Mapping Radiation Before the Machine: Indonesian Team Builds a Baseline for a Future Medical Cyclotron

Before the first proton is ever accelerated, a team of Indonesian researchers has carefully measured what the natural radiation environment at a proposed medical cyclotron site in West Java already looks like. The study, published in the journal Environmental Geochemistry and Health, describes a pre-operational radiological baseline for a planned medical cyclotron facility in South Cikarang, an industrial area that will one day produce radioisotopes and radiopharmaceuticals for nuclear medicine. The work, led by Dikdik Sidik Purnama of the Bandung Institute of Technology and the National Research and Innovation Agency (BRIN), with colleagues from several BRIN research centers, offers a template that other countries preparing to build radiological facilities may find increasingly valuable.

The logic behind a baseline study is deceptively simple but scientifically crucial. Every patch of ground on Earth emits ionizing radiation, driven by naturally occurring radionuclides such as uranium-238, thorium-232, and potassium-40 in soils and building materials, along with a contribution from cosmic rays. When a facility that handles radioactive material begins operating, regulators and the public will inevitably ask whether the environment has changed. Without a rigorous, statistically defensible picture of conditions before operations start, it becomes nearly impossible to distinguish pre-existing geological variability from any future operational influence. The new study addresses that problem head-on by characterizing the ambient gamma-radiation field at the South Cikarang site with unusual methodological care.

The researchers designated nineteen monitoring locations across terrain that is anything but uniform, mixing engineered fill, natural clay, and vegetated ground. Because one designated point, labeled Point B, was physically inaccessible, direct measurements were ultimately obtained at eighteen locations. At each accessible point, the team measured the ambient dose equivalent rate, written H*(10), which is the standard operational quantity for estimating external exposure to penetrating radiation. Crucially, measurements were taken at two heights: at the ground surface and at one meter above ground, the height at which a standing human body would receive most of its external dose. Each detector-and-height configuration was repeated ten times, allowing the team to quantify measurement uncertainty rather than relying on single spot readings.

What makes the study technically interesting is its dual-detector strategy. The team used two fundamentally different radiation detection technologies in parallel: a Geiger-Müller tube, a gas-filled detector prized for ruggedness and simplicity, and a sodium iodide scintillation detector, NaI(Tl), which converts gamma-ray energy into flashes of light and offers higher sensitivity. The two detector types respond differently to the energy spectrum of environmental gamma rays, so agreement between them is a powerful internal check. Across all detector systems and both measurement heights, the ambient dose equivalent rates ranged from 0.030 to 0.120 microsieverts per hour, values comfortably within the range typical of natural background worldwide. The median reduction in dose rate from the surface to one meter height was 11.8 percent for the GM detector and 14.2 percent for the NaI(Tl) system, a pattern consistent with gamma rays originating primarily from radionuclides in the soil itself.

The statistical agreement between the two instruments was striking. Pearson correlation coefficients reached 0.958 at ground level and 0.919 at one meter, indicating that despite their different physical principles, the two detector systems told essentially the same story across the site. In radiation metrology, this kind of cross-validation matters enormously. A single detector can drift, suffer from energy-response artifacts, or be fooled by site-specific conditions. When two independent technologies converge on the same spatial pattern with nearly identical rankings of hot and cold spots, confidence in the resulting baseline rises dramatically. The authors also subjected their data to formal uncertainty analysis, following international guidance from the International Atomic Energy Agency on quantifying uncertainty in nuclear analytical measurements, which strengthens the study’s defensibility in a regulatory context.

Perhaps the most visually compelling part of the work is its use of geostatistics. Rather than treating the eighteen measurement points as isolated numbers, the team applied Ordinary Kriging, a spatial interpolation technique borrowed from mining geology and soil science. Kriging does not simply draw smooth contours between points; it models the underlying spatial structure of the data, using a variogram to describe how quickly radiation values become uncorrelated with distance. The analysis identified meaningful spatial dependence over a range of approximately 100 meters, meaning that measurements taken closer together than that distance carry information about one another, while points farther apart are effectively independent. That length scale is itself a finding: it tells future monitoring programs how densely they need to sample to capture the site’s true variability.

