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Development of deuterated polymer polarized targets materials
1,2L.Wang, 1W.Meyer, 1Ch.Hess, 1E.Radtke, 1A.Berlin, 1J.Herick, 1G.Reicherz, 1Institut of Experimental Physics AG I, Ruhr-University Bochum, Bochum, D-44780, Germany 2Physics Department, School of Science, Donghua University, Shanghai, , China 3N.Doshita, 3K.Kondo, 3T.Iwata, 3Physics Department, Faculty of Science, Yamagata University, Yamagata, , Japan 4N.Horikawa 4College of Engineering Chubu University, Kasugai, , Japan My topic is high deuteron polarization in polymer target materials. Li Wang SPIN2016 @ UIUC Sep.2016
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Content Dynamic polarized solid target (DNP) for particle physics experiments The trityl radicals – progress for deuterated target materials 3. D-polymer materials: CD2 and C8D8 4. The Bochum DNP-apparatus 5. ERP investigation and Polarization results for — trityl radical doped CD2 C8D8 6. Conclusion and outlook The contents consist six parts. At first, it is the introduction of the polarized solid targets for scattering experiments. Secondly, the trityl radicals in the progress for deuterated target materials will be introduced. Thirdly, it is the introduction to two kind of deuterated polymer materials. And the next is to show the DNP apparatus in Bochum Group. Fifthly, two kinds of deuterated polymer by the two DNP doping method will be introduced as well the EPR line and polarization results will be presented. Finally, it is the conclusion and outlook.
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Polarized Solid Targets
Used in high energy particle physics experiments for studying the nucleon structure since about 50 years Present target materials for high energy spin physics experiments: NH COMPASS experiment at CERN ( GeV) 6LiD COMPASS experiment at CERN ( GeV) CH2 , CD GDH experiment in SPRING-8 Butanol Experiments at ELSA (Bonn < 3.0GeV) and D-butanol MAMI (Mainz < 1.5GeV) accelerators Physics observable determined by single or double asymmetry measurements A Polarized Solid State Targets, which have been used in several scattering experiments since 1970, is used to investigate the hadrons structure and spin-dependent interactions. Up to now, various target materials are dynamically polarized and routinely used for scattering experiments, such as irradiated ammonia as proton target, irradiated deuterated lithium as deuteron target, in COMPASS experiment. In GDH experiment, polyethylene and deuterated polyethylene are used as polarized targets. Butanaol and deuterated butanol are as polarized targets in experiments at ELAS and MAMI accelerators. In scattering experiment, single and double asymmetry measurements are physics observable. From its definition, the value of target polarization and dilution factor of target material are two important parameters. The higher the polarization and the dilution factor, the better the asymmetry is. The definition of the dilution factor is the ratio of the number of polarizable particles to the all particles. DNP solid targets
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The Principle of Dynamic Nuclear Polarization
Thermal Equilibrium (TE) Dynamic Nuclear Polarization (DNP) Transfer of polarization from paramagnetic electrons to the nuclei Parameters of DNP: temperature; magnetic field; microwave power; electron relaxation time; the relation of EPR linewidth and nuclear Larmor frequency… Doping with paramagnetic electrons: Let us see the principle of dynamic nuclear polarization. The polarization of a spin system with spin I and magnetic moment u under the condition of thermal equilibrium is given by the Brillouin Funktion. In order to obtain a sizeable polarization of the deuteron spin system, the ratio of the magnetic energy uB and the thermal energy kT has to be as large as possible. But as the magnetic moment of a nucleus is lower by at least three orders of magnitude in comparison to that of electron. The polarization of deuteron at 2.5.T/1K is only 0.05%. By the technique of dynamic nuclear polarization, the high electron polarization can be transferred to the nuclei via a microwave induced excitation of coupled electron-nucleus Zeeman transitions. Concerning the DNP efficiency, some parameters like temperature, magnetic field, microwave power, the relation of EPR linewidth and nuclear larmor frequency, electron relaxation time and so on, all contribute to the polarization result. In order to implant unpaired electrons into the diamagnetic solids, two kinds of doping methods, chemical doping and radiation doping are always used. Up to know, the proton polarization can be in the range from 80% to 90%, but deuteron polarization is under 50%. ~ 103 nuclei feeded by 1 unpaired electron from: Chemically stable radical Solids Radiation induced defects Solids In the already % in protonated materials Until % in deuterated materials 4
