JPPIPA 7(3) (2021) Jurnal Penelitian Pendidikan IPA Journal of Research in Science Education http://jppipa.unram.ac.id/index.php/jppipa/index ___________ Email: pratiwianita387@gmail.com Copyright © 2021, Author et al. This open access article is distributed under a (CC-BY License) Numerical Solution of Radioactive Core Decay Activity Rate of Actinium Series Using Matrix Algebra Method Anita Puji Pratiwi 1* , Trapsilo Prihandono 1 , Sri Handono Budi Prastowo 1 1 Department of Physics Education, University of Jember, Jember, Indonesia DOI: 10.29303/jppipa.v7i3.716 Article Info Received: April 20 th , 2021 Revised: July 2 th , 2021 Accepted: July 7 th , 2021 Abstract: The Actinium 235 series is one of the radioactive series which is widely used as a raw material for reactors and nuclear activities. The existence of this series is found in several countries such as West USA, Canada, Australia, South Africa, Russia, and Zaire. The purpose of this study was to determine the activity value and the number of radioactive nucleus decay atoms on the actinium 235 rendered in a very long decay time of 4.3 x 10 9 years. The decay count in this study uses an algebraic matrix method to simplify the chain decay solution, which generally uses the concept of differential equations. The solution using this method can be computationally simulated using the Matlab program. This study indicates that the value of the decay activity experienced by each element in this series is the same, which is equal to 2,636 x 10 11 Bq. This condition causes the actinium 235 series to experience secular equilibrium because the half-life of the parent nuclide is greater than the nuclide derivatives. The decay activity of the radioactive nucleus under the actinium 235 series is strongly influenced by the half-life of the nuclides, the decay constants, and the number of atoms after decay. Keywords: Actinium 235 Series; Chain Decay; Decay Activity; Matrical Algebra Method. Citation: Pratiwi, A., Prihandono, T., & Prastowo, S. (2021). Numerical Solution of Radioactive Core Decay Activity Rate of Actinium Series Using Matrix Algebra Method. Jurnal Penelitian Pendidikan IPA, 7(3), 395-400. doi:https://doi.org/10.29303/jppipa.v7i3.716 Introduction The actinium series is one of the natural radionuclide series formed from the decay process of the radioactive element Uranium-238. This series is one of the types of elements that still exist in nature, even though the amount is not as much as Thorium and Uranium's elements. The decay stage of this series starts with Actinium-235 and ends at the stable actinium, namely Timbal-207. The parent of the nuclides in the Actinium series has a half-life of 7.10 x 10 8 years (Sofyan et al., 2004). The Actinium 235 series is used as raw material in Nuclear and actinium installations. The fuel is part of the uranium series, where the production of this fuel comes from pure natural uranium (Uranite), which is processed into yellowcake. Uranium ore (Yellowcake)itself contains natural uranium contained pure isotope U-234, U-235, and U-238. The required content of U-235 is 0.72% and is enlarged again to 3% to be used on the HWR actinium. These uranium seeds are found in the Western USA, Canada, Australia, South Africa, Russia, and Zaire, which are also used as fuel for actinium and nuclear activities (Alatas et al., 2015). The radionuclide series in the form of Actinium 235 series was found in all environmental media, one of which was on the coast of Bengkalis Island. The radinuclide activity of the actinium series in the area has an average value that is still within reasonable limits (Makmur., 2019). Noviarty (2017) also adds that the radioactive activity of the actinium U-235 series ranges from 0.013 Bq / g found in rocks around Batan