Influence of crystalline surface quality on TlBr radiation detector performance
In this study, TlBr detectors were fabricated from crystals purified by the multipass zone refining and grown by the Bridgman method. Detectors were prepared using TlBr 0.3-mm-thick wafers, with surface submitted to different mechanical and chemical treatments. Optical microscopy and scanning electron microscopy evaluated the TlBr wafers surface quality. To analyze the surface quality influence in the detector response, systematic measurements of the pulse height spectra and energy resolution were carried out for each prepared radiation detector. The radiation response for these detectors was performed under /sup 241/Am gamma radiation excitation at room temperature. The influence of the surface quality of the TlBr wafer on its performance as a radiation detector was observed.
Fabrication Methodology of Enhanced Stability Room Temperature TlBr Gamma Detectors
Thallium bromide (TlBr) is a material of interest for use in room temperature gamma ray detector applications due to is wide bandgap 2.7 eV and high average atomic number (Tl 81, Br 35). Researchers have achieved energy resolutions of 1.3% at 662 keV, demonstrating the potential of this material system. However, these detectors are known to polarize using conventional configurations, limiting their use. While high quality material is a critical starting point for excellent detector performance, we show that the room temperature stability of planar TlBr gamma spectrometers can be significantly enhanced by treatment with both hydrofluoric and hydrochloric acid. By incorporating F or Cl into the surface of TlBr, current instabilities are eliminated and the longer term current of the detectors remains unchanged. In addition the choice of electrode metal is shown to have a dramatic effect on the long term stability of TlBr detector performance 241Am spectra are also shown to be more stable for extended periods; detectors have been held at 4000 V/cm for 50 days with less than 10% degradation in peak centroid position.
Intraoperative detection of radiolabeled compounds using a hand held gamma probe
Abstract Scintillation cameras in Nuclear Medicine allow external detection of cancerous lesions after administration of a specific radiopharmaceutical to the patient. In some particular cases the affinity of the tracer is sufficient to consider the use of an intraoperative probe which enables the surgeon to identify radioactive tissues. A radiopharmaceutical consists of a radioisotope bound to a carrier molecule. The radioactive emissions must represent certain criteria in terms of half-life and energy to be detected during an operation. In the field of intraoperative detection radionuclides like 99m Tc, 111 In, 125 I and 131 I fall into this category. Their energy, which ranges from some 10 to 364 keV, cannot be properly detected by a single type of detector. Two technologies have been developed to yield detectors which are handy and sufficiently sensitive: semiconductor CdTe or CdZnTe to detect low energies and scintillator CsI(Tl) for higher energies. Today the intraoperative detection has been evaluated in the case of several pathologies such as osteoid osteoma, colorectal cancer, neuroblastoma, reoperation of differentiated thyroid carcinoma and localization of sentinel node in breast cancer and cutaneous melanoma. Obviously, the results obtained are not comparable from one indication to the other. Nevertheless, the surgeons have noted a considerable advantage in using the intraoperative probe in the case of neuroblastoma and thyroid surgery, especially when the reoperation is difficult or the localizations are ectopic or unusual. As regards the sentinel node, this concept represents a major new opportunity in the field of intraoperative detection and the results actually reported in the literature demonstrate that, when it is detected, elective node excision renders the staging of the disease more accurate. In conclusion, intraoperative detection supplies the surgeon with additional knowledge to be used in correlation with the patient's medical history.