Light can be emitted from the atom but light is not part of the atom. Electron can be emitted from the atom but electron is not part of the atom.
Alpha Particle and Gold Foil
Eric Su
eric.su.mobile@gmail.com
https://sites.google.com/view/physics-news/home
(Dated: April 24, 2026)
The discovery of the nucleus depends critically on the momentum of projectile. If Rutherford
had used protons, the nucleus would have remained hidden to him because proton backscattering
is essentially zero. Low momentum probe reveals less while high momentum probe reveals most
internal structure of the atom. The atom is not what Rutherford thought as mostly empty. The
scattering pattern implies a possible layer structure inside the atom.
I.
INTRODUCTION
Rutherford’s scattering experiment-also known as the
gold foil experiment-was performed by Hans Geiger and
Ernest Marsden between 1906 and 1913. In this experiment, a beam of alpha particles (helium nuclei) was directed at an extremely thin sheet of gold foil to study
how the particles scattered. The results revolutionized
atomic theory.
A radioactive material like radium emitted alpha particles toward gold foil which was very thin (about 100
nm). Zinc sulfide screen surrounded the foil and produced tiny flashes of light when struck by alpha particles. The detector was used to observe the flashes and
measure scattering angles.
Hans and Ernest observed that most particles passed
straight through the foil. Some particles deflected
slightly. A very small number (1 in 12,000) bounced
back. Rutherford concluded that the atom contains a
tiny, dense nucleus holding most of its mass and all positive charge. Electrons orbit this nucleus, meaning the
atom is mostly empty space.
The imagination ran wild. Rutherford did not ”see”
the nucleus. He inferred it. This leads to imaginary
electrons moving in the orbit as if they are moons around
the earth. Inference is not fact but Rutherford did not
understand the difference.
II.
A.
PROOF
Experiment
When alpha particles pass through a thin foil:
• Almost all go straight through with almost no deflection
• A tiny fraction scatter at large angles
• An extremely tiny fraction scatter backward
These observations alone do not prove the atom is mostly
empty. They simply show that alpha particles rarely experience strong forces inside the foil. Rare interactions
do not logically imply emptiness. For example:
• Neutrinos pass through the Earth with almost no
interaction
• That does not mean the Earth is empty
• It means neutrinos interact weakly
What convinced physicists was:
• the pattern of scattering
• the existence of large-angle events
• the failure of the plum-pudding model
• the success of the Coulomb point-charge model
Rutherford’s conclusion was a powerful inference not a
logical necessity.
B.
Electron Beam
Two types of experiment (Low-Energy Electron Scattering (RIKEN + Tohoku) and High-Precision Electron
Scattering (Mainz Microtron)) measure the same observable: the elastic scattering cross-section as a function of
angle and momentum transfer. From this, they extract
the form factor, which is just the Fourier transform of
the charge distribution. Across both experiments, the
measured form factor shows:
• A slow falloff at low momentum transfer
• Diffraction minima at the same momentumtransfer values
• Identical angular dependence
The shape of the scattering curve is the same across:
• different beam energies
• different detectors
• different laboratories
• different target nuclei
What the data show instead is:
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• the absolute angles move with energy
• scattering is smooth
• the relative pattern stays almost fixed
• no dips appear
The internal structure is essentially the same at all
these energies and the beam energy just changes how
that fixed structure maps into angles. So the consistent
relation between DIP angles across energies is strong evidence that there is internal structure and it’s stable, not
being reshaped by the beam. A repeating pattern in the
dip angles across different beam energies is direct evidence of a stable internal length scale inside the target.
At high beam energy:
• the projectile has enough momentum to probe tiny
distances
• the diffuse atom becomes irrelevant
• the projectile interacts with the tiny dense core
• dips appear
C.
Internal Structure
The experimental data show that
• There are multiple dips (minima) in the angular
distribution.
• Dip 1 is at a smaller angle than Dip 2, Dip 2 smaller
than Dip 3, etc.
• As beam energy increases, all dip angles shift toward smaller angles.
• The shifts are smooth, not random.
• The ratios between dip angles change slowly with
energy
This is direct evidence of internal structure. As beam
energy increases, all dip angles decrease. This is the crucial experimental fact.
But the atom didn’t shrink. The probe became
sharper. The data (angle) shows the perspective picture.
The actual object never changes. For low energy beam,
the target is as big as atom. For high energy beam, the
target is a small nucleus. None of them tell the true story.
The low-energy picture is incomplete because it cannot
resolve small structure. The high-energy picture is incomplete because it ignores the diffuse outer region. The
true object contains both the large atomic cloud and the
tiny dense core.
The beam energy simply selects which layer becomes
visible. Rutherford did not ”see” the nucleus. He inferred
it from the resolution-dependent appearance of the atom.
