Reaction Rates and Nuclear Properties Relevant for Nucleosynthesis in Massive Stars and Far From Stability

Explosive nuclear burning in astrophysical environments produces unstable nuclei which again can be targets for subsequent reactions. In addition, it involves a large number of stable nuclides which are not fully explored by experiments, yet. Thus, it is necessary to be able to predict reaction cross sections and thermonuclear rates with the aid of theoretical models. Such predictions are also of interest for investigations at radioactive ion beam facilities. An extended library of theoretical cross sections and reaction rates is presented. The problem of alpha+nucleus potentials is addressed and new parametrizations presented. The problem of properly predicting cross sections at low level densities is illustrated by the 62Ni(n,gamma) reaction.Comment: 7 pages, invited talk, to appear in proceedings of CGS11 (Prague), World Scientific (new version: fixed typo in potential parameters; note: they will still be incorrect in the printed version

Experimental opportunities at the pulsed neutron source ORELA

The authors have developed an improved C{sub 6}D{sub 6} detector system, a high-purity germanium n-type detector system, and a new BaF{sub 2} system for capture and fission measurements at ORELA. With their set of different detectors, they are able to measure high-precision data for total cross-section measurements, as well as fission, elastic scattering, {gamma}-ray, and neutron-production cross section data. Additional capabilities at ORELA include an intense, pulsed positron, source of {approximately} 10{sup 8}e{sup +}/sec

High-resolution neutron capture and transmission measurements and the stellar neutron capture cross sections of {sup 116,120}Sn

Improved astrophysical reaction rates for {sup 116,120}Sn(n, {gamma}) are of interest because nucleosynthesis models have not been able to reproduce the observed abundances in this mass region. For example, previous s-process calculations have consistently underproduced the s-only isotope {sup 116}Sn. Also, these studies have resulted in residual reprocess abundances for the tin isotopes which are systematically larger than predicted by reprocess calculations. It has been suggested that these problems could be solved by reducing the solar tin abundance by 10-20%, but there is no experimental evidence to justify this renormalization. Instead, it is possible that the problem lies in the (n,T) cross sections used in the reaction network calculations or in the s-process models. One reason to suspect the (n, {gamma}) data is that previous measurements did not extend to low enough energies to determine accurately the Maxwellian-averaged capture cross sections at the low temperatures (kT=6-8 keV) favored by the most recent stellar models of the s process. Also, the two most recent high-precision measurements of the {sup 120}Sn(n, {gamma}) cross section are in serious disagreement. Because of its small size, this cross section could affect (via the s-process branching at {sup 121}Sn) the relative abundances of the three s-only isotopes of Te

Non-Statistical Effects in Neutron Capture

There have been many reports of non-statistical effects in neutron-capture measurements. However, reports of deviations of reduced-neutron-width distributions from the expected Porter-Thomas (PT) shape largely have been ignored. Most of these deviations have been reported for odd-A nuclides. Because reliable spin (J) assignments have been absent for most resonances for such nuclides, it is possible that reported deviations from PT might be due to incorrect J assignments. We recently developed a new method for measuring spins of neutron resonances by using the DANCE detector at LANSCE. Measurements made with a 147Sm sample allowed us to determine spins of almost all known resonances below 1 keV. Furthermore, analysis of these data revealed that the reduced-neutron-width distribution was in good agreement with PT for resonances below 350 eV, but in disagreement with PT for resonances between 350 and 700 eV. Our previous (n,alpha) measurements had revealed that the alpha strength function also changes abruptly at this energy. There currently is no known explanation for these two non-statistical effects. Recently, we have developed another new method for determining the spins of neutron resonances. To implement this technique required a small change (to record pulse-height information for coincidence events) to a much simpler apparatus: A pair of C6D6 gamma-ray detectors which we have employed for many years to measure neutron-capture cross sections at ORELA. Measurements with a 95Mo sample revealed that not only does the method work very well for determining spins, but it also makes possible parity assignments. Taken together, these new techniques at LANSCE and ORELA could be very useful for further elucidation of non-statistical effects.Comment: 8 pages, 3 figures, for proceedings of CGS1

Choroidal metastases in testicular choriocarcinoma, successful treatment with chemo- and radiotherapy: a case report

<p>Abstract</p> <p>Background</p> <p>Choriocarcinoma is a very rare cause of ocular metastasis. Only 18 male patients have been reported on, 4 of whom survived, but with significant loss of vision.</p> <p>Case presentation</p> <p>A 26-year-old Caucasian man, suffering from testicular choriocarcinoma with pulmonary, cerebral, renal, hepatic and osseous metastases, underwent left radical orchiectomy. While being treated with chemotherapy, he presented with loss of vision in the left eye. Ophthalmoscopy revealed bilateral non-pigmented, hemorrhagic choroidal tumours, compatible with secondary lesions. Continued chemotherapy and stereotactic radiotherapy of the skull and spine lead to full remission with excellent vision, after more than 4 years of follow up.</p> <p>Conclusion</p> <p>Testicular choriocarcinoma is an exceptional cause of choroidal metastasis, potentially asymptomatic and with specific clinical features. Radiotherapy can complement radical orchiectomy and chemotherapy, to achieve full remission and maintain good vision.</p