Project

Discipline

nuclear astrophysics; nuclear data; radiochemistry; half-life measurements; cross sections

Lead
Kernphysikalische Daten haben grosse Bedeutung in verschiedenen Wissenschaftszweigen, die mit radioaktiven Materialien umgehen. Zum Beispiel erfordert die Untersuchung astrophysikalischer Prozesse bei Sternexplosionen oder die Erklärung der Isotopenhäufigkeiten auf der Erde die Kenntnis fundamentaler Daten wie Halbwertszeiten und Wirkungsquerschnitten. Die Halbwertszeiten sehr langlebiger Radionuklide sind häufig nur ungenau bekannt, weil das entsprechende Probenmaterial fehlt.
Lay summary
Inhalt und Ziel des Forschungsprojekts Wir wollen mit unserem Projekt die erforderliche Menge 146Sm – ein Radionuklid mit erheblicher Bedeutung für den astrophysikalisch bedeutsamen p-Prozess, aus bestrahlten Tantal-Proben extrahieren. Das Material soll dann zur Messung der Halbwertszeit verwendet werden. Dafür kommen Alpha-Spektrometrie und Massenspektrometrie zum Einsatz. Ausserdem wollen wir die Produktionsraten von Radionukliden in protonenbestrahltem Tantal und Wolfram in Abhängigkeit von der Projektilenergie messen und so die Wirkungsquerschnitte bestimmen. Bedeutung der Ergebnisse Die bis jetzt nur sehr ungenau bekannte Halbwertszeit des 146Sm wird besser bestimmt. Damit ist die bessere Erklärung astrophysikalischer Prozesse der stellaren Elementsynthese möglich. Die Informationen über die Produktion von Radionukliden in Tantal und Wolfram unter Protonenbeschuss verbessern die Datenbasis auf dem Gebiet der Wirkungsquerschnitte.

Direct link to Lay Summary

Last update: 30.03.2015

Active participation

Communication	Title	Media	Place	Year

Number	Title	Start	Funding scheme

PSI operates one of the most powerful high-energetic proton accelerators world-wide. The surrounding components like targets, shielding or construction materials become highly activated, and, due to the complex nuclear reactions taking place, contain very rare and exotic radionuclides in considerable amounts, which are urgently needed in several scientific research fields. Therefore, an initiative called ERAWAST (exotic radionuclides from accelerator waste for science and technology) was launched by the RadWasteAnalytics group at PSI several years ago with the aim to establish a collaboration between PSI as “isotope producer” and users of those exotic radionuclides. However, the RadWasteAnalytics group does not act only as an isotope deliverer, but is actively involved in the follow-up scientific applications, for instance as a member of the n_TOF collaboration at CERN or in half-life measurements. Several remarkable successes during the last years like the re-measurement of the 60Fe half-life (press release PSI, University Munich and Spiegel online in 2010) and the first study of the astrophysical important nuclear reaction 44Ti(alpha,p)47V in inverse kinematics at CERN-ISOLDE (press release PSI, CERN and New Scientist 2014) encourage us to work for developing an expert center for radiochemical separation and target preparation at PSI, aimed to produce the urgently necessary sample material for front end experiments in nuclear astrophysics, nuclear physics, and other related science fields. In the present proposal, we focus on two matrix materials, W and Ta, activated by protons. In order to improve the nuclear data basis for spallation induced production of long-lived radionuclides in these two materials, we intend first to determine excitation functions for isotopes like 148/150Gd, 146Sm and 154Dy. Additionally, volatiles like 129I or 36Cl shall be studied. For this part of the work, we use thin samples, which were irradiated with protons of different energies at the proton irradiation facilities in Uppsala and Saclay (in collaboration with the University of Köln, Germany) about 20 years ago. The results will have a high impact on the performance of the planned rotating W target for the European Spallation Source to be built in Lund (Sweden).For the second part of the project, we plan to extract lanthanide isotopes from highly activated Ta samples produced at PSI in the frame of the material research program STIP. We expect to obtain up to 1017 atoms of the pure alpha-emitters 148/150Gd, 146Sm and 154Dy, respectively. Comparable amounts of beta- and gamma-emitting long-lived lanthanides are expected to be available as well. These isotopes provide unique material for astrophysical studies with a high impact to understanding the nuclear processes of the element synthesis in the lanthanide region.Finally, we want to improve the accurateness and precision of the half-life value for 146Sm by performing two independent measurements with identical samples, one at PSI in collaboration with the University of California (Los Angelos), USA, and the other one at the Hebrew University Jerusalem, Israel. These results will contribute to clarify the present astrophysical and geophysical discrepancies of the two last measurements, which differ by more than 30%.