The muon depolarization rate in β-palladium hydride

A depolarization rate σ = 0.1205 ± 0.0050 μsec^?1, due to the proton nuclear dipolar fields, was observed for polarized muons implanted in Pd-H_0.97 in the β phase, at temperatures below 50 K, independent of temperature and applied field. The results indicate that the muon substitutes for one of the protons, and that nearest-neighbor protons are at octahedral lattice sites. On comparing our results with recent NMR data, it appears that the mean muon-proton nearest neighbor distance is significantly larger than that between protons alone. Also, a search for muon local moment magnetism gave a null result.     

Experimental investigations of fast-proton production in a picosecond laser plasma

Results of experimental investigations of fast-proton production in a laser plasma are presented for the case where the intensity of laser radiation at the targets is 2 × 10¹⁸ W/cm². Three processes of fast-proton acceleration in laser plasma are investigated: (1) the acceleration of protons from the front surface toward the laser pulse, (ii) the acceleration of protons from the front surface of the target toward its interior, and (iii) the acceleration of protons from the rear foil surface in the outward direction. The activation procedure and CR-39 tracker detectors featuring a set of various-thickness aluminum filters were used to record fast protons. It turned out that the proton-acceleration process is the most efficient in the case of proton acceleration from the rear foil surface in the outward direction. Experimental results revealed that about N _p = 10⁷ protons of energy in the region E _p > 1.9 MeV that are accelerated from the target surface toward a laser ray, N _p = 4× 10⁷ protons of energy in the region E _p > 1.9 MeV that are accelerated fromthe front surface of the target toward its interior, and N _p = 4×10⁸ protons of energy in the region E _p > 1.9 MeV that are accelerated from the rear foil surface in the outward direction are generated at a laser-radiation intensity of 2 × 10¹⁸ W/cm² at the surface of aluminum, copper, and titanium targets. Experimental investigations aimed at optimizing the process of proton acceleration from the rear surface of aluminum foils were performed by varying the foil thickness over the range between 1 and 100 μm. The results of these experiments showed that there is an optimum foil thickness of 10 μm, in which case protons of maximum energy 5 MeV are generated.     

Production of Tb from gold by 0.2 to 0.5 GeV protons

The production of ¹⁴⁹Tb from gold by 200–450 MeV protons has been observed with cross sections (α-branch only) as follows: 0.0028 ± 0.0011 μb at 218 ± 14 MeV, 0.23 ± 0.09 μb at 384 ± 21 MeV, and 0.84 ± 0.34 μb at 434 ± 24 MeV.     

Direct and beta-delayed proton decay of very neutron-deficient rare-earth isotopes produced in the reaction58Ni+92Mo

Using on-line mass separation of evaporation residues from the reaction⁵⁸Ni +⁹²Mo→¹⁵⁰Yb*, a proton line of 1,055±6 keV energy and 0.42±0.10 s half-life was observed at mass number 147. The origin of this activity is very likely the direct proton decay of¹⁴⁷Tm. Beta-delayed protons registered at the same mass position show a pronounced peak structure in their energy distribution. A lower limit of their half-life was set to 1 s.     

Two-proton radioactivity search

Two-proton radioactivity, a spontaneous breakup of elements with emission of two protons, was predicted to exist near the proton drip line by V.I. Goldansky long time ago. The recent theoretical and experimental progress in a search for such an exotic nuclear decay is reviewed. In theory, the new three-body model which treats two-proton radioactivity as a genuine three-particle nuclear decay is considered. In experiment, the first evidence for two-proton decay of ⁴⁵Fe is described. Four atoms of ⁴⁵Fe, produced at the fragment separator of GSI, decayed via particle emission with a total energy of 1.1(1) MeV and a half-life of 3.2 _?1.0 ^+2.6 ms. A possible experiment for a direct observation of two-proton emission from the ground state of ¹⁹Mg is considered for its decay in-flight. The half-life of ¹⁹Mg, as well as proton-proton correlations, might be derived from the distribution of the ¹⁹Mg decay vertices extrapolated from the measured trajectories of all fragments.     

