Detector Development
TACTIC
A cylindrical ionization chamber for measuring cross-sections of astrophysically relevant reactions at TRIUMF. The gas-filled cylinder with anode pads on the walls allows reconstuction of the reaction ejectile tracks and therefore a good separation between wanted and unwanted events.
(Click on an image to view it full size.)
AGATA
The Advanced Gamma Tracking Array (AGATA) is the next generation European gamma ray detector array which will be used for nuclear spectroscopy studies at various facilities in Europe. Its principle of operation is based upon a new concept where the full energy of Compton scattered gamma ray events in the detector array are recovered using a newly developed technique called gamma ray tracking. This should yield an increase in the resolving power of up to 3-4 orders of magnitude compared to the best current gamma-ray detector arrays. More details about various aspects of the project can be found at the official website of the AGATA project.
This project involves 44 institutes from 11 countries, 6 of them being from the UK. The University of York is one of these UK institutions and is working on simulations and data analysis aspect of the project as well as a future physics programme that will be carried out with the array. The York involvement is led by Prof. R. Wadsworth and Prof. M. Bentley.
AGATA Links
Talks from the UK AGATA meeting March 2009 (Hosted at Daresbury Lab)
Talks from the UK AGATA meeting November 2009 (Hosted at Daresbury Lab)
Talks from the UK AGATA meeting July 2010 (Hosted at Daresbury Lab)
Talks from AGATA week January 2010 (Hosted at LNL)
Talks from AGATA week November 2010 (Hosted at IN2P3, Lyon)
Talks from AGATA week September 2011 (Hosted at TU Darmstadt)
Key parameters of the AGATA detector array are shown above. The result of a simulation for the full 4-pi array with a 60Co gamma ray source located at the center of the array is shown below along with a schematic picture of the full array. This simulation yields a peak to total of 64%.
LYCCA
One of the numerous detector development projects at York focuses on the development of diamond timing detectors which will make up part of a large array of detectors called LYCCA. LYCCA is a device designed to track and identify the vast number of fragments generated when a radioactive beam hits a target. It does this by measuring the energy loss and total energy of a particle, as well as its time of flight. This device will be based at the new FAIR facility (Facility for Antiproton and Ion Research) at GSI in Germany, where it will detect nuclei at the end of the Super-FRS, a new beamline which, when built, will be able to produce and separate high intensity, radioactive secondary beams using superconducting magnets.
Over the past decade, the use of diamond as material for timing detectors has become more and more popular due to its radiation hardness properties and fast electron and hole mobilities, an essential characteristic for fast timing detectors. Simulations show that if LYCCA is to be able to distinguish between isotopes, a resolution of below 50 ps (FWHM) needs to be achieved. Diamond detectors have achieved this in the past, however the dimensions of these detectors have usually been around 1cm x 1cm. For LYCCA, we require diamond detectors on a much larger scale, with an eventual aim of building a large wall of detectors.
The current prototype, LYCCA-0, has been built and recently tested at GSI, the results of which are being analysed. The diamond detector for this prototype is shown in the photograph. A timing resolution of just over 100ps (FWHM) was achieved at tests at the cyclotron facility at Texas A & M University, and we believe further developments can reduce this, hopefully edging below 50ps FWHM resolution.
PARIS
PARIS or the Photon Array for the studies with Radioactive Ion and Stable Beams, is a newly formed collaboration, the aim of which is to design and build a high efficiency detector consisting of two shells of crystals for medium resolution spectroscopy and to detect gamma-rays over a large range of energies (100keV – 50MeV). It is designed to be modular and to complement the new SPIRAL2 RIB Beam facility in GANIL, France.
The inner shell of crystals will be highly granular, and made from LaBr3:Ce, with the readout done in either a Phoswich arrangement with another crystal, APD’s or with another configuration involving digital electronics and possible light-guide to limit dead space and allow for pulse shape analysis. The inner hemisphere of crystals (5cm long) will be used as multiplicity filter of high resolution, sum-energy detector, detector for gamma transitions up to 10MeV with resolution better than 3%. It will serve as an absorber in front of the larger detectors and be utilised for fast timing applications.
