Short-lived radionuclides (SLRs) with half-lives less than 100 Myr are known to have existed around the time of the formation of the solar system around 4.5 billion years ago. Understanding the production sources for SLRs is important for improving our understanding of processes taking place just after solar system formation as well as their timescales. Early solar system models rely heavily on calculations from nuclear theory due to a lack of experimental data for the nuclear reactions taking place. In 2013, Bowers et al. measured 36 Cl production cross sections via the 33 S(α,p) reaction and reported cross sections that were systematically higher than predicted by Hauser-Feshbach codes. Soon after, a paper by Peter Mohr highlighted the challenges the new data would pose to current nuclear theory if verified. The 33 S(α,p) 36 Cl reaction was re-measured at 5 energies between 0.78 MeV/A and 1.52 MeV/A, in the same range as measured by Bowers et al., and found systematically lower cross sections than originally reported, with the new results in good agreement with the Hauser-Feshbach code TALYS. Loss of Cl carrier in chemical extraction and errors in determination of reaction energy ranges are both possible explanations for artificially inflated cross sections measured in the previous work.

The half-life of the neutron-rich nuclide, 60 Fe has been in dispute in recent years. A measurement in 2009 published a value of (2.62 ± 0.04) × 10 6 years, almost twice that of the previously accepted value from 1984 of (1.49 ± 0.27) × 10 6 years. This longer half-life was confirmed in 2015 by a second measurement, resulting in a value of (2.50 ± 0.12) × 10 6 years. All three half-life measurements used the grow-in of the γ-ray lines in 60 Ni from the decay of the ground state of 60 Co (t 1/2 =5.27 years) to determine the activity of a sample with a known number of 60 Fe atoms. In contrast, the work presented here measured the 60 Fe activity directly via the 58.6 keV γ-ray line from the short-lived isomeric state of 60 Co (t 1/2 =10.5 minutes), thus being independent of any possible contamination from long-lived 60g Co. A fraction of the material from the 2015 experiment with a known number of 60 Fe atoms was used for the activity measurement, resulting in a half-life value of (2.72 ± 0.16) × 10 6 years, confirming again the longer half-life. In addition, 60 Fe/ 56 Fe isotopic ratios of samples with two different dilutions of this material were measured with Accelerator Mass Spectrometry (AMS) to determine the number of 60 Fe atoms. Combining this with our activity measurement resulted in a half-life value of (2.69 ± 0.28) × 10 6 years, again agreeing with the longer half-life.

Short-lived radionuclides (SLRs) with half-lives less than 100 Myr are known to have existed around the time of the formation of the solar system around 4.5 billion years ago. Understanding the production sources for SLRs is important for improving our understanding of processes taking place just after solar system formation as well as their timescales. Early solar system models rely heavily on calculations from nuclear theory due to a lack of experimental data for the nuclear reactions taking place. In 2013, Bowers et al. measured 36 Cl production cross sections via the 33 S(α,p) reaction and reported cross sections that were systematically higher than predicted by Hauser-Feshbach codes. Soon after, a paper by Peter Mohr highlighted the challenges the new data would pose to current nuclear theory if verified. The 33 S(α,p) 36 Cl reaction was re-measured at 5 energies between 0.78 MeV/nucleon and 1.52 MeV/nucleon, in the same range as measured by Bowers et al., and found systematically lower cross sections than originally reported, with the new results in good agreement with the Hauser-Feshbach code TALYS. Loss of Cl carrier in chemical extraction and errors in determination of reaction energy ranges are both possible explanations for artificially inflated cross sections measured in the previous work.

No abstract

Equilibrium charge state distributions of stable 60 Ni, 59 Co, and 63 Cu beams passing through a 1µm thick Mo foil were measured at beam energies of 1.84 MeV/u, 2.09 MeV/u, and 2.11 MeV/u respectively. A 1-D position sensitive Parallel Grid Avalanche Counter detector (PGAC) was used at the exit of a spectrograph magnet, enabling us to measure the intensity of several charge states simultaneously. The number of charge states measured for each beam constituted more than 99% of the total equilibrium charge state distribution for that element. Currently, little experimental data exists for equilibrium charge state distributions for heavy ions with 19 Z p , Z t 54 (Z p and Z t , are the projectile's and target's atomic numbers respectively). Hence the success of the semi-empirical models in predicting typical characteristics of equilibrium CSDs (mean charge states and distribution widths), has not been thoroughly tested at the energy region of interest. A number of semi-empirical models from the literature were evaluated in this study, regarding their ability to reproduce the characteristics of the measured charge state distributions. The evaluated models were selected from the literature based on whether they are suitable for the given range of atomic numbers and on their frequent use by the nuclear physics community. Finally, an attempt was made to combine model predictions for the mean charge state, the distribution width and the distribution shape, to come up with a more reliable model. We discuss this new "combinatorial" prescription and compare its results with our experimental data and with calculations using the other semi-empirical models studied in this work.