Neutron capture cross section measurement of 151Sm at the CERN neutron time of flight facility (n_TOF)

n_TOF: Measurements of Key Reactions of Interest to AGB Stars

In the last 20 years, the neutron time-of-flight facility n_TOF at CERN has been providing relevant data for the astrophysical slow neutron capture process (s process). At n_TOF, neutron-induced radiative capture (n,γ) as well as (n,p) and (n,α) reaction cross sections are measured as a function of energy, using the time-of-flight method. Improved detection systems, innovative ideas and collaborations with other neutron facilities have lead to a considerable contribution of the n_TOF collaboration to studying the s process in asymptotic giant branch stars. Results have been reported for stable and radioactive samples, i.e., 24,25,26Mg,26Al, 33S, 54,57Fe, 58,59,62,63Ni, 70,72,73Ge, 90,91,92,93,94,96Zr, 139La, 140Ce, 147Pm, 151Sm, 154,155,157Gd, 171Tm, 186,187,188Os, 197Au, 203,204Tl, 204,206,207Pb and 209Bi isotopes, while others are being studied or planned to be studied in the near future. In this contribution, we present an overview of the most successful achievements, and an outlook of future challenging measurements, including ongoing detection system developments.

Neutron Capture on the s-Process Branching Point ^{171}Tm via Time-of-Flight and Activation

The neutron capture cross sections of several unstable nuclides acting as branching points in the s process are crucial for stellar nucleosynthesis studies. The unstable ^{171}Tm (t_{1/2}=1.92  yr) is part of the branching around mass A∼170 but its neutron capture cross section as a function of the neutron energy is not known to date. In this work, following the production for the first time of more than 5 mg of ^{171}Tm at the high-flux reactor Institut Laue-Langevin in France, a sample was produced at the Paul Scherrer Institute in Switzerland. Two complementary experiments were carried out at the neutron time-of-flight facility (n_TOF) at CERN in Switzerland and at the SARAF liquid lithium target facility at Soreq Nuclear Research Center in Israel by time of flight and activation, respectively. The result of the time-of-flight experiment consists of the first ever set of resonance parameters and the corresponding average resonance parameters, allowing us to make an estimation of the Maxwellian-averaged cross sections (MACS) by extrapolation. The activation measurement provides a direct and more precise measurement of the MACS at 30 keV: 384(40) mb, with which the estimation from the n_TOF data agree at the limit of 1 standard deviation. This value is 2.6 times lower than the JEFF-3.3 and ENDF/B-VIII evaluations, 25% lower than that of the Bao et al. compilation, and 1.6 times larger than the value recommended in the KADoNiS (v1) database, based on the only previous experiment. Our result affects the nucleosynthesis at the A∼170 branching, namely, the ^{171}Yb abundance increases in the material lost by asymptotic giant branch stars, providing a better match to the available pre-solar SiC grain measurements compared to the calculations based on the current JEFF-3.3 model-based evaluation.

Measuring neutron capture rates on ILL-produced unstable isotopes (147Pm, 171Tm and 204Tl, and plans for 79Se and 163Ho) for nucleosynthesis studies

Neutron capture cross sections are among the main inputs for nucleosynthesis network calculations. Although well known for the majority of the stable isotopes, this quantity is still unknown for most of the unstable isotopes of interest. A recent collaboration between ILL, PSI, U. Sevilla and IFIC aims at producing the isotopes of interest at ILL, preparing suitable targets at PSI, and measuring their capture cross sections at facilities such as n_TOF/CERN, LiLiT and the Budapest Research Reactor (BRR). This work is focused on the description of the different beams and techniques and shows some highlights of the preliminary results of the capture measurements on 171Tm, 147Pm and 204Tl, along with the future plans for 79Se and 163Ho.

Production, separation and target preparation of 171Tm and 147Pm for neutron cross section measurements

The knowledge of the neutron capture cross sections of s-process branching point isotopes represents a basic requirement for the understanding of star evolution. Since such branching point isotopes are by definition radioactive, the measurement of their cross sections from thermal to stellar energies becomes a challenging task. Considerable amounts of material have to be produced, representing a significant radioactive hazard. We report here on the production and separation of 3.5 mg 171Tm from 240 mg 170Er2O3 and 72 μg 147Pm from 100 mg 146Nd2O3 irradiated at the ILL high flux reactor. Thin targets were prepared with high chemical and radioisotopic purity suitable for neutron capture measurements at n_TOF CERN and the SARAF-LiLiT facility.

Common risk factors for chronic non-communicable diseases among older adults in China, Ghana, Mexico, India, Russia and South Africa: the study on global AGEing and adult health (SAGE) wave 1

BACKGROUND

Behavioral risk factors such as tobacco use, unhealthy diet, insufficient physical activity and the harmful use of alcohol are known and modifiable contributors to a number of NCDs and health mediators. The purpose of this paper is to describe the distribution of main risk factors for NCDs by socioeconomic status (SES) among adults aged 50 years and older within a country and compare these risk factors across six lower- and upper-middle income countries.

METHODS

The study population in this paper draw from SAGE Wave 1 and consisted of adults aged 50-plus from China (N=13,157), Ghana (N=4,305), India (N=6,560), Mexico (N=2,318), the Russian Federation (N=3,938) and South Africa (N=3,836). Seven main common risk factors for NCDs were identified: daily tobacco use, frequent heavy drinking, low level physical activity, insufficient vegetable and fruit intake, high risk waist-hip ratio, obesity and hypertension. Multiple risk factors were also calculated by summing all these risk factors.

RESULTS

The prevalence of daily tobacco use ranged from 7.7% (Ghana) to 46.9% (India), frequent heavy drinker was the highest in China (6.3%) and lowest in India (0.2%), and the highest prevalence of low physical activity was in South Africa (59.7%). The highest prevalence of respondents with high waist-to-hip ratio risk was 84.5% in Mexico, and the prevalence of self-reported hypertension ranging from 33% (India) to 78% (South Africa). Obesity was more common in South Africa, the Russia Federation and Mexico (45.2%, 36% and 28.6%, respectively) compared with China, India and Ghana (15.3%, 9.7% and 6.4%, respectively). China, Ghana and India had a higher prevalence of respondents with multiple risk factors than Mexico, the Russia Federation and South Africa. The occurrence of three and four risk factors was more prevalent in Mexico, the Russia Federation and South Africa.

CONCLUSION

There were substantial variations across countries and settings, even between upper-middle income countries and lower-middle income countries. The baseline information on the magnitude of the problem of risk factors provided by this study can help countries and health policymakers to set up interventions addressing the global non-communicable disease epidemic.