Radioactivity & Nuclear Physics
At the heart of every atom lie phenomena that reveal the deepest workings of the universe. This chapter opens a window into the invisible world of radioactivity and nuclear physics through smartphone-powered experiments and investigations. From detecting high-energy particles with your phone’s camera to visualizing the trails of cosmic rays, we explore radioactive decay, nuclear interactions, and the quiet presence of natural radiation all around us.
These topics once belonged solely to advanced laboratories and specialized equipment—but now, with clever adaptations and modern mobile sensors, they’re accessible in classrooms and living rooms alike. The goal here isn’t just to measure, but to demystify—to make nuclear physics tactile, visible, and approachable. Throughout, safety remains a top priority: all experiments stay firmly within low-risk, educational territory.
Natural & Safe Radioactive Sources
Radioactive Curiosities — Natural and Collectible (NUCL-01)
Sensors Used: Camera (with radiation detection app)
What’s Measured: Qualitative detection of weak radioactive emissions
Description
Radioactivity isn’t confined to labs or nuclear power plants—it quietly surrounds us in everyday materials. In this experiment, students explore natural and collectible sources of radioactivity, using a smartphone equipped with a radiation detection app to observe faint traces of ionizing emissions. Common food items like Brazil nuts and bananas contain potassium-40, a naturally occurring radioactive isotope, while potassium chloride (“NoSalt”) and some varieties of granite countertops also emit weak levels of radiation. These sources are often too faint to trigger a smartphone detector but serve as excellent conversation starters about the omnipresence of background radiation.
For a more noticeable signal, students can turn to slightly more active—yet still generally safe—items. These include vintage radium-dial watches, tritium glow vials used in keychains and watches, thoriated TIG welding rods from hardware stores, and uranium glassware (also known as Vaseline glass), which glows under ultraviolet light and exhibits mild radioactivity. Antique ceramic tiles or pottery glazes can also occasionally contain detectable levels of radiation. While these items make for intriguing experiments in detection, they should always be handled responsibly: kept sealed, stored with care, and never brought into direct or prolonged contact with skin or food.
This exploration transforms what might otherwise seem like mundane household or collector’s items into tools for engaging with nuclear physics—and opens a fascinating window into the hidden activity of the atomic world.
Smartphone Radiation Detection
Smartphone Geiger Counter: Detecting Radiation with Your Camera (NUCL-02)
Sensors Used: Camera (with radiation detection app)
What’s Measured: Count rate of ionizing radiation (beta and gamma particles)
Description
With nothing more than a smartphone and a little software, students can transform their device into a basic Geiger counter. By installing an app like RadioactivityCounter and covering the camera lens with thick black tape or foil to block visible light, the phone’s camera sensor becomes sensitive to high-energy particles. When placed near a low-level radioactive source—such as an old radium watch dial, a piece of uranium glass, or simply ambient background radiation—the app can detect rare, random flashes caused by beta and gamma particles interacting with the sensor.
While this DIY detector is not as sensitive or accurate as professional instruments, it is a remarkable example of how consumer technology can open a door into nuclear physics. Students can go further by exploring shielding experiments—placing different materials between the source and sensor to observe changes in count rate. Paper, aluminum foil, books, and even lead alternatives can all be tested for their ability to block radiation.
Another fascinating extension is to carry the phone on a commercial flight, with the app running in airplane mode. Sealed in darkness, the phone can continue recording during ascent, cruise, and descent. The increase in altitude—and corresponding decrease in atmospheric shielding—results in a measurable increase in cosmic radiation, often two to three times greater than at sea level. It’s a striking demonstration of how radiation exposure changes with elevation and how smartphones can reveal the normally invisible interactions of our high-energy environment.
