D. Coster

On the empty electron bands of lowest energy of the transition metals Mn and Fe and their oxides

Abstract The X-ray K-absorption spectra of the transition metals Fe and Mn have been investigated using the photographic method. Our results are equivalent to those obtained by Beeman and Friedman with the double X-ray spectrometer. The initial absorption jump found on the long wave-length-side of the edge of the transition metals is attributed to a transition of the K-electron into an empty state of the 4 s -band having p -character. The intensity of the corresponding absorption and the conductivity of the metal in question increase with varying atomic number in the same direction. Besides the X-ray absorption spectra of the same metals were photographed, when they were present in one of their various oxides. These spectra have much in common with the absorption spectrum of the corresponding metal; the initial jump referred to above is much weaker. The absorption spectrum of zinc, when forming part of zinc-oxide has been photographed. It is nearly identical with that of metallic zinc.

The fine structure of x-ray absorption edges of copper and zinc in copper-zinc alloys

Summary X-ray absorption edges of Cu and Zn in α-, β-, γ- and -brass are investigated and compared with those for pure elements in the same kind of crystal lattice. As to the position of the maxima and minima of absorption it has been shown that in agreement with Kronigs theory of fine structure they are found in equivalent places for crystal lattices of the same type. In some cases more of less important deviations of the special form of the maxima and minima are found which may easily be understood from the theory.

Predissociation in the Ångström-bands of CO

Abstract Predissociation of the upper level of the Angstrom bands at v = 0 and J = 38 fixes the dissociation energy of the normal CO-molecule at 9,82 volt. An electronic level diagram of CO with the dissociation states is given and the dissociation energy of most of the electronic levels could be computed.

The resonance levels for neutron capture II1)

Abstract After a short introduction in § 1, § 2 deals with some changes made in the experimental arrangement and a thorough discussion of various corrections. § 3 gives the measurements and § 4 their discussion. They include: A. self-absorption curves for Cu (5 min period), Ag (2.3 min), Ag (22 sec), Al. B. boron absorption measurements from which resonance energies could be calculated. C. Doppler-effect for Ag (22 sec) and Cu (5 min). In the latter case, where the resonance energy is rather high (110 eV), a very definite effect has really been found. D. Activabilities both for resonance and thermal neutrons for the same elements. E. gives for the same elements and moreover for Zn (dealt with in a former paper), the different methods of calculation of the effective level width Г eff ; they are: 1. from the Breit-Wigner one level formula; 2. from the activability; 3. from scattering experiments. This is a new method, a fuller account of which will be given in a following paper, part III. In this paper only the results are used. 4. from Doppler-width. It is shown that methods 1 and 2 in many cases give too high values, as more than one resonance level plays its part. § 5 From a thorough discussion of all results it follows that the effective width Г eff does not increase at higher resonance energy, while the neutron width does not seem to depend upon the resonance energy and the atomic weight. The average distance between resonance levels for neutron capture is about 15 eV for Ag (A = 100) and about 150 eV for Cu (A = 65) in agreement with Bethes theory.

Auger-effect and relative intensity of L-emission lines

Summary The relative intensities of the lines Lβ1, Lβ3 and Lβ4 are determined for Zr, Nb and Mo by a photographic method. The lines Lβ3 and Lβ4 relative to Lβ1 are more intense for Mo than for Zr and Nb. This is in accordance with the theory of Coster and Kronig for the Auger-effect LI → LII with ejection of an MIV V electron, which can take place for Zr but not for Mo since for this the energy difference LI—LII is too small. Also the intensity of satellites of Lβ1 for the same elements has been measured.

The resonance levels for neutron capture III: Scattering of resonance neutrons1)

Abstract An introduction is given in § 1. In § 2 a new method is dealt with for determining the cross-section for neutron scattering. In § 3 a theoretical treatment has been given of a new method for calculating the level width Г by relating it to the energy-loss in elastic collisions. § 4 gives the measurements and the calculation of: I. the cross-section for neutron scattering, and of II. the level width for neutron capture. In § 5 attention has been drawn to a new effect, for which the name refilling effect has been proposed: If a certain group of neutrons has been absorbed by a resonance absorber, a “hole” is present in the neutron distribution. This hole at the energy Er may be refilled by interposing a second (scattering) absorber (properly speaking, the hole is of course shifted to lower energies).

The resonance levels for neutron capture of silver, copper and zinc

Summary The A- and B-neutrons of silver do not exist. There is only one resonance level of 6.5 volts, having a natural width Γ = 0.42 volts, whereas the Doppler width is 0.07 volts. The curve for self-absorption of the Ag-resonance neutrons almost exactly coincides with the theoretical curve, only a small background of no more than 5 per cent remains. This is probably due to one or more higher energy levels. For the (η, γ)-processes Cu (12.8 hr per.), Cu (5 min per.) and Zn (56 min per.) rather high resonance energies of respectively 600, 650 and 5200 volts are found. The self-absorption curves do not coincide with a theoretical one, calculated from the one level formula of Breit and Wigner; the deviations indicate the presence of at least two levels, which contribute to the activation. Here the level widths are not accurately known, but they certainly exceed the Doppler width and they are of the order of several volts. The final analysis of the absorption curves of copper and zinc into the contributions due to the different levels will be the object of a following paper.

Slow neutron experiments in Groningen

Abstract Values are given for the energies and the effective widths of the resonance levels of the following nuclei Au 198 , Ag 108 , Ag 110 , Cu 64 , Cu 66 , Al 28 , Zn 69 and Cd 117 . They have been derived from previous measurements applying a correction for impurity of our boron samples. The thus corrected values for the resonance energies of Au and Ag are in agreement with those obtained with the aid of the time of flight method. It is shown that of the three levels of Ag (5.1, 16 and 45 eV) the first belongs to Ag 110 (22 sec) and the second to Ag 108 (2.3 min). Overlapping levels of Ag 110 , Cu 66 and Cd 117 were found at about 100 eV.

The resonance levels for neutron capture IV1): Overlapping of levels

In part III we found the Cu 5 min resonance neutrons to be strongly absorbed in Ag and Cd. These striking anomalies have been the subject of our present investigations. The results are: 1. 1o. The large absorption coefficients of Cd and Ag for Cu 5 min resonance neutrons must be ascribed to the overlapping of a resonance level of Cu, with one of Cd and at the same time with one of Ag. 2. 2o. The resonance energies involved are: Cu-a level 135 (± 15) eVolts. Ag-b level 125 (± 15) ” Cd level 145 (± 15) ” 3. 3o. The Cu 5 min resonance activity must be ascribed to the contribution of at least three groups of neutrons; they are Cu-a (Er = 135 eV), Cu-b (very high energy: Er > 1000 eV) and some group of low energy. The latter has presumably to be ascribed to the 1v region above the cadmium cut-off corresponding to a level of a small negative energy. 4. 4o. The isotopes responsable for the overlapping are: 65Cu (5 min); 109Ag (22 sec); that of Cd is not yet known. 5. 5o. A quantitative calculation of the overlapping by means of formulae given by Bethe has been performed. In this way it was possible to determine the difference in the resonance energies |EI  EII| and to estimate the ratio of the widths of the levels concerned, independently of the methods used in parts II and III. The results of these measurements have been given in tables I and II.

High potential equipment of the neutron generator of 500 kV — 1 mA at Groningen

Summary A description is given of a stepdown transformer for heating the filaments of six rectifying tubes belonging to the high potential equipment of the Philips noutron generator at Groningen. This transformer has been made in the workshop of the laboratory.