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The Trityl Radicals (Malmö Group(Sweden); General Electric)
— Important Progress for Deuterated Materials Finland D36’(AH deutero acid form)used for butanol-d10 Ox063(AH sodium salt)used for propandiol-d8 Ox063Me (AH sodium salt) used for pyruvic acid In resent years, trityl radicals play a important role in the progress of deuterated materials. Here shows the three kinds of trityl radicals. Because of the different solubility in different materials, the first one is Finland D36 used in D-butanol. The second one is Ox063 used in D-propandiol. The last one is Ox063Me used in pyruvic, which carben thirteen can be polarized up to 74% at 900 mili Kalvin and 5 Teslar. The trityl radical used in D-polymer is Finland D36. 13C nuclei, which are similar to deuterons, can be polarized up to comparably difficult to polarize highly with conventional radicals.Because of their small EPR linewidth ,even at higher fields,trityl radicals work very well as DNP agents also for 13C nuclei. For the use with pyruvic acid,which is quite polar,a third type of trityl Ox063Me is used,where the 12 hydroxyl groups are substituted with methoxy groups(see Fig. 1) to prevent reactions of the pyruvic acid with the radical [16]. Deuteron : up to 79% at 150mK/2.5T Deuteron: up to 81% at 150mK/2.5T 13C: up to 74% at 900mK/5.0T St.Goertz et al.NIMA 526 (2004) W.Meyer, et al., NIM A 631 (2011) 1
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Important parameter: EPR linewidth
Zeeman Energy of a free electron Contributions to the Electron Zeeman linewidth Hom. Dipol-Dipol interaction between electrons As the EPR linewidth and shape of radicals strongly influence the deuteron polarization result, let us see the details of the contribution of linewidth. A free electron at external magnetic field has Zeeman effect. By the irradiation of microwave, a very narrow EPR line occurs with the transitions between energy levels. But in practice, an unpaired electron always is located in a complicated circumstance. The contributions to the Zeeman linewidth by the local magnetic field consist inhomogeneous boarding and homogeneous boarding. Homogeneous and inhomogeneous appear at the same time. They lead to a broadening of the Zeeman transition energy of unpaired electron system. Dipole-dipole interaction among the unpaired electrons leads to a homogeneous boarding. It depends on the electron concentration. Hyperfine interaction of the unpaired electron with one or more adjacent spin carrying nuclei and the boarding is depend on the structure of paramagnetic center and independent of the external magnetic field. The boarding of g-factor anisotropy caused by the orientation of the crystal or molecular axes with respect to the external magnetic field. In order to get a high deuteron polarization, the energy borading must be minimized. So we can find a suitable doping method or try radiation doping. Inhomogeneous local field such as electric fields caused by the symmetry or by defects of the lattice can lead to a degenerated symmetry of the electronic wave function. And consequently, to a distribution of the Larmor frequencies depending on the orientation of the crystal or molecular axes with respect to the external field. Anisotropy of the g-factor due to a nonvanishing angular momentum of the unpaired electron. The relation between the width σ of the EPR line and the size of the nuclear Larmor frequency WI If the EPR line width is of the same size or larger than the trasition energy between the nuclear Zeeman levels, it is not possible to induce only one of the forbidden electron nucleus transitions as it assumed by the solid effect. A new concept had to be found and to understand the DNP process with a boarding EPR line. So the spin temperature theory was invented and describe the DNP process in a thermodynamical language ESR linewidth is a crucial parameter with respect to the polarization behavior, emphasizes the importance of ESR measurements at DNP relevant magnetic fields. Inhom. Hyperfine interaction magnetic nuclei indep. of B0 Inhom. g-factor anisotropy crystal field dep. of B0 Try to minimize the energy spread Find a suitable doping method Try radiation doping if only low μ nuclei 6
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Bochum measurements Material Radical g/g [10–3] FWHM [mT] at 2.5T PD,max [%] Here shows the deuteron polarization result in Bochum measurement. Here shows the deuteron materials, chemically doped radicals, g-factor anisotropy value of unpaired electrons in the samples, as well the value of the Full Wave at Half Maximum of EPR linewidth at DNP conditions, the last row shows the polarization result. From this table, we can understand that the smaller EPR linewidth, the higher the deuteron polarization value. J. Heckmann, et al., Phys. Rev. B 74 (2006) Result: The smaller the EPR linewidth, the higher the deuteron polarization value.
