The photo-evaporation database contains nuclear deexcitation data starting 
from a given nuclear level. Each file contains data for a given isotope, 
identified by Z and A.

The database must first be downloaded from

http://geant4.web.cern.ch/geant4/support/download.shtml

and stored in a local directory.  The environment variable 
G4LEVELGAMMADATA must then be set to point to this directory.
 
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Each line contains a de-excitation *step* from a given energy level to a lower 
one (which might be the ground state). Notice that if multiple de-excitation 
channels are allowed for the starting energy level, these channels will be 
described in more lines (all having the same starting level).


Each line contains 17 columns:

1) Energy of the starting nuclear level (keV)
   As mentioned before, it is possible to have more lines describing the same 
   starting level, in the case where multiple de-excitation schemes are
   allowed.
	
2) Energy of the transition (keV)
   This is the energy difference between the initial and the final level.

3) Transition probability (%)
   Note1: if the probability is less than  minProbability = 1e-8%, it is forced
          to be 1e-8%.
   Note2: transition probabilities from a given level do not always sum up to 
	  100% exactly. They are re-normalized internally.

4) Polarity 
   Spin-parity variation in the transition
   [never used in real simulation]

5) Level half-life (s)

6) Angular Momentum
   Spin of the initial level
   [never used in real simulation]

7) Total internal conversion probability 
   Note: the value in item (3) is the *transition* probability, so the 
         actual *gamma* probability is calculated taking into account the 
         probability of internal conversion.

8-17) Partial conversion probabilities for
	K-shell
	L1-3 shells
	M1-5 shells
	Outer shells (shellID = 9 is used, when applicable)

Note: if the nuclear excitation energy does not match any of the known levels,
      the *nearest* level is always considered.  In G4RadioactiveDecay, 
      metastable states are treated correctly if the excitation energy is 
      within 2.0 keV of the values in $G4RADIOACTIVEDATA.

      For instance: take file $G4LEVELGAMMADATA/z28.a60 (Ni-60)
      Co-60 radioactive decay populates the 1332.5080-keV level of 
      Ni-60 (0.12%) or the 2505.7480-keV level of Ni-60 (99.88%).

      Deexcitation from the 2505.7480-keV level is described in lines 
      6-8 of $G4LEVELGAMMADATA/z28.a60 (Ni-60)
      The nucleus will release
      1) 347 keV with 7.6e-3% probability, ending up in the 2158-keV level 
      (following de-excitation hence takes place, lines 2-4 of the file)
      2) 1173 keV with 100% probability, ending up in the 1332-keV 
      excited state (following de-excitation hence takes place, line 1)
      2) 2505 keV with 2e-6% probability ending up in the ground state.