ORRUBA - a large-area Si detector array for FRIB
ORRUBA (the Oak Ridge Rutgers University Barrel Array) is a silicon detector array optimized for measuring light ions from transfer reactions in inverse kinematics.
Transfer reactions are a cornerstone of nuclear physics, providing a probe of single-particle structure which can, with the appropriate theoretical analysis, be quantitatively associated with occupancies of single-particle orbitals. Such information is a crucial test of nuclear structure models, and can enable astrophysically-important reaction rates to be calculated.
ORRUBA forms a twelve-sided barrel of silicon detectors, providing a quasi-cylindrical geometry, with mm-position sensitivity parallel to the optic axis and coarser segmentation around the circumference of the barrel. This geometry is suited to the measurement of polar emission angle of reaction products, which is crucial to separate kinematic loci from different states in the residual nucleus, due to the strong kinematic shifts associated with reactions measured in inverse kinematics (heavy beam particles incident on lighter target).
Detectors
ORRUBA detectors are operated as single layers and, when particle identification is required, in detector ‘telescopes`enabling ions to be separated by their characteristic rate of energy loss in a transmission detector.
ORRUBA is based upon superX3 detectors, manufactured by Micron Semiconductor Ltd. These detectors are comprised of a 75 mm by 40 mm active area, divided into four 75 mm by 10 mm resistive strips on the junction side, enabling position determination by charge division, with ~1 mm resolution at 6 MeV. The Ohmic side of the detectors is divided into four contacts for energy determination without the ballistic deficit associated with the resistive readout. Typically, 1000-um-thick sX3 detectors are employed, with some 500-um-thick units.
When thin transmission detectors are required, the BB10 design is employed. These detectors are packaged with an identical footprint to the sX3 detectors, and are divided on the junction face into eight 75 mm by 5 mm strips.
Electronics
ORRUBA uses a custom electronics and data acquisition system. Charge-sensitive preamplifers, in 36- and 72-channel custom preamplifer boxes, are used for front-end instrumentation of the silicon detectors.
