Proton Polarization Research Articles

Determination of the scalar polarizabilities of the proton using beam asymmetry $\Sigma_{3}$ Σ 3 in Compton scattering

The scalar dipole polarizabilities, $\alpha_{E1}$ and $\beta_{M1}$, are fundamental properties related to the internal dynamics of the nucleon. The currently accepted values of the proton polarizabilities were determined by fitting to unpolarized proton Compton scattering cross section data. The measurement of the beam asymmetry $\Sigma_{3}$ in a certain kinematical range provides an alternative approach to the extraction of the scalar polarizabilities. At the Mainz Microtron (MAMI) the beam asymmetry was measured for Compton scattering below pion photoproduction threshold for the first time. The results are compared with model calculations and the influence of the experimental data on the extraction of the scalar polarizabilities is determined.

Form factor ratio from unpolarized elastic electron-proton scattering

A reanalysis of unpolarized electron-proton elastic scattering data is done in terms of the electric to magnetic form factor squared ratio. This observable is in principle more robust against experimental correlations and global normalizations. The present analysis shows indeed that it is a useful quantity that contains reliable and coherent information. The comparison with the ratio extracted from the measurement of the longitudinal to transverse polarization of the recoil proton in polarized electron-proton scattering shows that the results are compatible within the experimental errors. Limits are set on the kinematics where the physical information on the form factors can be safely extracted. The results presented in this work bring a decisive piece of information to the controversy on the deviation of the proton form factors from the dipole dependence.

Large dose hyperpolarized water with dissolution-DNP at high magnetic field

We demonstrate a method for the preparation of hyperpolarized water by dissolution Dynamic Nuclear Polarization at high magnetic field. Protons were polarized at 6.7T and 1.1K to >70% with frequency modulated microwave irradiation at 188GHz. 97.2±0.7% of the radical was extracted from the sample in the dissolution in a two-phase system. 16±1mL of 5.0M 1H in D2O with a polarization of 13.0±0.9% in the liquid state was obtained, corresponding to an enhancement factor of 4000±300 compared to the thermal equilibrium at 9.4T and 293K. A longitudinal relaxation time constant of 16±1s was measured.The sample was polarized and dissolved in a fluid path compatible with clinical polarizers. The volume of hyperpolarized water produced by this method enables angiography and perfusion measurements in large animals, as well as NMR experiments for studies of e.g. proton exchange and polarization transfer to other nuclei.

Characterization of the primary hydration shell of the hydroxide ion with H2 tagging vibrational spectroscopy of the OH- ⋅ (H2O)n=2,3 and OD- ⋅ (D2O)n=2,3 clusters.

We report the isotope-dependent vibrational predissociation spectra of the H2-tagged OH- ⋅ (H2O)n=2,3 clusters, from which we determine the strongly coordination-dependent energies of the fundamentals due to the OH groups bound to the ion and the intramolecular bending modes of the water molecules. The HOH bending fundamental is completely missing in the delocalized OH- ⋅ (H2O) binary complex but is recovered upon adding the second water molecule, thereby establishing that the dihydrate behaves as a hydroxide ion solvated by two essentially intact water molecules. The energies of the observed OH stretches are in good agreement with the values predicted by Takahashi and co-workers [Phys. Chem. Chem. Phys. 17, 25505 (2015); 15, 114 (2013)] with a theoretical model that treats the strong anharmonicities at play in this system with explicit coupling between the bound OH groups and the O-O stretching modes on an extended potential energy surface. We highlight a surprising similarity between the spectral signatures of OH- ⋅ (H2O)3 and the excess proton analogue, H3O+ ⋅ (H2O)3, both of which correspond to completed hydration shells around the proton defect. We discuss the origin of the extreme solvatochromicity displayed by both OH- and H+ in the context of the anomalously large "proton polarizabilities" of the H5O2+ and H3O2- binary complexes.

Efficient Batch-Mode Parahydrogen-Induced Polarization of Propane.

We report on a simple approach for efficient NMR proton hyperpolarization of propane using the parahydrogen-induced polarization (PHIP) technique, which yielded ≈6.2 % proton polarization using ≈80 % parahydrogen, a record level achieved with any hyperpolarization technique for propane. Unlike in previously developed approaches designed for continuous-flow operation, where reactants (propene and parahydrogen) are simultaneously loaded for homogeneous or heterogeneous pairwise addition of parahydrogen, here a batch-mode method is applied: propene is first loaded into the catalyst-containing solution, which is followed by homogeneous hydrogenation via parahydrogen bubbling delivered at ≈7.1 atm. The achieved nuclear spin polarization of this contrast agent potentially useful for pulmonary imaging is approximately two orders of magnitude greater than that achieved in the continuous-flow homogeneous catalytic hydrogenation, and a factor of 3-10 more efficient compared to the typical results of heterogeneous continuous-flow hydrogenations.

