Proton Spin-flip Research Articles

On the Transfer of Polarization from the Initial to the Final Proton in the Elastic Process $$e\vec {p} \to e\vec {p}$$

The $Q^2$ dependence of the ratio of the cross sections with and without proton spin flip, as well as the polarization asymmetry in the process $e \vec{p} \to e \vec{p}$ has been numerically analyzed using the results of JLab polarization experiments on the measurements of the ratio of the Sachs form factors in the $\vec{e} p \to e \vec{p}$ process. The calculations have been made for the case where the initial (at rest) and final protons are fully polarized and have a common spin quantization axis, which coincides with the direction of motion of the final proton. The longitudinal polarization transfer to the proton has been calculated in the case of the partially polarized initial proton for a kinematics used in the experiment reported in [A. Liyanage et al. (SANE Collaboration), Phys. Rev. C 101, 035206 (2020)], where the double spin asymmetry was measured in the $\vec{e} \vec{p} \to e p$ process. A noticeable sensitivity of the polarization transfer to the proton to the form of the $Q^2$ dependence of the ratio $\mu_p G_E/G_M$ has been found. This sensitivity may be used to conduct a new independent experiment to measure this dependence in the $ e \vec{p} \to e \vec{p}$ process. A criterion to assess the reliability of measurements of the ratio of Sachs form factors using the Rosenbluth technique has been proposed and used to analyze the results of two experiments.

Generalized Sachs Form Factors and the Possibility of Their Measurement in Processes without and with Proton Spin Flip

The differential cross section for elastic electron proton scattering has been calculated taking into account the two photon exchange within the phenomenological description of the electromagnetic electron proton interactions. The calculation is based on the consistent evaluation of the matrix elements of the proton current in a diagonal spin basis, which makes it possible to naturally obtain expressions for the generalized Sachs form factors. A new method has been proposed to independently measure these form factors in the elastic $e \vec{p} \to e \vec{p}$ process in the case where the initial proton at rest is fully polarized along the direction of the motion of the final proton.

On the Measurement of Sachs Form Factors in Processes without and with Proton Spin Flip

The physical meaning of the decomposition of the Rosenbluth formula into two terms containing only squares of Sachs form factors has been established. A new method has been proposed for their independent measurement in the $e \vec{p} \to e \vec{p}$ elastic process when the initial proton at rest is fully polarized along the direction of motion of the final proton.

Nuclear Data Sheets for A = 87

The evaluated experimental data are presented for 14 known nuclides of mass 87 (Ga, Ge, As, Se, Br, Kr, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru). New datasets have been added for 87Ga, 87Se, 87Kr, 87Rb, 87Sr, 87Nb, and 87Tc. The observation of and new lifetime measurements for 87As at the NSCL Coupled Cyclotron Facility and the Oak Ridge Isochronous Cyclotron at the HRIBF–ORNL Facility are included in the adopted levels for this isotope. The new evaluation also includes an isomeric level at unknown energy for 87Tc, changes to the adopted levels for 87Nb based on newly published data including an extension of the high spin levels and new lifetime measurements, and new heavy ion data for 87Kr. New high spin levels for 87Rb were observed, indicating possible neutron core excitations. In addition, the ground state lifetime of 87Rb has been revised and a new lifetime measurement for an excited level in 87Rb indicates a possible proton spin flip. New excitation levels have been observed for the first time in 87Se. New direct and precise measurement of atomic masses of 87Tc, 87Mo, 87Nb, 87Zr, 87Mo and 87Tc have greatly improved the Q value landscape in this mass region. This work supersedes the previous A=87 evaluation published in 2002He09, and Q values for all isotopes were updated to incorporate the mass evaluation in 2012Wa38.

Particle gamma correlations in 12C measured with the CsI(Tl) based detector array CHIMERA

The gamma decay of the first excited 4.44MeV 2+level of 12C, populated by inelastic scattering of proton and 16O beams at various energies was studied in order to test γ-ray detection efficiency and the quality of angular distribution information given by the CsI(Tl) detectors of the 4π CHIMERA array. The γ-decay was measured in coincidence with ejectile scattered particles in an approximately 4π geometry allowing to extract the angular distribution in the reference frame of recoiling 12C target. The typical sin2(2θ) behavior of angular distribution was observed in the case of 16O beam. Besides that, for the proton beam, in order to explain the observed distribution, the addition of an incoherent flat contribution was required. This latter is the effect of proton spin flip events allowing the population of M=±1 magnetic substates, that is not possible in reactions induced by 16O beam. A comparison with previously collected data, obtained measuring only in and out of plane proton-γ-ray coincidences, confirms the good quality of the angular distribution information given by the apparatus. Possible applications with radioactive beams are outlined.

