Acrylic Material Specifications for the 4-Meter Daya Bay Acrylic Vessels

Transcription

1 Acrylic Material Specifications for the 4-Meter Daya Bay Acrylic Vessels August 25, 2008 Revision 1.0 A material specification for the acrylic to be used for the 4-m acrylic vessels (AV s) for the Daya Bay neutrino experiment is presented. This document outlines the requirements for the material, the testing to be done by the acrylic manufacturers, and the reporting requirements. Table of Contents I. Introduction II. III. IV. Batch Size, Labeling, and Sampling Requirements Optical Requirements Mechanical Requirements V. Thickness Requirements VI. VII. Contamination Control and Acrylic Inclusions Radioactivity Requirements VIII. Chemical Compatibility Requirement Appendix A Technical Contacts at the University of Wisconsin-Madison Appendix B Check List for Polycast Samples and for Polycast Sheet Appendix C Check List for Reynolds Samples and for Reynolds Cast Material 1

2 I. INTRODUCTION Acrylic is the material of choice for the 3-m and 4-m acrylic vessels because it is optically transparent in the frequency produced by the scintillator and detected by the PMTs, it is chemically compatible with the liquids, it has low radioactivity, and it has adequate strength for handling the empty vessels and the full set of vessels. It is common practice to include additives in acrylic to improve its resistance to UV, but these chemicals reduce the transmission in the optical range of interest. UVT acrylic manufactured by Polycast (Spartech) and other suppliers does not have these additives or less thereof. Polycast UVT material been used successfully by the SNO experiment, and appears to be acceptable for the Daya Bay experiment. Reynolds UVT cast may be acceptable as well. Eight 4-m vessels will be constructed by Reynolds Polymer Technology, located in Colorado, USA. Reynolds plans to use a combination of UVT material supplied by Polycast (Spartec) and UVT cast material manufactured in house at Reynolds. Current plans are to manufacture the walls of the Daya Bay 4-m vessels from Polycast sheet and the top and bottom out of Reynolds cast if it meets the transmission specifications and UV stability requirements. This document outlines the specifications for this material. Generally ASTM standard 4802 applies to the supplied material. Wherever specific specifications appear in this document they supercede the ASTM 4802 standard. While there are absolute requirements for the acrylic material, there is also a desire to make pairs of vessels as identical as possible to reduce some of the error sources in our measurements. This drives the requirements for batch size and labeling. This document is part of the procurement contract between the University of Wisconsin Madison and Reynolds Polymer Technology.. We, us, our, and UW refer to University of Wisconsin - Madison. Reynolds and RPT refer to Reynolds Polymer Technology. 2

3 II. BATCH SIZE, LABELING, AND SAMPLING REQUIREMENTS 1. All the material for the walls of all eight 4-m tanks will be ordered from the manufacturer Polycast (Spartec) at the same time. Ideally, all of the sheet of a given thickness will come from the same batch of material. If batch sizes are too small to allow this to happen, corresponding pieces of the pair of vessels will come from the same batch (for example both lids from batch 1, all side pieces from batch 2, and both bottoms from batch 3). 2. All pieces will be clearly labeled by Polycast (Spartec) with a code that uniquely identifies the piece, the batch, and its date of manufacture. 3. Polycast (Spartec) will perform optical measurements on each sheet it supplies as specified in the optical requirements section. 4. RPT will supply samples of each acrylic cast batch they manufacture. Their samples will be sent to Dr. Thomas Wise at UW for optical testing. See Appendix A for contact information. 5. Samples will be taken from each batch after the acrylic material arrives at Reynolds or is cast by the Reynolds and shipped to UW for optical measurements to fully characterize the material. 6. Thickness measurements will be taken from each sheet by Polycast or RPT respectively and supplied to UW for analysis of possible sorting as specified in the thickness requirements section. 7. Samples will be taken from each batch, regardless of the origin of the batch. Those samples will be sent out to an independent testing lab for tests of the mechanical properties specified in the mechanical requirements section. The results of the tests will be reported to UW. 8. Samples will be provided from typical material to test for radioactivity and chemical compatibility. These tests will serve to qualify all batches. If there is a change in raw materials or procedures that could impact radioactivity or chemical compatibility, the manufacture will provide notification and new samples. III. OPTICAL REQUIREMENTS The interaction of neutrinos in the detector will produce charged particles that will in turn cause light production in the scintillator liquids inside the vessels. The combination of the light production spectrum and the self-absorption of the liquid limit the "window" for light 3

