Proton states in143Pm and145Pm populated in the (3He,d) reaction

The (³He,d) reaction on targets of¹⁴²Nd,¹⁴⁴Nd and on a target of natural Nd have been studied, using a beam of 24 MeV³He from the McMaster University Tandem Van de Graaff accelerator. The reaction products were analyzed with an Enge type magnetic spectrograph and recorded on photographic emulsions. Information on thel-values was obtained from the (³He,d) angular distribution. In the¹⁴³Pm nucleus no fragmentation of the shell model strength was found while in the¹⁴⁵Pm nucleus the fragmentation of thed _3/2 ands _1/2 states was significant, giving a total of 11l=2 and 51=0 transitions. The results are analyzed in terms of the spherical shell model and the agreement with pairing theory is excellent in both cases. A survey of the stripping strength to promethium isotopes with mass numbers ranging fromA=143 toA=151 is presented, using normalizations based on the results from the experiments on the target of natural neodymium.     

Proton states in theN = 86 nuclei147Pm and149Eu populated in the (3He,d), (α,t) and (t, α) reactions

The (³He,d) and (α, t) reactions on targets of¹⁴⁶Nd and¹⁴⁸Sm have been studied, using beams of 24 MeV³He and 27 MeV⁴He from the McMaster University tandem van de Graaff accelerator. Also the (t, α) reaction on a target of¹⁴⁸Sm has been studied, using 17 MeV tritons from the Los Alamos Scientific Laboratory tandem accelerator. The reaction products were analyzed with magnetic spectrographs. Information on thel-values was obtained from (³He,d) angular distributions and from ratios of (α,t) and (³He,d) cross sections. In each nucleus a severe fragmentation of the shell-model strength is found. In particular a total of 13(7)l=2 transitions and 6(6)l=0 transitions have been identified in¹⁴⁷Pm(¹⁴⁹Eu). The results are analyzed in terms of the spherical shell model, which accounts fairly well for the summed spectroscopic strengths. However, with the existence of the (t, α) data a more detailed investigation of the emptiness of individual levels observed in¹⁴⁷Pm gives some indication that a deformed scheme might be more successful in describing these nuclei.     

The formation of hypernuclei by K− capture

K^? capture leading to the formation of hypernuclei takes place with the kaon either in a Bohr orbit (capture at rest), or in flight. We analyze both situations in the framework of the distorted-wave impulse approximation (DWIA), derive cross sections and formation rates, and compare the results with experimental data on the reaction ¹²C(K^?, π^?)¹²_ΛC¹. Corrections to the DWIA which arise from rescattering, from binding energy effects and from the intermediate formation of a ∑-hyperon, are estimated and found not to be negligible.     

A search for K−p → Λγ and K−p → Σ0γ at rest

A search has been made for photons from the reactions K^?p → Λγ and K^?p → Σ⁰γ produced by K^? stopping in a liquid hydrogen target. No signal from these reactions was found; upper limits on the branching ratios are K^?p → Λγ/K^?p → anything ? 4 × 10^?4, K^?p → Σ⁰γ/K^?p → anything ? 4 × 10^?3. The first of these is in conflict with a theoretical prediction using recent values for coupling constants and scattering amplitudes. This may reflect the influence of the Λ(1405) on the radiative capture.     

Spinless bosons in electron-positron annihilation

The contributions to the processes \(e^ + e^ - \to \mu ^ + \mu ^ - ,q\bar q,\gamma \gamma ,e^ + e^ - \) , mediated by scalar and/or pseudoscalar bosons are calculated. The constraints on their coupling constants and their masses are investigated as they arise from the radiative decayZ ⁰→⁺ e ^? γ and from the experimental data for the annihilation processes into lepton, photon and quark pairs. Data one ⁺ e ^?→μ⁺ μ^?, γγ ande ⁺ e ^? seriously reduce the domain of coupling constants to leptons and photons still allowed by the probable value of the width ofZ ⁰→e ⁺ e ^? γ. Experimentse ⁺ e ^?→μ⁺ μ^?, γγ,e ⁺ e ^? at 45 GeV c.m.s. energy with a sensitivity of 10% will decide about the existence of a heavy spinless boson with the presumed phenomenological couplings to leptons and photons. Assuming universality of the coupling to leptons and quarks a conservative bound on the contribution toR arising from spinless boson exchange is already in conflict with the presumed radiative width ofZ ⁰→e ⁺ e ^? γ.     