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Introduction to D-polymer materials
Poly(Ethylene-D4) CD2 dilution factor Styrene-D8, polymerized C8D8 Now I will introduce two kinds of polymer materials, deuterated polyethylene and deuterated polystyrene. The structures are here. The repeating units of deuterated polyethylene is two carbons and four deuteron. The dilution factor is one fourth. The other polymer is deuterated polystyrene. The repeating units consists of one benzene ring plus one ethylene. The dilution factor is zero point one four. Concerning the dilution factor, CD2 is better than C8D8 as polarized material.
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Motivation to use D-polymer materials
Spin physics Thin targets for scattering experiments at low energies Polarized scintillator targets Merits of CD2, C8D8 High purity of D 0.98, 0.99 D with spin 1 and C with spin 0 Easy formable to any thickness at room temperature Up to now the maximum polarizations of D-polymer 1. D-polyethylene CD2 : Paramagnetic Center---Irradiation 35% at 6.5T/1K D.G.Crabb, Nucl. Instr. and Meth. A 526, 56 (2004) 2. D-Polystyrene C8D8 : Paramagnetic Center---D-TEMPO 40% at 2.5 T/100mK B.van den Brandt,et al., Nucl. Instr. and Meth. A 526, 53 (2004) Let us the motivation to use D-polymer materials. In spin physics, the deuterated polymer target can be used as thin polarized targets for scattering experiments at low energies and also can be made as scintillator targets. The advantage of polyethylene and polystyrene are the high purity and simple structure. The most important is that they can be easy formable to any thickness at room temperature. Up to now the maximum polarization value of D-polymer, one is 35% at 6.5/1K in irradiated CD2 made by Virginia group. The other one is 40% at 2.5T/100mK in D-TEMPO doped C8D8 made by PSI group.
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Doping methods for DNP Mechanism of Dynamic Nuclear Polarization Paramagnetic centers are needed Chemical (Tempo, Trityl radical) doping Melting point 36ºC Boiling point 67ºC Irradiation with electron beam Here shows the two doping methods for D-polymer. One is Chemical doping, which need stable radicals. Here shows the structure of TEMPO radical and the unpaired electron is located in the red part. Here is the structure of trityl radical, Finland D36. The unpaired electron is located in the center. The other method is irradiation doping. In our case, the D-polyethylene was irradiated by electron beam. C-D and C-C bonds of polyethylene or poly(Ethylene-D4) can be cleaved by electron beam and paramagnetic centers are produced.
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The Bochum EPR Apparatus
It is our x-band ERP spectrometer. It was made by our group. The measurement can be done between 4K to room temperature.
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The Bochum DNP Apparatus
Magnet+cryostat They are two kinds of cryostat. This one is 4He evaporation refrigerator with C-magnet. The cooling power is 4000m3/h roots blower system. The temperature can be around 1 K. The other one is dilution refrigerator with supper conducting magnet. The maximum magnet field is 8 T and the temperature can be low as several hundreds miliKelvin. TE calibration and relaxation measurement the 4He bath temperature was determined using anAllen-Bradley carbon composition resistor.
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Introduce Finland D36 Radicals in CD2
Preparation of trityl radical in CD2 Introduce Finland D36 Radicals in CD2 In order to implant Finland D36 radical into CD2. We found the solvent of tetralin, which has a good solubility of CD2. The preparation shows here, at first, CD2 powder and liquid tetralin were puted in a normal glass. After the nitrogen supply strategy of 5-10 min, the mixture was put inside the nitrogen box in order to oxidize radical at high temperature. After the mixture were heated and stirred at a temperature of 150 ºC. Finland D36 was added and the mixture was stirred for several minutes at a temperature of 190 ºC in order to dissolve radical. Finally, a thin foil was made . From the ESR line, it is relative very narrow. From bolometric measurement, by using carbon resistor as a bolometer was done while keeping the microwave frequency at GHz, the g-factor anisotropy of Finland D36 doped in C8D8 is very small.
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Polarization of Finland D36-doped CD2
The build-up curve shows that the unpaired electrons of the radicals are not well coupled with the CD2 ,which leads to a low polarization. The build-up curve of CD2 doped with Finland D36 is shown here. The reason for the spikes in the curve is the very low and noisy deuteron signal. However, a tendency is clearly visible. That means the coupling between the radicals and CD2 or the diffusion of the radicals inside the CD2 material is not so tight and homogenous. Polarization and depolarization occurred at the same time. CD2 as a candidate for deuteron polarized target has a few advantages such as the highest dilution factor among all other used polymer materials up to now and a simple structure. Several polarizations can be obtained from the CD2 sample doped with Finland D36 at 2.5 T / 1.0 K. The NMR signal of positive polarization is much better than that of the negative polarization. The build-up curve shows that the unpaired electrons of the radicals are not well coupled with the CD2 ,which leads to a low polarization. In the future, maybe if another radical, nearly related to Finland D36, can be developed and it has a good solubility in tetralin, CD2 material can be made as a good deuteron polymer target.
