Proton Resonance Data Research Articles

Evaluated the level density for proton induced nuclear resonances in (P+48Ti) reaction using different models

The experimental proton resonance data for the reaction P+48Ti have been used to calculate and evaluate the level density by employed the Gaussian Orthogonal Ensemble, GOE version of RMT, Constant Temperature, CT and Back Shifted Fermi Gas, BSFG models at certain spin-parity and at different proton energies. The results of GOE model are found in agreement with other, while the level density calculated using the BSFG Model showed less values with spin dependence more than parity, due the limitation in the parameters (level density parameter, a, Energy shift parameter, E1and spin cut off parameter, σc). Also, in the CT Model the level density results depend mainly on two parameters (T and ground state back shift energy, E0), which are approximately constant in their behavior with the proton energy compared with GOE model. The RMT estimation used to calculate the corrections of the incompleteness proton resonance measurement data by using two methods; the conventional analysis method, which depends on the resonance widths and the updated, developed, tested and applied a new analysis method, which depends mainly on the resonance spacings. The spacing analysis method is found much less sensitive to non-statistical phenomena than is the width analysis method. Where the analysis of a given data set via these two independent analysis methods indicated the increasing in the reliability of the determination of the missing fraction of levels, the observed fraction f between 0.87+0.13−0.11 – 0.68+0.12−0.12 for different spin-parity of this reaction and then the distinguishability in the level density calculations can be achieved. The modified Porter Thomas distribution along with the maximum likelihood function have been used to get the missing levels corrections for 5 proton resonance sequences in the present reaction. To estimate the present long-range correlations for pure sequence of levels the mean square of the deviation of the cumulative number of levels from a fitted straight line represented by the Dyson and Mehta Δ3 statistic has been employed for spin parity 12+, and calculated the <Δ3> against the cumulative number of proton levels.

Parity dependence of nuclear level densities

High resolution proton resonance data have been examined for a possible parity dependence of nuclear level densities. Five spin-parity ${\mathrm{combinations}\mathrm{---}1/2}^{+},$ ${1/2}^{\ensuremath{-}},$ ${3/2}^{\ensuremath{-}},$ ${3/2}^{+},$ and ${5/2}^{+}$---have been analyzed for three ${\mathrm{datasets}\mathrm{---}}^{44}\mathrm{Ca}(p,p),$ ${}^{48}\mathrm{Ti}(p,p),$ and ${}^{56}\mathrm{Fe}(p,p).$ Much of the uncertainty in the level density arises from the determination of the fraction of levels that are not observed. The missing fraction of levels was determined by (a) the standard width analysis method that assumes a Porter-Thomas distribution for the reduced widths and (b) a recently developed method that analyzes the spacing distribution and assumes the Wigner distribution for the nearest-neighbor spacings. There are indications of parity dependence of the level densities for several of the spin-parity combinations.

Detailed-balance tests of time-reversal invariance with interfering charged-particle resonances.

Detailed-balance tests of time-reversal invariance (TRI) with charged-particle resonance reactions are reexamined from the view that there may be large enhancement of TRI violation near two interfering resonances. In our proton resonance data on $^{23}\mathrm{Na}$, $^{27}\mathrm{Al}$, $^{31}\mathrm{P}$, $^{35}\mathrm{Cl}$, and $^{39}\mathrm{K}$ targets, there are 41 pairs of adjacent resonances with the same angular momentum and parity. Using experimental resonance parameters, the difference in the differential cross sections for the (p,${\mathrm{\ensuremath{\alpha}}}_{0}$) and (\ensuremath{\alpha},${\mathit{p}}_{0}$) reactions was calculated for each of these resonance pairs. An appropriate figure-of-merit involving both the difference of the two cross sections and the magnitudes of the cross sections was determined for each resonance pair. Both the differences and the figures-of-merit show very strong dependence on energy, angle, and the particular pair of resonances; the relative sensitivity varies by many orders of magnitude. These results suggest that suitably chosen charged-particle resonance tests of TRI violation would be much more sensitive than previous detailed-balance tests.

