Beta-decay endstation

To study the decay properties of short-lived, low intensity radioactive beams more efficiently, a new beta counting endstation has been developed. This system employs a silicon microstrip detector to correlate fragment implants with subsequent beta decays. Silicon microstrip detectors have received wide use in both proton decay studies and superheavy element searches due to their high efficiency for charged particle detection and high detector segmentation in a compact geometry. The goal was to take advantage of the high pixelization of the microstrip detector to continuously implant short-lived activities over the entire active area of the detector. Due to the relatively long half-lives associated with beta decay ( tens of millisecond to seconds and longer) compared to proton and superheavy alpha decay (microseconds to milliseconds), it is important to maintain an implantation rate that allows sufficient time between implants to cleanly correlate a successive beta decay event.  

The beta-decay endstation uses of a Micron Semiconductor Ltd. type BB1-1000 double-sided silicon strip detector (DSSD) as the implantation detector. The DSSD is a single silicon wafer segmented in 40 1-mm wide strips in both the x and y dimensions.

The current detector arrangement has the DSSD sandwiched between two 5 cm x 5 cm Si PIN detectors, placed at a distance of 1.9 cm and 2.2 cm, respectively from the center of the DSSD. This permits beta-particle detection in both the thick DSSD and the surrounding PIN detectors.

The PIN detectors and the DSSD are mounted on an ISO-160 flange for easy coupling to a beam-line vacuum. Two 50-pin feed-throughs on this flange are used to bring the DSSD signals to a grounding board placed immediately outside the vacuum chamber. The grounding board provides a common ground for each output channel and six 34-way ribbon cables to transmit the DSSD output to the preamplifiers. The preamplifiers currently in use were designed and manufactured by Multi Channel Systems (MCS). The MCS preamps accept 16 input channels per unit (via 34-pin 2-row connector, Au plated) and provide both low (0.1V/pC) and high (2V/pC) gain outputs. The signal rise time is 320 ns for both low and high gain channels. A schematic of the DSSD electronics is depicted below. 

The current vacuum chamber has a ISO-100 flange on one end for connection to a standard 4-inch beamline. The downstream flange is ISO-160, and the vacuum chamber is tapered to adapt to the two flange sizes. A mount is available to place 6 of the NSCL 32-fold segmented Ge detectors in close geometry around this chamber. (Note: sketch below is not to scale.)