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Introduce Finland D36 Radicals in C8D8
Preparation of trityl radical in C8D8 g-factor anisotropy: Introduce Finland D36 Radicals in C8D8 Now I will introduce the preparation of trityl radical doping in D-polystyrene, not D-polyethylene ,because it is much easier for D-polystyrene find out a suitable solvent for solution. Finally, we found out THF solvent, in which both D-polystyrene and Finland D36 can dissolved at room temperature. Here is the picture of D-polystyrene doping in trityl radical. It is a homogenous and transparent thin foil. Here shows the EPR lines of two radicals, TEMPO and Finland D36 in D-polystyrene. From bolometric measurement by using carbon resistor as a bolometer, the g-factor anisotropy is about three ten to minus 4, which is one order smaller than TEMPO. The EPR linewidth is about zero point one eight mili teslar at the density of D-polystyrene plus two percentage Finland D36. Homogenous and transparent A thin foil ( 70μm)
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Polarization of Finland D36-doped C8D8
1K/5.0T Let’s look at the polarization result. At first, in order to find the optimum spin concentration, the samples with spin concentration range from 0.4×1019spins/g to 1.56×1019 spins/g were prepared and investigated in 4He refrigerator at magnetic fields of 2.5 and 5.0T. The optimum density is about 1.2 ×1019spins/g. the maximum polarization at 2.5 T is about 12% and at 5.0T it is more than 30% within several hours.
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Polarization of Finland D36-doped C8D8
PT= % In 3He/4He dilution refrigerator at 5.0T the maximum polarization is more than 60% within 5 hours. Li Wang, et al., NIM A 729 (2013) 36
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Deuteron Polymer Polarizations
The polarization results of deuterated polymer are summarized here.
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Conclusion & Outlook Concerning CD2 material, chemical doping method with TEMPO or Trityl Finland D36 , there are no remarkable polarization values obtained. The problem of Finland D36 seems to be its solubility into the solvent. Chemically doped C8D8 with trityl radical can be polarized to more than 30% at 5.0T/1K and more than 60% at 5.0T/400mK with potential to values higher than 80%. But the dilution factor is much lower than that of C8D8. 3. A new approach for C2D2 with trityl radical doping is needed. The conclusion and outlook is firstly, Irradiated D-polyethylene with a relative high dilution factor can be polarized to more than 30% at 2.5T/150mK. The produced paramagnetic centers have hyperfine interaction with the 5 neighboring deuterons. Secondly, Chemically doped D-polystyrene with trityl radical can be polarized to more than 30% at 5.0T/1K and 60% at 5.0T/400mK within several hours. But the dilution factor is much lower than that of D-polyethylene. Thirdly, A approach of trityl radical doped with D-polyethylene is needed.
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a new method called “mechanical doping”
nano - level Ball mill P7 made by Fritsch
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Thanks for your attention!
That is all.
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EPR spectra of Radiation-doped CD2
Here we can clearly see that 11-line pattern, which corresponds to the hyperfine interaction of 5 adjacent deuteron. From the simulation, the splitting of one Alfa site deuteron and four beta site deuteron have almost the same hyperfine constant. Dα =0.485 mT(1D); Dβ =0.480 mT(4D) D(FWHM)=3.0±0.2 mT According to HFS, 11-line pattern corresponds to 5 adjacent D,
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Polarization of radiation-doped CD2
NMR Signal of Deuteron -31% Let us see the polarization result of irradiated D-polyethylene. The values of polarizations were calculated by fitting the area and asymmetry method. The asymmetry method is to calculate the polarization from the ratio of the two peaks height, which were produced by the quadrupole interaction. The maximum polarization is 31.0% with the statistical errors plus and minus 5%. The microwave power is 150mW by IMPATT diode. The optimum frequency distance of positive and negative polarization is about 215MHz. * The large difference of positive and negative polarization values is still not understood.