Tests of the reduced width amplitude distribution with proton resonance data

The assumption that the distribution of reduced partial-width amplitudes is multivariate Gaussian is tested by separate measurement of width and amplitude correlations. Two approaches to the analysis are employed:1) analyzing the data sets separately and then averaging the results;2) combining the data sets and then performing the analysis. Although the latter procedure provides a nuclear width ensemble (1117 widths), several tests suggest that it is preferable to analyze the individual data sets and then average the results. When the data are transformed to a representation in which the amplitude correlation is zero, the average width correlation for 21 data sets is ¯r w =−0.01+0.03, consistent with the Gaussian assumption.

Comparison of average s-wave resonance spacings from proton and neutron resonances.

Average s-wave resonance spacings were derived from high-resolution proton resonance data for 11 odd-Z nuclei in the mass range A=41--67 and compared with the average s-wave spacings obtained from neutron resonances for their odd-N isobars. After careful correction for missing levels the neutron and proton results are consistent; proton resonance data can be used to increase the data base for nuclear level densities. After correction to a common excitation energy, the spacings show a correlation with the shell correction energy ${E}_{\mathrm{shell}}$, especially for A=41, 55, and 59, where data exist for three isobars with quite different shell correction energies. The dependence of the average level spacing D\ifmmode\bar\else\textasciimacron\fi{} on ${E}_{\mathrm{shell}}$ is approximately exponential, in good agreement with the theoretical models of Ignatyuk et al. and Kataria et al. The data also have been used to calculate asymptotic a parameters in these two models. The mass dependence of these parameters can be described by the simple relation a=0.137A with an rms deviation of 4.3%. Attempts to describe the data within the Fermi gas model resulted in much larger fluctuations of the parameters with A and Z. Finally, the data were compared to the predictions of the microscopic Fermi gas model, using the single particle level scheme of Seeger and Perisho. At present, the quality of this description is still somewhat worse than with the phenomenological models of Ignatyuk et al. and Kataria et al.

Many-body forces in finite nuclei and amplitude correlations in nuclear reaction cross sections

The correlations observed recently in high-resolution proton resonance data on medium-mass targets for resonances distant from analogue states are traced back to the modification of nuclear wavefunctions by the continuum. The modifying part of the wavefunction is excited by a 'direct' reaction mechanism. The correlations are shown to be of the same type as those between resonances in the vicinity of analogue states.

Test of Direct Reaction Theory from Amplitude Correlations

It is shown that the new proton resonance data on targets $A\ensuremath{\sim}48$ provide a crucial check on the validity of direct reaction theory, viz. the existence of amplitude correlations between channels. These are often large ($|\ensuremath{\rho}|g~0.5$) and are not simply related to width correlations. Analysis with a simple reaction model shows that the large correlations must imply some failure of the distorted-wave Born-approximation theory of direct reactions.

Proton and deuteron magnetic resonance in single crystals of Fe(NH4)2(SO4)2∙6H2O

Single crystal proton and deuteron magnetic resonance in Fe(NH4)2(SO4)2∙6H2O and Fe(ND4)2(SO4)2∙6D2O, respectively, are studied at room temperature. From the proton magnetic resonance study are found the orientations of the proton–proton vectors of the water molecules with respect to the crystallographic axes. Proton resonance data are used to determine the positions of the hydrogen atoms belonging to the water molecules in the crystal. A deuteron resonance study shows that the D2O molecules are flipping fast at room temperature. The quadrupole coupling tensor at the deuteron sites of D2O in the crystal are determined. The positions of the hydrogen atoms are also determined from the directions of the principal components of the quadrupole coupling tensor.