EPR detected polarization transfer between Gd3+ and protons at low temperature and 3.3 T: The first step of dynamic nuclear polarization

Electron-electron double resonance pulsed electron paramagnetic resonance (EPR) at 95 GHz (3.3 T) is used to follow the dynamics of the electron spin polarization during the first stages of dynamic nuclear polarization in solids. The experiments were performed on a frozen solution of Gd(+3) (S=7/2) in water/glycerol. Focusing on the central vector -1/2 --> vector +1/2 transition we measured the polarization transfer from the Gd(3+) electron spin to the adjacent (1)H protons. The dependence of the echo detected EPR signal on the length of the microwave irradiation at the EPR "forbidden" transition corresponding to an electron and a proton spin flip is measured for different powers, showing dynamics on the microsecond to millisecond time scales. A theoretical model based on the spin density matrix formalism is suggested to account for this dynamics. The central transition of the Gd(3+) ion is considered as an effective S = 1/2 system and is coupled to (1)H (I = 1/2) nuclei. Simulations based on a single electron-single nucleus four level system are shown to deviate from the experimental results and an alternative approach taking into account the more realistic multinuclei picture is shown to agree qualitatively with the experiments.

SKYRME-RANDOM-PHASE-APPROXIMATION DESCRIPTION OF SPIN-FLIP AND ORBITALM1GIANT RESONANCES

The self-consistent separable random-phase approximation (SRPA) with Skyrme forces is extended to the case of magnetic excitations and applied to the description of spin-flip and orbital M1 giant resonances in the isotopic chain142-152Nd . The Skyrme forces SkT6, SkM*, SLy6 and SkI3 are used. The calculations show an onset of the scissors mode with increasing deformation. A specific three-peak structure of the spin-flip response is found and explained by particular neutron and proton spin-flip transitions. Although the employed forces provide an acceptable qualitative description, the Skyrme functional still needs further improvement to reproduce quantitatively the experiment for spin modes.

Protein proton–proton dynamics from amide proton spin flip rates

Residue-specific amide proton spin-flip rates K were measured for peptide-free and peptide-bound calmodulin. K approximates the sum of NOE build-up rates between the amide proton and all other protons. This work outlines the theory of multi-proton relaxation, cross relaxation and cross correlation, and how to approximate it with a simple model based on a variable number of equidistant protons. This model is used to extract the sums of K-rates from the experimental data. Error in K is estimated using bootstrap methodology. We define a parameter Q as the ratio of experimental K-rates to theoretical K-rates, where the theoretical K-rates are computed from atomic coordinates. Q is 1 in the case of no local motion, but decreases to values as low as 0.5 with increasing domination of sidechain protons of the same residue to the amide proton flips. This establishes Q as a monotonous measure of local dynamics of the proton network surrounding the amide protons. The method is applied to the study of proton dynamics in Ca(2+)-saturated calmodulin, both free in solution and bound to smMLCK peptide. The mean Q is 0.81 +/- 0.02 for free calmodulin and 0.88 +/- 0.02 for peptide-bound calmodulin. This novel methodology thus reveals the presence of significant interproton disorder in this protein, while the increase in Q indicates rigidification of the proton network upon peptide binding, confirming the known high entropic cost of this process.

Possible method for measuring the proton form factors in processes with and without proton spin flip

The ratio of the squares of the electric and magnetic proton form factors is shown to be proportional to the ratio of the cross sections for the elastic scattering of an unpolarized electron on a partially polarized proton with and without proton spin flip. The initial proton at rest should be polarized along the direction of the motion of the final proton. Similar results are valid for both radiative ep scattering and the photoproduction of pairs on a proton in the Bethe-Heitler kinematics. When the initial proton is fully polarized in the direction of the motion of the final proton, the cross section for the ep → ep process, as well as for the ep → epγ and γp → \( e\bar ep \) processes, without (with) proton spin flip is expressed only in terms of the square of the electric (magnetic) proton form factor. Such an experiment on the measurement of the cross sections without and with proton spin flip would make it possible to acquire new independent data on the behavior of GE2(Q2) and GM2(Q2), which are necessary for resolving the contradictions appearing after the experiment of the JLab collaboration on the measurement of the proton form factors with the method of polarization transfer from the initial electron to the final proton.

