A prototype of a polarized deuterium target which employs the spin exchange method is being developed. The mixing cell for mixing deuterium atoms and potassium vapor requires a surface that will reflect these atoms without being destroyed by the corrosive potassium. Thin film coating methods and a technique for coating pyrex are described. Results of spin relaxation measurements are given. (LEW

Boyer, D.

Green, M.C.

Holt, R.J.

Kowalczyk, R.S.

Thomas, G.E.

Young, L.

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Submitted for the 13th World Conference, International Nuclear Target Development Society,SepS. 17-19, 1986, Chalk River, Canada.CONP-860939—2Tho submitted manuscript has been outiioredbv n contractor of the U. S. Governmentundur contracl No. W-3M09-ENG-38.Accordingly, tho U. S. Government retains anonexclusive, royalty-free license to publishor roproduco the published form of thiscontribution, or allow others to do so, lorU. S. Government purposes.DE87 004715Thin Film Coatings Which Inhibit SpinRelaxation of Polarized Potassium AtomsG.E. Thomas, R.J. Holt, D. Boyer, M.C. Green, R.S. Kowaiczyk, and L. Young,Argonne National Laboratory, Argonne, IL 60439IntroductionIt has been discussed by Holt et al, 1) and Holt 2,3,4) that polarizedinternal targets in storage rings should be a powerful method for the study ofnucleons and nuclei. This method should be compatible not only with existingelectron rings but also with the recently proposed linac-stretcher ringaccelerator design of MIT 5). At present, laser-driven polarized targetsappear to be the most promising technology under consideration.A prototype of a polarized deuterium target which employs the spin-exchange method, see reference 6, 7 for detailed calculation by Green, isbeing developed at Argonne National Laboratory as illustrated In Fig. 1. Thetarget polarization can be detected by the D( He,p) He reaction. A 625-keVHe beam was incident upon the gas jet of deuterium atoms and the •- 14 MeVprotons were counted in Si surface-barrier detectors. At the 3/2 resonancethis reaction exhibits a 0.7-b cross section as shown by King 8) and maximumanalyzing power as shown by Ohlsen 9) for t2Q a n d thus is ideal for the studyof a thin tensor polarized deuterium target. A field of - 4 gauss wasmaintained near the target to provide an orientation axis for the spin stateof deuterium and K. The mixing ceil was heated in an oven to ~ 500°K in orderto vaporize the K,The cell is a critical component of this system. Deuterium atoms enterfrom the side of one end and K vapor from the other side. The laser beamThis research was supported by the U. S. Department of Energy, Nuclear ,Physics Division, under Contract in part W-31-109-Eng-38. i hDISTRIBUTION BF THIS OQOUIHENT J$enters the K-D mixing cell through the optical window and polarizes the Katoms and they in turn polarize the deuterium atoms by spin-exchangescattering. I t is cri t ical that there is a surface that will reflect theseatoms many times and that this surface not be destroyed by the K as i t is avery corrosive material. Also, a vacuum of ~ 10 Torr. must be maintained toprevent the reflecting surface from being oxidized. The polarized K atomsexit the cell from the other end of the mixing after an average ofapproximately 1000 wall bounces.Thin Film Coating MethodsSince H atoms have long spin-relaxation times 10) on a teflon surface,one of the reflecting coatings tried was a teflon product produced by DuPont11) called PTF-852-201 Line. In this method, the solution was diluted withdistil led water by ~ 3:1. The cell to be coated was f i rs t cleaned with ethylalcohol and then distilled water using an ultrasonic cleaner. Then paintedcarefully the thin coat of solution was applied with a swab only onto thesurface of the oxidized Al cell which was exposed to the K and then i t washeated to 375°C for ~ 30 minutes. A second thin coat was applied and reheatedto ~ 415°C for 30 minutes. None of the tests using this coating on the cellswere successful owing to the rapid chemical reaction rate of potassium withteflon.The most successful method for coating metal was that using drifilm 12)as suggested by Anderson and Swenson 13). After cleaning, the cell was placedin solution A [(Dimethyl dimethoxysllane (CH3)2 Si(OCH3)2], and then solutionB [ (Triraethylmethoxysilane (CH3).j SiOCH.j], was poured gently on top and theacetic acid was added. Two distinct layers of solution were seen, but thesewill gradually reacted with each other. The cell was removed from thecontainer and baked under vacuum (10 Torr) at 220°C for 3 hours. It takes24 hours to achieve the required first layer of drifilm reflector needed.After observation it may be determined that a second thin layer may beneeded. Drifilm was applied to both a Cu and an anodized Al cell.Technique for Coating PyrexThe pyrex optical windows on the mixing cell must also be coated withdrifilm. The technique rot coating pyrex is quite different then that formetal. It is advisable to use a good fume hood for the glass (pyrex)coating. The pyrex is first cleaned thoroughly. Next, approximately 10ml ofSC-77 solution 14) was poured into a glass container having a glass cover,(i.e. beaker with a watch glass). The part was placed in the container and(approximately 5 ml) of distilled water was added and covered. The parts wereallowed to sit at room temperature for approximately 15 minutes. A thick mistformed on top