Nuclear Magnetic Resonance of 1H and 27Al and Al–Si Order in Low Cordierite, Mg2Al4Si5O18 · nH2O

Proton resonance data in the low-temperature form of cordierite indicate the presence of isolated water molecules in the channel formed of the AlSi5O18 rings, with H–H directions along the crystallographic c axis and with large vibration amplitudes. Two crystallographically nonequivalent aluminum sites have been observed. The quadrupole coupling constant e2qQ/h, the asymmetry parameter η, and the principal axes directions are: AlI: | e2qQ/h |=10.6 MHz; η=0.38; X ‖ c; Z and Y, 30° away from a and b.AlII: | e2qQ/h |=5.6 MHz; η=0.34; Y ‖ c; Z and X, 20° away from a and b.The AlI and AlII sites correspond to the distorted tetrahedral T1 site outside the six-membered ring and T5 site within the ring in the cordierite structure. The AlI NMR data also agree with Fe3+ paramagnetic resonance data, indicating that the Fe3+ ions preferentially occupy the larger T1 sites. The 27Al NMR results indicate a high degree of Al–Si order in low cordierite.

Stereochemical course of the cyclization of olefinic aldehydes

The stereochemistry of the homoallylic alcohols produced in the stannic chloride-catalysed cyclization of aldehydes (Ia), (Ib), and (IX), determined by X-ray crystallography and proton resonance data using lanthanide shift reagents, are consistent with a concerted intramolecular ‘ene reaction’ mechanism for the cyclization and afford the first example of a nearly undistorted twist-chair conformation for a cycloheptane.

Nuclear Resonance Determination of the Magnetic Space Group of MnCl2·2H2O

The Cl and H nuclear magnetic resonance spectra have been used to study magnetic ordering in MnCl2·2H2O. It was found that the material orders antiferromagnetically with a Néel temperature of 6.8°K. The magnetic space group deduced from the Cl data was shown to be C2c2 / m. The proton resonance data were shown to substantiate the magnetic space group assignment. The compound is isostructural with CoCl2·2H2O. Both compounds contain linear chains of magnetic ions running along the c axis. However, in the Mn compound the chains are antiferromagnetically coupled while in the Co compound they are ferromagnetically coupled.

Studies on some new neutral tris-complexes of trivalent rhodium and chromium

Synthesis of tris-chelates of Rh(III) and Cr(III) derived from several triazene-1-oxides is described. The electronic spectra of the complexes are discussed. A typical Cr(III)-complex is characterised by the crystal field parameters: D q = 1740 cm −1 and B = 508 cm −1. Proton resonance data unequivocally established the trans stereochemistry for the Rh(III) complexes. The sterically unfavorable cis form could not be synthesised.

Proton Relaxation Times and Translational Diffusion in Ferroelectric Potassium Ferrocyanide Trihydrate

Proton spin—lattice relaxation times (T1) and relaxation times along the rf field (T1ρ) have been measured from 120° to 330°K in ferroelectric K4Fe(CN)6·3H2O(KFCT). The T1 data show a single minimum at 220°K which is to ascribed a 180° flip motion of the water molecules detected in a previous study of deuteron magnetic resonance. The T1ρ data exhibit two minima: one at 140°K associated with the 180° flip motion and another at 285°K which is ascribed to an exchange of water molecules due to translational diffusion. The presence of translational diffusion was confirmed by measurement of the exchange of heavy water with KFCT particles using a direct weighing method. The previously proposed model for the water molecule positions in KFCT is revised to agree with a recent neutron-diffraction structural determination. Deuteron and proton resonance data are reinterpreted in terms of the new structure which agrees with a previous proposal by Kiriyama et al., and in terms of two types of water molecular motions, the translational diffusion and 180° flip.

