The size of the proton

The root-mean-square (rms) charge radius r _p of the proton has so far been known only with a surprisingly low precision of about 1% from both electron scattering and precision spectroscopy of hydrogen. We have recently determined r _p by means of laser spectroscopy of the Lamb shift in the exotic “muonic hydrogen” atom. Here, the muon, which is the 200 times heavier cousin of the electron, orbits the proton with a 200 times smaller Bohr radius. This enhances the sensitivity to the proton’s finite size tremendously. Our new value r _p?=?0.84184 (67) fm is ten times more precise than the generally accepted CODATA-value, but it differs by 5 standard deviations from it. A lively discussion about possible solutions to the “proton size puzzle” has started. Our measurement, together with precise measurements of the 1S–2S transition in regular hydrogen and deuterium, also yields improved values of the Rydberg constant, R _?∞??=?10,973,731.568160 (16) m^???1.     

Electron scattering studies of magnetic isovector transitions in 12C at high momentum transfer

The inelastic electron scattering cross sections for the M1 transition to the 15.11 MeV (1⁺, T = 1) level and for the M2 transition to the 16.58 MeV (2^?, T = 1) level in ¹²C have been measured in the momentum transfer region q = 0.4–3.0 fm^?1, with emphasis on precise data at high momentum transfers. Additionally, a broad state near 15.4 MeV excitation has been observed and its excitation energy and natural width have been established as 15.44 ± 0.04 MeV and 1.5 ± 0.2 MeV, respectively. The Fourier-Bessel technique for determining the Mλ transition current density has been applied to the M1 and M2 transitions. Particular attention has been paid to the Coulomb corrections required to deduce the PWBA form factors. The M1 radiative width is Γ_γ0 = 38.5 ± 0.8 eV.     

Comparison between bremsstrahlung cross section measurements at the short wavelenght limit and theoretical results

Recent precise measurements of the electron bremsstrahlung cross section d²σ/dk dΩ_k at the short wavelength limit for an incident electron energy of 1.84 MeV important discrepancies between experimental results and earlier theoretical calculations. A new exact theoretical result, for a point Coulomb potential is presented: descrepancies with experimental results remain.     

Q values of the Ge and Mo double-beta decays

Penning trap measurements using mixed beams of ⁷⁶Ge–⁷⁶Se and ¹⁰⁰Mo–¹⁰⁰Ru have been utilized to determine the double-beta decay Q-values of ⁷⁶Ge and ¹⁰⁰Mo with uncertainties less than 200 eV. The value for ⁷⁶Ge, 2039.04(16) keV is in agreement with the published SMILETRAP value, 2039.006(50) keV. The new value for ¹⁰⁰Mo, 3034.40(17) keV is 30 times more precise than the previous literature value, sufficient for the ongoing neutrinoless double-beta decay searches in ¹⁰⁰Mo. Moreover, the precise Q-value is used to calculate the phase-space integrals and the experimental nuclear matrix element of double-beta decay.     

On the octupole excitation in236U

Measurements of theK,L _I,L _II andM _I conversion lines of the 687.7 keV transition in²³⁶U are evaluated within the electron penetration formalism. The spin-parity assignment of the octupole bandhead is found to be 1^? in accordance with reaction data, and an assignment of 2^? to the 687.7 keV state is ruled out. The penetration matrix element ∥η∥ has the value of 13.5 for theK-shell and increases slightly for higher main shells. An estimate of the anomalous amplitudes is compared with values reported for transitions in the odd even actinide nuclei. Furthermore electron conversion data for the 1^?→2⁺ and 1^?→4⁺ transitions are given. Radioactivity²³⁶U from²³⁵U(n,e ^?); measured: conversion electron decay; deduced: conversion coefficients fromK, L andM shells; evaluated: dynamic matrix elements.     

