Spectrum neutron

H/D Atomic Ratio Average Leakage Neutron Energy (Mev) Thermal Leakage (%) First Collision Dose (rads/n/cm ) x 10  

Calculation of Lattice Porametert of H,0 Moderated UO, Fueled Critical Asson-blies, W. B. Amaid, Jr. (WAPD). A stem, consisting largely of hand calculations, is described which pr cts to edthin 1% in reactivity the critical masses of fourteen sepa rate UO, B,0 critical assemblies. Kght of these were the A1 clad 1.3% enriched cores done by the Bettis TRX group. One was an experiment on steel clad 4% enriched UO, performed imder the Nuclear Ship Savannah program. The other five were performed by WAPIV three on steel clad 2.7% UO, Yankee criticals, two on steel clad 4,4% BR criticals. Table 1 contains a brief description of these experimental results. 

The calculation is based on a scheme similar to the simple four factor model, except that an additional factor is added to account for the effect of U 23 resonance fissions on reactivity. This additional factor is derived from a feedback loop analysis of resonance fissions, which yields a reactivity formula as follows  

a number less than 1 which elqiresses the fraction of slowing down taking place above the 25 resonances, This term brin about an interaction between leakage and resonance fission. 

Water height experiments were performed with fuel elements (638 gm U-235 fuel cell size 3 X 3 X 36 in. metal-to-water ratio 0.298) arranged in various slab cohfigura-tions, either rod-free or with a single, fully inserted, B -SS, box-shaped control rod. Reactivity control was by water height only and measurements included those of critical hei t, he, and Incremental water height worth. Experimental results are given in the table, where lattices are described by the array of circles for elements and crosses for poison rods. 

---

If two irradiations are undertaken in similar neutron spectra to the same total number of atomic displacements and at the same temperature, but at different rates (i.e., over different time intervals), the graphite sample with the shorter exposure time will show more damage (i.e., a flux or rate effect). This is because the net observed damage is a function not only of the total damage produced (dependant on the neutron dose), but also on the extent of annealing of that damage, which is... 

Figure 2. Inelastic neutron spectra from 36Ar monolayers adsorbed on Graf oil at 5 K (9). Curves plotted immediately below data are computed spectra for two different particle-orientation distribution functions (a) in-plane configuration with momentum transfer Q parallel to the preferred orientation of the graphite basal planes (b) out-of-plane configuration with Q perpendicular to the preferred basal planes. Curves at the bottom represent the calculated contribution to the observed spectra caused by in-plane scattering from misoriented crystallites.

C. A model system for neutron vibrational spectroscopy of adsorbed molecules monolayer butane on graphite. In this section we concentrate on a particular system, monolayer n-butane adsorbed on graphite, for which a considerable effort has been made to analyze the inelastic neutron spectra for the orientation of the adsorbed molecule and the forces bonding it to the substrate (10,19,20). By treating one system in greater detail, we can better illustrate the capabilities and limitations of the technique. 

Figure 8. Inelastic neutron spectra from adsorbed species on Raney Ni (30). Each spectrum was smoothed with a 3-point smoothing routine statistical error bars are indicated at various data points the lower vertical scale marker refers to Spectra a,...

Although not exhaustive, the above summary of experiments with hydrogen chemisorbed on transition-metals serves to illustrate how neutron vibrational spectroscopy is performed with catalytic substrates and the methods used to analyze the inelastic neutron spectra. In concluding this section we note that the technique can be extended to supported catalysts such as in recent experiments with hydrogen adsorbed on both MoS and alumina supported MoSp (38). Also, as another indication of the variety of systems which can be studied, we note earlier experiments with ethylene (39) and acetylene (40) adsorbed on silver exchanged 13X zeolites. "Tn this work, deuteration of the molecules was helpful in identifying the surface vibratory modes on these ionic substrates of greater complexity. 

The neutron inelastic scattering spectra of 2,4-dinitroimidazole have been registered and calculated by solid-slate calculation methods at BLYP/dnd, BP/dnd, and PWC/dnd theory levels [682], Comparison of the observed and calculated neutron spectra reveals that the BLYP/dnd calculations provide the best description of the experimental spectrum. 

Fig. 2.14 compares the Raman and neutron spectra of the amorphous silicon network modes, which occur at wavenumbers up to 500 cm" with the calculated phonon density of states of crystalline silicon. It should not be surprising that the amorphous spectrum is a broadened... 

Irons can be determined by means of reactions with energy thresholds, such as (n, p) or (n, a) reactions. By application of several detectors with dilTcrcnt thresholds information about neutron spectra may be obtained. 

Some Instrumental Considerations We have previously touched on some of the practical considerations, like sample temperature, that limit the generality of the theoretical forms outlined above. It is also appropriate to focus, briefly, on some aspects of the ISIS instrumentation used in collecting the neutron spectra discussed here [17]. The instruments fall into two general classes... 

Fig. 10. Comparison of typical IR, Raman and neutron spectra for ice Ih shows that there are significant differences in emphasis in the different techniques. The IR and Raman data show the main peak at 27 meV. The early neutron spectrum [48] shows a lack of detail due to poor resolution and intensity. The new neutron spectrum measured on TFXA clearly shows two peaks at 28 and 37 meV. The higher energy peak is twice as intense as the lower energy peak.

Fig. 13. Neutron spectra for a number of recovered exotic phases of ice and ice Ih (H2O) were measured using HET spectrometer on ISIS with incident energy of Ei = 600 meV at temperature T 10 K. The data show very small differences among the different phases, indicating there is little effect to the intramolecular frequencies from the external structures.

Fig. 14. Neutron spectra from ice VIII measured using HET (Ej = 600 meV, at T 10 K) on ISIS. The spectrum for ice Ih is also plotted for comparison.

The m< t extensive and complete normal-mode analyses to date have been made for polyethylene and the n-paraffins. Certain of these analyses that have been particularly useful for the interpretation of neutron spectra will be reviewed to show the kind of information obtained and how it can be used to interpret qrectra. 

A comparison of neutron spectra with theory was made by Danner et al. (7). These workers obtained data for Marlex 6050 at temperatures below and above the glass-transition interval and the melting point, and for samples of branched, irradiated, and quenched polyethylene at room temperature. The spectrum at 100 K (Fig. 3) showed two peaks with shapes characteristic of acoustic modes at 550 and 200 cm" (peaks C and E in Fig. 3). Five additional peaks were observed at 1360,750,340,... 

Table 1. Comparison of the calculated optically active frequencies (in cmr -) of the fundamental vibrational modes for an isotactic helical polypropylene chain with the observed hands in inf raved and neutron spectra...

Figure 9. Map of the Q-E inelastic neutron spectra for cristobalite and tridymite at room temperature and temperatures corresponding to their high-temperature phases. Lighter regions correspond to larger values of the inelastic scattering function S(Q,E).

---