Hyperpolarization of Frozen Hydrocarbon Gases by Dynamic Nuclear Polarization at 1.2 K.

We report a simple and general method for the hyperpolarization of condensed gases by dynamic nuclear polarization (DNP). The gases are adsorbed in the pores of structured mesoporous silica matrices known as HYPSOs (HYper Polarizing SOlids) that have paramagnetic polarizing agents covalently bound to the surface of the mesopores. DNP is performed at low temperatures and moderate magnetic fields (T = 1.2 K and B0 = 6.7 T). Frequency-modulated microwave irradiation is applied close to the electron spin resonance frequency (f = 188.3 GHz), and the electron spin polarization of the polarizing agents of HYPSO is transferred to the nuclear spins of the frozen gas. A proton polarization as high as P((1)H) = 70% can be obtained, which can be subsequently transferred to (13)C in natural abundance by cross-polarization, yielding up to P((13)C) = 27% for ethylene.

Polarized proton spin density images the tyrosyl radical locations in bovine liver catalase.

A tyrosyl radical, as part of the amino acid chain of bovine liver catalase, supports dynamic proton spin polarization (DNP). Finding the position of the tyrosyl radical within the macromolecule relies on the accumulation of proton polarization close to it, which is readily observed by polarized neutron scattering. The nuclear scattering amplitude due to the polarization of protons less than 10 Å distant from the tyrosyl radical is ten times larger than the amplitude of magnetic neutron scattering from an unpaired polarized electron of the same radical. The direction of DNP was inverted every 5 s, and the initial evolution of the intensity of polarized neutron scattering after each inversion was used to identify those tyrosines which have assumed a radical state. Three radical sites, all of them close to the molecular centre and the haem, appear to be equally possible. Among these is tyr-369, the radical state of which had previously been proven by electron paramagnetic resonance.

Wigner distributions and orbital angular momentum of a proton

The Wigner distributions for u and d quarks in a proton are calculated using the light front wave functions (LFWFs) of the scalar quark-diquark model for nucleon constructed from the soft-wall AdS/QCD correspondence. We present a detail study of the quark orbital angular momentum(OAM) and its correlation with quark spin and proton spin. The quark density distributions, considering the different polarizations of quarks and proton, in transverse momentum plane as well as in transverse impact parameter plane are presented for both u and d quarks.

Overhauser Geomagnetic Sensor Based on the Dynamic Nuclear Polarization Effect for Magnetic Prospecting.

Based on the dynamic nuclear polarization (DNP) effect, an alternative design of an Overhauser geomagnetic sensor is presented that enhances the proton polarization and increases the amplitude of the free induction decay (FID) signal. The short-pulse method is adopted to rotate the enhanced proton magnetization into the plane of precession to create an FID signal. To reduce the negative effect of the powerful electromagnetic interference, the design of the anti-interference of the pick-up coil is studied. Furthermore, the radio frequency polarization method based on the capacitive-loaded coaxial cavity is proposed to improve the quality factor of the resonant circuit. In addition, a special test instrument is designed that enables the simultaneous testing of the classical proton precession and the Overhauser sensor. Overall, comparison experiments with and without the free radical of the Overhauser sensors show that the DNP effect does effectively improve the amplitude and quality of the FID signal, and the magnetic sensitivity, resolution and range reach to 10 pT/Hz@1 Hz, 0.0023 nT and 20–100 T, respectively.

Analysis of the SABRE (Signal Amplification by Reversible Exchange) Effect at High Magnetic Fields

A detailed study of the Signal Amplification By Reversible Exchange (SABRE) effect at high magnetic fields is performed. SABRE is formed by spin order transfer from parahydrogen to a substrate in a transient organometallic complex. Typically, such a transfer is efficient at low magnetic fields; at high fields it requires radio-frequency (RF) excitation of spins in the SABRE complex. However, recently it has been shown (Barskiy et al. in J. Am. Chem. Soc. 136:3322–3325, 2014) that high-field SABRE is also feasible due to “spontaneous” spin order transfer (i.e., transfer in the absence of RF excitation) although the transfer efficiency is low. Here, we studied the SABRE field dependence for protons in the field range 1.0–16.4 T and found an increase of polarization with the field; further optimization of proton polarization can be achieved by varying the viscosity of the solvent. As previously, polarization transfer is attributed to cross-relaxation; this conclusion is supported by additional experiments. For spin-½ hetero-nuclei, such as 15N and 31P, spontaneous spin order transfer is also feasible; however, in contrast to protons, it is based on a coherent mechanism. Consequently, higher transfer efficiency is achieved; moreover the 15N and 31P spectral patterns are remarkably different from that for protons: multiplet (anti-phase) polarization is seen for hetero-nuclei. Our study is of importance for enhancing weak nuclear magnetic resonance (NMR) signals by exploiting non-thermally polarized spins. Although the efficiency of high-field SABRE is lower than that of low-field SABRE; the high-field SABRE experiment is easy to implement for improving the sensitivity of NMR methods.

