Activation foils

The measurement of neutron fluxes by foil activation is more complicated because the neutrons are not monoenergetic and the monitor cross sections are energy dependent. The simplest case is monitoring slow neutron fluxes. Radiative capture (ivy) reactions have their largest cross sections at thermal energies and are thus used in slow neutron monitors. Typical slow neutron activation detectors are Mn, Co, Cu, Ag, In, Dy, and Au. Each of these elements has one or more odd A isotopes with a large thermal (n,y) cross section, 1-2000 barns. The (n,y)... 

Neutron detection by foil activation is based on the creation of a radioisotope by neutron capture, and subsequent counting of the radiation emitted by that radioisotope. Foil activation is important not only for neutron flux measurements but also for neutron activation analysis, which is the subject of Chap. 15. This section presents the basic equations involved. 

Determination of the Neutron Flux by Counting the Foil Activity... 

Foil activation may be used for detection of the number of either fast or thermal neutrons. The use of foils for fast-neutron energy measurements is discussed in Sec. 14.6. Foil activation is not used generally for measurement of the energy of thermal neutrons. 

The LSL-M2 program package determines the neutron energy spectrum based on information obtained from a combination of neutron flux calculations and threshold foil activation measurements. The results of LSL-M2 are used primarily for the determination of radiation damage to reactor components and... 

E 1 MeV Foil activation Organic scintillatois Threshold reactioiu Time-of-fiight... 

Neutron dosimetry by foil activation is not used so much to record doses received by personnel as it is to record doses to materials, instruments, or other components that may suffer radiation damage as a result of neutron bombardment. The principle of this method was presented in Secs. 14.4 and 14.6. A target, in the form of a thin small foil, is exposed to the neutron field and becomes radioactive. The relationship between activity and neutron flux is... 

Like Fermi s and Anderson s previous experiment, the new project involved measuring neutron production in a tank of liquid. For a more accurate reading the experimenters needed a longer exposure time than their customary rhodium foils activated to 44-second half-life would allow. They planned instead simply to fill the tank with a 10 percent solution of manganese, an ironlike metal that gives amethyst its purple color and that activates upon neutron bombardment to an isotope with a nearly 3-hour... 

The neutron flux calculation error rate was evaluated to be less than 5% in the fuel region according to the comparison between MAGI and reactor dosimetry test results (see Table 5). Figure 10 shows an example of adjusted neutron spectrum based on the foil activation method at the core center position of the MK-II. 

All measurements in this series were normalized by comparing gold foils activated in graphite hole 44 during each run. 

A soln. of startg. benzyl bromide in THF added slowly to cut zinc foil activated with 1,2-dibromoethane at 0°, after stirring for 2-3 h at 5° the soln. added to CuCN and LiCl in THF at —70°, warmed to —20° for 5 min, re-cooled to —70°, a soln. of allyl bromide in THF added, the mixture warmed slowly to 0°, and worked up after 5 min - product. Y 96%. The method is mild, and formation of 1,2-diarylalkane crosscoupling products minimal functional groups such as esters, nitriles, halides, and ketones are tolerated. F.e. and electrophiles s. S.C. Berk et al., J. Org. Chem. 53, 5789-91 (1988). 

Foil activation ofl-axis and away from the central plane showed that the fluxes are separable to within experimental error throughout the core. Only in the outer corner of the reflector did the activation increase (by about 40%) over the product of the separated fluxes. 

The lattice parameters were all determined from foil activation measurements made in the central cells of the full critical lattice loadings in the Process Development Pile (PDP). Thermal and epithermal flux distributions were determined from bare and cadmium covered irradiations of Cu, Mn, and U-235 foils placed In both the hiel and moderator. 

The foil activities were then determined by a least-squares fit with a parabola in the slab, and by Simpson s rules fit in the water. The resulting disadvantage foctors are listed in Table I. 

The power distribution as shown on Figure 1 was determined by circumferential U-23S foil activations on each rod in an octant of the plane located 12 inches below the top active surface of the core. The four central control rods were inserted 24.38 inches from the top active surface of the core during this measurement. The peak element power to the plane average was under-predicted by approximately 5% AP/P. The power-distribution measurements were of specific interest due to the large circumferential power variations both predicted and measured around the large superheat fuel elements 20% AP/P). 

The disadvantage factor was obtained by the so-called integral technique. Foils of a uranium-aluminum alloy of 17.5 wt% uranium that was enriched to 92.75 wt% U-235 were shaped to measure the U-235 fission rate in representative portions of the fuel and moderator volumes of a unit cell. Cadmium ratios in both fuel and moderator sections were determined with 0.051-cm cadmium covers. Various thicknesses (0.0051 to 0.066 cm) of foils were used. The foil activities were corrected for thermal self-shielding. Ih the cadmium-covered irradiations, various masses of cadmium were used and the cadmium ratios were corrected to zero cadmium mass. 

Gold-Foil Activation Ratio Radially from the Outer Edge of the Fuel to the Core Center 1.73 1.57... 

Detailed parameter measurements made in the SE included determinations of the thermal-neutron distributions in terms of subcadmium foil activation thermal-neutron temperatures in terms of Lu/l/v activity ratios epithermal-neutron fractions in terms of Th capture and u fission cadmium ratios U production in terms of neutron captures in Th and lattice fissions in terms of the Th/ U fission ratios. The HAMMER computations generally agreed with the intracell activation profiles. The spectral index measurements agreed poorly because the computations overestimated the spectral index in all coolants. 

Earlier buckling measurements were reported with similar lattices surrounded by bond and paraffin. The interpretation of those measuremoits, which used In foil activations, presented some difficulties, presumably due to the boral-paraffin reflector, since it was not possible in every case to establish a unique material buckling. 

W. N. McELROY, S. BERG, T. B. CROCKETT, and R. J. TUTTLE, Measurement of Neutron Flux Spectra by a Multiple Foil Activation Iterative Method and Comparison with Reactor Physics Calculations and Spectrometer Measurements, IVucl. Sci. Eng., 36, 15 ( 969). 

Foil activation Reactivity-compensating changes In fuel density, neutron spectrum, and power profile Needed to Supplement reactivity measurement. Limited sample size because of counting requirements and short half-lives. 

---