Energy flux density spectrum

The local energy-density spectrum of cosmic rays is related to the observed flux (particles per cm2 per GeV per second per steradian) by... 

Sources to be observed are stored as a list of parameters describing the position and energy spectrum of point sources or as flux density images of extended sources for a particular energy. 

Polymers that have pigments with other colors of the spectrum and/or can scatter light might also be expected to show differences in absorption of infrared energy. This is because the flux density of the radiation from a normal quartz-halogen souree is greater on the red side of the spectrum than it is at the blue end of the spectrum. 

A basic requirement for accurate NAA is the correct characterization of the irradiation facility (Becker 1987). Local and temporal neutron flux density gradients as well as gradients in the neutron energy spectrum of the irradiation position must be well understood and known for each irradiation. O Figure 30.5 illustrates the gradients in an irradiation capsule as measured by flux monitor foils. A difference of 1 mm in sample positioning will result in a 0.6% relative difference in the measured concentration. 

The spectral distribution of the radiant flux from a source is called its emission spectrum. The thermal radiation discussed in Sect. 2.2 has a continuous spectral distribution described by its spectral energy density (2.13). Discrete emission spectra, where the radiant flux has distinct maxima at certain frequencies Vik, are generated by transitions of atoms or molecules between two bound states, a higher energy state Ek and a lower state Ei, with the relation... 

Since most of the nuclear reactions In N Reactor occur at thermal or near-thermal neutron energies the most Important cross sections are those at these energies. The Vestcott formulation Is particularly useful since It defines an effective cross section for a materiel, vhlch when multiplied by the prqper flux gives the total reaction rate over the entire thermal and slowlng-down neutron spectrum. The flux employed Is nvo vhere Vq Is 2200 m/s (the velocity of neutrons corresponding to a neutron temperature of 20 c) and n Is the total neutron density (Integrated over all energies). 

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