First experimental evidence of D(p, γ)3He reaction in titanium deuteride in ultralow collision energy region

The article is devoted to the investigation of a pd-reaction (p + d → ³He + γ(5.5 MeV)) under-going in titanium deuteride in astrophysical collision energy region of protons and deuterons ranging from 5.3 to 10.5 keV. The experiments have been performed using the Hall NR TPU (Tomsk, Russia) pulsed plasma accelerator. The number of accelerated protons in 10 μs pulse was 5 × 10¹⁴ at a repetition rate of 7 × 10^?2 Hz. Detection of 5.5 MeV gamma rays was carried out using eight detectors based on crystals of NaI(Tl) (100 × 100 × 400 mm) placed around the TiD target. For the first time, the dependencies between the astrophysical S-factor and the effective cross section of the pd-reaction from proton-deuteron collision energy, and the potential electronic screening of the interacting protons and deuterons in titanium deuteride have been measured.     

Do right-handed neutrinos exist?

The weak interaction of the four components of the muon is discussed. Using a high-energy pion beam as a source of polarized muons, the components μ^?_R or μ⁺_L can be selected and used in a sensative search for massive right-handed neutrinos. This search may be extended to higher mass by the use of colliding beams of protons and polarized electrons.     

A method for evaluating correlation times for tumbling and internal motion in macromolecules using cross-relaxation rate constants from proton NMR spectra

A method of estimating the correlation times and extent of internal motion of macromolecules using ¹H NMR is proposed. The method relies on measuring the cross-relaxation rate constant between resolved, identified protons separated by a fixed distance, for example 2, 3 protons of tyrosine residues or 4, 5 protons of tryptophan residues in proteins, and the 5, 6 protons of cytosine residues in DNA. For a rigid body, the cross-relaxation rate constant yields directly an estimate of the tumbling time. Deviation of its dependence on viscosity and temperature from expectations for a rigid body allows one to estimate the degree to which internal motions contribute to the relaxation. The method is illustrated for Ribonuclease A and a 20 base pair fragment of DNA corresponding to the trp operator of Escherichia coli. The calculated correlation time of RNAse A is about 8 ns at 298 K, in good agreement with expectations from hydrodynamic measurements. Tyrosine 25 has significant internal motion, characterized by an apparent amplitude of 50–60°, a correlation time of about 5 ns, and low activation energy. The correlation time of the fragment of DNA is about 6.4 ns at 298 K, in agreement with expectations for a rigid rod. The apparent activation energy was 3.8 kcal/mol, close to the value for the dependence of the viscosity of D₂O on temperature. Further, the same result was obtained regardless of the position of the base in the sequence, indicating that bending motions are of small amplitude on the nanosecond time scale for short fragments of DNA.     

Nuclear reactions of medium and heavy target nuclei with high-energy projectiles

Nuclear reactions induced by 3·65 A GeV¹²C-ions and 3·65 GeV protons on target elements⁵⁵Mn,⁵⁹Co,^nat Ni and^natCu were investigated by using the foil stack activation technique and Ge(Li) gamma-ray spectroscopy. Charge dispersions and mass-yield distributions of radioactive residues were obtained from the parametrization of measured spallation cross sections. Discussion of results from this and other radiochemical reactions of high-energy protons and¹²C-ions with complex nuclei is presented in terms of the concepts of limiting fragmentation and factorization.     

124Sn target residues in the interaction of heavy ions at intermediate energies

Cross sections, recoil energy distributions for residues produced by¹⁴N,²⁰Ne,⁴⁰Ar on¹²⁴Sn targets have been measured in the 10–70 MeV/u intermediate energy range. As the projectile energy increases, processes as complete fusion-evaporation, incomplete fusion-evaporation and intranuclear cascade-evaporation participate progressively in the nuclear collisions. Peculiar residues corresponding to a gain of 4, 5 or even 6 protons for the¹²⁴Sn target have been observed in the 30–50 MeV energy range.     

Experimental observation of electron screening for the D(p, γ)3He nuclear reaction in titanium Deuteride TiD

Characteristics of the pd reaction (p + d → ³He + γ(5.5 MeV)) in titanium deuteride at astrophysical proton-deuteron collision energies ranging from 5.3 to 10.5 keV are investigated. Experiments are conducted on the pulsed plasma Hall accelerator at Tomsk Polytechnic University (Tomsk, Russia). The number of accelerated protons in a pulse 10 μs long is 5 × 10¹⁴ at a repetition rate of 7 × 10^?2 Hz. Gamma rays with an energy of 5.5 MeV are recorded by eight detectors based on NaI(Tl) crystals (100 × 100 × 400 mm) arranged around the TiD target. The dependence of the astrophysical S factor for the pd reaction on the proton-deuteron collision energy and the electron screening potential of protons interacting with deuterons in titanium deuteride are measured for the first time.     