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EPR spectra of irradiated CH2 and CD2 at 77K
Here shows the EPR spectra of both polyethylene and deuterated polyethylene after irradiation by 7MeV electron beam. The spectrums were measured at 77K in X-band spectrometer. From the differential spectrum of CH2, we can understand that the six clear lines came from alkyl radical, derived from [C-H2-C-H2] by losing one of its hydrogen. From the differential spectrum of CD2, a structure composed of eleven nearly equidistant lines is observed. According to HFS, 6-line pattern conresponds to 5 adjacent H, 0 m= Alkyl-radical
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The Solid State Effect Dipolar Coupling Positive Negative B = 2.5 T
the It is only when σ«wI, that it is possible to excite the forbidden transitions. In this case the microwave frequencies leading to the highest nuclear polariztion values are given by the electron Larmor frequency plus or minus the nuclear Larmor frequency. If the condition is not fulfilled, both transitions take place simultaneously. polarizable electrons, paramagnetic centers are necessary in the diamagnetic material nucleons induce a magnetic field on the paramagnetic centre -> which causes a dipolar coupling between the two spin species B=2.5T => Larmor frequencies electrons 70GHz protons MHz deuterons 16.3 MHz applying saturating microwaves a forbidden transition (m = 1 : magnetic dipol radiation) can be pumped t1e few tens of seconds t1p few msec fe – fp => positive polarization fe + fp => negative polarization the electron relaxes very fast in its ground state and is again available for further transitions the energy from the microwaves and the relaxation process is transferred to the lattice homogenous polarization over the whole probe happens by spin-diffusion => dipol-dipol-transition between the nucleons that‘s a random walk like process By SSE a polarization almost equal to the electron polarization is reachable relaxation processes are working in contradiction to polarization build up and is direct correlated to number of paramagnetic centers B = 2.5 T
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Introduce Finland D36 Radicals in C8D8
EPR spectra of Finland D36-doped C8D8 Bolometric X-band Full width half maximum=FWHM Introduce Finland D36 Radicals in C8D8 dissolve C8D8 polymer in toluene dissolve Finland D36 in isobutanol mix and evaporate solvents
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Polarized target system
Cooling system ~ 100mK Magnet system T C-yoke normal conduction magnet (JM-611made by JEOL) homogeneity: 2×10-4 (ø70mm×25mm) Microwave system 70GHz Oscillator: 68.5GHz-71.5GHz 150mW (IMPATT H-1115 made by HUGHES) NMR measurement system Larmor frequency of D: 16.35MHz Digital Synthesizer: 1MHz-250MHz Accuracy: 0.1MHz (PTS250 made by PTS inc.) L=590nH
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ESR linewidth and shape
Zeeman Energy of a free electron Contributions to the Electron Zeeman linewidth Hom. Dipol-Dipol interaction between electrons ESR linewidth is a crucial parameter with respect to the polarization behavior, emphasizes the importance of ESR measurements at DNP relevant magnetic fields. If the EPR line width is of the same size or larger than the trasition energy between the nuclear Zeeman levels, it is not possible to induce only one of the forbidden electron nucleus transitions as it assumed by the solid effect. A new concept had to be found and to understand the DNP process with a boarding EPR line. So the spin temperature theory was invented and describe the DNP process in a thermodynamical language Inhomogeneous local field such as electric fields caused by the symmetry or by defects of the lattice can lead to a degenerated symmetry of the electronic wave function. And consequently, to a distribution of the Larmor frequencies depending on the orientation of the crystal or molecular axes with respect to the external field. Anisotropy of the g-factor due to a nonvanishing angular momentum of the unpaired electron. Hyperfine interaction of the unpaired electron with one or more adjacent spin carrying nuclei. Dipole-dipole interaction among the unpaired electrons. Homogeneous and inhomogeneous appear at the same time. They lead to a broadening of the Zeeman transition energy of electron system. The relation between the width σ of the EPR line and the size of the nuclear Larmor frequency WI Inhom. Hyperfine interaction magnetic nuclei indep. of B0 Inhom. g-factor anisotropy crystal field dep. of B0 Try to minimize the energy spread Find a suitable doping method Try radiation doping if only low μ nuclei present 28
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δ a homogeneous EPR linewidth Δ an inhomogeneous EPR linewidth
