The TRIGRESS Array at TRIUMF
What is TIGRESS?
The TRIUMF-ISAC Gamma-Ray Escape Suppressed Spectrometer or TIGRESS, currently under construction at TRIUMF, is a versatile γ-ray spectrometer for use at TRIUMF’s Isotope Separator and Accelerator (ISAC) radioactive beam facility. In 2009 the TIGRESS array will be fully operational and will comprise 12 germanium detectors. However, many experiments are planned with a small number of the detectors. Each of the 12 elements will consist of a 32-fold segmented High-Purity Germanium (HPGe) γ-ray detector and a Compton-suppression shield to suppressed scattered γ rays.
Shown below is the TIGRESS array as it was used in the first experiment at TRIUMF. Six of ultimately 12 high-purity germanium gamma-ray spectrometer units were installed in one-half of the aluminum truncated-cube support structure. The target chamber is shown in the center of the array.
Why do nuclear scientists need TIGRESS?
For decades precision γ-ray spectroscopy with large detector arrays was the main experimental tool for nuclear structure experiments. Gamma rays from nuclear reactions initiated by the accelerated radioactive ion beams from ISAC-II will generally be emitted from nuclei recoiling with velocities 3-5% of speed of light. Their energies will thus be Doppler shifted and the γ-ray energy resolution will ultimately be determined by the ability to reconstruct the angle of emission of the γ-ray on an event-by-event basis. A key feature of the TIGRESS HPGe detector is therefore its sensitivity to γ-ray interaction locations due to the segmentation of the detectors.
First experiment using TIGRESS: Gamma Rays from 29Na
The aim of the first experiment with TIGRESS was to measure the electromagnetic excitation probability for the neutron-rich unstable nucleus 29Na using the technique of coulomb excitation. An unstable neutron-rich 29Na beam accelerated to 7% of speed of light was bombarding a 110Pd target situated in the center of TIGRESS. The beam energy was chosen such as that the nuclei interacted only through the electromagnetic interaction. The excited nuclei then relaxed by emitting gamma rays which were observed with TIGRESS. A CD-shape like detector, called BAMBINO, was mounted in the vacuum chamber 3.0 cm downstream of the target. The background from isobaric contaminants was eliminated with the BAMBINO CD silicon detector. The silicon and trigger TIGRESS to look for gamma rays coming at nearly the same time. For more information please visit http://www.triumf.info/index.php?headline=65.
Greg Hackman and TIGRESS at TRIUMF.
TIGRESS was developed by an international group of scientists under the direction of Guelph physics professor Carl Svensson and with NSERC financial support.
Future TIGRESS experiments with radioactive beams at TRIUMF
Future experiments involving TIGRESS will investigate a variety of nuclear structure, nuclear astrophysics, and fundamental interactions topics. For a list of approved experiments see http://www.triumf.info/facility/experimenters/expdb/public.php?
TIGRESS will be coupled to different ancillary detectors for detecting charged particles, neutrons, and with a electromagnetic mass analyzer. These detectors are currently under construction at TRIUMF.
Links
TIGRESS at GUELPH http://www.physics.uoguelph.ca/Nucweb/tigress.htm
TIGRESS AT TRIUMF http://tigress.triumf.ca/
Mike’s MSc thesis on TIGRESS
http://www.physics.uoguelph.ca/Nucweb/files/schumakerthesis.pdf
TIGRESS Papers:
TIGRESS: TRIUMF ISAC Gamma-Ray Escape-Suppressed Spectrometer
C.E. Svensson et al.
J. Phys. G 31, S1663 (2005)
TIGRESS Highly Segmented High-Purity Germanium Clover Detector
H.C. Scraggs et al.
Nucl. Instrum. Meth. A 543, 431 (2005)
Position Sensitivity of the TIGRESS 32-Fold Segmented HPGe Clover Detectors
C.E. Svensson et al.
Nucl. Instrum. Meth. A 540, 348 (2005)
Radioactive Beam Experiments with Large Gamma-Ray Detector Arrays
C. E. Svensson et al.
Nucl. Instrum. Meth. Phys. Res. B 204, 660 (2003)
First TIGRESS experiment at TRIUMF http://www.triumf.info/index.php?headline=65
Experiments database
http://www.triumf.info/facility/experimenters/expdb/public.php?