Detectors, from surfaces to fields
Berkeley Lab has a long history developing semiconductor detectors for radiation spectrometry and imaging. Improving the efficiency of these detector systems is the goal of the second major project that DOE is funding in NSD's Applied Nuclear Physics program. The effort, led by Vetter and Mark Amman of the Engineering Division, focuses on improving fabrication processes and shaping the electric fields that collect signals from gamma rays caught by detectors made of high-purity germanium.
"Recently it has been possible to realize a concept first proposed by Berkeley Lab's Paul Luke 20 years ago, with the result that the 'application space' of these detectors is still expanding," says Vetter. "We want to expand it further. We want to reduce electronic noise and enhance charge collection properties in a variety of semiconductor detectors, to make them more efficient and capable of higher resolution."
Depending on what it's used for, a typical semiconductor detector may be eight centimeters in diameter (3.15 inches) and two to eight centimeters thick. Its surfaces are typically divided into segments by strips of metal that act as contacts to collect the charge carrierselectrons and holesreleased when a gamma ray photon is absorbed.
"The problem is the noncontact surfaces, which degrade the charge-collection process and cause leakage current," Vetter says. "Those include the areas between the metal strips and also the sides of the detectors. To prevent leakage, the edges are often shielded by a thick guard ring, which may be of metal or other material, which severely cuts into the area of the detector."
For better radiation detection, the researchers first need to maximize the usable surface area. To get rid of guard rings it will be necessary to find better ways to isolate the bare surfaces of the semic
|Contact: Paul Preuss|
DOE/Lawrence Berkeley National Laboratory