15N–{1H} NOE experiment at high magnetic field strengths

The heteronuclear (15)N-{(1)H} NOE values are typically determined by taking the ratio of (15)N signal intensities recorded in the presence and absence of (1)H saturation prior to evolution of (15)N magnetization. Since the intensity ratio of two independent experiments is taken, complete recovery of (15)N magnetization during the scan repetition delay is critical to obtain reliable NOE values. Because it may not be practical to wait for the complete recovery of magnetization at high magnetic fields, Solomon equations may be used to correct measured NOE values. Here, based on experiments and simulations, we show that since the cross-correlation between (1)H-(15)N dipole and (15)N chemical shift anisotropy becomes significant at high fields for small or deuterated proteins, measured NOE values can not be accurately corrected based on the Solomon equations. We also discuss ranges of rotational correlation times and proton spin-flip rate, in which the NOE values can be corrected by the equations.

Single-pion production in pp collisions at 0.95 GeV/c (I)

The single-pion production reactions $pp\to d\pi^+$, $pp\to np\pi^+$ and $pp\to pp\pi^0$ were measured at a beam momentum of 0.95 GeV/c ($T_p \approx$ 400 MeV) using the short version of the COSY-TOF spectrometer. The implementation of a central calorimeter provided particle identification, energy determination and neutron detection in addition to time-of-flight and angle measurements. Thus all pion production channels were recorded with 1-4 overconstraints. The total and differential cross sections obtained are compared to previous data and theoretical calculations. Main emphasis is put on the discussion of the $pp\pi^0$ channel, where we obtain angular distributions different from previous experimental results, however, partly in good agreement with recent phenomenological and theoretical predictions. In particular we observe very large anisotropies for the $\pi^0$ angular distributions in the kinematical region of small relative proton momenta revealing there a dominance of proton spinflip transitions associated with $\pi^0$ $s$- and $d$-partial waves and emphasizing the important role of $\pi^0$ d-waves.

Achieving 99.9% Proton Spin-Flip Efficiency At Higher Energy With A Small rf Dipole

We recently used a new ferrite rf dipole to study spin flipping of a 2.1 GeV/c vertically polarized proton beam stored in the COSY Cooler Synchrotron in Jülich, Germany. We swept the rf dipole's frequency through an rf-induced spin resonance to flip the beam's polarization direction. After determining the resonance's frequency, we varied the frequency range, frequency ramp time, and number of flips. At the rf dipole's maximum strength and optimum frequency range and ramp time, we measured a spin-flip efficiency of 99.92+/-0.04%. This result, along with a similar 0.49 GeV/c IUCF result, indicates that, due to the Lorentz invariance of an rf dipole's transverse integralBdl and the weak energy dependence of its spin-resonance strength, an only 35% stronger rf dipole should allow efficient spin flipping in the 100 GeV BNL RHIC Collider or even the 7 TeV CERN Large Hadron Collider.

Is the 4.742 MeV state in 88Sr the 1− two-phonon state?

A nuclear resonance fluorescence experiment on 88Sr has been performed with bremsstrahlung of 6.7 MeV endpoint energy. The γ-ray linear polarisation has been measured with a EUROBALL CLUSTER detector used as a Compton polarimeter. The results indicate positive parity for the J= 1 state at 4.742 MeV in 88Sr, in contrast to the previous interpretation as a 1− two-phonon (2+1⊗ 3−1) state and in conflict with the predictions of the quasiparticle-phonon model. On the basis of such calculations the 1+ state at 3.486 MeV may be considered as the 1+1 one-phonon state and the very strong 1+1→ 0+1 deexcitation as proton spin-flip 2p1/2→ 2p3/2 transition.

Magnetic dipole response in rare earth nuclei

Experimental observations in certain rare earth nuclei have established the presence of sizeable B(M1) strength of two peak structure lying in the 5–10 MeV region. The character of the states concerned, studied within a self-consistent Random Phase Approximation using Skyrme forces, are identified to be that of proton and neutron giant spin-flip resonances.

