Development of Sdd Array for Ultra-Fast Measurement

The performance of Silicon Drift Detectors (SDD), including the pre-amplifier, is constantly improving. Recently the energy resolution was improved even at short shaping time, allowing high throughput measurements in X-ray analysis. As a direct consequence the measurement time becomes shorter and industrial applications are expanding. To reduce the measurement time further, the active area and hence the solid angle of the detector also can be increased. However, in a SDD with large active area, the drift time of the signal charge becomes longer, and it makes the rise time of the signal longer, and then the signal processing time longer. Although using multiple detectors simultaneously is one of the good solutions, the aligned detectors have dead space in peripheral areas of the respective detectors. In a SDD array, multiple SDD elements are fabricated monolithically to achieve both high throughput and large solid angle. In such a SDD array if X-ray photons come into the boundary area between the different channels, generated charges divide and travel towards different adjacent anodes (charge sharing), or parts of the charges is not collected because of weak electric fields near the border areas. This phenomenon causes an unexpected tailing and background in the acquired spectrum. We're trying to reduce these boundary areas with weak electric fields. We add electrodes (drift rings) in these border areas on the radiation-entrance side to enhance a high electric field which drives signal charges to the read-out electrode swiftly. Our preliminary results from a single SDD prototype indicated that the added drift rings on the entrance side improve the tailing of the spectrum by 12%. Effects and technical problems of the drift rings on the entrance side will be reported and discussed