Fluence monitor

The dosimetry test results were used to correct MAGI calculations to assure the neutron fluence used in the post irradiation test analysis (see Table 5). A Helium Accumulation Fluence Monitor (HAFM) has been developed to improve the accuracy of long-term irradiation tests. 

The quantity of neutron fluence monitors (three sets) and variety in individual assemblies is insufficient to fully characterize the distribution of the neutron flux within the assembly and in individual surveillance specimens. 

This constant can either be calculated or measured accurately with respect to an adopted standard, which practically serves as the fluence monitor. If the monitor, s, which is usually a gold foil, is co-irradiated with the sample, the mass of the analyte is determined as ... 

A meaningful assessment of potential changes in the properties of the materials measured in these examinations is only possible when the neutron fluence the sample had been exposed to in the course of reactor irradiation is known. This neutron fluence can be determined by measurement of the radioactivity of specific radionuclides which have been produced by neutron reactions. However, out of the great number of radionuclides produced, only a few can be reasonably applied as fluence monitors, since there are several limitations which have to be taken into account ... 

In most cases, as a fluence monitor small disks or wires of an Al-Co alloy with 0.1 to 1% Co are used by such a dilution of the monitor substance, self-shielding and flux depression effects are avoided. In general, since interfering radionuclides produced in the diluting element are small, chemical separations before activity measurement of Co are normally not needed. Frequently, the cobalt impurities in stainless steels, which are in the range of 100 to 1000 ppm, can be directly used as a fluence monitor in such cases, however, the accurate cobalt concentration in the material has to be additionally determined by chemical analysis. 

Due to its favorable properties, the nuclear reaction Fe (n,p) Mn is one of the standard reactions for the determination of fast neutron fluences. Since iron is the main constituent of most of the materials to be investigated, this determination can be carried out without the use of a specific fluence monitor. The halflife of Mn of 312 days permits the use of this nuclear reaction for irradiation periods of up to about two years, provided that corrections for details of the irradiation history are made. Tlie favorable energy of the Mn y ray of 0.835 MeV (transition probability 100%) frequently allows a direct activity measurement by use of a high-resolution Ge detector only in the investigation of materials with low iron contents such as Zircaloy, a chemical isolation of the monitor nuclide prior to the activity measurement is leconunended. This can be carried out, for example, by precipita-... 

The linear relation between the PSL signal and neutron fluence was established to exist over three decades up to 6. lO cm. The IP-ND can be used as fast and efficient neutron monitors at rather low neutron fluxes. However, for neutron dosimetry individual IP-ND must be calibrated individually since their sensitiviy can differ from one plate to another. In Gd/film based direct NR the film fog below the exposure dose of about 8.10 cm is the limiting factor. 

When this resin was exposed as a thin film to the UV radiation of a medium pressure mercury lamp (80 W aiH), the crosslinking polymerization was found to develop extensively within a fraction of a second (18). The kinetics of this ultra-fast reaction can be followed quantitatively by monitoring the decrease of the IR absorption at 810 an-1 of the acrylic double bond (CHCH twisting). Figure 8 shows a typical kinetic curve obtained for a 20 pm thick film coated onto a NaCl disk and exposed in the presence of air to the UV radiation at a fluence rate of 1.5 x 10 6 einstein s-1 cm 2. 

OL behavior is assessed simply by monitoring the transmission of a (usually solution) sample as a function of the incoming laser fluence measured in joules per square centimeter (rather than intensity in watts per square centimeter).22,23 Limiting thresholds Fth, defined as the incident fluence at which the actual transmittance falls to 50% of the corresponding linear transmittance, are then commonly quoted. Since excited-state absorption processes generally determine the OL properties of molecules, the excited-state structure and dynamics are often studied in detail. The laser pulse width is an important consideration in the study of OL effects. Compounds (1-5)58-62 are representative non-metal-containing compounds with especially large NLO and/or OL... 

That these ideas have some merit is indicated by the work of Hart, Dunlap, and Marsh . These investigators deposited a fraction of a monolayer of copper onto a silicon wafer and then monitored the position and concentration of the copper using Rutherford backscattering. After deposition, the copper, which was then located on the immediate surface, was bombarded with 20 keV Ne ions to a fluence sufficient to sputter 90 A of Si from the surface. The Rutherford backscattering spectrum, which was taken after this bombardment, showed that the copper was uniformly distributed to a depth of 600 A which corresponds roughly to the projected range of the Ne" " ions, i.e., the depth of the altered layer was approximately equal to the projected range of the Ne. 

