Revisiting Rutherford's Alpha Scattering: A Glimpse into the Nucleus

by: Prof. B. P. Singh, Department of Physics, Aligarh Muslim University, Aligarh, INDIA

Ernest Rutherford (1871–1937), born in New Zealand, is known as the father of nuclear physics. Through his famous alpha scattering (Gold Foil) experiment, he demonstrated that atoms have a tiny, dense, positively charged nucleus. This overturned the earlier plum pudding model proposed by J. J. Thomson. He also achieved the first artificial nuclear reaction by converting nitrogen into oxygen. He was awarded the Nobel Prize in Chemistry in the year 1908. Rutherford’s pioneering work laid the foundation for modern atomic and nuclear science. As the Director of the Cavendish Laboratory, he mentored several great scientists, including Niels Bohr and James Chadwick. Let me now give you a brief glimpse of the his famous alpha scattering (gold foil) experiment using modern detector systems, being carried out regularly in our labs.

More than a hundred years ago, a simple gold foil changed the world. When Ernest Rutherford fired tiny alpha particles at a thin sheet (foil) of gold, he didn’t just watch them scatter, he looked straight into the heart of the atom and discovered the nucleus. Today, at the Experimental Nuclear Physics Laboratory, AMU Aligarh, our students get to relive that same scientific thrill. Using modern instruments and real radioactive sources, they repeat one of the most important experiments in the history of science, the Rutherford alpha particle scattering experiment, and witness the very evidence that revealed the atomic nucleus.

A Classic Experiment Reimagined

In our lab, a tiny capsule of Americium-241 acts as the alpha-particle beam. These alpha particles, each carrying about 5.485 MeV of energy, are guided through a precision collimator to form a narrow, straight beam. This invisible stream of charged particles then strikes a delicate extremely thin gold foil inside a vacuum chamber. Vacuum typically of the order of 10^-3 Torr is created employing a simple rotary oil pump.

Around the thin gold foil, a silicon surface-barrier detector mounted on a rotating arm records the scattered alpha particles at different angles. As the detector moves and the counts rise increase at forward angles and fall as the scattering angle increases. With this students realize they are tracing the same mysterious pattern that puzzled Rutherford’s team in 1909. Every spike and dip in the data tells a story. A story of invisible forces, electric repulsion, and the discovery of the nucleus itself.

What We Observe?

Here’s a glimpse of a typical dataset recorded during one of our student runs:

Figure 1: The angular dependence of scattered alpha particles, a steep fall in intensity at higher angles, just as Rutherford predicted.

At small angles, thousands of alpha particles pass almost straight through the foil, showing that most of the atom is empty space. At large angles, only a few alpha particles are scattered back, proving the presence of a small, massive, positively charged nucleus at the center that deflects them through strong Coulomb forces.

The Physics Behind the Wonder

The scattering follows the Rutherford formula;

It predicts that the number of particles scattered falls dramatically with the fourth power of the sine of half the angle. And when our students plot the data, the curve matches the theory — almost perfectly. That moment of agreement between experiment and equation is electrifying. It’s physics coming alive.

Here (above) is the single, final plot that beautifully represents the verification of Rutherford’s scattering experiment, showing experimental data and the theoretical Rutherford curve almost agreement to each other. This figure captures the essence of Rutherford’s discovery, a steep fall in scattering intensity at larger angles, confirms the existence of a small, dense nucleus. The results obtained from the experiment confirm the Rutherford’s groundbreaking discovery. The measured angular distribution of scattered alpha particles shows a sharp decline in intensity at higher scattering angles, precisely as predicted by the Rutherford scattering law (∝ 1/sin⁴(θ/2)). This clear agreement between the experimental data and theoretical curve demonstrates that most alpha particles pass undeflected through the thin gold foil, confirming that atoms are mostly empty space, while a small fraction undergo large-angle deflections, providing direct evidence for the existence of a tiny, massive, positively charged nucleus at the atom’s center. These results not only validate a century-old theory but also allow students to see the nucleus revealed through their own data. This works as a true bridge between classical discovery more than 100 years back and modern experimental physics.

A Moment That Changed Science

Rutherford’s astonishment lives on in every student of our M.Sc. class, who perform this experiment. Rutherford after looking at the data said: “It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.” Those words echo through our lab as students watch the data unfold on the plot. They suddenly grasp what it means to discover something no one expected. To challenge an existing idea and replace it with a new vision of reality was really a visionary point of view.

More Than Just Data

Beyond the graphs and counts, this experiment teaches so much more. Students learn to operate radiation detectors, vacuum systems, and electronic instrumentation. The same skills are used in nuclear research labs worldwide. But even more importantly, they learn what scientific curiosity feels like:

• the patience of aligning the semiconductor detector,

• the anticipation as the counts appear indicating alpha particle detection, and

• the thrill of seeing a law of nature emerge from their own data, when plotted.

Every run of the experiment becomes a bridge between history and discovery.

Why It Still Matters?

Revisiting Rutherford’s experiment reminds us that even the simplest setup, an alpha-source, a thin gold foil, and a semiconductor detector, can reveal the deepest secrets of matter. It connects generations of physicists, from Rutherford’s candle-lit lab to AMU’s modern experimental nuclear physics lab, through the same question:

What lies inside the atom?

For today’s students, it’s not just about confirming an old theory. It’s about exploring the unseen world within matter. Physics grows when we observe carefully, imagine boldly, and question fearlessly. Each discovery opens a new window into how nature works. The atom is not just a model from textbooks, it’s a story of curiosity, courage, and the human drive to understand the universe.

Such experiments spark a deep curiosity for nuclear physics. When students handle the setup themselves, placing the radioactive source, creating a vacuum, and recording scattering events. Here they don’t just learn theory, they experience discovery done hundred years back. The thrill of seeing results first-hand connects them directly to the spirit of Rutherford and the pioneers of atomic science.

Conclusion is nothing, but is considered as the the Spirit of Discovery

In every gold foil and every alpha particle scattering event, students find more than data, they find inspiration. At Nuclear Physics laboratory, AMU Aligarh, the Rutherford experiment isn’t just a part of the syllabus; it’s a journey back to the birth of nuclear physics. When students see that first scattering plot appear, they are not just verifying a century-old formula, they are rediscovering the nucleus, with Rutherford himself.

 Author of this blog: Prof. B. P. Singh, Experimental Nuclear Physicist, Aligarh Muslim University, working in the field of Nuclear Reaction Dynamics using particle accelerators, with more than 35 years of research experience. He is actively engaged in popularizing nuclear technologies for societal benefits. His work particularly focuses on promoting the role of nuclear energy in power generation, dispelling myths associated with nuclear science, and advancing the applications of nuclear techniques in the field of medicine and other areas.