Two-proton radioactivity of 45Fe

The decay of the extremely neutron-deficient isotope ⁴⁵Fe has been studied by using a new type of gaseous detector in which a technique of optical imaging is used to record tracks of charged particles. The two-proton radioactivity and the $ \beta$ -decay channels were clearly identified. For the first time, the angular and energy correlations between two protons emitted from the ⁴⁵Fe ground state were measured. The obtained results were confronted with predictions of a three-body model.     

Coincidence measurements of light particles and evaporation residues in the 16O+27Al fusion reaction

Energy and angular distributions of protons and α-particles in coincidence with fusion residues produced in the reaction of 150 MeV ¹⁶O with ²⁷Al were measured. Experimental results are reproduced by a statistical model calculation except a forward component of α-particle yield. About 20% of the total α-particle yield is considered to originate from incomplete fusion process.     

Structure of the product of intracomplex alkylation of target octanucleotide pd[TGTTTGGC] by means of 4-[N-methyl-N-(2-chloro-ethyl)-amino]benzyl-5′-phosphamido derivative of heptanucleotide pd[CCAAACA]: Two-dimensional1H-NMR spectroscopy and restrained molecular mechanics refinement

The spatial structure of a covalent adduct — the product of intracomplex alkylation at N-3-position of dC-8 nucleoside residue of target octanucleotide pd[TGTTTGGC] by means of 4-[N-methyl-N-(2-chloroethyl)amino]benzyl-5′-phosphamido derivative of heptanucleotide pd[CCAAACA] — has been investigated in aqueous solution by two-dimensional (2D)¹H-NMR spectroscopy and restrained molecular mechanics calculations. By using COSY, COSY-DQF and NOESY experiments the assignment of oligonucleotide protons as well as protons of modifying group was carried out. The correlation times of benzylamide fragment protons and those of neighbouring nucleotide residues dC-1 and dC-8 were shown to be equal and shorter thanτ _c of intraduplex nucleotides. The analysis of proton-proton coupling constants for H1′, H2′a, H2′b and H3′ protons showed all sugar residues to be in 2′-endo conformation. The distances between protons closed in the space were determined by means of a set of one-dimensional (1D) NOE experiments. The experimental distances were used as the constraints for energy minimization by molecular mechanics calculations. Eight conformations of benzylamide fragment of the covalent adduct differed with orientations of 4-N-methyl residue of the alkylating group and 1-methyleneamide linker function were constructed as starting structures in energy minimization procedure. Among of the resulting optimized structures only one S(Alk)8^* was found to satisfy both experimental data and energetic criteria. The benzylamide fragment in conformation S(Alk)8^* has been shown to localize in the region of lacked nucleoside residue of the duplex at the end of heptanucleotide chain less than 5 Å apart from the residues dC-1 and alkylated dC-8.     

Measurement of Relaxation Rates of N and H Backbone Protons in Proteins with Tailored Initial Conditions

Several methods are presented for the selective determination of spin–lattice and spin–spin relaxation rates of backbone protons in labeled proteins. The relaxation rates of amide protons in ¹⁵N labeled proteins can be measured by using two-way selective cross-polarization (SCP). The measurement of H^α relaxation rates can be achieved by combining this method with homonuclear Hartmann–Hahn transfer using doubly selective irradiation. Various schemes for selective or nonselective inversion of the longitudinal proton magnetization lead to different initial recovery rates. The methods have been applied to lysine K6 in ¹⁵N-labeled human ubiquitin and to leucine L5 in ¹⁵N- and ¹³C-labeled octapeptide YG*G*F*LRRI (GFL) in which the marked residues are ¹⁵N- and ¹³C-labeled.     

Decay of the compound nucleus179Au formed in the cold fusion reaction90Zr+89Y

For the compound nucleus¹⁷⁹Au formed at an excitation energy of 26 MeV in the fusion reaction⁹⁰Zr+⁸⁹Y, the energy spectra of promptly emitted protons,α particles andγ rays were measured in concidence with the evaporation residues. On the basis of the measured total decay energy, the 1p and 1α decay channels were separated from all other evaporation-residue channels. The energy spectra and absolute cross sections, together with previously measured excitation functions for various decay channels, are successfully described by statisticalmodel calculations with the Monte Carlo code CODEX.     

