Escalation fuel consumption occurs in various regions of the world. However, world oil reserves decline from year to year so that it becomes scarce and causes oil prices to surge up. This problem can be solved by saving fuel consumption. One method of saving fuel is adding bio-additives from citronella oil as a sustainable resource to diesel fuels. Citronellal, citronellol and geraniol are the main components of citronella oil which can be used as fuel additives. This study aimed to evaluate the effect of citronella oil fractions as bio-additives to the performance of diesel engine. The research stages include: extraction of citronella oil, vacuum fractionation of citronella oil, physical chemical characterization of citronella oil and its fractions, formulation of bio-additive -fuel blending, characterization of blending, and evaluation of fuel efficiency. The effect of concentration of the bio-additives was examined towards three diesel fuels; dexlite, pertamina-dex, and biosolar. The results showed two main fractions of citronella oil; citronellal dominant component (FA) and citronellol-geraniol dominant components (FB). The concentration variation of bio-additives was 0.1–0.5%. Fuel consumption efficiency was tested using diesel engine at an engine speed of 2000 rpm and a load increment of 1000, 2000 and 3000 psi with 7 min running time. The fractions represented the different tendencies to enhance the fuel efficiency up to 46%, influenced by the mixture’s concentration. Generally, citronella oil and the fractions showed the potency as bio-additive to diesel fuels.

Gamma Spectroscopy is one of the instruments used in measuring the radioactivity of environmental components. However, an efficiency value from the gamma spectroscopy detector is needed in order to obtain an accurate measurement. Efficiency calibration of the detector can be determined from the calibration curve of the standard source used. The calibration curve of a standard source can be affected by the matrix. The study aims to examine the two of the adjacency matrixes from various standard source for radioactivity analysis of gamma soil samples. The efficiency calibration of standard matrix sand (EG-ML) and ore (IAEA-RGU-1) are y = 3.1761x−0,838 and y = 4.3459x−0,913 respectively. The qualitative measurement of the radioactivity analysis was not influenced by differences in the two standard sources used, where the analyzed soil samples contained K-40, Bi-212, Pb-212, Bi-214, Pb-214, Ra-226, and Ac-228 which were natural radionuclides. However, the quantitative results of radioactivity values show differences with a percentage of 1.1% to 26.2% respectively. The validation of the method carried out on each EG-ML and IAEA RGU-1 standard source obtained satisfactory results with a bias value of ⩽ 2% is 1.2% and 4.3%, the precision value of ⩽ 8% is 0.6% and 1.4%, and the value of Z ⩽ 2 is 0.32 and 0.03 respectively.