15 research outputs found
Development of silicon interposer: towards an ultralow radioactivity background photodetector system
It is of great importance to develop a photodetector system with an ultralow
radioactivity background in rare event searches. Silicon photomultipliers
(SiPMs) and application-specific integrated circuits (ASICs) are two ideal
candidates for low background photosensors and readout electronics,
respectively, because they are mainly composed of silicon, which can achieve
good radio-purity without considerable extra effort. However, interposers, used
to provide mechanical support and signal routes between the photosensor and the
electronics, are a bottleneck in building ultralow background photodetectors.
Silicon and quartz are two candidates to construct the low background
interposer because of their good radio-purity; nevertheless, it is non-trivial
to produce through silicon vias (TSV) or through quartz vias (TQV) on the large
area silicon or quartz wafer. In this work, based on double-sided TSV
interconnect technology, we developed the first prototype of a silicon
interposer with a size of 10~cm10~cm and a thickness of 320~m. The
electrical properties of the interposer are carefully evaluated at room
temperature, and its performance is also examined at -110~C with an
integrated SiPM on the interposer. The testing results reveal quite promising
performance of the prototype, and the single photoelectron signals can be
clearly observed from the SiPM. The features of the observed signals are
comparable with those from the SiPM mounted on a normal FR4-based PCB. Based on
the success of the silicon interposer prototype, we started the follow-up
studies that aimed to further improve the performance and yield of the silicon
interposer, and eventually to provide a solution for building an ultralow
background photodetector system
The DAMIC-M experiment: Status and first results
The DAMIC-M (DArk Matter In CCDs at Modane) experiment employs thick, fully depleted silicon charged-coupled devices (CCDs) to search for dark matter particles with a target exposure of 1 kg-year. A novel skipper readout implemented in the CCDs provides single electron resolution through multiple non-destructive measurements of the individual pixel charge, pushing the detection threshold to the eV-scale. DAMIC-M will advance by several orders of magnitude the exploration of the dark matter particle hypothesis, in particular of candidates pertaining to the so-called “hidden sector.” A prototype, the Low Background Chamber (LBC), with 20g of low background Skipper CCDs, has been recently installed at Laboratoire Souterrain de Modane and is currently taking data. We will report the status of the DAMIC-M experiment and first results obtained with LBC commissioning data
Dark sectors 2016 Workshop: community report
This report, based on the Dark Sectors workshop at SLAC in April 2016,
summarizes the scientific importance of searches for dark sector dark matter
and forces at masses beneath the weak-scale, the status of this broad
international field, the important milestones motivating future exploration,
and promising experimental opportunities to reach these milestones over the
next 5-10 years
Exploration of Methods to Remove Implanted Pb and Po Contamination from Silicon Surfaces
Radioactive contaminants on the surfaces of detector components can be a
problematic source of background events for physics experiments searching for
rare processes. Exposure to radon is a specific concern because it can result
in the relatively long-lived Pb (and progeny) being implanted to
significant subsurface depths such that removal is challenging. In this article
we present results from a broad exploration of cleaning treatments to remove
implanted Pb and Po contamination from silicon, which is an
important material used in several rare-event searches. We demonstrate for the
first time that heat treatments ("baking") can effectively mitigate such
surface contamination, with the results of a 1200 C bake consistent
with perfect removal. We also report results using wet-chemistry and
plasma-based methods, which show that etching can be highly effective provided
the etch depth is sufficiently aggressive. Our survey of cleaning methods
suggests consideration of multiple approaches during the different phases of
detector construction to enable greater flexibility for efficient removal of
Pb and Po surface contaminationComment: 8 pages, 7 figure
Correction to Mass Spectrometric Determination of Uranium and Thorium in High Radiopurity Polymers Using Ultra Low Background Electroformed Copper Crucibles for Dry Ashing
Mass Spectrometric Determination of Uranium and Thorium in High Radiopurity Polymers Using Ultra Low Background Electroformed Copper Crucibles for Dry Ashing
A rapid new method for determining
the U and Th mass concentrations
in high radiopurity plastics is described, consisting of (1) dry ashing
the plastic sample and tracers in low mass crucibles made of ultra
low background electroformed copper (ULB EF-Cu) foil cut and folded
into boats, (2) dissolving both the ash and the boat in acid, (3)
performing a column separation to remove copper, and (4) determining
the elements of interest by isotope dilution mass spectrometry. This
method was demonstrated on both unfluorinated and fluorinated plastics,
demonstrating high tracer recoveries and detection limits to pg/g
(i.e., parts per trillion) levels or below, corresponding to μBq/kg
of material. Samples of biomedical polyester (Max-Prene 955) and a
fluoropolymer (polyvinylidene fluoride, PVDF) were analyzed in powder
raw material forms as well as solids in the form of pellets or injection
molded parts. The polyester powder contained 6 pg/g and 2 pg/g for <sup>232</sup>Th and <sup>238</sup>U, respectively. These levels correspond
to 25 and 25 μBq/kg radioactivity, respectively. Determinations
on samples of PVDF powder were typically below 1 pg/g for <sup>232</sup>Th and 2 pg/g for <sup>238</sup>U, corresponding to 4 and 25 μBq/kg
radioactivity, respectively. The use of low mass ULB EF-Cu boats for
dry ashing successfully overcame the problem of crucible-generated
contaminants in the analysis; absolute detection limits, calculated
as 3 × standard deviation of the process blanks, were typically
20–100 fg within a sample set. Complete dissolution of the
ash and low mass boat provided high tracer recoveries and provides
a convincing method to recover both the tracer and sample isotopes
when full equilibration of tracer isotopes with sample isotopes is
not possible prior to beginning chemical sample processing on solids
Ultra-low radioactivity flexible printed cables
Abstract Flexible printed cables and circuitry based on copper-polyimide materials are widely used in experiments looking for rare events due to their unique electrical and mechanical characteristics. However, past studies have found copper-polyimide flexible cables to contain 400-4700 pg 238U/g, 16-3700 pg 232Th/g, and 170-2100 ng natK/g, which can be a significant source of radioactive background for many current and next-generation ultralow background detectors. This study presents a comprehensive investigation into the fabrication process of copper-polyimide flexible cables and the development of custom low radioactivity cables for use in rare-event physics applications. A methodical step-by-step approach was developed and informed by ultrasensitive assay to determine the radiopurity in the starting materials and identify the contaminating production steps in the cable fabrication process. Radiopure material alternatives were identified, and cleaner production processes and treatments were developed to significantly reduce the imparted contamination. Through the newly developed radiopure fabrication process, fully-functioning cables were produced with radiocontaminant concentrations of 20-31 pg 238U/g, 12-13 pg 232Th/g, and 40-550 ng natK/g, which is significantly cleaner than cables from previous work and sufficiently radiopure for current and next-generation detectors. This approach, employing witness samples to investigate each step of the fabrication process, can hopefully serve as a template for investigating radiocontaminants in other material production processes