Peter Ekström

Study of the Δ isobar excitation in nuclei with the (3He,t) reaction

Abstract Data for the Δ excitation by the (3He,t) reaction at 2.0 GeV on various nuclei are presented together with results on 12C at 1.5 and 2.3 GeV. The Δ peak position and width are found to be target mass independent. Comparison with the p(3He,t) Δ++ reaction, however, shows a shift of the position in energy of the Δ peak. Implications of these results are discussed.

The p(3He,t)Δ++ reaction

Abstract Data are presented for the p(3He,t)Δ++ reaction at 2.0, 2.3 and 1.5 GeV. The reaction specifically excites the Δ++ with very little yield outside the resonance. The data are analysed as one pion exchange and the hadronic form factor for the 3He−1 system is extracted and compared with the magnetic form factor from electron scattering.

High-spin spectroscopic study of 167Lu

Abstract Three decay sequences associated with the 7 2 + [404], 9 2 − [514] and 1 2 − [541] Nilsson states of 167 Lu have been established to high spin using the 123 Sb( 48 Ca,4n) 167 Lu reaction. The quasineutron and quasiproton band crossings, the energy signature splittings, and the B (M1)/ B (E2) values are discussed and compared with similar quantities for the lighter lutetium isotopes. Configuration-and isotopic-dependent deformations, reflected in such comparisons, indicate that 167 Lu has a larger and more stable prolate deformation than the lighter isotopes and that the 1 2 − [541] configuration has a larger quadrupole deformation than the 9 2 − [514] configuration. The shift of the AB neutron band crossing occurring in the 1 2 − [541] sequences to a larger rotational frequency cannot be understood in terms only of deformation differences. The configuration and neutron-number dependent shapes are also discussed in a “gauge”-space analysis.

Superdeformed triaxial bands in Lu-163,165

An experimental investigation of the nucleus 165Lu, using the reactions 138Ba(31P,4n) 165Lu and 150Sm(19F,4n) 165Lu at beam energies of E = 155 and 95 MeV, respectively, has been performed. Among other additions to the existing level scheme, a new band, with transition energies almost identical to a strongly deformed (β2 0.42) πi13/2[660 1/2+] band recently discovered in 163Lu has been established. A theoretical analysis of the structure of the two Lu isotopes, 165Lu and 163Lu is carried out by detailed calculations of total potential energy surfaces for specific configurations. By a diabatic treatment of crossings specific proton configurations as πi13/2[660 1/2+] are identified throughout the deformation space and as a function of spin. It is found as a general feature that well deformed local minima of considerable nonaxial symmetry coexist with a normal deformed global minimum. The depth of these local minima depend on configuration. The structure of the different global and local minima found in these surfaces are analysed and discussed in terms of occupation of available basis configurations and their orientation relative to the rotation axis. The strongly deformed minima are found to belong to a group of superdeformed triaxial structures, expected to appear at low energies for certain favourable combinations of proton and neutron numbers.

Spin structure of the Δ excitation

Spin structure and cross section data for Δ production in the (n, p-like reaction (d, 2p[1S0]) on p, d and 12C targets are presented. At laboratory kinetic energies 2 GeV and 1.6 GeV, and forward scattering angles, we find dominance of spin transverse over spin longitudinal cross section for free Δ production. On the nucleus 12C we find significant enhancement of the transverse dominance, and a large downwards shift in the peak position of the laboratory energy transfer associated with the production of the Δ.

14CO2 dispersion around two PWR nuclear power plants in Brazil

Atmospheric air samples were taken within 3 km from power plants encompassing five different distances and wind directions. Samples were taken between 2002 and 2005 aiming to evaluate the environmental (14)C enrichment due to the operation of Brazilian nuclear power plants. The sampling system consisted of a pump connected to a trapping column filled with a 3M NaOH solution. The trapped CO(2) was analyzed for (14)C by using a single stage accelerator mass spectrometry (SSAMS). All sampling sites revealed measurable (14)C excess values. The maximum excesses were of 15 and 14 mBq/m(3) for sampling sites placed at NE of the power plants, which is the main wind direction in the area. The mean excesses values were 12 mBq/m(3) to the NE direction, 8 mBq/m(3) to the E, 10 mBq/m(3) to the N, 8 mBq/m(3) to the WNW and 7 mBq/m(3) to the W direction (increasing distances from NE to W). Compared to other Light Water Reactors (LWR) data, these means values are significantly higher than the average worldwide reported value of 3 mBq/m(3). Available data indicate that the observed values are not related to (14)C emission by the power plants vent stack. Other factors, such as topography, seem to have an important role because it affects wind dispersion thus favoring (14)C accumulation in the sampled area. Moreover, the high elevations around the power plants enhance the chances to measure high values of (14)C since the plume can be intercepted before it is drawn to the ground. Modeling of the plume has shown that its dispersion does not follow a Gaussian model and that agreement between atmospheric CO(2) and vegetation (14)C activities occurs only for sampling sites placed at NE of the power plants.

Motion on an Inclined Plane and the Nature of Science.

Friction is an important phenomenon in everyday life. All children are familiar with playground slides, which may thus be a good starting point for investigating friction. Motion on an inclined plane is a standard physics example. This paper presents an investigation of friction by a group of 11-year olds. How did they plan their investigations? What aspects of friction could they discern? What understanding of the nature of science was revealed—and developed—during their investigation and subsequent discussion with the teacher?