GRIFFIN consists of 16 large-volume HPGe clovers providing excellent gamma-ray energy resolution, and is augmented by a suite of ancillary detectors for measuring e±, alphas, and neutrons, as well as gamma rays in temporal coincidence.
Experiments are normally run in a cycling mode. Each cycle begins by moving the tape and collecting a background spectrum. The radioactive beam is then implanted into the tape (like VHS or cassette tape and actually computer tape) at the center of the detector array. The beam implantation is then stopped and the decay of the sample observed. When the species of interest has decayed away the cycle begins again. The tape is moved to physically remove the daughter nuclei activities from sight of the detectors. These cycles can dramatically increase the signal-to-background ratio of the decay of interest. The tape is pictured here with the Zero-Degree Scintillator behind it.
GRIFFIN uses 16 Compton-suppressed High-Purity Germanium (HPGe) Clover detectors for a total of 64 Ge crystals. The germanium crystals are held at a temperature below -175 degrees Celsius with the use of liquid nitrogen. The crystals also require a bias voltage of around 3500 volts to operate correctly.
SCEPTAR (SCintillating Electron-Positron Tagging ARray) is a set of plastic scintillators which surround the radioactive sample at the center of GRIFFIN. The scintillators detect the beta particles which are emitted when a nucleus decays. The signal from these detectors is used in coincidence with the Ge detectors to increase the sensitivity of the measurements.
There are 8 locations in the GRIFFIN support frame to house these fast scintillator detectors. The 2 inch by 2 inch cylindrical crystals are made of cerium-doped lanthanum bromide (LaBr3(Ce)). These detectors are used to observe gamma rays emitted from excited states in daughter nuclei, just like the Ge detectors. Whereas Ge detectors have excellent energy resolution for gamma rays, these fast scintillators have a very good timing resolution for gamma rays but poorer energy resolution. The fast-timing can be used to measure the lifetime of excited states in daughter nuclei which live for as short a time as 10 picoseconds, thats a hundred thousandth of a millionth of a second.
PACES (Pentagonal Array for Conversion Electron Spectroscopy) is an array of 5 lithium-drifted silicon (Si(Li)) detectors located inside the vacuum chamber. They are used to detect internal conversion electrons which can be emitted during the decay of excited states in daughter nuclei. These detectors are also used to detect alpha particles which can be emitted when a heavy nucleus decays; this capability is especially important when working with actinide beams at ISAC. The crystals and FETs are cooled to liquid nitrogen temperatures to improve the energy resolution of the detectors.
GRIFFIN has also been designed to be fully compatible with the new DESCANT array (Deuterated Scintillator Array for Neutron Tagging) being developed by the University of Guelph and TRIUMF. DESCANT is an array of 70 deuterated scintillators for detecting neutrons. This addition will allow the sensitive study of beta-delayed neutron emission in neutron-rich nuclei.