The outer hemisphere of crystals will have a lower granularity, larger volume (15cm long), and large stopping power (e.g. CsI:Na). This outer shell of inorganic alkali halide crystals will be used to measure high energy photons, and act as a Compton suppressor. The crystals might be taken from previously existing calorimeters such as Chateau de Cristal of HECTOR.
To date, a lot of R&D experimental work has been done. Additional simulations have been done to further test whether a cubic or spherical design will be constructed, and small lab experiments with Phoswich and Silicon PM detectors are being tested to see if good pulse shapes and spectra resolution can be achieved in a way that does not compromise the detector efficiency (increase in dead space).
Bragg Detector
Two detectors are being designed and constructed for use with radioactive beams. They will be used in combination with the MINIBALL and TIGRESS gamma ray arrays at the REX-ISOLDE and TRIUMF facilities, respectively, to study shape co-existence phenomena in exotic nuclei. For more information and images visit here.
Neutron array
York is part of an international collaboration that is seeking to design and construct a new neutron detector array that can be used at GANIL and other facilities in Europe. The array is currently in the early design stage at present, but it is planned to use liquid scintillators for the neutron detection and digital pulse shape technology for the analysis of the signals from the array. Further information can be found at the official neutron detector array (NEDA) website. The York group plans to use the array to further its studies of exotic proton rich nuclei.
SHARC
This detector has been designed to further our knowledge and understanding of the nucleus, the way nuclear structure works, and how the structure of nuclei determines how nuclear explosions in stars proceed.
The Silicon Highly-segmented Array for Reactions and Coulex (SHARC) is a multi-purpose array for charged-particle detection. The very compact array is designed to have high spatial resolution, as well as a large solid angle coverage and particle identification of the measured reaction products. The array can furthermore be used in a variety of dynamic ranges in energy, and will thereby address a diverse set of outstanding nuclear physics questions. This combination offers unique capabilities when integrated with the TIGRESS gamma-ray detectors and the post-accelerated beams at the new ISAC-II facility at TRIUMF, Canada. The project is lead from the University of York and funded by a major grant from the STFC.
During August 2009, the collaboration completed the first SHARC experiment. This experiment was also the first of a series of experiments investigating nuclear structure and astrophysics using neutron transfer reactions with neutron-rich sodium isotopes. The goal of the experiment was to investigate the changes in shell structure in exotic (far from stable) nuclei, in particular 26Na through a reaction where a neutron is transferred into the already neutron-rich 25Na nucleus. A preliminary data analysis is shown in the figure. Here the kinematic loci for the transfer reaction can be seen in the right half of the figure (angles above 90 degree).
Two major research programs will gain significantly from the utilisation of SHARC: Reaction studies (such as the above experiment) and Coulomb excitations (Coulex). Both of these will be led by UK physicists. In the reaction studies, particular emphasis will be on transfer reactions used as a tool to indirectly probe nuclear reaction rates important for explosive stellar scenarios such as X-ray bursters, novae, and super novae. The Coulex experiments on the other hand will offer unique insight into nuclear structure at the extremes. In these experiments the reduced transition matrix elements - such as e.g. B(E2) for Coulomb excitation of the 0+ ground state to the first 2+ excited state of neutron rich or neutron deficient even-even nuclei - will be probed.
The figure above shows the SHARC setup as seen by the beam, through the upstream QQQ2 CD-detector. Visible are (from outside to centre):downstream box detectors, downstream CD, reflections of all detectors, and the 10.5 mm by 10.5 mm exit hole through the downstream CD.
The project is carried out by a collaboration of scientists from University of York, Daresbury Laboratory, University of Manchester, University of Surrey, Colorado School of Mines (USA), Louisiana State University (USA), Saint Mary's University (Canada), University of McMaster (Canada) and TRIUMF (Canada), and is led from York by Prof. B. R. Fulton and Dr C. Aa. Diget.
