
\section{The Total Probability for Photon Evaporation}
\hspace{1.0em}As the first approximation we 
 assume that 
 dipole $E1$--transitions is the main source of $\gamma$--quanta from 
highly--excited nuclei \cite{evap.Iljinov92}.
The probability to evaporate $\gamma$
 in the energy interval $(\epsilon_{\gamma}, \epsilon_{\gamma}+d\epsilon_{\gamma})$ 
 per unit of time is given
\begin{equation}
\label{SPE7}W_{\gamma}(\epsilon_{\gamma}) =
 \frac{1}{\pi^2 (\hbar c)^3}\sigma_{\gamma}(\epsilon_{\gamma})
\frac{\rho(E^{*}-\epsilon_{\gamma})}
{\rho(E^{*})}\epsilon^2_{\gamma},
\end{equation}
where  $\sigma_{\gamma}(\epsilon_{\gamma})$ is the inverse (absorption of  $\gamma$)
reaction cross section, 
$\rho$ is a nucleus level density is defined by Eq. ($\ref{evap:6}$).
  
 
The photoabsorption reaction cross section is given by the expression
\begin{equation}
\label{SPE8} 
\sigma _{\gamma}(\epsilon_{\gamma}) = 
\frac{\sigma_0 \epsilon^2_{\gamma} \Gamma^2_{R}}
{(\epsilon^2_{\gamma} - E_{GDP}^2)^2 + \Gamma^2_R\epsilon^2_{\gamma}},
\end{equation}
where $\sigma_0=2.5A$ mb, $\Gamma_R=0.3E_{GDP}$ and $E_{GDP}= 40.3 A^{-1/5}$ MeV are 
empirical parameters of the giant dipole resonance \cite{evap.Iljinov92}.
The total radiation probability is
\begin{equation}
\label{SPE9}W_{\gamma} =\frac{3}{\pi^2 (\hbar c)^3}\int_{0}^{E^{*}}
 \sigma_{\gamma}(\epsilon_{\gamma})
\frac{\rho(E^{*}-\epsilon_{\gamma})}
{\rho(E^{*})}\epsilon^2_{\gamma}d\epsilon_{\gamma}.
\end{equation}
The integration is performed numericaly.

\subsection{Energy of evaporated photon}
\hspace{1.0em}The energy of $\gamma$-quantum is sampled 
according to the Eq. $(\ref{SPE7})$
distribution.

\section{Discrete photon evaporation}

\hspace{1.0em} The last step of evaporation cascade consists of evaporation of 
photons with discrete energies. The competition between photons and 
fragments as well as giant resonance photons is neglected at this step. 
We consider the discrete E1, M1 and E2 photon transitions 
from  tabulated isotopes. 
There are large number of isotopes  \cite{evap.ENSDF} with the experimentally
 measured exited level energies, spins, parities and relative transitions 
 probabilities. This information is 
 implemented in the code.
\section{Internal conversion electron emission}

\hspace{1.0em} An important conpetitive channel to photon emission is internal
conversion. To take this into account, the photon evaporation data-base was
entended to include internal conversion coeffficients.

The above constitute the first six columns of data in the photon evaporation 
files. The new version of the data base adds eleven new columns corresponding 
to:

\begin{enumerate}
\setcounter{enumi}{6}
\item ratio of internal conversion to gamma-ray emmission probability 
\item - 17. internal conversion coefficients for shells K, L1, L2, L3, 
M1, M2, M3, M4, M5 and N+ respectively. These coefficients are normalised 
to 1.0
\end{enumerate}

The calculation of the Internal Conversion Coefficients (ICCs) is 
done by a cubic spline interpolation of tabulalted data for the 
corresponding transition energy. These ICC tables, which we shall 
label Band \cite{spe.band}, R\"{o}sel \cite{spe.rosel} and Hager-Seltzer 
\cite{spe.hagsel}, are widely used 
and were provided in electronic format by staff at LBNL. The reliability
of these tabulated data has been reviewed in Ref. \cite{spe.rys}.  From 
tests carried out on these data we find that the ICCs calculated from all 
three tables are comparable within a 10\% uncertainty, which is better than 
what experimetal measurements are reported to be able to achive. 

The range in atomic number covered by these tables is Band: $1 <= Z <= 80$; 
R\"{o}sel: $30 <= Z <= 104$ and Hager-Seltzer: $3, 6, 10, 14 <= Z <= 103$. 
For simplicity and taking into account the completeness of the tables, 
we have used the Band table for $Z <= 80$ and R\"{o}sel for $81 <= Z <= 98$.

The Band table provides a higher resolution of the ICC curves used in 
the interpolation and covers ten multipolarities for all elements up 
to $Z=80$, but it only includes ICCs for shells up to M5. In order to 
calculate the ICC of the N+ shell, the ICCs of all available M shells 
are added together and the total divided by 3. This is the scheme adopted 
in the LBNL ICC calculation code when using the Band table. The R\"{o}sel 
table includes ICCs for all shells in every atom and for $Z>80$ the N+ 
shell ICC is calculated by adding together the ICCs of all shells above M5. 
In this table only eight multipolarities have ICCs calculated for.


\subsection{Multipolarity}
The ENSDF data provides information on the multipolarity of the transition. 
The ICCs included in the photon evaporation data base refer to the 
multipolarity indicated in the ENSDF file for that transition. Only one 
type of mixed mulltipolarity is considered (M1+E2) and whenever the mixing 
ratio is provided in the ENSDF file, it is used to calculate the ICCs 
corresponding to the mixed multipolarity according the the formula:

\begin{tabbing}
\= xxx \= xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx \kill
\>     \> - fraction in $M1 = 1/(1+\delta^{2})$ \\
\>     \> - fraction in $E2 = \delta^{2}/(1+\delta^{2})$ \\
\> \\
\> where $\delta$ is the mixing ratio.\\
\end{tabbing}

\subsection{Binding energy}
For the production of an internal conversion electron, the energy of the 
transition must be at least the binding energy of the shell the electron 
is being released from. The binding energy corresponding to the various 
shells in all isotopes used in the ICC calculation has been taken from 
the Geant4 file G4AtomicShells.hh.

\subsection{Isotopes}
The list of isotopes included in the photon evaporation data base has been 
extended from $A<=240$ to $A<=250$. The highest atomic number included is 
$Z=98$ (this ensures that Americium sources can now be simulated).

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