Software

1. Introduction Blowfish The Blowfish neutron detector array is a joint project between the University of Saskatchewan in Saskatoon, Saskatchewan, Canada and the University of Virginia in Charlottesville, Virginia, USA. It is housed at the High Intensity Gamma-Ray Source (HIGS) at Duke University, Durham, North Carolina, USA. Blowfish consists of 88 liquid scintillator neutron detectors arranged in a spherical shell. These detectors can detect fast neutrons with good angular resolution. Combined with the linearly and circularly polarised gamma-ray beams produced by HIGS, Blowfish can be used to study the angular distribution of neutrons emitted in photonuclear reactions. Light Output and Efficiency The neutron detectors in Blowfish use the organic, liquid scintillator BC-505 encased in acrylic cells coupled to Photonis XP2262/B photomultiplier tubes. We have measured the light output of BC-505 (R. E. Pywell, et. al., Nucl. Instr. and Meth. A, 565, 725 (2006)). The Blowfish Neutron Detector Array The Blowfish neutron detector array consists of 88 liquid scintillator neutron detectors. These detectors are arranged in 8 groups of 11. Each group of 11 is mounted on an aluminum support arm as can be seen in the above picture. The Blowfish detectors cover about 1/4 of the 4π steradian solid angle of a sphere. We are also working to better understand the absolute efficiencies of our detectors by comparing a measured 252Cf light output spectrum to that generated by a Geant4 simulation using our measured light output response. Physics Blowfish will be used to study photoneutrons from different light nuclei. It has already been used to produced two PhD theses which study the photodisintegration of deuterium (B. Sawatzky, University of Virginia and M. Blackston, Duke University). Data Acquisition System GDH Integral Blowfish will be used to study the GDH sum rule for deuterium and the photodisintegration of light nuclei such as helium and lithium. The GDH study will provide an interesting insight into quantum mechanics and the light nuclei work will provide needed data for comparison with theoretical predictions. The Data Acquisition System Used with Blowfish Gain Monitoring System The experimenter controls the experiment using a Linux PC with Lucid installed. This computer connects to a frontend PC running the real-time operating system RTEMS. The frontend computer connects to the VME Bus through a fibre optic link. The frontend PC replaces an older VME module with a slower Motorola 68k series microcontroller. The frontend computer can read the VME modules though this link and CAMAC modules through a CAMAC branch driver. We have moved as many services as possible from the older CAMAC and FastBus systems. The FastBus system has been completely replaced and the CAMAC system is used only for infrequent triggers. In determining the efficiency of a neutron detector, it is very important to know what the threshold is for that detector. In order to know the value of the threshold, one must know the gain of the detector. A radioactive source can be used to measure the gain of a neutron detector when the accelerator is not running. We use a light emitting diode (LED) to inject light pulses into the neutron detector during and experiment to measure the gain shift. The LED and associated equipment is referred to as the gain monitoring system (B. Bewer, MSc Thesis, University of Saskatchewan). Total Photodisintegration Cross Section for 6Li (S. Bacca, et al, Phys. Rev. C 69, 057001 (2004)). Lines are theoretical predictions, points are experimental measurements. Conclusion Photon Flux Monitor The Blowfish neutron detector array will be an important tool in the next generation of photodisintegration measurements. With its unique spherical design and the advance of polarised gamma-ray beams, studies of the angular dependence, asymmetries and cross sections of photodisintegration reactions will shed new light onto old problems. While not technically a part of Blowfish, the new photon flux monitor designed and built at the University of Saskatchewan will be an important part of obtaining absolute photoneutron cross sections in experiments using Blowfish. Photon Flux Monitor The photon flux monitor uses an absorber to produce electrons and positrons through Compton scattering and pair production. These particles are detected in triple coincidence by three scintillating paddles. A fourth paddle before the absorber provides a veto and a fifth paddle before that is used in the calibration of the device. Blowfish Neutron Detector Array W. A. Wurtz1, R. E. Pywell, B. E. Norum, B. D. Sawatzky, N. R. Kolb, R. Igarashi, B. Bewer, D. Chabot, J. Ives, O. Mavrichi Software Lucid is the data acquisition software used with Blowfish. It allows the user to control the experiment, provides output, generates histograms and has some data analysis capabilities that are useful for debugging experiments at run-time and simple analysis tasks when examining the data offline. The Lucid Data Acquisition Software We use the Geant4 Simulation Toolkit (Geant4 Collaboration, Nucl. Instr. and Meth. A 506, 250 (2003)) to simulate the interaction of particles with Blowfish. Our simulation can output data in the Lucid format so the simulated data can be analysed using the exact same software as the experimental data. The Blowfish Geometry in Geant4 The ROOT Data Analysis Framework (http://root.cern.ch/) provides the framework for the Blowfish-ROOT Analysis Package. This package provides a graphical way to perform routine analysis tasks such as finding pedestals, pulse shape discrimination (PSD) and calibrating ADC and TDC data. A Blowfish-ROOT Analysis Package Example Window Acknowledgements Homepage: http://nucleus.usask.ca/ Funding Agencies: NSERC of Canada University of Saskatchewan University of Virginia Facilities: Duke Free Electron Laser Laboratory Triangle Universities Nuclear Laboratory Author Legend: 1. Poster Author