Selective Correlation of Amide Groups to Glycine Alpha Protons and of Arginine Guanidine Groups to Delta Protons in Proteins by Multiple Quantum Spectroscopy

A new 3D pulse sequence correlates backbone amide proton and nitrogen with alpha proton resonances selectively for glycine residues in a fully doubly labeled (¹⁵N,¹³C) protein. The excitation of multiple quantum coherences provides optimized resolution and sensitivity. Degenerate alpha proton groups can be promptly recognized. Correlation of guanidine NH groups to delta protons of arginine side chains is also obtained.     

Dirac-neutrino magnetic moment and the dynamics of a supernova explosion

The double conversion of neutrino chirality ν_L → ν_R → ν_L has been analyzed for supernova conditions, where the first stage is due to the interaction of the neutrino magnetic moment with plasma electrons and protons in the supernova core, and the second stage, due to the resonance spin flip of the neutrino in the magnetic field of the supernova envelope. It is shown that, in the presence of the neutrino magnetic moment in the range 10^?13 μ_B < μ_ν < 10^?12 μ_B and a magnetic field of ～10¹³ G between the neutrinosphere and the shock-stagnation region, an additional energy of about 10⁵¹ erg, which is sufficient for a supernova explosion, can be injected into this region during a typical shock-stagnation time.     

Polarization in the quasielastic scattering of 1-GeV/c protons on light nuclei

Polarization measurements in the A(p, 2p)B reactions on ⁶Li, ⁷Li, and ²⁸Si nuclei at a proton-beam energy of 1 GeV were performed in a kinematically complete experiment. By using a two-arm magnetic spectrometer, two secondary protons were recorded in coincidence at asymmetric scattering angles of θ₁=15°?26° and θ₂=58.6° for residual-nucleus momenta in the range K _B=0–150 MeV/c. Either arm of the spectrometer was equipped with polarimeters based on proportional chambers. The data coming from this experiment are analyzed within the distorted-wave impulse approximation. It is shown that the polarization of recoil protons formed at angle θ₂ in the interaction featuring a proton from the P shell of the ⁷Li nucleus can be described under the assumption of an effective intranuclear-proton polarization by using the single-particle shell-model wave function of the nucleus. Our data on the polarizations of the two protons from the reaction (p, 2p) on a ²⁸Si nucleus also suggest the effective polarization of the protons in the D shell of the ²⁸Si nucleus. It is found that, for high recoil-nucleus momenta of K _B≥90 MeV/c, the effective polarization of the protons in the P shell of the ⁶Li nucleus—this polarization was discovered in studying the polarization of recoil protons in the reaction ⁶Li(p, 2p)⁵He—cannot be described within the shell model assuming LS coupling. As might have been expected, the polarization of recoil protons knocked out from the S shells of the ⁶Li and ⁷Li nuclei comply well with the predictions obtained in the impulse approximation with allowance for the depolarization effect alone.     

Energetic ion generation by Coulomb explosion in cluster gas and a low-density plastic foam with an intense femtosecond laser

The energy distributions of protons emitted from the Coulomb explosion of hydrogen clusters by an intense femtosecond laser have been experimentally obtained. Ten thousand hydrogen clusters were exploded, emitting 8.1-keV protons under laser irradiation of intensity 6 × 10¹⁶W/cm². The energy distributions are interpreted well by a spherical uniform cluster analytical model. The maximum energy of the emitted protons can be characterized by cluster size and laser intensity. The laser intensity scale for the maximum proton energy, given by a spherical cluster Coulomb explosion model, is in fairly good agreement with the experimental results obtained at a laser intensity of 10¹⁶–10¹⁷ W/cm² and also when extrapolated with the results of three-dimensional particle simulations at 10²⁰–10²¹ W/cm². Energetic proton generation in low-density plastic (C₅H₁₀) foam by intense femtosecond laser pulse irradiation has been studied experimentally and numerically. Plastic foam was successfully produced by a sol-gel method, achieving an average density of 10 mg/cm³. The foam target was irradiated by 100-fs pulses of a laser with intensity 1 × 10¹⁸ W/cm². A plateau structure extending up to 200 keV was observed in the energy distribution of protons generated from the foam target, with the plateau shape explained well by Coulomb explosion of lamella in the foam. The laser-foam interaction and ion generation were studied qualitatively by two-dimensional particle-in-cell simulations, which indicated that energetic protons are mainly generated by the Coulomb explosion. From the results, the efficiency of energetic ion generation in a low-density foam target by Coulomb explosion is expected to be higher than in a gas-cluster target.