Flux monitoring

Laser stimulation of a silver surface results in a reflected signal over a million times stronger than that of other metals. Called laser-enhanced Raman spectroscopy, this procedure is useful in catalysis. The large neutron cross section of silver (see Fig. 2), makes this element useful as a thermal neutron flux monitor for reactor surveillance programs (see Nuclearreactors). 

The advanced control room uses fiber optics, microprocessors, and digital monitoring and control. This includes self-testing, automatic calibration, user interactive from panels, full multiplex, standardization of the man-machine interface, common circuit cards, and wide-range flux monitors to eliminate range switching on startup. 

Pu-240 is principally used in flux monitors for fast reactors. Available enrichments range from 99+% to 93%. 

All impactor and filter samples were analyzed for up to 45 elements by instrumental neutron activation analysis (INAA) as described by Heft ( ). Samples were irradiated simultaneously with standard flux monitors in the 3-MW Livermore pool reactor. The x-ray spectra of the radioactive species were taken with large-volume, high-resolution Ge(Li) spectrometer systems. The spectral data were transferred to a GDC 7600 computer and analyzed with the GAMANAL code (1 ), which incorporates a background-smoothing routine and fits the peaks with Gaussian and exponential functions. 

A piece of the Shallowater aubrite is typically included in every irradiation as a flux monitor, and the inferred initial I29I/I27I ratios of the samples are determined relative to the... 

Irradiation I. The samples and standards (with appropriate flux monitors) are individually exposed to a neutron flux of 1 X 1013 neutrons cm"2 sec-1 for periods of V2 min for fly ash and 1 min for coal via a pneumatic rabbit system. The samples are irradiated and counted individually because of the short half-life of the (n/y) products of some of the elements and the requirement of counting at a specific time after irradiation. A copper flux monitor is irradiated with each sample to allow... 

Au foils are to be used as flux monitors in a nuclear reactor. What is the maximum thickness that can be used if the self-shielding corrections are to be less than 10% ... 

Haszpra L. Barcza Z. Davis K.J. and Tarczay K. (2005). Long-term tall tower carbon dioxide flux monitoring over an area of mixed vegetation. Agricultural and Forest Meteorology, 132(1-2), 58 -77. 

The selected samples were sent to the University of Maryland. They were opened in a Class 100 clean room and half of each filter was cut from the holder with a stainless steel scalpel, folded and transferred to an acid-washed polyethylene bag. The bags were placed into pneumatic tube sample carriers ("rabbits") along with standards and flux monitors, and irradiated in the National Bureau of Standards (NBS) reactor at a flux of 5 x 10 n/cm -sec. Gamma-ray spectra of the irradiation products were observed with Ge r-ray detectors using procedures discussed by... 

Instead of direct counting, neutron fluxes can also be determined by activation methods. Activation by (n, y) reactions (chapter 8) and subsequent measurement of the induced activity is a widely used technique. Au, In and Co are frequently applied as flux monitors. The presence of epithermal neutrons makes corrections necessary. Epithermal neutrons may be measured independently by wrapping the flux monitors in Cd or Gd which absorb the thermal neutrons. Fluxes of high-energy (fast) neu-... 

Calibration Changes of flux +1- Absence of flux monitor (y spectro.) or check of Compton effect (X-ray spectro.) Flux monitors added in the irradiation process matrix matching for major elements in energy dispersive X-ray fluorescence... 

Type 4 To determine the fluxes of substances and pollutants to major water bodies (e.g. regional seas, oceans) (flux monitoring). 

In the determination of the number of fissions in an irradiated sample by the use of flux monitors, account must be taken of the flux depression in the sample due to self-shielding to obtain an effective flux. Also, the capture cross sections of the monitors and the fission cross sections of the sample are neutron energy dependent. It is, therefore, necessary to know the eneigy distribution of the neutrons or the neutron temperature and to determine effective cross sections (Section IV). This can be done by using two monitors such as cobalt and samarium, the one monitor being used to determine the neutron temperature corresponding to the neutron distribution as described by Fritze et al. (35). 

The classical calibration of NAA methods involves comparison of sample activities with those of co-irradiated standards of the same element. Especially at multi-element analysis, the need for a large number of standards has limited the sample throughput capacity. To circumvent this, alternative calibration techniques have been elaborated. The single comparator method makes multi-element determinations possible, by use of a single element standard (neutron flux monitor). The mass of the analyte is calculated by use of an experimentally determined element-specific factor (k-value), valid for the analytical equipment in question (Girardi et al., 1965 Linekin, 1973 Simonits et al., 1975). Later, a more generalized standardization method, based on accurately determined constants for the active compound nuclei (ko-factors), and applicable to various analytical equipments, has been proposed (Moens et al., 1984 De Code et al., 1987). 

Each tube irradiated was provided with three zinc foil flux monitors (10-15 mg., 0.2 mm. thick) to provide normalization for neutron flux. Sample tubes were irradiated for three days, flux about 2.5 10 neutrons/ cm. sec. Previously, a set of dilute standard solutions of all the lanthanides, in sealed quartz ampoules, had been irradiated under identical conditions. The specific activities of the elements normalized to a constant neutron flux were shown to be constant in nine subsequent irradiations (7). These normalized specific activities were used in the determination of the concentration of the lanthanides in the samples. 

Monitoring of core power level during power operation is provided by ex-vessel neutron flux detectors. Flux monitoring at lower powers and at shutdown conditions is provided by source range detectors which are located in the side reflector. The reactor core and reflectors rest vertically on a support structure below the core and are restrained by a core lateral restraint structure located between the outer side reflector and the reactor vessel. 

The need for startup neutron detectors in-vessel is dictated by the low neutron flux at the ex-vessel detector location at startup and to ensure a controlled startup. Therefore, in-vessel startup detectors are used for flux monitoring while the reactor is brought to a critical configuration and during reactor shutdown periods. Three startup neutron detectors are installed to ensure adequate neutron flux measurements during these low power intervals. 

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