Double-beta decay Q values of Cd and Te

The Q values of the ¹¹⁶Cd and ¹³⁰Te double-beta decaying nuclei were determined by using a Penning trap mass spectrometer. The new atomic mass difference between ¹¹⁶Cd and ¹¹⁶Sn of 2813.50(13) keV differs by 4.5 keV and is 30 times more precise than the previous value of 2809(4) keV. The new value for ¹³⁰Te, 2526.97(23) keV is close to the Canadian Penning trap value of 2527.01 ± 0.32 keV (Scielzo et al., 2009) [1], but differs from the Florida State University trap value of 2527.518 ± 0.013 keV (Redshaw et al., 2009) [2] by 0.55 keV (2σ). These values are sufficiently precise for ongoing neutrinoless double-beta decay searches in ¹¹⁶Cd and ¹³⁰Te. Hence, our Q values were used to compute accurate phase-space integrals for these double-beta decay nuclei. In addition, experimental two-neutrino double-beta decay nuclear matrix elements were determined and compared with the theoretical values. The neutrinoless double-beta decay half-lives for these nuclei were estimated using our precise phase-space integrals and considering the range of the best available matrix elements values.     

Interactions between metastable Xe atoms in the afterglow plasma

By measurements of the electron energy distribution function in a Xe afterglow plasma, the rate constants of the binary ionizing collisions between metastable Xe atoms were determined. The value of β₂₂ = (7.3 ± 1) × 10^?10cm³s^?1 satisfactorily agrees with the value for a van der Waals capture.     

Accurate determination of the 17O16O + n coupling constant and spectroscopic factor

We have measured ¹⁶O¹⁷O elastic cross sections at 22 MeV between 65°–140° to ± 1 %. The observed oscillatory interference between Coulomb scattering and the neutron transfer process is analyzed using exact finite-range DWBA. A model-independent value of $\text{C}\text{?}{}^2\text{= 0.82 ± 0.07}$ is obtained for the coupling constant of the 1d_{$\text{5}\text{2}$} neutron in ¹⁷O. We also present an analysis of data on magnetic electron scattering from ¹⁷O, which yields precise information on the magnitude and the radial shape of the $\text{1}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ neutron bound-state wave function. With this we relate the coupling constant to the spectroscopic factor and find S = 1.04 ± 0.11. We show that the magnetic electron scattering data alone yield S = 1.04 ± 0.10. Combining these results with earlier work we recommend $\text{C}\text{?}{}^2\text{= 0.79 ± 0.04}$ and S = 1.03 ± 0.07 as best values. This spectroscopic strength corresponds to (91 ± 7) % of the full single-particle value.     

Transient InSb spin-flip laser - a measurement of T1

A double pulse spin-flip laser technique has been used to evaluate the InSb conduction electron spin-relaxation time T₁; a value of 60 ± 20 nsec (n = 1.2 × 10¹⁶cm^?3, H = 60 kG, T = 20 K)is obtained. The effects of electron heating by free carrier absorption are measured and an energy relaxation time of 20–40 nsec is obtained. A calculation of T₁ based on ionized impurity scattering in the quantum limit regime is in order of magnitude agreement with the experiment.     

Tuning and validation of hadronic event generator for R value measurements in the tau-charm region

To measure the R value in an energy scan experiment with e⁺e^- collisions, precise calculation of initial state radiation is required in the event generators. We present an event generator for this consideration, which incorporates initial state radiation effects up to second order accuracy. The radiative correction factor is calculated using the totally hadronic Born cross section. The measured exclusive processes are generated according to their cross sections, while the unknown processes are generated using the LUND Area Law model, and its parameters are tuned with data collected at √s=3.65 GeV. The optimized values are validated with data in the range √s=2.2324-3.671 GeV. These optimized parameters are universally valid for event generation below the DD threshold.     

