Gamma ray production cross sections in proton induced reactions on natural Mg, Si and Fe targets over the proton energy range 30 up to 66 MeV

Gamma-ray excitation functions have been measured for 30, 42, 54 and 66 MeV proton beams accelerated onto C + O (Mylar), Mg, Si, and Fe targets of astrophysical interest at the separate-sector cyclotron of iThemba LABS in Somerset West (Cape Town, South Africa). A large solid angle, high energy resolution detection system of the Eurogam type was used to record Gamma-ray energy spectra. Derived preliminary results of Gamma-ray line production cross sections for the Mg, Si and Fe target nuclei are reported and discussed. The current cross section data for known, intense Gamma-ray lines from these nuclei consistently extend to higher proton energies previous experimental data measured up to Ep ~ 25 MeV at the Orsay and Washington tandem accelerators. Data for new Gamma-ray lines observed for the first time in this work are also reported.Comment: 11 pages, 6 figures. IOP Institute of Physics Conference Nuclear Physics in Astrophysics VII, 28th EPF Nuclear Physics Divisional Conference, May 18-22 2015, York, U

The effect of tinted spectacle lenses on contrast sensitivity and colour vision

Aim: Spectacle wearers often prefer tintedlenses to clear or non-tinted lenses for their protection against harmful radiation, improved cos- mesis, enhancement of visual performance and effects on colour vision. Among the available tinted lenses on the market blue, brown and grey tinted spectacle lenses are popular with varying grades ranging from A to D. Due to reduced transmission of light through such lenses, the optical system of the eyes and the environmental vision may be temporarily altered. Colour vision (CV) and con- trast sensitivity (CS) are important aspects of this altered visual world. This study investigated the effect of spectacle lenses of varying grades of tint on CS and CV. Method: The study adopted a pre- and postest research design and a sample of 90 participants were selected from the University of KwaZulu-Natal student population using convenience sam- ling. Each participant was screened for patholgy, dyschromatopsia, severe dry eyes (TBUT<5 seconds), and the presence of any more than low metropia. Thereafter each successful participant was tested for CS and CV with their habitual precription and then tested randomly with a white clear) lens (placebo) and tinted (blue, brown, and grey) spectacle lenses made of CR39 material each having grades A, B and C over their habitual state. Light transmission was 85%, 75%, and 50% for grades A, B, and C respectively. The Functional Acuity Contrast Test (FACT) chart and American Optical Hardy, Rand, and Rittler (AO HRR) were used for the assessment of CS and CV respectively. Results: The data was analysed using the Statistical Package of Social Science (SPSS) version18. Compared to the habitual state, contrast sensitivity was enhanced with all the tinted lenses The greater enhancement was for low spatial frequencies (LSF) and least for high spatial frequencies (HSF). With all tints Grade C had the least enhancement for very HSF. Many subjects showed no change in CV with any of the lensesused. The grey tint showed greater enhancement of CV as the density increases. Blue and brown tints showed a similar trend with grade B enhancing CV the most while grade C resulted in theleast reduction of CV. Conclusion: Grade A, B, and C of blue, brown and grey tinted spectacle lenses do not alter colour vision significantly but for the selected levels of transmission of the tints used, contrast sensitivity can be improved to some extent

Nuclear Level Density and γ\gamma-ray Strength Function of 67Ni^{67}\mathrm{Ni} and the impact on the i-process

Proton-$\gamma$ coincidences from $(\mathrm{d},\mathrm{p})$ reactions between a $^{66}\mathrm{Ni}$ beam and a deuterated polyethylene target have been analyzed with the inverse Oslo method to find the nuclear level density (NLD) and $\gamma$-ray strength function ($\gamma$SF) of $^{67}\mathrm{Ni}$. The $^{66}\mathrm{Ni}(\mathrm{n},\gamma)$ capture cross section has been calculated using the Hauser-Feshbach model in TALYS using the measured NLD and $\gamma$SF as constraints. We confirm that $^{66}\mathrm{Ni}(\mathrm{n},\gamma)$ acts as a bottleneck when relying on one-zone nucleosynthesis calculations. However, we find that the impact of this reaction is strongly damped in multi-zone low-metallicity AGB stellar models experiencing i-process nucleosynthesis.Comment: Submitted to Phys. Rev.

Nuclear level density and γ-ray strength function of Ni67 and the impact on the i process

Proton-γ coincidences from (d,p) reactions between a Ni66 beam and a deuterated polyethylene target have been analyzed with the inverse-Oslo method to find the nuclear level density (NLD) and γ-ray strength function (γSF) of Ni67. The Ni66(n,γ) capture cross section has been calculated using the Hauser-Feshbach model in TALYS using the measured NLD and γSF as constraints. The results confirm that the Ni66(n,γ) reaction acts as a bottleneck when relying on one-zone nucleosynthesis calculations. However, the impact of this reaction is strongly dampened in multizone models of low-metallicity AGB stars experiencing i-process nucleosynthesis

High resolution 148Nd(3He,nγ) two proton stripping reaction and the structure of the 02 + state in 150Sm

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Observation of γ vibrations and alignments built on non-ground-state configurations in Dy 156

The exact nature of the lowest Kπ=2+ rotational bands in all deformed nuclei remains obscure. Traditionally they are assumed to be collective vibrations of the nuclear shape in the γ degree of freedom perpendicular to the nuclear symmetry axis. Very few such γ bands have been traced past the usual backbending rotational alignments of high-j nucleons. We have investigated the structure of positive-parity bands in the N=90 nucleus Dy156, using the Nd148(C12,4n)Dy156 reaction at 65 MeV, observing the resulting γ-ray transitions with the Gammasphere array. The even- and odd-spin members of the Kπ=2+γ band are observed up to 32+ and 31+, respectively. This rotational band faithfully tracks the ground-state configuration to the highest spins. The members of a possible γ vibration built on the aligned yrast S band are observed up to spins 28+ and 27+. An even-spin positive-parity band, observed up to spin 24+, is a candidate for an aligned S band built on the seniority-zero configuration of the 02+ state at 676 keV. The crossing of this band with the 02+ band is at ?ωc=0.28(1)MeV and is consistent with the configuration of the 02+ band not producing any blocking of the monopole pairing

Investigation of negative-parity states in Dy 156: Search for evidence of tetrahedral symmetry

An experiment populating low/medium-spin states in Dy156 was performed to investigate the possibility of tetrahedral symmetry in this nucleus. In particular, focus was placed on the low-spin, negative-parity states since recent theoretical studies suggest that these may be good candidates for this high-rank symmetry. The states were produced in the Nd148(C12,4n) reaction and the Gammasphere array was utilized to detect the emitted γ rays. B(E2)/B(E1) ratios of transition probabilities from the low-spin, negative-parity bands were determined and used to interpret whether these structures are best associated with tetrahedral symmetry or, as previously assigned, to octupole vibrations. In addition, several other negative-parity structures were observed to higher spin and two new sequences were established