4 production to the wavelengths between 360 and 580 nm. The general optical requirement is to maximize the light transmission in this window. Requirements for the vessel wall, top, and bottom material supplied by Polycast (Spartec): 1) For vessel wall, top, and bottom material made from sheet with nominal thickness from 10 mm to 18 mm transmission requirements are: a. >92% transmission at 360 nm with controlled reflection b. >96% transmission at 380 nm with controlled reflection c. >98% transmission at 400 nm with controlled reflection d. > 98% transmission at 500 nm with controlled reflection When measurements are made in air, an allowance of 7.5% for reflection is added to these numbers a. >84.5% transmission at 360 nm in air b. >88.5% transmission at 380 nm in air c. >90.5% transmission at 400 nm in air d. >90.5% transmission at 500 nm in air 2) For ribs, brackets, and other reinforcements made from sheet with nominal thickness of 50 mm transmission requirements are: a. >85% transmission at 360 nm with controlled reflection b. >92% transmission at 380 nm with controlled reflection c. >95% transmission at 400 nm with controlled reflection d. >95% transmission at 500 nm with controlled reflection When measurements are made in air, an allowance of 7.5% for relfection is added to these numbers a. >77.5% transmission at 360 nm in air b. >84.5% transmission at 380 nm in air c. >87.5% transmission at 400 nm in air d. >87.5% transmission at 500 nm in air Requirements for the cast material supplied by Reynolds Polymer Technology: 1) For ribs, brackets, and other reinforcements made from sheet with nominal thickness of 50 mm transmission requirements are: a. >80% transmission at 360 nm with controlled reflection b.>90% transmission at 380 nm with controlled reflection c. >93% transmission at 400 nm with controlled reflection d.>93% transmission at 500 nm with controlled reflection When measurements are made in air, an allowance of 7.5% for relfection is added to these numbers a. >72.5% transmission at 360 nm in air b. >82.5% transmission at 380 nm in air c. >85.5% transmission at 400 nm in air d. >85.55% transmission at 500 nm in air 4

5 Optical Test Requirements: 1. An optical measurement will be made on each sheet in air by Polycast (Spartec). These measurements will be used for sheet acceptance. The actual transmission measured at 360, 380, 400, and 500 nm will be recorded and reported electronically to the list of technical contacts at the University of Wisconsin. See Apendix A. A paper report including the measurement results, the date of the measurement, the piece of equipment used and the initials of the measuring technician will be delivered with the material. 2. An optical measurement will be made on each cast batch from Reynolds Polymer Technology. RPT will supply samples to UW who will perform the spectrometer tests. These measurements will be used for material acceptance. 3. Two samples from each batch of sheet from Polycast (Spartec) will be submitted to UW for measurements. These measurements will be used to fully characterize the optical properties of the material. If these numbers vary from the expected values this will trigger discussions with Polycast and possible changes to the measurement technique or specifications. 4. No material with transmission below the specifications can be used without the permission of the Daya Bay collaboration. 5. Recent data indicate that some UVT formulations are more resistant to UV exposure than other samples. The Polycast UVT samples are the current reference for the required UV stability of the UVT acrylic. Based on these samples we will develop criteria giving a minimum required tolerance to UV light exposure. Batch samples will be tested for UV stability at Wisconsin before approval for manufacturing from a batch is given. The UV stability criteria of the acrylic material will be added as an Appendix to this document. IV. MECHANICAL REQUIREMENTS The vessels are designed for low stress to prevent creep and crazing in the long term. The guidelines used for design were based on Reynolds experience with correctly polymerized acrylic with typical mechanical properties. The function of the mechanical tests is to verify that the materials meet typical acrylic mechanical specification. The tests may be performed by the material manufacturer or by an independent testing lab. The results and documentation of these tests will be provided to the technical contacts at UW listed in Appendix A. 1) Tensile test result requirements are: a. Minimum tensile strength: 10,000 psi b. Minimum elongation: 4% for base material and 3% for bonds. c. Tensile Modulus of Elasticity between 430,000 and 470,000 psi 5

6 2) Rockwell Hardness requirement is a minimum value of 96 on the M scale 3) Two samples from each batch of sheet will be mechanically tested by Polycast (Spartec). Alternatively the material may be sent out to an independent testing lab for measurements. Two samples of each batch of cast material from RPT will be sent out to an independent testing lab for measurements. 4) The actual tensile strength, elongation, tensile modulus, and hardness measured will be recorded and reported electronically to the list of agreed contacts shown in Appendix A. A paper report including the measurement results, the date of the measurement, the piece of equipment used and the initials of the measuring technician will be delivered with the material. 5) No material with mechanical properties outside the specifications can be used without the permission of the Daya Bay Project. All communication with the Daya Bay Project will be faciltitated through the technical contacts listed in Appendix A. V. THICKNESS REQUIREMENTS The thickness allowance for sheets is as specified in ASTM The thickness tolerance is approximately +/-10% of sheet thickness. This range of thickness could present an issue for both bonding and uniformity of the pair of vessels. Instead of tightening the specification the acrylic sheet material will be measured and if necessary sorted. Thickness data on the raw acrylic sheets will be provided by Polycast and/or Reynolds respectively, The thickness analysis and selection of piece location in the vessels will be performed jointly between UW and RPT. 1) The thickness of each sheet will be measured by Polycast (Spartec) with an agreed upon pattern that provide adequate characterization of the edge thickness and average thickness. 2) The thickness measurements will be recorded and reported electronically to the list of technical contacts listed in Appendix A of this document. A paper report including the measurement results, the date of the measurement, the piece of equipment used and the initials of the measuring technician will be delivered with the material. 3) No material with thickness outside the specifications can be used without the permission of the Daya Bay collaboration. All communication with the Daya Bay Project will be faciltitated through the technical contacts listed in Appendix A. 6

