Showing papers by "Chalk River Laboratories published in 1984"

Effects of roots and litter on mineralization processes in forest soil

Abstract: Leaf litter breakdown and fine root production, including exudation, are two major influences upon carbon and nitrogen mineralization rates in forest soil. Sieving and root removal experiments were used to examine their effects. Although carbon mineralization rates declined in smaller particle size fractions of forest litter, this trend largely disappeared when results were calculated on an ash-free basis. Nitrogen mineralization by contrast, was greatest in smaller fractions.

Deflection of high energy channeled charged particles by elastically bent silicon single crystals

Abstract: An experiment has been carried out to observe the deflection of charged particles by planar channeling in bent single crystals of silicon for protons with energy up to 180 GeV. Anomolous loss of particles from the center point of a three point bending apparatus was observed at high incident particle energy. This effect has been exploited to fashion a “dechanneling spectrometer” to study dechanneling effects due to centripital displacement of channeled particle trajectories in a bent crystal. The bending losses generally conform to the predictions of calculations based on a classical model.

GeV channeling in bent crystals with slowly varying curvature

Abstract: In a recent Fermilab experiment, the deflection of charged particles by planar channeling in bent single crystals in the 100 GeV/c regime was observed. The experiment shows the necessity of taking into account the variation of curvature along the bend. Here a theory is developed to treat the case of slowly varying curvature and it is shown that the predictions are in qualitative agreement with the experimental data.

On the use of tapered bismuth germanate crystals in positron emission tomography

Abstract: An analytical model of gamma ray transport within the detectors of a positron camera, based on exponential absorption, has been developed and verified experimentally. The model has been used to study the intrinsic resolution obtained with scintillation detectors that have had their front corners removed. It is concluded that for crystals greater than 0.8 cm wide, tapering the face of the detector results in improved uniformity of resolution. Thus it is useful for medium and low resolution scanners. In these cases, it has been found that the loss in sensitivity resulting from the use of tapered crystals is less than that which occurs when septa are placed between crystals to achieve comparable uniformity of resolution. It has also been established that, in some instances, reducing the length of the detectors results in a more uniform resolution than that obtained with tapered crystals, although this leads to a loss in ring sensitivity and an increase in the detected scatter fraction.

Development of sphene-based glass-ceramics for disposal of some Canadian wastes

Abstract: Intermediate-level alkaline waste from an experimental thorium fuel reprocessing facility was partitioned into actinide contaminated and nonactinide contaminated fractions by using sodium titanate. The /sup 232/U//sup 233/U-contaminated titanate was converted into a glass-ceramic, on the basis of the natural mineral sphene, by the addition of glass-making chemicals followed by heat treatment. A novel process was developed to simplify the treatment of such liquid wastes. Stainless steel or Inconel cartridges are prepared to contain suitable mixtures of sodium titanate, mordenite, and bone char, all of which possess good ion-exchange capacity, together with an insoluble source of Ca and Si, such as wollastonite. After use in decontamination of the waste stream, the cartridges and their contents are heat treated in a tube furnace to produce durable sphene-based glass ceramics. Processing of wastes is easier and volumes of products are smaller compared with rival immobilization methods. 17 references, 1 figure, 3 tables.

Neutron Inelastic Scattering as a Probe of Moments in Metallic Systems

Abstract: Neutron inelastic scattering is one of the most powerful methods for investigating the excitations in solids because the kinetic energy of a thermal neutron falls in the same range as typical excitations in solids. In a scattering event a large relative change usually occurs in the kinetic energy and this is easily measured precisely. The range of frequencies that may be probed is impressively wide with modern methods, ranging from 107 to 1014 Hz, and wave vector transfers in the range 10−3 to 102 A−1 are currently accessible.

The Economic Benefits to Visitors of an Interpretive Facility

Abstract: Benefits derived from interpretive experiences have been notoriously difficult to quantify. This paper uses a cost-based technique (a travel cost method) to quantify the benefits received by visitors to Petawawa National Forestry Institute's (Ontario, Canada) public awareness facilities. An analysis of data from 697 visitors provided a basis for the calculation of benefits which are reported in monetary terms. Benefits were estimated to range in value from $2.89 to $6.64 (U.S.) per visit.

A Network Approach To Least-Cost Daily Transfers Of Forest Fire Control Resources

Abstract: Most Canadian forest fire control agencies have adequate levels of manpower, equipment, and aircraft to handle all but the worst fire situations. These resources are usually allocated to regions in proportion to average historic fire loads; butat any one time it is not uncommon for a region to have far more fire activity than it can handle, while neighbouring regions’ resources remain almost idle. The result can be large, expensive fires. Positioning, on a daily basis, of under-utilized detection and initial attack resources into regions expecting high fire occurrence would significantly improve the effectiveness of existing fire control methods. This paper describes a network formulation and corresponding “out-of-kilter” solution for identifying least-cost resource transfer options, given current and desired resource allocations and transfer costs. The procedure is illustrated with a hypothetical example that identifies the leaist-cost transfer plan for a fleet of N detection aircraft located at ...

Perturbed Angular Correlation Measurements of Vacancy Trapping at Indium Atoms in Quenched Aluminum

Abstract: The perturbed angular correlation (PAC) method was used to study vacancy trapping at 111In atoms in quenched Al single crystals containing up to 10 ppm In. During annealing from 200–230 K, two different electric field gradients appeared, characterized by the interaction frequencies ν01 = 67 MHz with asymmetry parameter η = 0.41, and ν02 = 133 MHz with η = 0. The assignment of ν01 to a single vacancy-In atom pair is discussed. The results indicate that the migration energy of single vacancies in Al is = 0.55 eV.

Response in Canada of Jack Pine Provenances to Gremmeniella abietina

Abstract: In a series of range-wide jack pine provenance tests planted in boreal and eastern Canada, resistance to Scleroderris canker was consistently found among sources from western, northern, and eastern Quebec. Low infection levels were also evident in particular provenances from New Hampshire, New Brunswick, and Cape Breton. Generally, provenances from the milder southern limits of the jack pine range were highly susceptible to the disease, as well as being subject to winter dessication, when planted in severe boreal or high altitude environments. Winter-hardy provenances from western Canada, Ontario and the maritime provinces were intermediate in susceptibility to Scleroderris canker. No Scleroderris canker was found in test plantations located within the milder parts of the jack pine range in central and eastern Canada. In addition to seed origin, level of infection and mortality were related to climate, exposure, inoculum level, and micro-environment within a site. Operational trials of selected provenances of jack pine are warranted in areas and environmental conditions conducive to development of Scleroderris canker.

Release of Short-Lived Fission Products from Intact and Defected UO2 Fuel Elements

Abstract: The rates of escape of short-lived isotopes of xenon and krypton to the coolant from a deliberately defected UO2 fuel element are at least 100 times greater than the release rates for identical species within an intact element. The enhanced escape is consistent with accelerated transport mechanisms under defect conditions. The rate of escape to the coolant of radioiodines is less than that for the short-lived gases, reflecting strong bonding between the iodine species and internal UO2 and zirconium alloy surfaces.