Blue: a database for high-fold γ-ray coincidence data

Optimal sensitivity in large HPGe γ-ray spectrometers such as Gammasphere and Euroball is achieved with 4-fold γ-ray coincidences or higher. Analysis of coincidence data at these folds is difficult as storage constraints make histogram-based techniques impractical. To address the problem of efficient storage of and access to high-fold coincidence data we have developed Blue, a specialized database program. Each coincidence event in this database is stored in its native fold eliminating statistical artifacts which can be introduced by unfolding a high-fold event to several lower-fold events. Partition of the dataset is based on the density distribution of coincidence events which makes data access efficient. A simple yet flexible query system is implemented by using a tree-like index for these partitions. This program is capable of executing a variety of queries, such as taking gates on a multi-fold database, at timescales which are interactive (s) or near-interactive (min). Simple compression techniques are employed so that databases with sizes of 109 coincidences can easily be stored in a space of 10 Gb or less.