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
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.
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.