Paul Sellin Detector Research at the University of Surrey Dr Paul Sellin Centre for Nuclear and Radiation Physics Department of Physics University of Surrey, Guildford

Paul Sellin CdTe/CdZnTe are the most mature high-Z bulk materials for X-ray and gamma ray detectors: High-Z materials for room temperature gamma ray detectors single crystal HgI 2  CdTe and CdZnTe offer good spectroscopic performance for X-rays and gammas  For higher photon energies very high-Z materials such as mercuiric iodide (HgI 2 ) are actively being developed

Paul Sellin Cadmium Zinc Telluride for X-ray/gamma spectroscopy CdZnTe material quality has improved recently, with various new suppliers in the US/Canada, Europe and Japan:  wafers of large single-crystal areas are available, with excellent charge transport  High resistivity  =3x10 11  cm, and  e =1.8x10 -2 cm 2 /V 4x4 pixellated devices have shown very good resolution  1.35% FWHM at 662 keV

Paul Sellin ‘Hexitec’ Basic Technology project Surrey is one of the major members of the recent Hexitec Basic Technology project – a £3M 4 year project Project aim – development of CdZnTe pixel detectors for X-ray imaging  Manchester – detector applications  Durham – CdZnTe material growth  Surrey – Material and detector characterisation and prototyping  CCLRC RAL – Pixel detector fabrication

Paul Sellin Synthetic diamond for detector applications Single-crystal natural diamonds have been studied in the past for detector applications – excellent electronic properties are seen in a tiny number of gem stones. P. Bergonzo et al, Dia Rel Mat 10 (2001)

Paul Sellin Single-crystal CVD diamond detectors Specialist applications of diamond detectors:  as tissue-equivalent rad-hard detectors, eg megavoltage therapy beams, neutrons  detectors for very high temperature, high radiation environments True single-crystal material removes charge trapping associated with grain boundaries:  100% CCE demonstrated from alpha particles  Extreme radiation hardness  High mobility  very fast signals (~10ps timing resolution) silicon detector diamond detector Ref: M. Pomorski et al, phys stat sol a 203 (2006)

Paul Sellin Semiconducting polymer – a new radiation detector material? Various candidate semiconducting polymers are of interest for radiation detection applications, eg:  Poly-acetylene  PPV (poly-phenylene-vinylene) These materials have the following properties:  A ‘band gap’ energy low enough to give semiconducting properties (eg. ~1.5 eV)  High resistivity combined with reasonable charge transport:  Electron and hole mobilities are low  Carrier concentrations are low (<10 14 cm -3 )  good depletion thickness  Sufficient radiation hardness Potential Benefits:  large area, low cost sensor technology  fabrication onto flexible, complex geometry, substrates  tissue equivalent for dosimetry applications

Paul Sellin X-ray response from the PFO detector X-ray response photocurrent was measured from the PFO device for dose rates up to 18.5 mGy/s Photocurrent vs bias voltage shows an approximately linear increase Dark current is ~ V Photocurrent vs dose rate gives the detector sensitivity. For a 10  m thick device: ~ V ~ V X-ray Dose Rate (mGy/s)

Paul Sellin Other plastic dosimetry materials Various organic and plastic bulk materials have been investigated since Fowler’s work in the 1950’s Early measurements investigated X-ray induced photocurrents, and showed long time transients Recent data at Surrey on newer material have studied dosimetry response of thick (~mm) plastic layers to 50 kV X-rays:  signal-background ratio of ~500x  ‘fast’ X-ray response of <100 ms

Paul Sellin New MSc course in Radiation Detection and Instrumentation A new MSc programme for September 2008 – exploring the operation, characterisation and development of radiation detectors and instrumentation Application areas will include medical physics, dosimetry, particle physics, synchrotrons, space science and homeland security Core programme modules:  Radiation Physics and Laboratories  Radiation Measurement  Detector Instrumentation  Interfacing and Signal Processing  Imaging and Remote Sensing Applications modules:  Particle Physics Detector Technology  Astronomy Detector Technology  Radiation Protection  Medical applications of Ionising Radiation