Event Data Description

in August 1999 a event file header was introduced which precedes every event data file and contains all necessary information describing the specific experimental setup.

It was also decided to reduce the original ADC and TDC resolutions whenever appropriate to standard sizes in event data files.

Spectrum  channels 
Germanium 2048
Na-I 512
Particle 1024
Time 1024

Event file header structure

      struct eventhead {
        char name[32];		/* text field */
        int  byteorder;	 	/* byte order indicator == 7 OK */
        int  nrun;              /* run number */
        int  type;		/* = 0 default
				   = 1 clover version
                                   = 2 clover gain matched */
        int  ndet;		/* number of detectors */
        int  mon;		/* monitor detector */
        int  npar;		/* number of events in file (since 2008) */
        int  parl;		/* particle spectrum length */
        int  gaml;		/* gamma spectrum length */
        int  monl;		/* monitor spectrum length */
        int  tdcl;		/* tac spectrum length */
	int  date;              /* time stamp of experiment */
        int  time;              /* "time in seconds since the Epoch" */

The event sorter programs use this information for sorting and histogram-ming the data.

Event format

Data are stored in Blocks of 8192 short (16 bit) integers. An event starts with a header word, which besides being a header, contains the magnetic field direction at the target and the number of gamma detectors in this event (indirectly: the size of the event).

header word bitmap

A data word with bit 15 set is a header word unless all bits are set (filler at end of buffer). The lower 8 bits contain the number of coincidences recorded for this event (usually number of detectors). The field information is in bits 10 and 11.

For each accepted gamma the detector number, the gamma energy and the tac (coincidence time) is recorded.

header particle det# gamma tac
det# gamma tac
.... .... ....

A monitor detector is usually a germanium detector placed at a forward angle and setup like all other detectors. The sorting programs treat this detector separately. The monitor detector is placed after the regular detectors in the histograms.

Regular detectors are either 4 Germanium or 4 Na-I detectors. The preferred setup uses 4 Clover detectors, each containing 4 Germanium detectors clustered together, a total of 16 detectors. For these detectors Compton scattered gammas within the same cluster (after energy matching) can be added back increasing the efficiency of a cluster to ~150%.

All data taken at the Yale tandem  or the 88" cyclotron  in Berkeley with different data acquisition systems and even Gamma sphere  data are converted to this simple format for further analysis.

Since Jan. 2006 our group operates it's own data acquisition system, a PIXIE-4 20 channel fully digitized pulse processing system. All data are recorded as singles (energy and time) from which particle-γ coincidence event files are constructed.

Related Programs

Gerfried Kumbartzki
Last modified: Tue Nov 24 16:08:50 EST 2009