Rachel format nuclear data files

Rachel accepts the standard Gosia data 

* Excited states' lifetimes
* Measured matrix elements (signed)
* Measured branching ratios (not including internal conversion branches)
* Measured E2/M1 mixing ratios  

in addition to the measured relative gamma-ray yield data in the file <tt>rachel_nuclear_data.txt</tt>, which must be in the working directory in order for Rachel to find it.

The Rachel file format differs from the standard Gosia input for these data and is "human readable."  It is easiest to learn this format from an example:

<pre>
# This is an example file.  Data are meaningless!
lifetime gsb 2.0                   400. 80.          # The known lifetime of the first 2+ state in picoseconds
<  gsb 2.0 || E2 || gsb 0.0 >   =  2.17 0.02         # An E2 matrix element [eb] (read right-to-left) 
mixing gam 2.0 gsb 2.0             0.35 0.05         # An E2/M1 mixing ratio
< gamod 3.0  || E2 || gsb 4.0 > = -0.45 0.12         # Sign is interpreted as negative
< gsb 2.0 || E2 || gamod 3.0 >  =  0.23 0.08         # If the gsb 2+ state appears first in the level scheme,
                                                     #   then this matrix element will be automatically 
                                                     #   time-reversed.
branching gam 8.0 gamod 7.0 gsb 6.0      0.042 0.005 # Gamma decay branching ratio--not including conversion
#branching band3 3.5 band1 1.5 band1 2.5 0.04 0.01   # This line is commented out.  Half-integer spin example.
lifetime gam 2.0   5.  2.                            # cite Jane Doe, PRC 5, 289 (1994)
</pre>

The general format has four line types for branching ratios, mixing ratios, lifetimes and measured matrix elements:
<pre>
branching initial_band initial_spin final_band_1 final_spin_1 final_band_2 final_spin_2 branching_ratio error
mixing    initial_band initial_spin final_band   final_spin   mixing_ratio error
lifetime  band         spin         lifetime[ps] error[ps]
< final_band final_spin || multipolarity || initial_band initial_spin > = signed_matrix_element error
...
</pre>

Here "branching," "mixing," "lifetime" and the bra and ket notation are fixed formatting symbols and ''band'' is a valid text band name in Rachel.  The "<", ">" and "||" symbols should be delimited by spaces.  Note the "upward" direction for the matrix element (from lower- to higher-numbered state) and the standard units of the appropriate powers of e, b and nuclear magnetons.  The individual entries can be given in any order, for example in the file <tt>rachel_nuclear_data.txt.EXAMPLE</tt>, which comes with the Rachel distribution:


The order of the individual lines is completely arbitrary.  The file is re-read each time Gosia is called, so individual lines can be "commented out" before a Gosia fit iteration.  Note that the sixth line contains a matrix element given in the ''decay direction'', whereas Gosia requires it to be in the ''excitation direction''--from lower-numbered state to higher-numbered state.  This phase of this matrix element will be automatically time-reversed before being included in the fit data.  ''Pay special attention to the mixing ratios, which are the amplitude ratios with a phase as defined in Krane and Steffen, PRC 2:724.  These are not intensity ratios which may be found in some catalogs.  Refer to the Gosia manual section on OP,YIEL for units.''

The weights given to each of these four data sets can be set via the ''Gosia controls'' button menu, for example to test whether there are systematic conflicts between the different data sets (and/or the gamma-ray yield data).