Comparative ESR study of C 60 and C 70 radical anions produced in γ-irradiated organic solid solutions at 77 K

ESR spectra of C 70 radical anions were detected for C 70/methylcyclohexane (MCHX) and C 70/2-methyltetrahydrofuran (MTHF) solid solutions which were γ-irradiated at 77 K and subsequently annealed at 107–117 K. The ESR spectrum for C 70/MCHX was a singlet which was ascribed to C 70 −, and was flanked by a pair of satellites due to matrix proton spin flip lines. The ESR spectrum for C 70/MTHF was a superposition of a singlet and a deformed doublet. The latter was unstable and disappeared at 109 K, and was tentatively ascribed to C 70 2−. ESR spectra of C 60 radical anions were partly reinvestigated and are compared to those of C 70. The relative electron attachment efficiencies for C 60 and C 70 at 77 K were estimated, and the former was about twice as large as the latter. Isothermal decay at 77 K was observed for both C 60 and C 70 radical anions.

ESR spectra of C 60 radical anions produced in γ-irradiated organic solid solutions at 77 K

ESR spectra of C 60 radical anions were detected for C 60/MCHX and C 60/MTHF solid solutions which were γ-irradiated at 77 K and subsequently annealed at 110–140 K. The g-factors were 2.0019 and 1.9997 for C 60/MCHX (or C 60/MCHX- d 14) and C 60/MTHF, respectively. Δ H pp = 0.26 mT was obtained for those solutions and was smaller than the values reported for electrolytically produced C 60 − by about 50%. Matrix proton spin flip satellite lines were observed in C 60/MCHX.

Ion cyclotron and spin-flip emissions from fusion products in tokamaks

Power emission by fusion products (i.e. protons and/or alpha particles) of tokamak plasmas in their ion cyclotron range of frequencies (ICRF) and at their spin-flip resonance frequency is calculated for some specific model fusion product velocity space distribution functions. Single 'dressed' test particle spontaneous emission calculations are presented first and the radiation temperature for ion cyclotron emission (ICE) is analysed both for black body emission and non-equilibrium conditions. Thresholds for instability and overstability (i.e. negative radiation temperature) conditions are then examined and quasi-linear and non-linear theories of the electromagnetic ion cyclotron modes are discussed. Some numerical estimates are presented for typical tokamak parameters. Semiquantitative remarks are offered on wave accessibility, mode conversion and parametric decay instabilities as possible mechanisms for spatially localized ICE. Calculations are carried out both for k|| = 0 and for k|| not= 0. The effects of the temperature anisotropy (i.e. T⊥ not= T||) and large drift velocities in the parallel direction are also examined. Finally, proton spin-flip resonance emission and absorption calculations are also presented both for thermal equilibrium conditions and for an 'inverted' population of states. Reasonably good agreement is obtained between theory and experiment. Distinctions between 'kinetic or causal instabilities' and 'hydrodynamic instabilities' are drawn in the Appendix

Thermally excited proton spin-flip laser emission in tokamaks.

Based on statistical theormodynamic fluctuation arguments, it is shown here for the first time that thermally excited spin-flip laser emission from the fusion product protons can occur in large tokamak devices that are entering the reactor regime of operation. Existing experimental data from TFTR support this conjecture, in the sense that these measurements are in complete agreement with the predictions of the quasilinear theory of the spin-flip laser.

Dielectrons in pi -p collisions via the two-photon mechanism.

Dielectron production in 16 GeV {pi}{sup {minus}}{ital p} collisions is studied using the double equivalent photon method. Equivalent photon spectra of hadrons are calculated analytically in a fully quantal and semiclassical approach. The limitation of the latter approach and the influence of the proton spin-flip terms are studied. Conclusions at variance with those of a recent letter by Bottcher {ital et} {ital al}. are obtained.

EPR spin flip transitions in some metal dithiolenes

Small line widths (Δ B pp ≅ 0.25–0.40 mT) in the EPR spectra of 63 Cu 2+ in the matrices of some transition metal dithiolenes permit the observation of not-so-easily realizable proton spin flip transitions even at room temperature and at low microwave power. These transitions, studied in four different lattices as a function of crystal orientation, microwave power and temperature, have been found to be from the protons of the counter ions and a few ångströms away from the unpaired electron-containing metal centre. It has been possible to identify the protons and estimate their distances from the metal centre by two different methods. A temperature-dependent evaluation of the distance parameters as well as the observation of the “double” and “triple” flips are reported. The differential saturation of the “main” and “satellite” (due to spin flip) lines studied by the CW saturation method has provided information on the mechanism of spin relaxation in these systems.