References:
[1] RadioactivityCounter app (hotray-info.de), https://www.hotray-info.de/html/radioactivity.html
[2] DIY Webcam Particle Detector — Physics Open Lab, https://physicsopenlab.org/2016/05/18/diy-webcam-particle-detector/
[3] Webcam Particle Detector Measurements — Physics Open Lab, https://physicsopenlab.org/2016/05/22/webcam-particle-detector-measurements/
Measuring the Half-Life of Tritium with a Smartphone (NUCL-03)
Sensors Used: Camera (with radiation detection app)
What’s Measured: Relative beta decay rate over time
Description
Tritium (³H), a rare radioactive isotope of hydrogen, undergoes beta decay with a well-established half-life of about 12.32 years. While this sounds like the domain of advanced laboratories, students can observe this decay process using a smartphone and a bit of experimental patience. Using a glow-in-the-dark tritium vial—commonly found in keychains or watches—as a source, and a radiation detection app that utilizes the smartphone camera, it’s possible to track changes in activity over time.
The key to this experiment is consistency. Set up your smartphone in a fixed, light-tight enclosure that ensures minimal background interference and a constant geometry between the phone and the tritium source. Record a baseline count rate using the radiation app over a period of days or weeks to average out short-term fluctuations. Then, one year later, repeat the measurement under identical conditions.
If done carefully, students should detect a small but measurable decrease in count rate, corresponding to the natural decay of the tritium. From this data, they can estimate the half-life and compare it to the known value. It’s a powerful way to explore radioactive decay, long-term measurement techniques, and the challenges of detecting subtle changes in an otherwise stable system—all using a smartphone and a dose of scientific patience.
Shielding Experiments: What Blocks Radiation? (NUCL-04)
Sensors Used: Camera (with radiation detection app)
What’s Measured: Count rate vs. shielding material
Description
Radiation is invisible—but its interaction with matter reveals important physical principles. In this experiment, students test how different materials block ionizing radiation, using a smartphone as a basic particle detector. Once your phone is equipped with a radiation detection app and shielded from light (typically with black tape or foil), it can record radiation counts from a low-level source like a radium dial, uranium glass, or tritium vial.
Place the source at a fixed distance from the phone and insert different materials between them—such as paper, plastic, aluminum foil, or a lead substitute. Record the count rate for each material over a fixed period. Even simple materials can dramatically affect the number of particles reaching the sensor, depending on the type and energy of the radiation. For example, beta particles may be blocked by something as thin as cardboard or foil, while gamma rays require denser shielding.
This simple test introduces students to key concepts in radiation physics: attenuation, shielding efficiency, particle type, and the inverse-square law. It’s a hands-on way to understand how hospitals, nuclear facilities, and even spacecraft are designed to protect against radiation—one layer at a time.
Cloud Chamber Builds
Cloud Chamber with Gel Ice Packs and Smartphone Light (NUCL-05)
Sensors Used: Camera, flashlight
What’s Measured: Ionizing particle tracks (alpha, beta, muons)
Description
One of the most beautiful ways to observe radioactivity is through a cloud chamber—a device that makes the invisible visible by revealing the trails of subatomic particles. This version uses everyday materials: soak a piece of black felt in isopropyl alcohol and place it inside a transparent container, such as a Tupperware box. Turn the container upside down onto a layer of flat gel ice packs and let it chill for several minutes. The alcohol vapor near the bottom of the chamber becomes supersaturated, creating the perfect environment for particle tracks to form.
In a darkened room, illuminate the chamber from the side with one smartphone flashlight, while using a second phone to record video from above or in front. After a few minutes, delicate white trails will begin to appear—these are the paths of ionizing particles like alpha particles, beta particles, or cosmic ray muons, slicing through the vapor. The thicker, shorter tracks typically indicate alpha particles, while longer, wispier lines suggest beta or muon paths.
You can analyze these trails by reviewing your footage frame by frame or asking ChatGPT for help interpreting angles, track lengths, and particle types. This experiment brings particle physics into your own home or classroom, offering an unforgettable glimpse into the invisible world of radiation and high-energy particles.
