[en] The PETRRA positron camera consists of two 60 cmx40 cm annihilation photon detectors mounted on a rotating gantry. Each detector contains large BaF₂ scintillators interfaced to large area multiwire proportional chambers filled with a photo-sensitive vapour (tetrakis-(dimethylamino)-ethylene). The spatial resolution of the camera has been measured as 6.5±1.0 mm FWHM throughout the sensitive field-of-view (FoV), the timing resolution is between 7 and 10 ns FWHM and the detection efficiency for annihilation photons is ∼30% per detector. The count-rates obtained, from a 20 cm diameter by 11 cm long water filled phantom containing 90 MBq of ¹⁸F, were ∼1.25x10⁶ singles and ∼1.1x10⁵ cps raw coincidences, limited only by the read-out system dead-time of ∼4 μs. The count-rate performance, sensitivity and large FoV make the camera ideal for whole-body imaging in oncology

[en] Several investigations have been undertaken to ascertain the suitability of gaseous electron multipliers (GEMs) for use as a neutron detector on the ISIS spallation neutron source. Our initial investigations focused purely on whether these devices could be operated at the elevated pressure of ³He and CF₄ necessary for 1mm position resolution (2.6 bars of CF₄). In fact we were able to operate the GEMs at suitable gains with 3.5 bars of CF₄. However encouraging these results were, we found that the GEMs charged up over time, which we postulated was due to the kapton substrate. A similar problem was seen at the early stages of the development of the microstrip gas chamber (MSGC), a solution of which was to use the semiconducting glass Schott S8900 as the substrate. Therefore we focused our attention to the manufacture of a GEM structure on an S8900 substrate. Our first devices were manufactured from 1mm thick glass and exhibit gains in excess of 1 × 10⁴ for a single GEM stage in an argon isobutane gas mixture, when illuminated with ⁵⁵Fe x-rays. A small amount of charging under irradiation has been observed in a flowing gas mixture, but the GEMs quickly stabilise and track atmospheric conditions. Further measurements in a ³He:CF₄ atmosphere will show how suited these devices are to the needs of ISIS.

[en] The performance of the position sensitive neutron detector array of the WISH diffractometer is discussed. WISH (Wide angle In a Single Histogram) is one of the seven instruments currently available for users on the second target station (TS2) of the ISIS spallation neutron source, and is used mainly for magnetic studies of materials. WISH is instrumented with an array of 10 detector panels, covering an angular range of 320^o, orientated in two semi-cylindrical annuli around a central sample position at a radius of 2.2m. In total the 10 detector panels are composed of 1520 ³He based position sensitive detector tubes. Each tube has an active length of one metre, a diameter of 8mm and is filled with ³He at 15 bar. The specification for the WISH detectors included a neutron detection efficiency of 50% at a neutron wavelength of 1Å with good gamma rejection. A position resolution better than 8 mm FWHM along the length of the tubes was also required which has been met experimentally. Results obtained from the detector arrays showing pulse height and positional information both prior to and post installation are shown. The first 5 of the 10 detector panels have been operational since 2009, and comparable diffraction data from powder and single crystal samples taken from the remaining 5 panels (installation completed in 2013) shows that we have a detector array with a highly stable performance which is easily assembled and maintained. Finally some real user data is shown, highlighting the excellent quality of data attainable with this instrument

[en] The performance of the new position sensitive neutron detector arrays of the Small Angle Neutron Scattering (SANS) instrument SANS2d is described. The SANS2d instrument is one of the seven instruments currently available for users on the second target station (TS2) of the ISIS spallation neutron source. Since the instrument became operational in 2009 it has used two one metre square multi-wire proportional detectors (MWPC). However, these detectors suffer from a low count rate capability, are easily damaged by excess beam and are then expensive to repair. The new detector arrays each consist of 120 individual position sensitive detector tubes, filled with 15 bar of ³He. Each of the tubes is one metre long and has a diameter of 8mm giving a detector array with an overall area of one square metre. Two such arrays have been built and installed in the SANS2d vacuum tank where they are currently taking user data. For SANS measurements operation of the detector within a vacuum is essential in order to reduce air scattering. A novel, fully engineered approach has been utilised to ensure that the high voltage connections and preamps are located inside the SANS2d vacuum tank at atmospheric pressure, within air tubes and air boxes respectively. The signal processing electronics and data acquisition system are located remotely in a counting house outside of the blockhouse. This allows easy access for maintenance purposes, without the need to remove the detectors from the vacuum tank. The design will be described in detail. A position resolution of 8mm FWHM or less has been measured along the length of the tubes. The initial measurements taken from a standard sample indicate that whilst the detector arrays themselves only represent a moderate improvement in overall detection efficiency (∼ 20%), compared to the previous detector, the count rate capability is increased by a factor of 100. A significant advantage of the new array is the ability to change a single tube in situ within approximately one day with a relatively small staff effort. The results obtained from the first user trials are reported

[en] The PETRRA positron camera is a large-area (600 mm x 400 mm sensitive area) prototype system that has been developed through a collaboration between the Rutherford Appleton Laboratory and the Institute of Cancer Research/Royal Marsden Hospital. The camera uses novel technology involving the coupling of 10 mm thick barium fluoride scintillating crystals to multi-wire proportional chambers filled with a photosensitive gas. The performance of the camera is reported here and shows that the present system has a 3D spatial resolution of ∼7.5 mm full-width-half-maximum (FWHM), a timing resolution of ∼3.5 ns (FWHM), a total coincidence count-rate performance of at least 80-90 kcps and a randoms-corrected sensitivity of ∼8-10 kcps kBq^-1 ml. For an average concentration of 3 kBq ml^-1 as expected in a patient it is shown that, for the present prototype, ∼20% of the data would be true events. The count-rate performance is presently limited by the obsolete off-camera read-out electronics and computer system and the sensitivity by the use of thin (10 mm thick) crystals. The prototype camera has limited scatter rejection and no intrinsic shielding and is, therefore, susceptible to high levels of scatter and out-of-field activity when imaging patients. All these factors are being addressed to improve the performance of the camera. The large axial field-of-view of 400 mm makes the camera ideally suited to whole-body PET imaging. We present examples of preliminary clinical images taken with the prototype camera. Overall, the results show the potential for this alternative technology justifying further development