Neutron production rate

A neutron production rate (not including the cosmogenic components) was calculated by Andrews et al. (1986) for a granitic rock as a function of U, Th contents,... 

As given in Equation (5.7), the neutron production rate can be expressed as a function of U content. From the production rate, we can calculate the neutron flux (X) with the relation fn = v x n, where v denotes the mean velocity of neutrons and n is an equilibrium concentration of neutrons. The latter quantity is related to the neutron production rate (pn) as n = (pjt) where T denotes the time constant for the neutron absorption in the medium (-2500 s1). Andrew et al. (1986) estimated the average neutron flux in the Stripa granite to be 5.5 x 10 4 neutrons cm 2s, which is in good agreement with the measured flux of 4.7 x 10 4 neutrons cm 2s 1 in the borehole in the granite. 

For a given mass and isotopic composition of plutonium and contaminant concentration, neutron production rate and allowable concentration of a given contaminant can be estimated from data in Tables 8.13 and 8.14. Estimates for Pu containing 1000 ppm Pu and for containing 100 ppm are given in Table 8.15. By comparison, plutonium undergoing... 

Figure 3. Martel et al. (1990, show the calculated neutron production rate as a function of grain size for spherical uraninite and monazite grains in a biotite matrix. The valnes are relative to an arbitrary value of 100 assigned to the yield from Al bombarded by mono-energetic 5.3MeV alpha particles.

The core delayed neutron fraction () ) varies from 0.0065 at beginning of cycle in the Initial core to 0.005 at the end of an equilibrium cycle. This average delayed neutron fraction was obtained by weighting the P s of each of the three major core fission Isotopes, U-235, Pu-239, and U-233, by their relative contribution to the neutron production rate. For example, the relative production rate contribution from U-235 varies from 100% at the beginning of the initial cycle to 57% at the end of an equilibrium cycle. The relative production rates of these three nuclides are given In Table 4.2-13a. 

Figure 6 shows the variation in high energy neutron production with depth. The curve is derived from an approximate table of neutron production rates per cosmic muon versus depth as measured by Aglietta et al. multiplied by the relative number of cosmic muons at the same depth. 

For a spherical shell 1 m in thickness with a 50 m inner diameter (to account for a 2.5 m thick water buffer) the scaled neutron production rate is about 56,000 events/day. After attenuation through the buffer, no more than 13 neutrons per day with energies greater than 1 MeV will enter the 45 m diameter fiducial volume. The rate of correlated events using the KamLAND selection criteria is about 0.3 per day. The event rate in a water detector from these neutrons will be smaller than this due to the stricter energy and time coincidence requirements. 

The thermal neutron production rate within the detector is difficult to estimate accurately. However, our previous estimate of the rate of muon generated neutron production in rock can be scaled to give a conservative upper bound on the rate of thermal neutron production in water. The previous estimate assumes a rock density of 2.7 gm/cm. ... 

Criticality (nuclear)— A fission process where the neutron production rate equals the neutron loss rate to absorption or leakage. 

Despite the many experiments designed to detect neutrons, their production in the Pd/D system has been difficult to prove [3,4]. This problem is explained by the small neutron production rate of 5-50 s in active Pd/D cells reported by Pons and Reischmann in 1992 [13]. Recent studies at the US Navy SPAWAR laboratory have reported significant evidence for neutron production using CR-39 integrating detectors [14]. These experiments used codeposition methods, where both Pd and D are deposited onto a substrate from a PdCl2 + LiCl + D2O solution [12]. The Navy SPAWAR CR-39 results also gave a low neutron production rate of 2.5 cm s , and it would be difficult to measure this low neutron flux using real-time detectors (P.A. Mosier-Boss, personal communication see also Ref. [14]). 

The neutron production rate source terms were derived from a common origin, this bdng polynomial fits to measured axial and radial profiles supplied by JAPC. The data was taHasn from reactor information and normalised to a core average of 6.327 x n cc s. A 15 group neutron energy scheme was used for the output fluxes is giv below in Table 1 and fifteen selected reaction rates were also calculated for those reactions listed below in Table 2. 

Numerical calculations have shown that the use of this relation in reactor calculations yields an overestimate of the critical mass. This may be seen from the fact that in estimating the removal rate (effectively the neutron absorption rate) we have ignored the contributions of the higher modes in (8.314). Thus the neutron production rate in the core has been underestimated, and the resulting computation of the critical mass will be larger than that required to maintain the system at steady state. For this reason we call (8.316) the upper approximation. 

A redundant system of counters were placed external to the vacuum containment to further reduce the background neutron production rate. Four slabs of scintillator coupled to 857.5 photomultiplier tubes were arranged above and below the target (Fig. IX.A.2). 

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