Investigation of photon-photon angular correlations in atomic mercury

By application of the time differential coincidence technique developed in nuclear spectroscopy, for the first time the angular correlation of light quanta of atomic decays was observed. The experiments were carried out with the 7³ S ₁-6³ P ₁-6¹ S _o-cascade of mercury excited by electron impact at energies of 50 eV. The two transitions of 4358 and 2536 Å were selected by interference filters and detected by photomultipliers. Time differential coincidence spectra were measured at the two angular positions 0=90 ° and 0=180 °. It was found that the excitation of the 7³ S ₁-state by the electron beam leads to no alignment. Therefore the usual γ-γ angular correlation theory is applicable. Perturbations occur by static interaction with external magnetic fields and by free hyperfine interaction in the odd isotopes of mercury. The interaction frequencies of the free hyperfine interaction are in all cases too high to be resolved. Measurements were performed using mercury of natural abundances, with and without external magnetic fields. First of all the spin rotation in the magnetic field of the earth (690 mG) was observed, giving for theg-factor of the 6³ P ₁-state $$g(Hg, 6^3 P_1 ) = 1.35 \pm 0.10.$$ This value is in agreement with the more precise values determined by other techniques. Shielding of the earth's field gave a nearly unattenuated angular correlation, with an integral attenuation factor of $$G_2 = 0.98 \pm 0.06.$$ The value of the angular correlation coefficientA ₂. $$A_2 = - 0.188 \pm 0.009,$$ is in good agreement with the expected average value for the natural isotope mixture $$\overline {A_2^{theor} } = - 0.196.$$ A third measurement in an external magnetic field of 5.6 G showed several complete spin rotations. A nice fit was possible by using the superposition of all six participating cascades in the hyperfine level schemes of the different isotopes. The theoretical anisotropies,g _F -values, and intensities were inserted according to natural isotope abundances. From the time differential measurements also a value for the lifetime of the Hg-6³ P ₁-level was derived. The result $$\tau (Hg, 6^3 P_1 ) = (120 \pm 2) nsec$$ is in agreement with earlier measurements. Further applications of the method are discussed.     

Anomalous spin-orbit effects in a strained InGaAs/InP quantum well structure

There is currently a large effort to explore spin-orbit effects in semiconductor structures with the ultimate goal of manipulating electron spins with gates. A search for materials with large spin-orbit coupling is therefore important. We report results of a study of spin-orbit effects in a strained InGaAs/InP quantum well. The spin-orbit relaxation time, determined from the weak antilocalization effect, was found to depend nonmonotonically on gate voltage. The spin-orbit scattering rate had a maximum value of 5×10¹⁰ s^?1 at an electron density of n=3×10¹⁵ m^?2. The scattering rate decreased from this for both increasing and decreasing densities. The smallest measured value was approximately 10⁹ s^?1 at an electron concentration of n=6×10¹⁵ m^?2. This behavior could not be explained by either the Rashba or the bulk Dresselhaus mechanisms but is attributed to asymmetry or strain effects at dissimilar quantum well interfaces.     

Electric-field dependent electron mobility in anthracene single crystals

We observed the electric-field dependence of electron drift velocity in the c′ direction of anthracene single crystals at low temperature and found out that it tends to almost constant value above the electric-field of 1.8 × 10⁵ V cm^-1 at 140 K deviating from the linear proportionality to the field below this value. This result may be regarded as an experimental verification for the recent theoretical prediction by Sumi.     

Assessment of the equivalent photon approximation for the process ee → ee π+π−

The contribution of the virtual process γγ → π⁺π^? is evaluated, first treating the quantum electrodynamics exactly and then using the equivalent photon approximation. The dependence on electron scattering angles, electron energies, ππ invariant mass and γπ momentum transfer is investigated. The approximation is very good if both electron scattering angles are less than 0.1 rad, but is 20%–40% too big (depending on the precise version used) if either angle is integrated over. It is explained that the approximation is not Lorentz invariant; numerical results are given only for beams with anti-parallel momenta.     

On the resonant neutrinoless double-electron-capture decay of Ce

The double-electron-capture Q value for the ¹³⁶Ce decay to ¹³⁶Ba has been determined at JYFLTRAP. The measured value 2378.53(27) keV excludes the energy degeneracy with the ⁰⁺$0^{+}$ excited state of the decay daughter ¹³⁶Ba at 2315.32(7) keV in a resonant 0νECEC$0\nu \mathrm{ECEC}$ decay by 11.67 keV. The new Q value differs from the old adopted value 2419(13) keV (Atomic Mass Evaluation 2003) by 40 keV and is 50 times more precise. Our calculations show that the precise Q   value renders the resonant 0νECEC$0\nu \mathrm{ECEC}$ decay of ¹³⁶Ce undetectable by the future underground detectors. We measured also the double-β decay Q value of ¹³⁶Xe to be 2457.86(48) keV which agrees well with the value 2457.83(37) keV measured at the Florida State University.     

