Mean neutron energy

The sensitivity of this activation ratio method between 13 MeV and 15 MeV, on average, is 50%/MeV and 64%/MeV for Zr and Cr, respectively. This method is also applied to determine the mean neutron energy for an extended sample. In this case, the Zr and Nb foils are placed back-to-back in different positions inside the sample. The angular yield of D-D neutrons can be measured either by the U(n,f) using a depleted U layer in a fission chamber or by the In(n,n ) In reaction. The curve is relatively well known and its change between... 

The measured fission rates were input to the SAND-II code together with a starting spectrum calculated with the KENO Monte Carlo-code. The SAND-II code produced an adjusted dalcubted spectral shape which agreed vrith the measured data. Table I presents these SAND-II results for the thermal flux, flux of neutrons with energy. 1 and 1 MeV, total flux, and the mean neutron energy. A detailed error analysis was not made, but on the basis of similar Mrilyses, uncertainties in these spectral values are estimated to be 10 to 15% (1 o). 

The mean neutron energy is rather nearer to thermal in these reactors than it is in the corresponding cases. Consequently, losses to core vessel and to core salt tend to be higher. Both losses will be reduced substantially at higher thorium concentrations. 

Thermal neutrons, or neutrons in thermal equilibrium with the substance in which they exist most commonly, neutrons of kinetic energy about 0 025 eV, which is about of the mean kinetic energy of a molecule at 15°C. 

The neutron flux (the product of neutron concentration and velocity) is a strong function of neutron energy, position in the target island, and the reactor operating conditions. The means by which these variations are handled is discussed below. 

Table 8.2. Cross sections (Tn,r of nuclear fission by thermal neutrons (energy 0.025 cV) and mean number v of neutrons set free by fission.

These INS studies of the alkali metal hydrides provide an excellent example of the careful analysis of INS experimental data. It includes the application of corrections for multiple scattering, neutron absorption and heavy-ion scattering the extraction of quantities related to the hydrogen dynamics (the hydrogen mean square displacement, mean kinetic energy and the hydrogen Einstein frequency) and provided the density of vibrational states for each type of atom, shown individually and ab initio modelling of the full INS spectra. 

G. Corradi, D. Colognesi, M. Celli M. Zoppi (2003). Condensed Matter Physies, 6, 499-521. Mean kinetic energy and final state effects in liquid hydrogens from inelastic neutron scattering. 

The task of neutron spectroscopy is to obtain the neutron energy spectrum general methods used to unfold this equation are discussed next. 

The number of neutrons emerging from a collision is automatically determined when the collision is elastic scatter, absorption, (n, n ), ( , 2n), or an (n, 3n) reaction. At a fission, however, the number of secondaries is a function of the incident neutron energy. This function is described in the data library by the mean number of neutrons per fission, v, which is presented in the data library in a similar manner to cross section, except that, generally, fewer points are used and interpolation is linear for v against energy. The number of secondary neutrons released in a fission is an integral random variable whose expectation is equal to v. 

In this, Eq is the energy of thermal neutrons, r = ]nE/Eo where E is the neutron energy, D, which may be a function of r, is one-third of the transport mean free path, (r, x,y,z) is the smn of the velocities of those neutrons for which ItiE/Eq is in imit interval at r and which are in unit volume at ar, y, z, 5 = (7 is the slowing down power, a being the scattering cross section per... 

The X-rays and neutrons scatter elastically in these diffraction experiments, meaning the energy of the incident and diffracted radiation is comparable. Bragg reflections occur when the incident and scattered waves of radiation interfere constructively in accordance with Bragg s law. Bragg s law describes the condition whereby you have constmctive interference between successive atomic planes in a solid separated by an interlayer spacing d and is given by... 

The mean resonance energies were calculated by Jovanovic et al. (1987) by integrating over all the resonances for all the (n,y) reactions used in neutron activation analysis. 

Many methods have been developed to measure /and a. They all involve the activation and counting of a number of nuclides having a range of Qo values and mean resonance energies. The most accurate measurements of a use irradiations under cadmium cover to activate only with epithermal neutrons. However, many laboratories may not require such high accuracy or may not be permitted to irradiate under cadmium cover. Bare irradiations have been shown to give sufficient accuracy if carefully done. Since the parameters are determined by subtraction of the thermal neutron-produced activity from the total activity- two possibly similar quantities -accurate element masses, peak areas, and detection efficiencies are needed. The minimum number of monitors that need to be irradiated for the simultaneous determination of the thermal neutron flux, the factor /, and a. is three. 

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