7 VI. CONTAMINATION CONTROL AND ACRYLIC INCLUSIONS The level of cleanliness during fabrication can impact the amount of contamination, particulates, and inclusions in the acrylic. All material used in the construction of the vessels will conform to ASTM 4802 or better. The same standard will be applied to the bonds made by Reynolds Polymer Technology. VII. RADIOACTIVITY REQUIREMENTS Acrylic is expected to be intrinsically low radioactivity. However, it may be possible that radioactive components are inadvertently introduced into the material. Tests performed by the Daya Bay collaboration have shown that Polycast UVT sheet contains typically background levels of < 0.3ppb of U-238, < 1 ppb of Th-232, and < 0.3 ppm of K. UW will perform tests to verify that the acrylic materials used for the Daya Bay vessels meet these background levels. 1. A 1 kg sample of the production batch must be submitted by each manufacturer to the Daya Bay collaboration (contacts in Appendix A) for radioactivity tests. Chemical compatibility tests require significantly less material and will be conducted with the same material. 2. The manufacturer will be notified that the results of the test were acceptable (or not). Unexpected levels of background beyond the levels stated above will trigger a discussion between the manufacturers and UW. 3. If the manufacturer changes raw materials or makes significant changes to the manufacturing process after qualification, the Daya Bay Collaboration should be notified. Retesting may be required. VIII. CHEMICAL COMPATIBILITY REQUIREMENTS Acrylic is expected to be chemically compatible with the liquid scintillator and oil formulations used in the Daya Bay experiment. The Daya Bay collaboration is responsible for performing these tests for the various raw acrylic materials and manufacturing practices. Test specimen from the samples supplied in Section VII will be used for these tests. 7

8 APPENDIX A Technical Contacts at the University of Wisconsin-Madison Lee Greenler - lead engineer for acrylic vessel design Physical Sciences Laboratory University of Wisconsin-Madison 3725 Schneider Dr. Stoughton WI lgreenler@psl.wisc.edu Office: Thomas Wise lead scientist for acrylic vessel QA and acrylic QA Department of Physics University of Wisconsin 1150 University Ave Madison, WI wise@physics.wisc.edu Office: Jeff Cherwinka lead engineer for assembly, lifting, transport Physical Sciences Laboratory University of Wisconsin-Madison 3725 Schneider Dr. Stoughton WI jeff.cherwinka@icecube.wisc.edu Cell: Karsten Heeger principal investigator Department of Physics University of Wisconsin 1150 University Ave Madison, WI heeger@wisc.edu Office: Cell:

9 APPENDIX B Check List for Polycast Samples and for Polycast Sheet 1. Polycast will label each sheet with a code that uniquely identifies the piece, batch. and its date of manufacture. 2. Polycast will perform optical measurements in air on each sheet it supplies as specified in the optical requirements section. 3. Two samples from each batch of sheets from Polycast will be submitted to the University of Wisconsin for a thorough optical characterization. 4. Polycast will measure the thickness of each sheet for possible sorting as specified in the thickness requirements section. 5. Two samples from each batch of sheets will be mechanically tested by Polycast or sent out to an independent testing lab for measurements. The results of these tests will be provided to the University of Wisconsin. 6. A 1 kg sample of each production batch will be submitted to the University of Wisconsin for radioactivity tests and chemical compatibility testing. 7. Polycast will report any unusual occurrences in the production of this material to the University of Wisconsin. 9

10 APPENDIX C Check List for Reynolds Samples and for Reynolds Cast Material 1. Reynolds will supply samples of each acrylic cast batch they manufacture to the University of Wisconsin for optical testing. 2. Reynolds will supply two samples of both the Polycast sheets and the acrylic cast material to the University of Wisconsin for optical characterization just before the material is used for the fabrication of the vessels. 3. Reynolds will make thickness measurements of the material they cast and supply these data to the University of Wisconsin if their material is used without machining. 4. Two samples from each batch of cast material will be mechanically tested by Reynolds or sent out to an independent testing lab for measurements. The results of these tests will be provided to the University of Wisconsin. 5. A 1 kg sample of each production batch of cast material will be submitted to the University of Wisconsin for radioactivity tests and chemical compatibility testing. 6. Reynolds will report any unusual occurrences in the production of the cast material to the University of Wisconsin. 10