Far-infrared laser oscillation in p-Ge

Time-resolved measurements, together with spectroscopic study with a grating monochromator, are made on far-infrared stimulated emission from p-Ge in crossed electric and magnetic fields. Gain saturation is confirmed, for the first time, to occur to establish laser oscillation. Small-signal gain per unit length deduced from the time constant of light amplification is 7.4 × 10^-3 cm^-1 and 2.7 × 10^-2 cm^-2, respectively, for samples with N_A − N_D ≅ 4.5 × 10¹³cm⁻³ and 1.7 × 10¹⁴ cm^-3. Output power detected at distance 28 cm from the sample is of order 1–10 W, but higher power over 100W is suggested for the total output from the sample.     

Gamma deexcitation of the 180m Ta isomer

Vibrational states built on the K ^π = 9^? isomer and on the ground state (K ^π = 1⁺) in ¹⁸⁰Ta are calculated within the quasiparticle-phonon nuclear model using the ¹⁷⁸Hf nucleus as a core. A procedure for calculating the rates of K-allowed γ-ray transitions from vibrational states built on the isomer to those built on the ground state is presented. The probabilities of two-step processes consisting of a dipole excitation of the isomer and successive E1 and E2 transitions from them to vibrational states built on the ground state of the ¹⁸⁰Ta nucleus are calculated. Two-step transitions from the isomer to vibrational states below 2.7 MeV and to the vibrational states built on the ground state appear to be very weak. There are many E1 transitions from the vibrational states built on the isomer to the vibrational states built on the ground state. They are weak and cannot be responsible for the strong deexcitation of ^180m Ta in the relevant (γ, γ′) reaction. A decisive role is played by collective E2 transitions from dipole excitations in several excitation energy intervals ranging between 2.7 and 4.0 MeV. These highly intense K-allowed two-step γ-ray transitions can be responsible for the strong deexcitation of the ^180m Ta state in the (γ, γ′) reactions.     

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.     

Search for the e + e − → K ± K S π ∓ process on the VEPP-2M e + e − collider

We report on the results of the search for the e ⁺ e ^? → K ^± K _S π ^? process. Data with an integrated luminosity of 1.36 pb^?1 collected in experiment with a spherical neutral detector (SND) on the VEPP-2M e ⁺ e ^? collider in the energy range from 1.36 to 1.38 GeV have been analyzed. The upper limits of the σ < 150 pb cross sections of the sought process have been established for an energy of 1.37 GeV at a confidence level of 90%.     

Search for e + e − → f 0(600)γ, f 0(980)γ, f 0(1350)γ, and f 2(1270)γ processes in the energy range from 1.05 to 1.38 GeV

In the energy range from 1.05 to 1.38 GeV, the upper limits for the cross sections of e ⁺ e ^? → f ₀(600)γ, f ₀(980)γ, f ₀(1350)γ, and f ₂(1270)γ → π⁰π⁰γ processes have been established. Measurements are performed in accordance with the statistics gathered in experiment with a spherical neutral detector (SND) on the VEPP-2M e ⁺ e ^? collider. The resultant upper limits vary from 6 to 42 pb depending on the energy and the model.     

Monolayer K-films on Ni(100) — II. Electronic excitations

Electronic excitations in a K layer adsorbed on Ni(100) have been observed by means of electron energy loss spectroscopy. The observed excitation energy depends on the density of K atoms in the layer. In the low density range the loss energy decreases from 3.5 to 1.5 eV as the density increases from 6.10¹³ to 3.10¹⁴ K atoms per cm². This loss is interpreted to be due to an excitation from below the Fermi level to the shifted K valence level Increasing the density further from 3.10¹⁴ to 6.10¹⁴ K atoms per cm² yields a loss peak that increases in energy from 1.5 to 2.3 eV. This loss peak merges into the surface-bulk plasmon complex for a thick K film and the energy vs density dependence is compatible with a plasmon excitation in the K layer.     