The geostatistical mapping also revealed a clear physical explanation for the radiation pattern. Higher dose rates clustered over areas of engineered sand and crushed-stone fill, materials that typically contain mineral grains enriched in naturally occurring radionuclides, while lower values were generally associated with natural clay-dominated and vegetated ground. This association between construction fill and elevated gamma readings echoes findings from other parts of Indonesia, including previous work by overlapping research teams in the Mamuju region of West Sulawesi, which is known for unusually high natural radiation. In a rapidly industrializing landscape like Cikarang, where ground is routinely reshaped and imported fill is common, understanding that human-modified ground can shift the local radiation field is essential context for any future facility monitoring.

To translate the measurements into human-health terms, the team performed screening-level dose and risk assessments. Annual external dose estimates for a hypothetical person at the site ranged from 0.052 to 0.172 millisieverts per year, and excess lifetime cancer risk estimates ranged from 1.76 times ten to the minus four to 5.86 times ten to the minus four. These figures should be read as conservative screening values rather than predictions of harm; they sit well within the range of doses people receive from natural background radiation everywhere on the planet, which averages a few millisieverts per year globally according to United Nations Scientific Committee assessments. The point of the exercise is not alarm but calibration: by quantifying the risk landscape before the cyclotron is built, the researchers have created a reference line against which any future change can be judged.

Medical cyclotrons occupy a distinctive niche in the radiological world. Unlike nuclear power plants, they accelerate charged particles to bombard targets and produce short-lived isotopes such as fluorine-18 and technetium precursors used in diagnostic imaging. Their routine emissions are modest, but neutron activation, activated components, and gaseous releases during target irradiation mean that regulators, following standards set by Indonesia’s nuclear regulator BAPETEN and international guidance from the IAEA and the International Commission on Radiological Protection, still require careful environmental surveillance. A credible pre-operational baseline is the foundation of that surveillance, and the South Cikarang study demonstrates how to build one with limited resources: replicate measurements, dual detectors, height-resolved sampling, and spatial statistics.

The broader significance of the study lies in its transferability. The authors describe their approach as a framework integrating measurement validation, uncertainty analysis, and spatial modeling for environmental surveillance around planned radiological facilities, and the recipe is deliberately generic. Any country planning a cyclotron, a radioisotope production plant, or even a research reactor could adapt the same workflow, adjusting the sampling density to the spatial correlation scale revealed by its own variogram. As nuclear medicine expands across Southeast Asia and the global south, demand for radiopharmaceuticals is growing faster than the infrastructure to produce them, and with that growth comes a parallel need for environmental science that earns public trust. This study, supported by BRIN and an ITB research grant, with site access provided by the state pharmaceutical company PT Bio Farma, shows that meticulous baseline work can be done before the first beam is ever switched on, ensuring that when questions arise about a facility’s environmental footprint, the answer will rest on data rather than doubt.

Subject of Research: Pre-operational environmental gamma-radiation baseline characterization at a proposed medical cyclotron facility in Indonesia

Article Title: Environmental radiological baseline characterization of a proposed medical cyclotron facility in Indonesia using dual-detector measurements and geostatistical analysis

Article References: Purnama, D. S., Muliawan, D., Santoso, M., Fitriana, R., Nugraha, E. D., Abdullah, A. R. A., & Permana, S. (2026). Environmental radiological baseline characterization of a proposed medical cyclotron facility in Indonesia using dual-detector measurements and geostatistical analysis. Environmental Geochemistry and Health, 48(15), Article 617. https://doi.org/10.1007/s10653-026-03505-0

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03505-0

Keywords: medical cyclotron, radiological baseline, ambient dose equivalent, Geiger-Müller detector, NaI(Tl) scintillator, Ordinary Kriging, geostatistics, environmental monitoring, radiation protection, nuclear medicine, Indonesia, West Java