And modern experiments even the most advanced still
operate under the same principle:
• We never see the object itself.
• We only see how it looks under a particular probe.
It’s the nature of probing the microscopic world.
• Higher beam energy: higher projectile momentum
D.
• The same internal structure produces the same
characteristic ”momentum change for each dip
• To reach that same momentum change with a
higher incoming momentum, the scattering angle
must be smaller
This gives the empirical relation that the dip angles
shrink inversely with momentum.
Rutherford interpreted the tiny, sharp part as a nucleus. But what he actually discovered was a change
in appearance when the resolution changes. He did not
directly observe a nucleus. Modern experiments do the
same thing just with sharper probes:
• electrons
• The beam energy does not change the object.
• muons
• The beam energy changes what part of the object
becomes visible.
• protons
• Neither the ”big atom seen at low energy nor the
”tiny nucleus seen at high energy is the full story.
• They are perspective-dependent appearances, not
transformations of the object.
At low beam energy:
Modern Experiment
• neutrinos
• high-energy photons
• entire particle beams at the LHC
Each probe has a different resolution. And each reveals
a different layer of structure:
• the projectile interacts with the whole atom
• low energy: atoms
• the atom looks like a large, diffuse object
• higher: nuclei
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• higher: nucleons
• higher: quarks
• higher: gluon distributions
• higher: parton fluctuations
At every stage, the object appears to ”change, but the
object itself never changes. Only the probe changes.
Here is the reality to most physicists:
• We never see the nucleus directly.
• The bleeding = a strong, unmistakable interaction
(large-angle scattering)
The needle easily penetrates the cloth, so the blind
man only detects the person when the needle hits something solid enough to resist the body beneath. This is
exactly what happens in scattering.
1. Low-energy probe:
the needle bends or stops at the cloth. If the needle
is dull or weak:
• it gets caught in the cloth
• We never see quarks directly.
• it never reaches the body
• We never see gluons directly.
• the blind man concludes: ”This person is soft
and wide.
• We never see the Higgs field directly.
We see how the world responds to our probes. And
from that, we build models. Those models are incredibly successful but they are still models, not photographs. Every layer of structure we ”discover is really
a resolution-dependent appearance. None of them is the
final truth.
These models are:
• quantum field theory
• renormalization
• effective field theories
• scale-dependent physics
• the idea that ”particles are not fundamental
• the idea that structure depends on the probe
However, the experimental data show that there is no
single, absolute picture of a particle or atom. What we
see depends on the scale at which we look.
E.
Blind Man and Needle
A blind man uses a needle to detect a person. If the
person is naked, the needle hits skin and the blind man
detects them. If the person is wearing clothes, the needle passes through the cloth and only detects the person
when it draws blood. To everyone watching, the blind
man’s conclusion (”this person is naked) is wrong, because the blind man’s method ignores the clothing.
This is a great analogy for what happens in high-energy
scattering.
• The blind man = the experimenter
• The needle = the probe (alpha particles, electrons,
protons)
• The cloth = the atom’s outer layers
This is the low-energy view of the atom. Everything looks smooth. No sharp features appear. The
atom appears large and soft.
2. High-energy probe:
the needle pierces the cloth and hits the body. If
the needle is sharp and strong:
• it passes through the cloth without noticing it
• it only reacts when it hits something dense
• the blind man concludes: ”This person is tiny
and hard.
This is the high-energy view of the atom. The
probe only ”feels the dense nucleus. Sharp deflections occur. The atom appears tiny and solid.
Neither picture is the whole truth. The actual object
never changes. Low energy sees the atom. High energy
sees the nucleus. None of them tell the true story.
The blind-man analogy expresses this perfectly. The
cloth is real. The body beneath is real. The needle only
reveals whichever layer it is sensitive to. The blind man
mistakes one layer for the whole person. This is exactly
what happens in physics:
• Rutherford’s beam saw the ”body” (nucleus).
• Low-energy experiments see the ”cloth”.
• Modern experiments see even deeper layers
(quarks, gluons).
But the object itself never changes. Only the probe determines what becomes visible. A probe can be too weak
to reveal inner structure. A probe can be too strong to
notice outer structure. Every measurement is a perspective, not the whole person.
This is the foundation of:
• effective field theory
• renormalization
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• scale-dependent structure
• the modern view that ”particles are not absolute
objects
• the idea that every observation is perspectivedependent
Rutherford was not too wrong about the nucleus. But
he did not see the whole atom. His probe determined his
perception. Modern physics sees more layers.
Let’s stop listening to the blind man (mainstream
physics). Let’s stand with the people who can see the
whole situation. This shift is the key to building a unified picture of matter. This also essentially constructs
the modern idea of scale-dependent structure:
• Matter has layers.
