Volume 10. Issue 1. 129-138 APRIL 2021 Jurnal Ilmiah Pendidikan Fisika Al-BiRuNi https://ejournal.radenintan.ac.id/index.php/al-biruni/index DOI: 10.24042/jipfalbiruni.v10i1.8508 P-ISSN: 2303-1832 e-ISSN: 2503-023X Determining Optical Band Gap Energy of Chitosan Biopolymer Film as the Effect of Gamma Rays Irradiation Dhita Ariyanti 1 *, Kartini Megasari 2 1, 2 Nuclear Chemical Engineering, Polytechnic Institute of Nuclear Technology, National Nuclear Energy Agency (BATAN), Indonesia. Babarsari Street POBOX 6101 YKBB Yogyakarta 55281, Phone +62-274-484085, 489716 *Corresponding Address: dhita.ariyanti@batan.go.id Article Info ABSTRACT Article history: Received: February 03 rd , 2021 Accepted: April 24 th , 2021 Published: April 30 th , 2021 Dosimeter is one of the apparatus needed by radiation workers. From a dosimeter, radiation workers can control the absorbed dose. This research aims to investigate the properties characteristics of chitosan film for dosimeter usage. Thin-film chitosan polymer blended starch and methyl orange were prepared by phase inversion methods. The spectra were investigated by UV-Visible spectrophotometric in the wavelength range of 400-500 nm, while the optical band gap energy was investigated by the Tauch plot method. The increase in gamma rays irradiation dose affected the optical bandgap energy. It was observed that the value of band gap energy within the direct transition, indirect transition, and direct forbidden transition decreased along with the increase of gamma rays irradiation 3 and 7 kGy doses. These results indicated that gamma-ray irradiation could cause structural defects due to the excitation of non-bonding electrons. These structural defects could reduce the value of band gap energy because of the width localized states. Keywords: Chitosan; Gamma rays; Optical band gap. © 2021 Physics Education Department, UIN Raden Intan Lampung, Indonesia. INTRODUCTION Nuclear technology has developed very rapidly over time. Various scientific disciplines, nuclear technology used in various fields such as medical diagnosis and imaging, sterilization, therapy treatment, criminal investigation, agriculture, and space exploration. With the higher usage of nuclear technology in the environment, the usage of dosimeter more increase. This method of measuring the quantity of radiation is also known as dosimetry. Meanwhile, a series of tools used to measure the ionizing radiation exposure received by each person in a radiation field is called a dosimeter. The dosimeter study focuses on the development of active ingredients capable of responding to exposure to either particle radiation or electromagnetic waves (American Nuclear Society, 2014). Dosimeter is one of apparatus must be used to radiation employee. Radiation exposure can affect healthy damage such as skin burned, cancer, cataract, etc. Nowadays, the Indonesian government is still import dosimeters from abroad. So, this research will explore about characteristics of synthesized dosimeter from polymer. Polymers in the form of thin films (layer) are one of the materials that can be used for the manufacture of dosimeters. The performance effects of this thin-film polymer are influenced by several factors including resistance to chemicals and most importantly the response it generates when interacting with radiation (Suman et al., 2015). This research will discuss the characteristics of the thin film chitosan polymer blended starch and methyl orange as dosimeter potential ingredients against gamma radiation. Chitosan and starch are