Study on strontium isotope abundance-ratio measurements by using a 13-MeV proton beam

• Published in: Journal of the Korean Physical Society 2016, 69(6), , pp.1121-1124
• Main Authors: Jeong, Cheol-Ki, Jang, Han, Lee, Goung-Jin
• Format: Article
• Language: English
• Subjects: Absorption cross sections; Abundance; Atomic properties; Cyclotrons; Dating techniques; Gamma rays; Isotope ratios; Isotopes; Kinetic energy; Mass spectrometry; Mathematical analysis; Mathematical and Computational Physics; Nuclides; Particle and Nuclear Physics; Physics; Physics and Astronomy; Proton accelerators; Proton beams; Radioactive decay; Radioisotopes; Strontium 87; Strontium isotopes; Theoretical; Transmutation; Yttrium isotopes; 물리학
• ISSN: 0374-4884; 1976-8524
• DOI: 10.3938/jkps.69.1121

The Rb-Sr dating method is used in dating Paleozoic and Precambrian rocks. This method measures the 87 Rb and the 87 Sr concentrations by using thermal ionization mass spectrometry (TIMS) [J. Hefne et al ., Inter. J. Phys. Sci. 3 (1), 28 (2008)]. In addition, it calculates the initial 87 Sr/ 86 Sr ratio to increase the reliability of Rb-Sr dating. In this study, the 87 Sr/ 86 Sr ratio was measured by using a 13-MeV proton accelerator. Proton kinetic energies are in the range of tens of megaelectronvolts, and protons have large absorption cross-sections for ( p , n ) reactions with most substances. After absorbing a proton with such a high kinetic energy, an element is converted into a nuclide with its atomic number increased by one via nuclear transmutation. These nuclides usually have short half-lives and return to the original state through radioactive decay. When a strontium sample is irradiated with protons, nuclear transmutation occurs; thus, the strontium isotope present in the sample changes to a yttrium isotope, which is an activated radioisotope. Based on this, the 87 Sr/ 86 Sr ratio was calculated by analyzing the gamma-rays emitted by each yttrium isotope. The KIRAMS-13 cyclotron at the Cyclotron Center of Chosun University, where 13-MeV protons can be extracted, was utilized in our experiment. The 87 Sr/ 86 Sr isotope ratio was computed for samples irradiated with these protons, and the result was similar to the isotope ratio for the Standard Reference Material, i.e ., 98.2 ± 3.4%. As part of the analysis, proton activation analyses were performed using 13-MeV protons, and the experimental results of this research suggest a possible approach for measuring the strontium-isotope abundance ratio of samples.