Yuzuka Sasaki photographs the light of radiation with an ordinary camera

Sasaki joined Accel Kitchen in her first year of junior high school. With a borrowed detector running at home, she measured cosmic rays and compared her data against the GOES satellites operated by NOAA and the geomagnetic observatories of the Japan Meteorological Agency, asking whether space weather is reflected in the cosmic rays arriving at ground level. She presented the results at the Hyper Interdisciplinary Conference in Osaka in 2022.

The question behind the present paper arose in her second year of junior high school. Supported by the SEEDS program of The University of Osaka and guided by Dr Yuuki Wada — a co-author of this paper — she set out to find whether the light a crystal emits under radiation could be captured with an ordinary camera. She presented that early work at the High School Radiation Class in 2023 and won an Award for Excellence. This paper is that same question, carried through over several years.

In her first year of senior high school she joined "Sakura Particles", a high-school team formed within Accel Kitchen, to enter Beamline for Schools, the international experiment competition run by CERN. Out of a record 461 proposals from around the world, the team became the first from Japan ever to win the grand prize, and spent two weeks running their experiment on a beamline at CERN in Geneva.

Then, in her second year of senior high school in 2025, she was chosen as one of four members of Japan's national team for the International Nuclear Science Olympiad (INSO) — a competition in nuclear science and radiation technology for entrants under 20 — and took part in the second edition, held in Malaysia. It was the first time Japan had ever sent a team.

An inquiry that began with a detector at home thus led to one international stage after another. The question at its origin — the wish to see invisible radiation with her own eyes — is what this paper answers.

For a long time the cloud chamber was the only educational tool that let students directly see radiation. In recent years small detectors pairing a scintillator — a material that glows when radiation strikes it — with an SiPM to turn that glow into an electrical signal have spread into schools, and Accel Kitchen has lent more than 300 of them to junior- and senior-high students. Yet what reaches the student is only a number on a display and an audible click: the scintillation light itself, the heart of the detector, stays hidden. The experience of measuring radiation breaks off at exactly the most interesting point.

Because that light is so faint, the received wisdom has been that a specialised, expensive photodetector is unavoidable. Meanwhile, however, the sensitivity of the sensors in everyday digital cameras has improved dramatically. This study starts from a simple question: could a camera of the kind schools already own capture that light directly?

The apparatus is a cardboard box lined with black light-blocking cloth. Inside it, a slender caesium iodide (CsI) crystal about 5 cm long lies on its side, with a radioactive source at its left-hand edge and a camera facing it side-on. Then the box is closed and the shutter is held open for ten minutes. Every indicator lamp is taped over so that no external light gets in at all.

Two deliberately different cameras were compared. One was an ordinary consumer compact digital camera; the other a cooled camera of the kind popular with school astronomy clubs and amateur astronomers. The latter cools its sensor to suppress noise, but it is a mass-produced product rather than a specialised scientific instrument — non-cooled models start from a few hundred dollars, cooled ones run to the order of $700–1000. The radiation came from three sealed sources (americium, barium and caesium), encapsulated in resin so that no material can escape.

The result: both cameras recorded the scintillation light. The edge where the source sat was brightest, fading with distance. And the width of the bright region differed clearly between sources — widest for the high-energy caesium, then barium, then americium. This puts directly before the eye the physics that higher-energy radiation penetrates deeper into the crystal.

The cooled camera gives less noise and a sharper distinction, but the same ordering is readable with the consumer digital camera alone. The team also captured the afterglow — the crystal continuing to emit for a while after the radiation is removed.

These results are a qualitative, educational comparison of how deep radiation penetrates, not a precise measurement. Even so, they show with real data that a single photograph from a consumer camera can distinguish the type and energy of radiation from the way the light spreads across it.

The point of the method is that an ordinary school can reproduce it as it stands. All it takes is a light-tight enclosure (a cardboard box lined with black cloth is enough), a camera capable of long exposures, a small tripod or stand, and one or more sealed check sources. No specialised high-sensitivity photodetector is needed. A consumer digital camera the school already owns will do; a cooled camera is available if a cleaner result is wanted, but since the difference between sources is visible with the consumer camera alone, it is an optional upgrade rather than a requirement.

On timing: building the box and setting up the camera takes roughly 15–20 minutes, each source needs a single exposure of about 10 minutes, and reading the images takes a further 20–30 minutes. The core activity therefore fits within a single class period, with the analysis optionally continued as homework. The student procedure has four steps: (1) assemble the light-tight box and confirm with a test exposure that no external light leaks in; (2) place the crystal on the stand with a sealed source at one edge; (3) expose for ten minutes without opening the box; (4) plot the brightness that appears against distance along the crystal.

Students see for themselves that the region near the source is bright, and that how wide that bright region is depends on the source. That leads naturally to questions: why does higher energy reach deeper? How does a crystal turn invisible radiation into light? Along with hands-on experience of long-exposure imaging and simple image analysis, the activity delivers something students rarely get — actually seeing the scintillation light at the heart of the detector.

On safety. Every source used here falls below the legal threshold of Japan's Act on the Regulation of Radioisotopes and is therefore not subject to regulation. The sources were kept in a locked, clearly labelled container and handled only under the supervision of a trained instructor. Note, however, that the availability and regulation of sealed sources differ from country to country. Teachers should use only sources permitted locally and follow their national regulations and institutional guidance.

This work was supported by the SEEDS program of The University of Osaka and The Mitsubishi Memorial Foundation for Educational Excellence.