The distance between the backscatter medium or body and the radiation detector elements in the holder of a personal monitor can also influence the response of the personal monitors. The backscatter fluence and resultant air kerma at the surface of a backscatter medium can decrease by a factor of two at a separation distance of 1 cm. Therefore, significant uncertainties can arise when the separation between personal monitor and the body surface varies during irradiation or differs from that used... 

The erosion yield of a polymer is typically measured by two methods (1) recession and (2) mass loss. Recession measurements are made by masking an area of a sample surface from attack and measuring the step height difference between exposed and unexposed areas. The thickness loss divided by the exposure fluence is the erosion yield. Mass loss measurements are made either by weighing a sample before and after exposure or by monitoring the mass loss in situ of a material that was coated onto a quartz crystal microbalance. Care must be taken in mass loss measurements to ensure that outgassing from the material in the vacuum of the exposure environment does not affect the results. The calculation of the erosion yield from a mass loss measurement requires knowledge of the density of the material and the surface area exposed, as well as the exposure fluence. 

The basic feature of these experiments consists first of producing a metal-cluster-adduct species, as described earlier. Second, a high-power infrared laser is aligned spatially with the cluster beam and fired at a predetermined time so as to intersect the clusters and cluster adducts prior to their arrival at the ionization zone. The effect of the infrared laser is then monitored as a change (loss) in ion signal of the species which have undergone IRMPD. From measurements of depletion as a function of laser frequency and fluence, an infrared dissociation spectrum of the complex is obtained, which can be... 

The ion beam produces a spot larger than the hole in the sample holder and currents in the range of 100 nA cm to tens of iA cm" . The integrated ion flux (fluence in ions cm" ) is measured, by a charge integrator, from the ion current monitored during irradiation. For further details on the experimental apparatus see [15]. 

This possibility is indicated in the study of the ablation of PMMA and PS doped with haloaromatic compounds (iodonaphthalene (NapI), iodo-phenanthrene (PhenI)). Experimentally these dopants offer the advantage that they exhibit negligible fluorescence, whereas their products are moderate or strong emitters. Thus, product formation can be conveniently monitored via laser-induced fluorescence (LIF). It is noted that the study has focused on the characterization of the species/products that remain in the substrate upon ablation. Thus, the experiment is of the pump-probe type, in which pump pulses at a particular wavelength (2=308, 248 or 193 nm) are used to irradiate the films, and laser pulses of very low fluence are employed to induce photoproduct fluorescence (FLaser<3 mj cm-2, probing effected always at 2=248 nm). Detailed information on the experimental setup and procedures is provided elsewhere [83-85]. 

Irradiation at the Threshold of Ablation 40 mj cm 2. To identify possible intermediates of the laser-induced decomposition of Kapton the threshold flu-ence of ablation was chosen. At this fluence ablation is just starting and changes in the material should be slow, giving the best chance to monitor intermediates. 

Figure 22 shows the time dependence of NO2 disappearance in a flash-heated nanoaluminum sample [201]. NO2 disappearance is measured using CARS spectroscopy to monitor the ONO2 totally symmetric stretching transition near 1300 cm . At the lowest fluence there is practically no NO2 consumption, but at higher fluences, NO2 consumption is seen to occur in two phases. The faster phase is characterized by an -300 ps time constant, and the amplitude of the faster phase increases with laser intensity. The slower phase occurs over -2 ns. The faster phase is associated with consumption of the shell of NO2 near each nanoaluminum particle. The slower phase is associated with NO2 consumption between the hot spots. 

Figure 14. Uses of isotropic optical fiber fluence probes for different applications, (a) interstitial probes placed into dog prostate during an intraoperative experimental procedure (courtesy Drs F. Hetzel and Q. Chen, Denver, USA) source fibers irradiating the prostate surface, bladder and bowel are also seen, (b) a probe on the surface of a transrectal ultrasound applicator to monitor the rectal dose during interstitial PDT of prostate cancer, (c) corresponding interstitial probes placed into the prostate, along with source fibers, through a template (courtesy Dr J. Trachtenberg, Toronto, Canada).

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