field spectra of PrBa 2 Cu 3 O 7 , including the position of a peak in the neutron spectrum near 280 meV, presented here for the first time, arising from 3 H 4 to 3 H 5 intermultiplet transitions. The analysis leads us to propose the sequence Γ 4 -Γ 2 -Γ 1 for the symmetries of the levels within the crystal-field-split quasi-triplet ground state, and we show that this level scheme is consistent with the observed magnetic anisotropy. We predict the excitation spectrum of Pr 4+ by scaling the Pr 3+ parameters, and use it to estimate an upper limit of 10% for the concentration of stable Pr 4+ ions on the yttrium site. The prevalence of Pr 3+ is consistent with a magnetic interaction, rather than hole-filling, as the major factor responsible for the absence of superconductivity in PrBa 2 Cu 3 O 7 .

Copper NMR has been studied as a function of temperature in a number of superconducting Nd2−x Ce x CuO4 samples. The electric field gradient is very small and the Knight shift is 2380 ppm at room temperature, both of these implying that the copper is in a Cu+ state. The Knight shift decreases with temperature particularly belowT c . The spin contribution to the Knight shift is estimated to be ∼ 200 ppm (about a factor ten smaller than in YBa2Cu3O7) indicating thatN s (E F ) at the copper sites is small in this material.

We have measured, by means of neutron inelastic scattering, the ground state crystalline electric field excitations in the system Nd2−xSrxNiO4+y for x = 0 and 0.4. The excitations occur at 8.0, 23, 38 and 49 meV in the undoped compound, and at similar energies for the Sr-doped material. A notable feature of the spectra is the large intrinsic width of the peaks, which could be due to disorder or to exchange interactions with the Ni-O planes.

We have measured the complete crystalline electric field (CEF) spectrum of Nd3+ in superconducting Nd1·85Ce0·15CuO4 and Nd2CuO3·7F0·3, and in the non-superconducting parent compound, Nd2CuO4, by neutron inelastic scattering. The best description of the ground-state excitations for both compounds is achieved by the addition of a molecular field parameter to the CEF hamiltonian that takes account of exchange interactions from Nd or Cu spin ordering.

Indoor radon concentrations, measured in 58 houses over a four to five month period during the winter and spring of 1981-1982, varied from 0.1 to 16 pCi 1{sup -1} (4-590 Bq m{sup -3}). Average infiltration rates were determined for each house over the same period, based on a measurement of the effective leakage area and an infiltration model, and found to range from 0.2 to 2.2 air changes per hour (hr{sup -1}). Indoor radon concentrations correlated poorly with infiltration rates for houses within each city as well as for the entire sample. Differences in radon entry rates among houses thus appear to be more important than differences in infiltration rates in determining whether a house has high indoor radon levels, consistent with previous indications from grab-sample measurements. Radon entry rates and indoor radon concentrations were generally higher in houses in Fargo, ND and Colorado Springs, CO than in houses in Portland, ME and Charleston, NC.

The transport of 222Rn from soil, through a vented crawl space, and into the living space of single-family residences was studied. Two houses were monitored in detail for periods of 5 and 7 weeks. With crawl space vents open, the average indoor 222Rn concentrations were 1.2 and 0.6 pCi 1.-1 (44 and 22 Bq m-3); with the vents sealed the averages rose to 2.2 and 1.0 pCi 1.-1 (81 and 37 Bq m-3). The data suggest that, of the Rn released into the crawl space from the soil beneath the house, a significant fraction, perhaps 50% or more, enters the living space. The effect of 3 meteorological parameters--wind speed, indoor-outdoor temperature difference, and rate of barometric pressure change--on Rn concentration and entry rate were examined. In 1 of the houses a higher temperature difference corresponded to a higher indoor concentration, suggesting that the increased infiltration rate is more than compensated by an increase in the Rn entry rate. On the other hand, a high wind speed tended to reduce the indoor concentration, presumably by increasing both cross-ventilation of the crawl space and the infiltration rate of the living space. Results suggest that Rn transport into the crawl space of at least 1 of the houses occurred by pressure-driven flow, rather than solely by molecular diffusion. The diffusion coefficient of 222Rn through polyethylene sheeting, such as was present on the ground beneath this house, was measured in the laboratory and found to range from 0.65 X 10(-7) cm2 s-1 at 11 degrees C to 1.6 X 10(-7) cm2 s-1 at 25 degrees C, implying that the maximum diffusive flux through the sheet was many times smaller than that necessary to account for the rate of Rn entry into the house. A third house was studied using a tracer gas injected into the crawl space at a controlled rate. The fraction of air leaving the crawl space that entered the living space ranged from 0.3 to 0.65, in good agreement with results for Rn transmission in the other 2 houses, assuming that the 222Rn flux into the crawl space was comparable to that which would have resulted from molecular diffusion from soil having a 222Rn diffusion length of 1.0 m. By sealing leaks in the floor of this house, the average infiltration rate was reduced by 25%, but the indoor concentration of the tracer gas remained constant.

Recent results from our group directly assist efforts to identify and control excessive concentrations of radon 222 and its decay products in residential environments. We have demonstrated directly the importance of pressure-induced flow of soil gas for transport of radon from the ground into houses. Analysis of available information from measurements of concentrations in U.S. homes has resulted in a quantitative appreciation of the distribution of indoor levels, including the degree of dependence on geographic location. Experiments on the effectiveness of air cleaning devices for removal of particles and radon decay products indicate the potential and limitations of this approach to control.