Table of contents

The paper presents a broad overview of the most recent developments in all the major subfields of physics together with illustrations of recent societal applications of these subfields and developments. It is argued that the past five years have been among the most exciting and productive of any in the history of the science in terms both of fundamental discoveries concerning the structure and dynamics of the natural universe and of practical application of these and other discoveries to the alleviation of human problems. Emphasis is placed on the unity of the science and on the challenges that lie ahead.

The Nature of Physics

"Science is knowing. What man knows about inanimate nature in physics, or rather the most lasting and universal things that he knows make up physics. As he gains more knowledge, what would have appeared complicated or capricious can be seen as essentially simple and in a deep sense orderly. And, to understand how things work is to see how, within environmental constraints and the limitations of wisdom, better to accommodate nature to man and man to nature."

Physics in Perspective, Vol. 1, p. 55. US National Academy of Sciences Washington, D.C., 1972

Cross-section formulas for jet production via the two-photon mechanism e ē → γγ → q are derived. These jets are probably easily observable at LEP energies (70 GeV + 70 GeV electron-positron collisions).

The reactions ²⁰⁵Tl(α, 2n)²⁰⁷Bi and ²⁰⁸Pb(d, 3n)²⁰⁷Bi were studied using α-particles in the energy range 30-43 MeV and deuterons at the energy 25 MeV. In-beam prompt and delayed γ-ray and conversion electron spectroscopy investigations reveal an isomeric 29/2^- state at 3887.7 keV with the half-life 13 ± 1 ns, which is suggested to have the configuration πh_9/2vi_13/2^-2. This isomeric state decays by a cascade of three γ-rays (386.8, E1; 899.3, M1; 499.7, E2) to states with J^π = 27/2⁺, 25/2⁺, and to the previously known 21/2⁺ isomeric state with the configuration πh_9/2vp_1/2^-1i_13/2^-1. In this state the probability of the spatial coincidence of all three valence nucleons is large and it may therefore be affected by a short-range three-body interaction. By comparing the experimental and calculated energies, assuming only two-body forces, it is found that the three-body energy is less than 10 keV in the 27/2⁺ state. This upper limit is not much larger than the expected effect, which is estimated to be of the order of 2 keV by comparing with the three-body energy in ³H.

The level structure of ²⁴Mg and decay properties of 129 ms ²⁴Al^m and 2.07 s ²⁴Al have been investigated by means of γ-ray and particle spectroscopy. The energy and intensity of the isomeric transition were measured to be 425.8 ± 0.1 keV and (82.5 ± 3.0)%, respectively. The isomer was observed to decay via a super-allowed transition with a log ft value of 3.51 ± 0.04 to its 1⁺, 9965.2 ± 1.5 keV analog state in ²⁴Mg. In addition, decay to seven particle-emitting levels and four levels depopulated by γ-ray emission were observed. In the decay of 2.07 s ²⁴Al a new delayed α-particle group with an energy 3.04 MeV and three new γ-transitions were observed. More accurate values than those reported in earlier studies are given for γ-ray energies and intensities, and also for deduced excitation energies in ²⁴Mg. Particle branches (per disintegration) were measured for the observed delayed particle groups.

The ¹⁶O + ⁹Be reactions have been studied from E_CM = 3.2 MeV to 7.2 MeV and at 9 MeV and 14.4 MeV. Gamma transitions in the nuclei ²⁴Mg, ²⁴Na, ²³Mg, ²³Na, ²¹Ne, ²⁰Ne and ¹⁷O have been identified with aid of particle-gamma and gamma-gamma coincidence technique. Excitation functions have been obtained by measuring the gamma ray yield for the residual nuclei ²¹Ne (351 keV), ²³Na (440 keV), ¹⁷O (871 keV), ²⁰Ne (1634 keV) and ²³Na (1636 keV).

The decay of the metastable state in ⁸⁴Rb has been studied by means of the ⁸⁵Rb(n, 2n)⁸⁴Rb and the ⁸⁵Rb(γ, n)⁸⁴Rb reactions. A possible but very weak feeding of excited states in ⁸⁴Kr directly from the metastable state is suggested. The cross sections for the (n, 2n), (n, p) and (n, α) reactions of the target nuclei ⁸⁵Rb and ⁸⁷Rb were measured by the activation method with 14.8 MeV neutrons.

By combining all available theoretical and experimental data we first derive expressions for the Z-dependence of the 2p²P splitting and of the resonance transitions 2s²S_1/2-2p²P_{1/2, 3/2}, thereby obtaining a check on reported wavelengths of these transitions and on their identification in solar flare spectra. Further, by combining the observed transitions 2p-3d with the 3d ionization energy, calculated on the basis of the polarization concept, we determine the ionization limit for each spectrum and summarize the results in a semi-empirical expression in Z. Finally, Z-dependent coefficients in 3-parameter Ritz formulae are derived for ns²S and np²P, which complete the accurate description of the energy structure of these spectra. Explicit results are tabulated up to Ni XXVI. They give an estimate of the errors in existing measurements and reveal a number of misidentifications in published line lists.

We have used the beam-foil technique to study spectra of aluminium in the wavelength range 300 Å to 2000 Å, and measured radiative mean lives for 22 levels in Al II-Al VII. Where possible, our results are compared with theory and other experimental work.

Regularities of the molecular band (λ 5725 Å) emission from a discharge potassium plasma were investigated. It was shown that molecules were obtained by the photorecombination of two resonant excited potassium atoms. The cross-section for this process was measured to be equal to (4 ± 0.8) × 10^-16 cm². The excited-state lifetime of molecules was determined.

A statistical theory of the dipole polarizability α is given for atoms and ions, described in the Thomas-Fermi model. A universal dependence of the polarizability of atoms and ions on their radius is constructed by numerical calculations. In the case of multiply-charged ions the expression for α has a simple analytical form. The results of the computation are in good agreement with available experimental and theoretical data especially when the outer electron shells are more than half-filled.

The absorption spectrum of Ag I in the 1850-930 Å region has been studied. The atomic vapours have been produced with both an induction heated furnace and with flash pyrolysis. Fifteen new series of lines corresponding to configurations 4d¹⁰5s²S-4d⁹5s np, nf and converging to the levels 4d⁹5s³D and ¹D of Ag II have been identified. For the strongly autoionized levels the Fano parameters of the profiles have been derived as well as the relative value of the photoionization cross section.

In the SiO spectrum the band systems G¹Π-X¹Σ⁺ and I¹Π-X¹Σ⁺ are situated in the spectral region 1300-1470 Å. The upper states perturb each other strongly. This paper contains a deperturbation calculation of the upper levels in Si¹⁶O and in Si¹⁸O. The isotopic shifts are also studied. The mutual interaction is treated in an adiabatic approximation and is found to increase linearly with v for near-degenerate vibrational G and I levels.

The real and the imaginary parts of the high-frequency mobility for predominant polar optic scattering in a semiconductor in a large longitudinal quantizing magnetic field are calculated by an iterative solution of the Boltzmann equation. The real and the imaginary parts of the mobility are found to decrease at large magnetic fields. The effect of the elastic scattering mechanisms is also examined and found to be significant at lower frequencies.