G. Turk

The GRT4 VME pulse processing card for segmented germanium detectors

A four channel VME card with 14 bit, 80 MHz digitizers and powerful on-board processing has been designed, built and used in tests of digital pulse processing techniques for gamma-ray tracking. This paper explains the background (rationale for the project), describes the VME card (known as the GRT4) and presents a 64 channel GRT4 digitizing system which was used to instrument two segmented Germanium detectors during in-beam tests. Results obtained using the GRT4 card are presented as well as some applications.

A gamma tracking detector for nuclear medicine

The concept of tracking the interactions of a gamma ray through a solid state detector is being pursued by several groups in the nuclear physics community. Here the ability to rid the detectors of the escape suppression shields and decrease the Doppler broadening of the spectroscopic lines will enable new physics measurements. Our group has embarked upon a project to apply this technology to medical imaging. We report on the progress in developing a planar germanium detector with gamma ray tracking ability, for positron emission tomography (PET). The prototype detector is a planar high purity germanium unit with X-Y readout electrodes. Using digital signal processing the timing and depth of individual interactions are recorded for each gamma ray. Compton scattering information for some of the events can be used to reconstruct the angle of the gamma ray to the first interaction point. In a similar technique to the Compton camera, this information can be used to reduce random coincidence rates in the PET system and provide the possibility for highly efficient use of events in the tomography reconstruction.

γ‐ray Spectroscopy of Proton Drip‐Line Nuclei in the A∼130 Region using SPIRAL beams

A fusion‐evaporation experiment has been performed with a SPIRAL 76Kr radioactive beam in order to study the deformation of rare‐earth nuclei near the proton drip‐line. The experimental setup consisted in the EXOGAM γ‐array, coupled to the light‐charged particles (LCP) DIAMANT detector and to the VAMOS heavy‐ion spectrometer. The difficulties inherent to such measurements are enlightened. The coupling between EXOGAM and DIAMANT has been used to decrease the huge background caused by the radioactivity of the beam. It further permits assigning new γ‐ray transitions to specific residual nuclei. A γ‐ray belonging to the 130Pm level scheme has thus been observed for the first time.

{gamma}-Spectroscopy and Radioactive Beams: How To Perform Channel Selection ?

An experiment has been performed using a SPIRAL 76Kr radioactive beam at GANIL to investigate rare‐earth nuclei near the proton drip‐line. The EXOGAM gamma array was coupled with the DIAMANT light charged‐particle detector and the VAMOS spectrometer. We report here on the powerful of this setup to extract fusion‐evaporation γ‐rays from a large beam contamination.

Characterisation of a clover detector for the development of a Compton camera

Gamma-ray imaging techniques, such as Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT), are becoming increasingly important for clinical diagnosis. As the power of these methods becomes more evident, the use of these techniques is becoming more widespread However, the performance of existing systems is restricted by the inherent properties of the scintillator detectors they are based on (e.g. poor energy resolution). The development of High Purity Germanium detectors has now reached the stage where they can be used as effective imaging devices. The electrical segmentation of the Germanium crystal coupled with digital signal processing electronics allows the measurement of energy, time, and position following the interaction of a gamma-ray. We propose to build a PET imaging system composed of two segmented planar HPGe detectors. The position and energy information are extracted following the digitisation of the detector charge signal, analysed using Pulse Shape Analysis (PSA) algorithms. Such a technique can potentially give a position resolution of about 1 mm/sup 3/ inside the detector volume. A prototype of a Compton camera has been built in order to test our pulse processing techniques and develop some gamma-ray tracking algorithms. The system is composed of a planar detector with 5mm strips in a 24/spl times/12 configuration, and a 16 segment coaxial Clover detector. Before being able to reconstruct the path of gamma-rays with the camera, it is necessary to calibrate the response of each detector as a function of the position. Several characterisation measurements have been made using an automated detector scanning systems. Preliminary results from the characterisation of the Clover will are presented in this paper.