Single-pion production in antineutrino-induced neutral-current interactions

Results are presented on antineutrino-induced processes in which a single π⁰or π^? is produced. The raw data come from analysis of film from Gargamelle filled with a propane-freon mixture. Comparison of the neutral-current production rates for π⁰and π^?, after correction for nuclear effects, indicates that pure isoscalar or pure isovector transitions are not favoured. The ratio of the neutral-to-charged-current single-π⁰ production rates is found to be compatible with the static model for Δ³³ resonance production in the framework of the Weinberg-Salam theory, yielding values for sin²θ_W in the range 0.15–0.52.     

Nuclear field theory predictions for 11Li and 12Be: Shedding light on the origin of pairing in nuclei

Recent data resulting from studies of two-nucleon transfer reaction on ¹¹Li, analyzed through a unified nuclear-structure-direct-reaction theory have provided strong direct as well as indirect confirmation, through the population of the first excited state of ⁹Li and of the observation of a strongly quenched ground state transition, of the prediction that phonon-mediated pairing interaction is the main mechanism binding the neutron halo of the 8.5-ms-lived ¹¹Li nucleus. In other words, the ground state of ¹¹Li can be viewed as a neutron Cooper pair bound to the ⁹Li core, mainly through the exchange of collective vibration of the core and of the pigmy resonance arizing from the sloshing back and forth of the neutron halo against the protons of the core, the mean field leading to unbound two-particle states, a situation essentially not altered by the bare nucleon-nucleon interaction acting between the halo neutrons. Two-neutron pick-up data, together with (t, p) data on ⁷Li, suggest the existence of a pairing vibrational band based on ⁹Li, whose members can be excited with the help of inverse kinematic experiments as was done in the case of ¹¹Li(p, t)⁹Li reaction. The deviation from harmonicity can provide insight into the workings of medium polarization effects on Cooper-pair nuclear pairing, let alone specific information concering the “rigidity” of the N = 6 shell closure. Further information concerning these questions is provided by the predicted absolute differential cross sections σ _abs associated with the reactions ¹²Be(p, t)¹⁰Be(g.s.) and ¹²Be(p, t)¹⁰Be(pv) (≈¹⁰Be(p, t)⁸Be(g.s.)). In particular, concerning this last reaction, predictions of σ _abs can change by an order of magnitude depending on whether the halo properties associated with the d _5/2 orbital are treated selfconsistently in calculating the ground state correlations of the (pair removal) mode, or not.     

The thermodynamics of solid solutions of argon and methane

The primary concern of this paper is with the estimation of the excess Gibbs energy G^E,S for solid solutions of two molecularly simple components which are completely miscible in the solid state. The method depends on combining information on the excess thermodynamic functions of liquid mixtures of the two components with a knowledge of the liquidus and solidus lines on the temperature-composition phase diagram. It is applied to the particular case of argon-methane. For this system, unit cell sizes and some heat of fusion measurements are also available, from which V^E,S and H^E,S have been calculated.A solid solution of argon and methane departs much more from ideality than does a liquid mixture of the same composition at the same temperature, the ratio r, = G^E,S/G^E,L, being about 3. Moreover, the concentration dependence of G^E,S is less symmetrical than that of G^E,L, and the ratio r increases markedly with increasing argon mole fraction. A dilute solution of methane (which has the larger molecules) in argon has a larger G^E,S than the corresponding dilute solution of argon in methane.For a solid solution at 71 K with an argon mole fraction of 0.60, H^E,S is ≈4801 Jmol^?1. This gives TS^E,S ≈ 220 J mol^?1, which is about the same as G^E,S. The solid solutions cannot therefore be regarded as even approximating to regular solutions.From the calculated G^E,S results, it is predicted that the face-centred cubic solid solutions of argon and methane should separate into two phases on cooling. The calculated coordinates of the upper critical solution point are T = 67 K and an argon mole fraction of 0.63, in reasonable agreement with the experimental values of 63 K and 0.65 respectively.     