of the solution after the water was added. As with the metalcell, the part was removed from container and baked under vacuum (10"° Torr)at 220°C for 3 hours. A thin coating was observed on the surface of theglass.This coating procedure tor glass was also tried on an anodized Al mixingcell. A good test for a coated surface is how well water beads upon it.Although the surface looked coated and water beaded up on it, the coating didnot have good vacuum properties and our tests indicated it was not resistantto the corrosive properties of the K.Results of Spin Relaxation MeasurementsThe results of the measurements using these various coatings can be seenin table 1. The entry for stainless steel is used as our standard since ithas essentially no reflecting ability and the polarization is lost on eachwall bounce. As a further test of the spin-relaxation measurement technique,an Ar buffer gas was added to an uncoated stainless steel cell in order tobuffer the K atoms from the walls. A corresponding rise in spin-relaxationtime was observed as shown in Table 1. The aluminum which has an anodizedsurface also has a relatively poor reflecting ability. This indicates thatthe coating may have considerable porosity and its ability to resist thecorrosive action of the K may be poor. The most recent cell tested was thatusing Cu as a base; the results are very encouraging as can be seen from thetable. It is apparent that we have a very good, solid coating with verylittle corrosion as this cell was used for approximately seven days with nosign of deterioration. The coating is suitable for use in the system.Future CellsIn the future the plans include replacing the stainless steel cell with apyrex system since it has several advantages. The drifilm produces a verygood film within about 15 minutes and a simple NMR system can be employed tomeasure both the K and D polarization in the mixing cell. Furthermore, withthis type of cell it should be easier to make the total system vacuum tight.AcknowledgementsWe wish to thank J. Gregor for fabrication of the complex pyrex cells anddissociator tubes.References1) R. J. Holt, M. S. Green, L. Young, R. S. Kcwalczyk, D. F. Geesaman, B.Zeidman, L. S. Goodman and J. Napolitano, Nucl. Phys. A 446 (1985) 389C-392C.2) R. J. Holt, Proceedings of CEBAF 1984 Summer Workshop, Newport News, VA23606 (1984) p. 334.3) R. J. Holt, Proceedings of the Workshop on Polarized Targets in StorageRings, Argonne National Laboratory, Argonne, IL (1984) p. 103.4) R. J. Holt, Proceedings of CEBAF 1985 Summer Workshop, Newport News, VA23606 (1985) p. 45.5) Proposal for a CW Upgrade for a Pulse Stretcher Ring at the William H.Bates Linear Accelerator Center, MIT (1986).6) M. C. Green, Proceedings of the Workshop on Polarized Targets in StorageRings, Argonne National Laboratory, Argonne, IL (1984) p. 307.7) M. Green, Conference on Nuclear Physics will Stored, Cooled Beams, AIPNo. 128, (1984) p. 268.8) W. E. King et al., Phys. Rev. _9_7_, 456 (1955).9) G. Ohlsen, Rep. Prog. Phys. 35, 717 (1972).10) M. D. Barker et al,, Proceedings of the Fifth International Symposium onPolarization Phenomena in Nuclear Physics, AIP, 931 (1981).11) DuPont TEFLON Coating fact sheet, DuPont Company, F & F Dept. Wilmington,DE 19898.12) Drifilm50% Sol A-(Dlmethyl dimethoxysilane (C H3)2 S1(OCH3)2,50% Sol B-(Trimethylmethoxysilane (CH^j SiOCl^,Acetic Acid (4 drops per 100 ml. solution)13) L. W. Anderson and D. Swenson, private communication (1986).14) SC-7760% Dimethyldillowsilane (CH^SiCL,40% TrimethyIchlorosilane (CH3)3 SiClTable 1. Observed spin relaxation times. TR(ps) represents the spinrelaxation times for various K mixing cells tested.SURFACE CONDITION TR(MS)Stainless Steel 6Stainless Steel + Ar Buffer 65Drifilm on A12O3 140"Drifilm" on Cu >1100>1300Figure CaptionsFig. 1. Schematic diagram of the system used to obtain polarized deuteriumatoms.Fig. 2. Drawing of the metal mixing cell used to obtain polarized deuteriumatoms.SCHEMATIC DIAGRAM OF APPARATUS TO MEASURE TARGET POLARIZATIOND INPUTOPTICALWINDOWMIXINGCELLPOWER METERHELMHOLTZ PAIRLINEAR«^^T"—POLARIZERX/4 PLATEK INPUTX/459a6nm P L A J ECu-FARADAYCUP SIDETECTORRING-DYE LASERVA r - I O N LASER625-keV HeFROM ANLDYNAMITRONFig. 1LASERBEAMQUARTZWINDOWPOTASSIUM/"ENTRYQUARTZWINDOWDEUTERIUMENTRYMIXINGCELLFig, 2DISCLAIMERThis report was prepared as an account of work sponsored by an agency of theUnited States Government. Neither the United States Government nor any agencythereof, nor any of their employees, makes any warranty, express or implied, orassumes any legal liability or responsibility for the accuracy, completeness, or use-fulness of any information, apparatus, product, or process disclosed, or representsthat its use would not infringe privately owned rights. Reference herein to any spe-cific commercial product, process, or service by trade name, trademark, manufac-turer, or otherwise does not necessarily constitute or imply its endorsement, recom-mendation, or favoring by the United States Government or any agency thereof.The views and opinions of authors expressed herein do not necessarily state orreflect those of the United States Government or any agency thereof.

Thin film coatings which inhibit spin relaxation of polarized potassium atoms

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Thin film coatings which inhibit spin relaxation of polarized potassium atoms

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