References:
[1] “Simple cloud chambers using gel ice packs,” https://iopscience.iop.org/article/10.1088/0031-9120/47/4/429
[2] “How to Build the World’s Simplest Particle Detector,” https://www.scientificamerican.com/blog/critical-opalescence/how-to-build-the-worlds-simplest-particle-detector/?redirect=1
Advanced Concepts
Triboluminescence: Strange Glows from Sugar (NUCL-06)
Sensors Used: Camera (slow-motion or night mode)
What’s Measured: Light emission during mechanical stress
Description
In complete darkness, snap a sugar cube or crush a wintergreen mint with pliers—and you may see a mysterious flash of blue-white light. This striking phenomenon, known as triboluminescence, occurs when the crystal structure of sugar fractures, separating electric charges that quickly recombine and discharge, emitting light in the process. With wintergreen mints, the effect is even stronger, thanks to methyl salicylate, which fluoresces and enhances the visibility of the flash.
Using your smartphone camera in slow-motion or night mode, try to capture these brief, bright flashes. You can even chew a mint in front of a mirror to observe the glow reflected from your teeth. The experiment blends chemistry, physics, and curiosity—and serves as an accessible introduction to light emission from mechanical stress. For deeper exploration, students can investigate molecular mechanisms, compare different crystal types, or consider practical uses, such as low-light sensors based on triboluminescent materials.
This quirky yet scientifically rich demonstration shows that even everyday objects like candy can reveal powerful physical principles hiding in plain sight.
References:
[1] “Strange Glows from Sugar,” The Naked Scientists, https://www.thenakedscientists.com/get-naked/experiments/strange-glows-sugar
[2] Glowing tape, https://www.thenakedscientists.com/get-naked/experiments/glowing-tape
Alpha Sparks: Observing Scintillation in ZnS(Ag) with a Smartphone (NUCL-07)
Sensors Used: Camera (video or night mode)
What’s Measured: Light flashes from alpha particle impacts
Description
Some of the most powerful interactions in nuclear physics happen silently—and invisibly—just millimeters from our eyes. In this experiment, students can witness the impact of individual alpha particles using a zinc sulfide scintillator and a smartphone camera. When an alpha-emitting source such as an old radium watch dial, an Am-241 button from a smoke detector, or a sealed uranium sample is brought close to a ZnS(Ag) surface in darkness, each particle that strikes the screen releases a tiny flash of light—just bright enough to be captured with the right tools.
To observe the effect, place the scintillator inside a light-tight tube or container and position your smartphone directly above it, using a macro lens or manual focus if available. Record in video or night mode, and carefully analyze the footage frame-by-frame. With patience, you may catch the elusive alpha sparks—each one a visual trace of a single nuclear decay. This demonstration not only visualizes radiation, but also connects students directly to the atomic scale, revealing how even tiny particles carry tremendous energy.
Capstone / Research Extension
Phone Radiation ≠ Radioactivity (NUCL-08)
Sensors Used: None required, but optional RF meter or smartphone EM field apps
What’s Measured: Qualitative distinction between types of electromagnetic radiation
Description
This experiment tackles one of the most persistent misconceptions in science communication: the belief that the radiation emitted by smartphones is the same as that from radioactive materials. The truth is more nuanced—and more fascinating. Smartphones do emit radiation, but it’s non-ionizing electromagnetic radiation, primarily in the microwave range between 800 MHz and 5 GHz, depending on the network (3G, 4G, 5G, or Wi-Fi). This is a far cry from the ionizing radiation associated with nuclear decay, which includes alpha particles, beta particles, gamma rays, and X-rays.
By framing this investigation as a capstone project, students can dive into the electromagnetic spectrum and clearly map out the boundary between “harmless” and “harmful” forms of radiation. A comparison chart or interactive display can show how radio waves, infrared, and visible light differ from the ionizing end of the spectrum. Using a smartphone EM field meter or a basic RF detector, students can measure signal strength and discuss Specific Absorption Rates (SAR) in real-world contexts.
This capstone makes an excellent bridge between physics and public understanding. It not only clarifies a critical concept but also encourages students to think critically about science media, health myths, and the role of measurement in resolving fear. It’s an ideal project for wrapping up the nuclear physics chapter with clarity, relevance, and a touch of myth-busting.
References:
[1] “How Much Radiation Are You Getting From Your Phone?,” https://www.youtube.com/watch?v=rKRTyEWj-EA