skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Properties of tree rings in LSST sensors

Abstract

Images of uniformly illuminated sensors for the Large Synoptic Survey Telescope have circular periodic patterns with an appearance similar to tree rings. Furthermore, these patterns are caused by circularly symmetric variations of the dopant concentration in the monocrystal silicon boule induced by the manufacturing process. Non-uniform charge density results in the parasitic electric field inside the silicon sensor, which may distort shapes of astronomical sources. Here, we analyzed data from fifteen LSST sensors produced by ITL to determine the main parameters of the tree rings: amplitude and period, and also variability across the sensors tested at Brookhaven National Laboratory. Tree ring pattern has a weak dependence on the wavelength. But the ring amplitude gets smaller as wavelength gets longer, since longer wavelengths penetrate deeper into the silicon. Tree ring amplitude gets larger as it gets closer to the outer part of the wafer, from 0.1 to 1.0%, indicating that the resistivity variation is larger for larger radii.

Authors:
 [1];  [2];  [3]
  1. Stony Brook Univ., NY (United States); Brookhaven National Lab. (BNL), Upton, NY (United States)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States)
  3. Stony Brook Univ., NY (United States)
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
OSTI Identifier:
1392233
Report Number(s):
BNL-114246-2017-JA
Journal ID: ISSN 1748-0221
Grant/Contract Number:
SC0012704
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Instrumentation
Additional Journal Information:
Journal Volume: 12; Journal Issue: 05; Conference: Precision Astronomy with Fully Depleted CCDs, Upton, NY (United States), 01-02 Dec 2016; Journal ID: ISSN 1748-0221
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; detectors for UV; visible and IR photons; photon detectors for UV; systematic effects

Citation Formats

Park, H. Y., Nomerotski, A., and Tsybychev, D. Properties of tree rings in LSST sensors. United States: N. p., 2017. Web. doi:10.1088/1748-0221/12/05/C05015.
Park, H. Y., Nomerotski, A., & Tsybychev, D. Properties of tree rings in LSST sensors. United States. doi:10.1088/1748-0221/12/05/C05015.
Park, H. Y., Nomerotski, A., and Tsybychev, D. Tue . "Properties of tree rings in LSST sensors". United States. doi:10.1088/1748-0221/12/05/C05015. https://www.osti.gov/servlets/purl/1392233.
@article{osti_1392233,
title = {Properties of tree rings in LSST sensors},
author = {Park, H. Y. and Nomerotski, A. and Tsybychev, D.},
abstractNote = {Images of uniformly illuminated sensors for the Large Synoptic Survey Telescope have circular periodic patterns with an appearance similar to tree rings. Furthermore, these patterns are caused by circularly symmetric variations of the dopant concentration in the monocrystal silicon boule induced by the manufacturing process. Non-uniform charge density results in the parasitic electric field inside the silicon sensor, which may distort shapes of astronomical sources. Here, we analyzed data from fifteen LSST sensors produced by ITL to determine the main parameters of the tree rings: amplitude and period, and also variability across the sensors tested at Brookhaven National Laboratory. Tree ring pattern has a weak dependence on the wavelength. But the ring amplitude gets smaller as wavelength gets longer, since longer wavelengths penetrate deeper into the silicon. Tree ring amplitude gets larger as it gets closer to the outer part of the wafer, from 0.1 to 1.0%, indicating that the resistivity variation is larger for larger radii.},
doi = {10.1088/1748-0221/12/05/C05015},
journal = {Journal of Instrumentation},
number = 05,
volume = 12,
place = {United States},
year = {Tue May 30 00:00:00 EDT 2017},
month = {Tue May 30 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Save / Share:
  • Imperfections in the production process of thick CCDs lead to circularly symmetric dopant concentration variations, which in turn produce electric fields transverse to the surface of the fully depleted CCD that displace the photogenerated charges. We use PhoSim, a Monte Carlo photon simulator, to explore and examine the likely impacts these dopant concentration variations will have on astrometric measurements in LSST. The scale and behavior of both the astrometric shifts imparted to point sources and the intensity variations in flat field images that result from these doping imperfections are similar to those previously observed in Dark Energy Camera CCDs, givingmore » initial confirmation of PhoSim's model for these effects. In addition, the organized shape distortions were observed as a result of the symmetric nature of these dopant variations, causing nominally round sources to be imparted with a measurable ellipticity either aligned with or transverse to the radial direction of this dopant variation pattern.« less
  • Fully depleted, thick CCDs with extended infra-red response have become the sensor of choice for modern sky surveys. The charge transport effects in the silicon and associated astrometric distortions could make mapping between the sky coordinates and sensor coordinates non-trivial, and limit the ultimate precision achievable with these sensors. Two new characterization techniques for the CCDs, which both could probe these issues, are discussed: x-ray flat fielding and imaging of pinhole arrays.
  • Elevated CO2 increases intrinsic water use efficiency (WUEi) of forests, but the magnitude of this effect and its interaction with climate is still poorly understood. We combined tree ring analysis with isotope measurements at three Free Air CO2 Enrichment (FACE, POP-EUROFACE, in Italy; Duke FACE in North Carolina and ORNL in Tennessee, USA) sites, to cover the entire life of the trees. We used 13C to assess carbon isotope discrimination ( 13C ci/ca) and changes in WUEi, while direct CO2 effects on stomatal conductance were explored using 18O as a proxy. Across all the sites, elevated CO2 increased 13C-derived WUEimore » on average by 73% for Liquidambar styraciflua, 77% for Pinus taeda and 75% for Populus sp., but through different ecophysiological mechanisms. Our findings provide a robust means of predicting WUEi responses from a variety of tree species exposed to variable environmental conditions over time, and species-specific relationships that can help modeling elevated CO2 and climate impacts on forest productivity, carbon and water balances.« less
  • A new technique is developed for examining non-climatic variations in widths of annual tree-rings. For each tree core, the technique involves making an adjustment for regional climate as inferred from a regional chronology based on surrounding sites. The final step involves the reconstruction of tree-ring widths sequence with the effect of climate removed. The technique is applied to two stands in Gila County, Arizona, where air pollution is potentially a limiting factor on tree-ring growth. The technique has general applicability to studies where it is desired to assess the magnitude of growth change in trees due to some external factor.