[1211] | 1 | The final state of radiative capture is described by either photon |
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| 2 | multiplicities, or photon production cross-sections, and the discrete and |
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| 3 | continuous contributions to the photon energy spectra, along with the angular |
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| 4 | distributions of the emitted photons. |
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| 5 | |
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| 6 | For the description of the photon multiplicity there are two supported data |
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| 7 | representations. |
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| 8 | It can either be tabulated as a function of the energy of |
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| 9 | the incoming neutron for each discrete photon as well as the eventual |
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| 10 | continuum contribution, or the full transition probability array is known, and |
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| 11 | used to determine the photon yields. If photon production cross-sections are |
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| 12 | used, only a tabulated form is supported. |
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| 13 | |
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| 14 | The photon energies $E_\gamma$ are associated to the multiplicities or the |
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| 15 | cross-sections for |
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| 16 | all discrete photon emissions. For the continuum contribution, the normalised |
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| 17 | emission probability $f$ is broken down into a weighted |
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| 18 | sum of normalised distributions $g$. |
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| 19 | $$f\left(E\rightarrow E_\gamma\right)~=~ |
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| 20 | \sum_{i}p_i(E)g_i(E\rightarrow E_\gamma)$$ |
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| 21 | The weights $p_i$ are tabulated as a function of the energy $E$ |
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| 22 | of the incoming neutron. |
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| 23 | For each neutron energy, the distributions $g$ are tabulated as a function |
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| 24 | of the photon energy. As in the ENDF/B-VI data formats\cite{ENDF}, several |
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| 25 | interpolation laws are used to minimise the amount of data, and optimise |
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| 26 | the descriptive power. All data are derived from evaluated data libraries. |
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| 27 | |
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| 28 | The techniques used to describe and sample the angular distributions are |
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| 29 | identical to the case of elastic scattering, with the difference that there |
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| 30 | is either a tabulation or a set of legendre coefficients for each photon |
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| 31 | energy and continuum distribution. |
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| 32 | |
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| 33 | As an example of the results is shown in figure\ref{capture} the energy |
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| 34 | distribution of the emitted photons for the radiative |
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| 35 | capture of 15~MeV neutrons on Uranium ($^{238}$U). |
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| 36 | Similar comparisons for photon yields, energy and angular distributions have |
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| 37 | been performed for capture on |
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| 38 | ${\rm^{238}U}$, |
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| 39 | ${\rm^{235}U}$, |
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| 40 | ${\rm^{23}Na}$, and |
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| 41 | ${\rm^{14}N}$ |
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| 42 | for a set of incoming neutron energies. |
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| 43 | In all cases investigated |
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| 44 | the agreement between evaluated data and Monte Carlo is very good. |
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| 45 | |
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| 46 | \begin{figure}[b!] % fig 1 |
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| 47 | % \centerline{\epsfig{file=hadronic/lowEnergyNeutron/neutrons/plots/cap92u238.energy.fine.epsi,height=5.5in,width=3.5in}} |
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| 48 | \includegraphics[angle=0,scale=0.6]{hadronic/lowEnergyNeutron/neutrons/plots/cap92u238.energy.fine.epsi} |
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| 49 | \vspace{10pt} |
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| 50 | \caption{Comparison of data and Monte Carlo for photon energy |
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| 51 | distributions for radiative capture of 15~MeV neutrons on Uranium ($^{238}U$). |
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| 52 | The points are evaluated data, the histogram is |
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| 53 | the Monte Carlo prediction.} |
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| 54 | \label{capture} |
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| 55 | \end{figure} |
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