The millimeter wave spectrum of the CO dimer

The millimeter wave spectrum of the isotopically substituted CO dimer, (¹³C¹⁶O)₂, has been studied for the first time, confirming and extending a recent infrared study. Eighty-seven transitions in the 77-180 GHz region have been assigned and analyzed in terms of a model-independent term value scheme involving 57 rotational levels with J=0-8. The levels can be classified into 7 “stacks” which have symmetry classifications of either A⁻/B⁺ or A⁺/B⁻ and K-values of either 0 or 1. For the normal isotope, symmetry and nuclear spin statistics cause alternate rotational levels to be missing, but for (¹³C¹⁶O)₂ all levels are present with an intensity alternation of 1:3 between A and B symmetries. The four A⁻/B⁺ stacks have not previously been observed, and the lowest of them establishes the tunneling splitting of (¹³C¹⁶O)₂ to be 3.769 cm⁻¹, slightly larger than the (¹²C¹⁶O)₂ value of 3.731 cm⁻¹. A large amount of precise experimental data is now available for the CO dimer, which should lead to greater theoretical insight into its structure and tunneling dynamics.     

Precise intensity measurements of internal conversion lines in the decay of 207Bi and systematic comparison with theoretical predictions

Relative intensities of internal conversion lines of the 569.6, 897.3, 1063.6 and 1770.2 keV transitions in the decay of ²⁰⁷Bi were precisely determined by spectrographical measurements with position-sensitive electron detectors installed on the focal plane of the INS iron-free π√2 β-ray spectrometer. Internal conversion coefficients were deduced with the measured relative electron intensities and with the recent precise γ-ray data, where we assumed that the ICC of the 569.6 keV K-line is equal to the theoretical α_k(E2) value. The experimental ICC thus obtained were systemati- cally compared with those by Rösel- Fries-Alder- Pauli (RFAP) and found to be satisfactorily in agreement with the theoretical values. L- and M-subshell ratios, and K- through O+P-shell ratios of the 569.6 and 1063.6 keV transitions determined for the first time in the present work were also found consistent with the predictions by RFAP.     

Comments on the calculation of the extended state electron mobility in amorphous silicon

In a recent paper Silver and his collaborators concluded that the extended state electron mobility micro_c in amorphous silicon was about 500 cm²V^-1s^-1. The calculations leading to this value were based on the multi-trapping transport model, the experimental drift mobility value of μ_e = 1 cm²V^-1s^-1, the tail state distribution suggested by field effect data and an assumed thermalisation depth of the electrons of 0.29eV. In the following it will be shown from experimental results that the above thermalisation depth is fundamentally inconsistent with the observations and, when used with the measured micro_e, leads to unrealistically high calculated micro_c -values. We also show that with a thermalisation depth appropriate to the conditions under which micro_e is determined, the experimental results and the computed micro_c-values (10 - 20 cm²V^-1s^-1) form a consistent picture.     

Electron-phonon interaction and current in strong electric fields

Using the Houston-wave approach we investigate the electron-phonon interaction in electric fieldsF which are sufficiently strong to change an electron's Bloch state drastically during the relaxation time τ, but still too weak to support standing electron waves between the band edges. We calculate τ for the low density, high temperature limit and find τ～F ^?1/2. The electric current in the field region of the “hot electrons” between its ohmic rise and its decrease proportional toF ^?1 is determined. Its increase withF ^+1/2 in the limit of relatively low fields agrees with Shockley's result.     

A study of 75Se by neutron capture and the SU(3)-SU(5) transition in the quadrupole-phonon representation

The γ and e^? spectra following thermal neutron capture in ⁷⁴Se were studied with curved-crystal, β, and pair spectrometers. Precise energies have been obtained for the transitions and levels at low energies. Two primary E2 transitions were found. The neutron separation energy for ⁷⁵Se was determined as 8027.6 keV. Precise γ-energies following the electron capture decay of ⁷⁵Se were also measured, resulting in precise level energies in ⁷⁵As. The calculation of the energy levels in ⁷⁵Se has been performed in the SU(6) particle-vibrational model (PTQM) and 27 theoretical states have been tentatively assigned to the experimental levels. The spectrum of the core nucleus ⁷⁴Se has been calculated in the SU(6) quadrupolephonon model (TQM). The structure of theoretical states, the relation to SU(3) and SU(5) limits, and potential energy surface are discussed. The E2, M1 and E1 transitions have been calculated in PTQM and compared to the experiment. Also, an overview is presented of theoretical explanations of the I = j, j?1, j?2 anomalous triplet emphasizing the rule with shell-model classification corrected for quadrupole phonons.