TRiP98 spectra file format


Spectra (SPC) files are binary files containing energy spectra and related histograms of the various particles created when an ion undergoes nuclear interactions with the traversed matter. There is one file per initial beam energy. Spectra are stored as a function of depth in water. The file is organized in a similar fashion as a TIFF file, i.e. each data entry is preceeded by a so-called tag field which identifies the following data item by a unique number and contains the length of that item. This way a reader progam can skip irrelevant or unknown data items. With a few exceptions the data items (including the tags) are binary, and thus can be directly read only on a CPU architecture with the same byte order. This was implemented deliberately, since spectra are meant to be memory-mapped read-only into CPU address space, which disallows byte swap operations. Memory mapping also implies that structured data must be written padded to 8-byte boundaries, otherwise data access time penalties and/or access violations may occur. Hence 4-byte integers are expanded to 8 bytes and character strings always end on 8-byte boundaries, with binary zeroes padded. Floating point numbers in TRiP98 are always 8-byte double precision IEEE numbers anyway.

A tag entry is defined as
struct STRPSPCBTAG { unsigned long ulTag; unsigned long ulLen; };
which is a sequence of two 4-byte integers. The Len field specifies the length (in bytes) of the data item to follow, excluding the tag entry. The currently supported Tag codes are:
enum {
       TRPSPCBTAG_FILETYPE   =1,      /* header info */
       TRPSPCBTAG_FILEVERSION=2,
       TRPSPCBTAG_FILEDATE   =3,
       TRPSPCBTAG_TARGNAME   =4,
       TRPSPCBTAG_PROJNAME   =5,
       TRPSPCBTAG_B          =6,
       TRPSPCBTAG_P          =7,
       TRPSPCBTAG_N          =8,
       TRPSPCBTAG_NZ         =9,
       TRPSPCDTAG_Z          =10,
       TRPSPCDTAG_N          =11,       
       TRPSPCDTAG_NS         =12,
       TRPSPCDTAG_S          =13,
       TRPSPCDTAG_CUM        =14,
       TRPSPCDTAG_NC         =15,
       TRPSPCDTAG_NE         =16,
       TRPSPCDTAG_E          =17,
       TRPSPCDTAG_EREF       =18,
       TRPSPCDTAG_HISTO      =19,
       TRPSPCDTAG_RUNNINGSUM =20,
};
The file format starts as follows:
BTAG_FILETYPE    <filetype> 
BTAG_FILEVERSION <fileversion> 
BTAG_FILEDATE    <filedate> 
BTAG_TARGNAME    <targname>
BTAG_PROJNAME    <projname>
BTAG_B           <B>        # double; beam energy [MeV/u]
BTAG_P           <P>        # double; peak position [g/cm**2]
BTAG_N           <N>        # double; normalization, usually =1
BTAG_NZ          <nz>       # 8-byte unsigned integer; number of depth steps.
<nz> depth data blocks
where <filetype> is an 80-byte ASCII character string starting with "SPCM" or "SPCI", specifying big ("Motorola") or little ("Intel") endian byte order, respectively.
<fileversion> is an 80-byte ASCII character string specifying the file format version as yyyymmdd. 19980704 is the "classic" format (fixed energy range), whereas 20020107 is reserved for future possible variable energy range.
<filedate> is an 80-byte ASCII character string with the file creation date as returned by the ctime() function. (<dow> <mmm> <dd> <hh>:<mm>:<ss> <yyyy>)
<targname> and <projname> are the names of target ("H2O") and projectile ("12C6"), respectively. Since both can have any length, they are padded to the right with binary zeroes up to the next 8-byte boundary.
A depth data block is organized as follows:
DTAG_Z <P>        # double; depth [g/cm**2]
DTAG_N <N>        # double; normalization for this depth step, usually =1.
DTAG_NS <nS>      # 8-byte unsigned integer; number of particle species.
<nS> species data blocks
A species data block is organized as follows:
DTAG_S    <ZA>     # double Z, double A, long Z, long A;
DTAG_CUM  <Cum>    # double
DTAG_NC   <nC>     # 8-byte unsigned integer; 
DTAG_NE   <nE>     # 8-byte unsigned integer; number of energy bins for this species
{
DTAG_EREF <lSRef>  # 8-byte unsigned integer; 
|
DTAG_E <E[nE+1]>   # double; energy bin values 
}
DTAG_HISTO <H[nE]>           # double; spectrum bin values 
DTAG_RUNNINGSUM <Cum[nE+1]>  # double; running cumulated spectrum bin values 
The scalar Cum value is the cumulated number (running sum) of fragments, i.e. the species sum over Cum[nE]. This number may exceed 1, since for an incoming primary particle many secondaries are created.
<nC> is reserved for later use, so that lateral scattering for each fragment can be included. At present nC=0.
If a species data block is flagged as EREFCOPY, its energy bins are not stored, but rather a reference index <lSRef> (0..<nS>-1) to a species with identical energy binning. This helps to reduce space requirements, since fragment spectra may share the same energy bins. If the energy bins for the species under consideration are not a reference copy, <nE>+1 double precision bin border values are stored.
The <H[]> are the spectrum contents divided by the bin width.
The <Cum[]> are the running integrated values of <H[]>

The usual file name extension is .spc.
The usual naming convention is <pp>.<tt>.<uuu><eeeee>.spc, where <pp> denotes the projectile, <tt> the target material, <uuu> the unit ( keV, MeV, GeV) and <eeeee> the energy in these units, with the decimal point after the middle digit. Example: 12C.H2O.MeV27000.spc refers to 270 MeV/u.
Last updated:
$Id: trip98fmtspc.html,v 1.4 2011/03/08 19:02:51 kraemer Exp $
M.Kraemer@gsi.de