Optimizing water hyperpolarization and dissolution for sensitivity-enhanced 2D biomolecular NMR

A recent study explored the use of hyperpolarized water, to enhance the sensitivity of nuclei in biomolecules thanks to rapid proton exchanges with labile amide backbone and sidechain groups. Further optimizations of this approach have now allowed us to achieve proton polarizations approaching 25% in the water transferred into the NMR spectrometer, effective water T1 times approaching 40s, and a reduction in the dilution demanded for the cryogenic dissolution process. Further hardware developments have allowed us to perform these experiments, repeatedly and reliably, in 5mm NMR tubes. All these ingredients – particularly the ⩾3000× 1H polarization enhancements over 11.7T thermal counterparts, long T1 times and a compatibility with high-resolution biomolecular NMR setups – augur well for hyperpolarized 2D NMR studies of peptides, unfolded proteins and intrinsically disordered systems undergoing fast exchanges of their protons with the solvent. This hypothesis is here explored by detailing the provisions that lead to these significant improvements over previous reports, and demonstrating 1D coherence transfer experiments and 2D biomolecular HMQC acquisitions delivering NMR spectral enhancements of 100–500× over their optimized, thermally-polarized, counterparts.

A cryostat to hold frozen-spin polarized HD targets in CLAS: HDice-II

The design, fabrication, operation, and performance of a 3/4He dilution refrigerator and superconducting magnet system for holding a frozen-spin polarized hydrogen deuteride target in the Jefferson Laboratory CLAS detector during photon beam running is reported. The device operates both vertically (for target loading) and horizontally (for target bombardment). The device proves capable of maintaining a base temperature of 50mK and a holding field of 1T for extended periods. These characteristics enabled multi-month polarization lifetimes for frozen spin HD targets having proton polarization of up to 50% and deuteron up to 27%.

NICA Facility in Polarized Proton and Deuteron Mode

NICA project at JINR is aimed at the experiments with polarized protons and deuterons at both as fixed target and colliding mode over beam momentum range from 2 to 13.5[Formula: see text]GeV/c. Polarized beams are injected into collider from the Nuclotron-superconducting synchrotron. Dynamic solenoid “Siberian snakes” are proposed to prevent resonance depolarization of proton beam during acceleration in the Nuclotron up to momentum of 6 GeV/c and further in the collider up to the maximum momentum after storage and stochastic cooling of necessary number of particles in each ring. By means of pair of the Snakes placed in the opposite collider straight sections “spin transparency” mode is provided. Stabilization and control of the polarization is reached due to “weak field” solenoids integrated in the lattice. The proposed scheme of the polarization control is universal and can be used for different ion spices (p, d, t, He3…).

Study of the Polarization Deterioration During Physics Stores in RHIC Polarized Proton Runs

As the only high energy polarized proton collider in the world, the Relativistic Heavy Ion Collider (RHIC) has achieved a great success in colliding polarized proton beams up to 255GeV per beam energy with over 50% average store polarizations for spin physics studies. With the help of Siberian snakes as well as outstanding beam control during the acceleration, polarization loss during acceleration up to 100 GeV is negligible. However, about 10% polarization loss was observed between acceleration from 100 GeV to 255 GeV. In addition, a mild polarization deterioration during long store for physics data taking was also observed. In this paper, studies in understanding the store depolarizing mechanism is reported, including the analysis of polarization deterioration data based on the past couple of RHIC polarized proton runs.

Polarimeters for the SPASCHARM Experiment

A beam channel of polarized protons and antiprotons produced from decays of [Formula: see text]- and anti-[Formula: see text]-hyperons for the SPASCHARM experiment is to be built at IHEP U-70 accelerator in Protvino, Russia. The methods for tagging and measuring polarization of the beam (anti)protons are discussed in this report. The fast on-line beam tagging exploits the correlations between polarization and kinematics of (anti)protons originated from (anti)[Formula: see text]-decays. In the intermediate focus of primary target, decay (anti)protons of different transverse polarizations are spatially dispersed transversely with respect to the beam axis. The tagging system, consisting of fast beam detectors with good spatial resolution, measures the momentum and trajectory of each beam particle, including its position at the intermediate focus, thus allowing instant (on-line) assignment of the transverse polarization value to each (anti)proton. This system is also extremely useful for the beam channel tuning. While being fast and convenient, the polarization tagging fully relies on computing of particle transportation in the beam channel. In order to verify the real beam polarization and operating of the tagging system and beam channel, the independent absolute beam polarimetry is to be used. It is based on measuring the spin asymmetries in elastic scattering of beam (anti)protons in Coulomb-Nuclear Interference (CNI) and diffractive kinematic regions. It is estimated that less than one week of data taking would allow measuring an absolute beam polarization at the statistical accuracy of [Formula: see text]4–5%.