• and deeper still, scale-dependent structure
that changes with energy
4. None of these layers contradict each other:
• They are not competing models.
• They are not different objects.
• They are not different atoms.
They are different layers of the same soft ball, revealed by different probes.
5. The key conclusion:
• The atom is not rigid.
• It has a soft outer layer.
• It has a dense inner layer.
• Different probes reveal different layers.
• No single measurement gives the whole object.
F.
Atomic Structure
Without the blind man’s confusion, without Rutherford’s historical framing, and without the probe’s bias,
the atom is not rigid. It is a soft ball with internal layers. The nucleus is one layer. The nucleus itself has
deeper layers.
1. The atom is a soft ball:
• The outer region is diffuse, gentle, and easily
penetrated.
• And that inner layer has its own internal
structure.
This is exactly how modern physics understands
matter.
Atomic Force Microscopy (AFM) is the perfect realworld demonstration of how a soft ball responds to different probes. It shows directly and visually that the
atom is not rigid.
AFM tip (gentle, molecular-scale probe)
• pushes atoms aside
• feels the soft outer layer
• maps the ”squishy surface
• A strong probe (like an alpha particle) passes
through it without noticing.
• maps the ”squishy surface
• A weak probe interacts with it and sees the
atom as large and soft.
• sees the atom as a soft ball
2. Inside the soft ball is a denser core:
• It is small compared to the atom.
• It is dense enough to push back on a strong
probe.
• A high-energy probe ”feels this layer and ignores the outer softness.
3. More structure inside the denser core:
This is the part Rutherford never saw because his
needle wasn’t sharp enough. Modern probes suggests:
• protons and neutrons
• inside them, quarks
• inside that, gluon fields
• inside that, quantum fluctuations
Alpha particle (fast, massive, high-energy probe)
• ignores the soft outer layer
• punches straight through
• only reacts when it hits the dense core
• sees the atom as a tiny hard point
Same atom. Different probe. Different appearance.
This is the resolution-dependent structure in action.
AFM doesn’t see the nucleus, but it proves the outer
layer is soft and extended. This is one of the most fundamental signatures of atomic structure.
Every one of these ”cloud” theories is actually a description of the Atom’s Material State. By replacing the
”cloud” with ”material,” these complex speculations become a single, mechanical reality that AFM can actually
map.
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TABLE I. Theoretical Cloud
Theoretical Term Material-Charge Equivalent
Electron Cloud
The Charged Material of the atom
Orbitals
The Physical Shape of that material
The Merging of that material
Bonding
Delocalization
The Flow of Property through the material
• Thick Foils/Filters:
A thicker 7.5 cm sapphire crystal can filter out or
capture up to 74% of fast neutrons. A 1 mm gold
sheet could capture nearly 45% of a thermal neutron beam.
H.
G.
Neutron Scattering
Neutrons are incredibly small compared to the space
between nuclei. Most neutrons simply ”miss” the nuclei
and fly straight through the foil. To capture 100% of
a beam, the foil must be thick enough to ensure a neutron eventually collides with a nucleus, a process known
as attenuation. Slow (thermal) neutrons have a much
TABLE II. Charge of the Universe
Foil Material Typical Capture Range
Gold (Thin)
0.1%–2%
Cadmium
≈100 % (Thermal)
Silver
40%–50% (Isotope dependent)
Aluminum
less than 0.1%
Proton Scattering
For a standard thin foil (e.g., 10 to 50 microns), the
vast majority of protons will pass through unless the
foil is thicker than the proton’s maximum range. Unlike neutron experiments where ”capture” is a primary
goal, proton-foil experiments typically focus on:
• Passing through:
About 99%+ for foils much thinner than the particle’s range.
• Nuclear Interaction (Capture/Reaction):
Only about 1.3% to 3% of protons undergo nonelastic nuclear interactions (like capture or fragmentation) in standard experimental setups.
• Stopping:
100% once the foil thickness exceeds the maximum
range for that specific energy
higher capture percentage. For example, the probability
of capture for certain isotopes increases dramatically as
neutron energy decreases below 1 eV.
• Thin Foils:
In a typical 10-micron gold foil, less than 1% of
thermal neutrons are captured. This is intentional,
as it allows the beam to pass through relatively
undisturbed while still providing enough data for
measurement.
[1] Eric Su: ”Two Centuries of Wrong Physics”,
https://sites.google.com/view/physics-news/physicserror
[2] Eric Su: List of Publications,
III.
CONCLUSION
Proton backscattering is essentially zero. If Rutherford
had used a proton beam instead of alpha particles, he
would not have seen the dramatic backscattering. He
would claim the nucleus is empty too.
The discovery of the atomic structure depends critically on the choice of projectile.
sites.google.com/view/physics-news/home/updates
[3] Eric Su: website,
https://sites.google.com/view/physics-news/home