DNP Mechanism Depend on the relationship of δ, Δ and ω0I δ a homogeneous EPR linewidth Solid Effect (SE) Cross effect (CE) Thermal mixing (TM) Δ an inhomogeneous EPR linewidth ω0I the nuclear Larmor frequency Contributions to the Electron Zeeman linewidth δ Δ Hom. Dipol-Dipol interaction between electrons The DNP mechanism has several models, which strongly depend on the relation of EPR linewidth and the nuclear Larmor frequency. The mechanism of the boarding of ESR line is related to the local and external magnetic field of the paramagnetic centers. The contribution to the boarding of ESR line by the local magnetic field include dipolar-dipolar interaction, Hyperfine interaction of unpaired electron with one or more adjacent spin carrying nuclei, isotropic and anisotropy g-factor boarding, which is due to the angular orbit of unpaired electron and the molecular orientation of the crystal to the external magnetic field. Dipolar-dipolar interaction produces homogenous boarding. Hyperfine interaction and anisotropy of g-factor produce inhomogeneous boarding. The two parameters, g factor and its anisotropy and A tensor as well are an important to analyze the boarding of ESR line width. Inhom. Hyperfine interaction magnetic nuclei indep. of B0 Inhom. g-factor anisotropy crystal field dep. of B0
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The Spin Temperature Theory
Deuteron with rather small gyromagnetic ratio Thermal Mixing is DNP mechanism for deuteron enhancement Three spin exchange process: EZS-EDS-NZS The TM effect is treated from a thermodynamic point of view, based on the concept of spin temperature. The electron-nuclear spin system can be described as a set of three interacting baths, each characterized by a spin temperature: the electron Zeeman system(EZS), the electron dipolar system (EDS), and the nuclear Zeeman system(NZS). Off resonance irradiation of the allowed EPR transition results in a large polarization gradient across the EPR line, which is equivalent to cooling the EDS. This bath is in thermal contact with the NZS, which is also cooled in an energy conserving three-spin electron-electron-nuclear exchange process, leading to DNP enhancement, which is caused by the direct coupling between the NZS and the EDS. In this picture an energy reservoir is assigned to each occurring interaction, characterized by a corresponding temperature. Namely, these are the electronic and nuclear Zeeman interactions and the electronic dipolar or spin-spin interaction. This dipolar interaction between the spins of the paramagnetic electrons causes a splitting of the electronic Zeeman levels into quasicontinuous bands, whose energy width is given by the socalled dipolar width D. The prediction for the maximum achievable nuclear polarization shows here. The (vector) polarization P of a spin system with spin I and magnetic moment m under the conditions of thermal equilibrium is given by the Brillouin Funktion BI ESR line of the paramagnetic electrons is predominantly inhomogeneously broadened by hyperfine interaction and g-factor anisotropy, but that the spin-spin interaction causing the homogeneous dipolar broadening of the ESR line is strong enough to provide a fast cross relaxation between the various spin packets in order to establish a common spin temperature. The model assumes saturating microwave fields, and that the nuclear larmor frequency is not much larger than the ESR linewidth. This is also realistic, especially for deuterated materials at low temperatures. tz/tD is the ratio of the electronic Zeeman and dipolar relaxation times.f can reduce the polarization due to nuclear relaxation time, mainly nulcear spin-lattice relaxation. The smaller is the dipolar width D and the weaker is the coupling to the lattice (the long tD), the better is the cooling (heating) efficiency to the dipolar reservior. The smaller EPR linewidth , the higher polarization
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Polarized Deuteron Targets Materials
13 C
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Radiation-doping of CD2 foil
Find an optimal radiation dose 7MeV electron beam (Osaka Uni.) beam spot ø60mm×20mm Irradiation dose ~ ~1017e-/cm2 Irradiation at liquid Nitrogen 77K CD2 foil thickness μm d density g/cm3 Here shows the some parameters of irradiation. The power of electron beam is 7MeV and irradiation was done at liquid nitrogen. Here shows the irradiation dose and the irradiation set-up. In order to measure EPR signal and polarization values, we made difference size of samples, respectively installed in the cavity of EPR spectrometer and that of cryostat. Here shows the two target holders. By comparing the integrated EPR line intensities with those of chemically doped solutions, the spin densities can be calculated. In order to compare the polarizations of CH2 and CD2 at the same irradiation dose, we prepared both samples of polyethylene and CD2 in the same run.
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Introduce Trityl radical
Trityl radical as dopant for D-Butanol Boiling point >200ºC Very stable radical Now I will introduce chemical-doping method for deuterated polymer. The radical we used is Finland D36, which is one of trityl radicals. Because its huge molar weight and the symmetrical structure, unpaired electron can be stably located in the center of the molecular and the g-factor anisotropy is weak from the EPR linewidth. In 2004, a new polarized target, D-butanol+Finland D36 was successfully developed by our group and the maximum polarization can be up to 80% at 2.5T in dilution refrigerator. Now this kind of target is used in MAMI experiment. Weak g-factor anisotropy in D-Butanol
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