Double-Polarized pd Scattering and Test of Time-reversal Invariance

The integrated proton-deuteron cross section σ˜ for the case of transversal polarization ppy of the proton and tensor polarization Pxz of the deuteron provides a null test signal for time-reversal invariance violating but P-parity conserving effects. The corresponding experiment is planned at COSY to measure the observable σ˜. Here we consider in general case the status of the null-test observable in pd scattering, calculate σ˜ within the Glauber theory of the double-polarized pd scattering at 100 - 1000 MeV and study the contribution of the deuteron S- and D-waves for several type of the T-odd NN interactions.

Superconducting racetrack booster for the ion complex of MEIC

The current design of the Medium-energy Electron-Ion Collider (MEIC) project at Jefferson lab features a single 8 GeV/c figure-8 booster based on super-ferric magnets. Reducing the circumference of the booster by switching to a racetrack design may improve its performance by limiting the space charge effect and lower its cost. We consider problems of preserving proton and deuteron polarizations in a superconducting racetrack booster. We show that using magnets based on hollow high-current NbTi composite superconducting cable similar to those designed at JINR for the Nuclotron guarantees preservation of the ion polarization in a racetrack booster up to 8 GeV/c. The booster operation cycle would be a few seconds that would improve the operating efficiency of the MEIC ion complex.

Use of the calorimeter to improve analyzing power of the reactions, investigating secondary proton polarization

The reaction p + CH2→ forward charge particle + X is used for this aim traditionally. Analyzing power of this reaction falls off as 1/p, where p is the laboratory momentum. At the proton momenta of order 8 GeV/c, which are expected at the JLab experiment, the low analyzing power creates problems for off-line analysis of data. On the other hand, it is well known that the reaction p+p → p+p has the much more analyzing power. So, the calorimeter is predestinated for suppression of inelastic events in this reaction. In the report it is shown that the problem is solved quite well.

Solvent responsive catalyst improves NMR sensitivity via efficient magnetisation transfer.

A bidentate iridium carbene complex, Ir(κC,O-L1)(COD), has been synthesised which contains a strongly electron donating carbene ligand that is functionalised by a cis-spanning phenolate group. This complex acts as a precursor to effective magnetisation transfer catalysts which form after reaction with H2 and a suitable two electron donor. In solvents such as benzene, containing pyridine, they are exemplified by neutral, chiral Ir(H)2(κC,O-L1)(py)2 with inequivalent hydride ligands and Ir-O bond retention, whilst in methanol, Ir-O bond cleavage leads to zwitterionic [Ir(H)2(κC,O(-)-L1)(py)3](+), with chemically equivalent hydride ligands. The active catalyst's form is therefore solvent dependent. Both these complexes break the magnetic symmetry of the hydride ligands and are active in the catalytic transfer of polarisation from parahydrogen to a loosely bound ligand. Test results on pyridine, nicotinaldehyde and nicotine reveal up to ≈1.2% single spin proton polarisation levels in their (1)H NMR signals which compare to the normal 0.003% level at 9.4 Tesla. These results exemplify how rational catalyst design yields a solvent dependent catalyst with good SABRE activity.

Review of Polarized Ion Sources

Recent progress in polarized ion sources development is reviewed. New techniques for production of polarized H[Formula: see text] ion (proton), D[Formula: see text] (D[Formula: see text]) and 3He[Formula: see text] ion beams will be discussed. A novel polarization technique was successfully implemented for the upgrade of the RHIC polarized H[Formula: see text] ion source to higher intensity and polarization. In this technique, a proton beam inside the high magnetic field solenoid is produced by ionization of the atomic hydrogen beam (from an external source) in the He-gas ionizer cell. Polarized electron capture from the optically-pumped Rb vapor further produces proton polarization (Optically Pumped Polarized Ion Source technique). The upgraded source reliably delivered beam for the 2013 polarized run in RHIC at [Formula: see text] = 510 GeV. This was a major factor contributing to RHIC polarization increase to over 60 % for colliding beams. Feasibility studies of a new polarization technique for polarized 3He[Formula: see text] source based on BNL Electron Beam Ion Source is also discussed.