TACTIC: A large solid angle particle detection system

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We propose the construction of a detector for the measurement of low and intermediate energy charged particle reactions covering nearly the full solid angle. This detector, named TACTIC, will be a cylindrical timeprojection chamber with an electric field in the radial direction. The central region of the detector will contain the gas target. The central region is at a constant potential and is not visible to detection. Ions pass through a grid of wires leaving the central region. They will then produce a trace in the field region. The free electrons are drawn towards the anode by the electric field applied. However, on their way the electrons will encounter a GEM (Gas Electron Multiplier) foil, thus amplifying the signal by a large factor. Signals registered at the anode strips will be digitized. The chamber will register full traces which includes directions, a full energy measurement and for each anode strip an energy loss measurement. An array of BGO detectors will be placed around the chamber for particle-gamma reactions. The anode strips will be divided in polar direction to allow for higher counting rates as well as for the detection of multiple particle reactions. The reactions so far proposed include measurements of the 8Li(alpha,n)11B, the 7Be(p,p)7Be elastic and inelastic scattering reaction, and a 12C+12C. Our tests have proven that the principle on which TACTIC is based is sound and the chamber feasible. We also have performed extensive GEANT simulations. A similar detector (BONUS) has been built at the Jefferson Laboratory and has been experimentally demonstrated to work. We request here construction costs, the necessary manpower and some travel money to build the final version of the TACTIC detector. With the seed money of this year, we were able to progress with the construction of a prototype detector that at present (Sept06)is under construction in the UK. In April, we expect to have this prototype detector available and some alpha-source and stable beam tests done. We are still lacking mainly in the area of the data acquisition system and system integration. Using the experience gained at the prototype detector, we plan to build the final detector, incorporating also the DRAGON BGO array.