John S. Eck

Systematics of backward-angle elastic alpha scattering☆

Abstract The systematics of backward-angle (θ > 90°) cross sections for elastic alpha scattering from target nuclei 32 ⪅ A ⪅ 100 in the bombarding energy range 15 ⪅ E ⪅ 40 MeV are investigated using all available data. A simple quantitative prescription for estimating the degree of backward enhancement is given. It is shown that this enhancement is strongly correlated with reaction Q -values and with compound-nucleus level densities. This correlation is discussed in terms of flux removal from high angular momentum entrance channels by l -dependent absorption potentials and by compound elastic scattering.

The proton optical-model potential near the Coulomb barrier☆

Abstract Proton elastic scattering data from 197 Au, 208 Pb and 209 Bi at energies near the Coulomb barrier are analyzed. The energy dependences of the real volume and imaginary surface-derivative potential depths V R and W SF of a local optical-model potential with fixed geometric parameters are found to be much more rapid than at higher energies. The strong energy dependence of V R near the Coulomb barrier is explained in terms of the non-locality of the nucleon-nucleus interaction.

State‐of‐the‐art time‐resolved emission Mössbauer spectrometer

We report on the design, construction, and operation of a time‐resolved emission Mossbauer spectrometer which has as its central component a microcomputer for data recording and manipulation. The philosophy of data acquisition affords previously unrealized flexibility in data handling and spectral analysis in both the time and frequency domains.

Dissipative forces and quantum mechanics

The dissipative forces of classical mechanics can be included in quantum mechanics by the use of non‐Hermitian Hamiltonians. The Ehrenfest theorem for such Hamiltonians is derived, and simple examples which show the classical correspondences are given. The viscosity coefficient for a nuclear collision is estimated.

Detailed test of distorting potentials for the transfer reactions 40Ca(7Li, 6Li/6He)

Abstract Angular distributions for the transfer reactions 40 Ca( 7 Li, 6 Li) 41 Ca and 40 Ca( 7 Li, 6 He) 41 Sc have been measured at 34 MeV, in small angular increments out to angles where the cross section has fallen by four orders of magnitude. Finite range DWBA calculations show a high sensitivity to different distorting potentials at the largest angle cross sections. It is found that a combination of Woods-Saxon and double-folded potentials does the best job of reproducing the data over the whole angular range.

The (7Li, 6Li) reaction on 28Si and 40Ca at E(7Li) = 45 MeV

Abstract Angular distributions for the ( 7 Li, 6 Li) reaction on 28 Si and 40 Ca to ground and excited states of 29 Si and 41 Ca have been measured at E( 7 Li ) = 45 MeV . The shapes of the angular distributions are well described by exact finite-range DWBA calculations. To test the sensitivity of the calculated angular distributions to the exit channel potential, calculations were made using a strongly absorbing 7 Li potential for both the entrance and exit channels. This calculation produced as good a fit to the shape of the angular distributions as did calculations with a 6 Li potential in the exit channel, even though 7 Li and 6 Li elastic scattering on these target nuclei are not very similar. However, the magnitudes of the calculated cross sections are sensitive to the choice of potentials, and agreement with light-ion spectroscopic factors is obtained when the more weakly absorbing 6 Li potentials are used. The spectroscopic factors obtained from the 40 Ca( 7 Li, 6 Li) reaction study are in good agreement with the extensive light-ion results showing that the absolute magnitude of the reaction is correctly predicted by exact finite-range DWBA calculations that use optical parameters determined from elastic-scattering data.

Optical‐model and coupled‐channels calculations in quantum‐mechanical scattering

Non‐Hermitian Hamiltonians are used in many research areas as approximate models of physical systems, for example, the optical‐model potential in nuclear physics. Such Hamiltonians are rarely treated in introductory quantum mechanics. Here the quantum scattering problem of a two‐state system is treated exactly for the case of one‐dimensional square‐well potentials. By introducing an appropriate optical‐model potential, an approximate solution for one of the two states is obtained. The exact and approximate solutions are compared for a realistic example.

Mössbauer effect studies of Fe(phen)2(NCBH3)2 - a spin triplet☆

Abstract Mossbauer spectroscopy and magnetic moment measurements have been used to study the compound Fe(phen) 2 (NCBH 3 ) 2 in conjunction with other octahedral Fe(II) complexes. The result of both sets of measurements indicate that Fe(phen) 2 (NCBH 3 ) 2 is an intermediate spin ( S = 1) complex at room temperature. Intermediate spin Fe(II) complexes are relatively unknown and very few, if any, are conclusively reported in the literature.

Letter to the editorDirect extraction of a 12C− beam from a diode ion source☆

Abstract The successful direct extraction of a C − beam from a High Voltage Engineering Corporation diode ion source is described.

Direct extraction of a 12C− beam from a diode ion source☆

Abstract The successful direct extraction of a C − beam from a High Voltage Engineering Corporation diode ion source is described.