HELIOS
The study of transfer reactions in inverse kinematics is a key focus of existing and emerging radioactive-beam facilities. These measurements typically suffer from low resolution brought on by the rapidly changing laboratory energy with angle, and a kinematic compression at forward c.m. angles. The new helical-orbit spectrometer, HELIOS, at Argonne National Laboratory (ANL) circumvents these problems by transporting the outgoing ions in the strong, homogeneous magnetic field of a solenoid, where the ions execute helical orbits before returning to the magnetic axis. The ions are dispersed according to their energy, angle of emission, and charge-to-mass ratio. The latter characterises the outgoing ion’s cyclotron period, which in turn provides particle identification. Along the axis is a hollow array of position-sensitive Si detectors, through which the beam travels, used to measure energy, position, and time of flight. This detector array can be coupled with recoil detection to provide a full kinematic description of the reaction. The potential of such a device for use in conjunction with radioactive-ion-beam programmes has been demonstrated at ANL.
The HELIOS collaboration was led by members of ANL, Western Michigan University, and the University of Manchester. As a postdoctoral researcher at ANL between 2007 and 2010, Dr B. P. Kay helped with the development of the instrument and led the first experiments with medium and heavy mass beams with measurements of the d(86Kr,p)87Kr and d(130,136Xe,p)131,137Xe reactions. The York involvement is led Dr B. P. Kay. Future interest lies in the development of a HELIOS-like spectrometer for use at facilities in Europe, namely SPIRAL2 at GANIL and HIE-ISOLDE at CERN.
With many people expressing interest in gamma-ray detection within the HELIOS, Dr D. G. Jenkins is pursuing the development of novel scintillators for use within the high-magnetic-field environment of HELIOS. This has natural synergies with the medical-imaging community where combining PET (positron emission tomography), SPECT (single-photon emission computed tomography) and MRI is a major goal. The challenges associated with this are identical to those with gamma-ray detection within HELIOS.
Figure left: A schematic of the HELIOS spectrometer. Mechanical drawing courtesy of B. DiGivine, Argonne National Laboratory.
Figure right: (Top) Outgoing proton energy versus longitudinal distance travelled between the target and the point of impact on the Si array. The two colours denote different target-array settings. (Bottom) Typical outgoing proton spectrum demonstrating an excitation-energy resolution of 96keV.
HELIOS Links
HELIOS at Argonne National Laboratory http://www.phy.anl.gov/atlas/helios/index.html
HELIOS on physicsworld.com http://physicsworld.com/cws/article/news/422969
List of recent HELIOS articles
15C(d,p)16C Reaction and Exotic Behaviour in 16C
A. H. Wuosmaa, B. B. Back, S. Baker, B. A. Brown, C. M. Deibel, P. Fallon, C. R. Hoffman, B. P. Kay, H. Y. Lee, J. C. Lighthall, A. O. Macchiavelli, S. T. Marley, R. C. Pardo, K. E. Rehm, J. P. Schiffer, D. V. Shetty, and M. Wiedeking.
Phys. Rev. Lett. 105, 132501 (2010).
http://dx.doi.org/10.1103/PhysRevLett.105.132501
First Experiment with HELIOS: The Structure of 13B
B. B. Back, S. I. Baker, B. A. Brown, C. M. Deibel, S. J. Freeman, B. J. DiGiovine, C. R. Hoffman, B. P. Kay, H. Y. Lee, J. C. Lighthall, S. T. Marley, R. C. Pardo, K. E. Rehm, J. P. Schiffer, D. V. Shetty, A. W. Vann, J. Winkelbauer, and A. H. Wuosmaa.
Phys. Rev. Lett. 104, 132501 (2010).
http://dx.doi.org/10.1103/PhysRevLett.104.132501
Commissioning of the HELIOS Spectrometer
J. C. Lighthall, B. B. Back, S. I. Baker, S. J. Freeman, H. Y. Lee, B. P. Kay, S. T. Marley, K. E. Rehm, J. E. Rohrer, J. P. Schiffer, D. V. Shetty, A. W. Vann, J. R. Winkelbauer, and A. H. Wuosmaa.
Nucl. Instrum. Methods Phys. Res. A662, 97 (2010).
http://dx.doi.org/10.1016/j.nima.2010.06.220
A Solenoid Spectrometer for Reactions in Inverse Kinematics
A. H. Wuosmaa, J. P. Schiffer, B. B. Back, C. J. Lister and K. E. Rehm.
Nucl. Instrum. Methods Phys. Res. A580, 1290 (2007)
http://dx.doi.org/10.1016/j.nima.2007.07.029