Decay of heavy and superheavy nuclei

We present here, an overview and progress of the theoretical works on the isomeric state α decay, α decay fine structure of even–even, even–odd, odd–even and odd–odd nuclei, a study on the feasibility of observing α decay chains from the isotopes of the superheavy nuclei Z = 115 in the range 271 ≤A ≤ 294 and the isotopes of Z = 117 in the range 270 ≤A ≤ 301, within the Coulomb and proximity potential model for deformed nuclei (CPPMDN). The computed half-lives of the favoured and unfavoured α decay of nuclei in the range 67 ≤Z ≤ 91 from both the ground state and isomeric state, are in good agreement with the experimental data and the standard deviation of half-life is found to be 0.44. From the α fine structure studies done on various ranges of nuclei, it is evident that, for nearly all the transitions, the theoretical values show good match with the experimental values. This reveals that CPPMDN is successful in explaining the fine structure of even–even, even–odd, odd–even and odd–odd nuclei. Our studies on the α decay of the superheavy nuclei ^271?294115 and ^270?301117 predict 4 α chains consistently from ^284,285,286115 nuclei and 5α chains and 3α chains consistently from ^288?291117 and ²⁹²117, respectively. We thus hope that these studies on ^284?286115 and ^288?292117 will be a guide to future experiments.     

Tuning fractional PID controllers for a Steward platform based on frequency domain and artificial intelligence methods

In this paper, two methods to tune a fractional-order PI ^λ D ^μ controller for a mechatronic system are presented. The first method is based on a genetic algorithm to obtain the parameter values for the fractionalorder PI ^λ D ^μ controller by global optimization. The second method used to design the fractional-order PI ^λ D ^μ controller relies on an auto-tuning approach by meeting some specifications in the frequency domain. The real-time experiments are conducted using a Steward platform which consists of a table tilted by six servo-motors with a ball on the top of the table. The considered system is a 6 degrees of freedom (d.o.f.) motion platform. The feedback on the position of the ball is obtained from images acquired by a visual sensor mounted above the platform. The fractional-order controllers were implemented and the performances of the steward platform are analyzed.     

Photoproduction of charged pions on deuterium in the first resonance region

Photoproduction of π⁺ and π^? on deuterium has been measured in the photon energy range from 240 to 400 MeV and for pion c.m. angles between 15° and 180°. The pions were analysed in angle and momentum by a magnetic spectrometer. From the measured π^?/π⁺ ratio, corrected for Coulomb interactions in the final state, differential cross sections of the reaction γ+n→π^?+p were calculated. Together with the π⁺ photoproduction our data show no isotensor contribution. Comparison of our data with the recent experiments done on the inverse reaction shows no evidence of a violation of time reversal invariance. With the measured π⁺ photoproduction on deuterium, a test of the spectator model has been made. Using the closure-approximation of Chew and Lewis our data agree within a range of ±10%.     

Spontaneous compactifications by Wetterich mechanism

We search for a ground state of Kaluza-Klein type in pure higher dimensional gravity, which differs from ?⁴ ×S ^m given by Wetterich. The situation depends on space-time dimensions. In the odddimensional case, we have a ground state ?⁴ ×S _g ^m with almost contact structure. On the other hand, in the even-dimensional case, we obtain ?⁴ × ?P _n with almost complex structure.     

Hadronic scaling and ratios of cosmic-ray components in the atmosphere

Using the scaling hypothesis of hadronic inclusive reactions at high energy and data from accelerators we compute ratios of cosmic-ray components in the atmosphere. For the μ⁺/μ^? ratio at sea level we find that the inclusion on nuclear effects results in a better agreement with experimental data. In the case of the (π⁺ + π^?)/p ratio, we predict a value at high energy that is considerably larger than the one usually inferred from lower energy data.     

Elastic and transition form factors of light pseudoscalar mesons from QCD sum rules

We revisit F _π(Q ²) and F _Pγ(Q ²), P = π, η, η′, making use of the local-duality (LD) version of QCD sum rules. We give arguments that the LD sum rule provides reliable predictions for these form factors at Q ² ≥ 5–6 GeV², the accuracy of the method increasing with Q ² in this region. For the pion elastic form factor, the well-measured data at small Q ² give a hint that the LD limit may be reached already at relatively low values of momentum transfers, Q ² ≈ 4–8 GeV²; we therefore conclude that large deviations from LD in the region Q ² = 20–50 GeV² seem very unlikely. The data on the (η, η′) → γγ* form factors meet the expectations from the LD model. However, the BaBar results for the π ⁰ → γγ* form factor imply a violation of LD growing with Q ² even at Q ² ≈ 40 GeV², at odds with the η, η′ case and with the general properties expected for the LD sum rule.