Proton Motion, Knight Shifts, and Quadrupolar Effects in the Lanthanum-Hydrogen System

The nuclear magnetic resonance of both the lanthanum and hydrogen nuclei in the lanthanum-hydrogen system has been studied as a function of hydrogen concentration and temperature. The concentrations ranged from 0.4 H/La to 2.85 H/ La and temperatures -197 deg C to 400 deg C. The existence of two phases, part La metal and part LaH/sub 2.0/ for concentrations with less than 2 H/La, is confirmed. Measurements of the proton linewidth and thermal relaxation time T/ sub 1/ unambiguously demonstrate that proton self-diffusion takes piace at moderate temperatures. Activation energies and attempt frequencies for the proton self-diffusion, which are determined as a function of hydrogen concentration, decrease abruptly at approximately 2 H/La from 23 kcal/mole and 10/sup 14/ sec/sup -1/, respectiveiy, to 3 kcal/mole and 10/sup 11/ sec/sup -1/at 2.85 H/La. The proton static linewidths vary continuousiy from 7.8 g at 2 H/La to 12.4 g at 2.85 H/La and the proton T/sub 1/ has a characteristic self- diffusion induced minimum of approximately 5 to 8 msec and a maximum of approximately 100 msec where spin diffusion to paramagnetic impurities dominates. The self-diffusing protons have a pronounced effect, via a quadrupole interaction, on the La resonances. For hydrogen concentrations slightlymore » greater than 2 H/La, a broadening and then narrowing again of the La linewidth, and a decrease with a subsequent recovery of the La Knight shift is observed as the proton self-diffusion rate increases with temperature. For concentrations greater than 2.4 H/ La, no La resonance is observed until a sufficiently high proton self-diffusion rate is attained to average out the quadrupolar effects. A detailed semiquantitative analysis incorporating the proton resonance data is made of these quadrupolar effects. At 400 deg C the La Knight shift is found to decrease from 0.23% for 2 H/La to 0.10% for 2.85 H/La while no Knight shift is observed for the proton resonance at any concentration or temperature. The thermal relaxation time of the La resonance in LaH/sub 2.0/ is found to be the result of a conduction electron hyperfine interaction with T/sub 1/T = 11.3 sec deg K when the protons are static. With proton motion the La T/sub 1/ decreases exponentially to a value somewhat greater than the La T/sub 2/ or about 100 mu sec at 400 deg C. A schematic picture of the band structure of the hydride consistent with the available data is suggested, based on an ionized hydrogen atom or proton, whose electron goes into a conduction band localized on the La ion. (auth)« less

States of Solid Methane as Inferred from Nuclear Magnetic Resonance

As there are different points of view concerning the molecular dynamical states in solid methane, especially concerning the $\ensuremath{\lambda}$-transition at 20.42\ifmmode^\circ\else\textdegree\fi{}K, we have investigated the manner in which the new method of nuclear magnetic resonance throws light on the problem. Both the one-parameter theory and the method of perturbation were applied to the analysis of the proton resonance data given by Thomas, Alpert, and Torrey.The characteristic time ${\ensuremath{\tau}}_{c}$ for molecular reorientation was estimated from the spin-lattice relaxation data, and it was found that above 20\ifmmode^\circ\else\textdegree\fi{}K molecules may be considered to reorient against some fixed hindrances due to neighboring molecules. At about 65\ifmmode^\circ\else\textdegree\fi{}K a marked alteration is present in the dominant mechanism of the above reorientation, which is considered to be either correlated or independent molecular rotation. However, below 20\ifmmode^\circ\else\textdegree\fi{}K most of the molecules seem to be in the ground state of rotational oscillation and occasionally (about ${10}^{7}$ times per second) tunnel or flip to neighboring equivalent orientations. It was proposed that we should discriminate between two pictures of the local magnetic field, possibly in relation to the frequency of resonance. This idea was confirmed by reproducing the line width data.A perturbation calculation, assuming the $F\overline{4}3m$ arrangement of the molecules and taking account of the above situation, gave the entire shape of the absorption line, which was in close agreement with experimental data observed in the lowest temperature range.