Atomic Nucleus
Atomic Nucleus
The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom.
It was discovered in 1911 by Ernest Rutherford based on the 1909 Geiger–Marsden gold foil experiment.
An atom is composed of a positively charged nucleus, with a cloud of negatively charged electrons surrounding it, bound together by electrostatic force.
Almost all of the mass of an atom is located in the nucleus, with a very small contribution from the electron cloud.
Protons and neutrons are bound together to form a nucleus by the nuclear force.
The diameter of the nucleus is in the range of 1.70 fm ( ) for hydrogen (the diameter of a single proton) to about 11.7 fm for uranium.
The branch of physics concerned with the study and understanding of the atomic nucleus, including its composition and the forces that bind it together, is called nuclear physics.
SCRIT
SCRIT
Researchers in the RIKEN Nishina Center for Accelerator-Based Science, in Japan – demonstrated a setup that can use electron scattering to ‘see’ inside unstable nuclei, including those that don’t occur naturally.
Using an apparatus to hold the nuclei of caesium-137 atoms as well as make sure electrons could interact with them, using a system called SCRIT.
First, the researchers accelerated electrons in a particle accelerator to energise them, and then smashed them into a block of uranium carbide.
This produced a stream of caesium-137 ions (atoms stripped of electrons).
This isotope of caesium has a half-life of around 30 years.
The ions were then transported to the SCRIT system, which is short for ‘Self-Confining Radioactive-isotope Ion Target’.
This method enables to trap the target ions in three dimensions along the electron beam using the electric attractive force between the ions and the … electrons.
This resulting in overlap between the target ions and the electron beam.
This ‘overlap’ meant that the electrons had a good chance of colliding with the ions.
SCRIT allowed the researchers to achieve this with as few as 108 caesium-137 ions. Without SCRIT, they would have required a trillion-times more.
The next step was to study the electron-ion interaction.
When an electron is scattered by an atom’s nucleus, it behaves like a wave during the interaction.
Once scattered off, the electron-waves interfere with each other.
The physicists used a device called a magnetic spectrometer to record the resulting interference pattern.
Information about a nucleus can be more readily obtained from the electrons’ interference patterns.
What the researchers found out?
Based on the magnetic spectrometer’s readings, the physicists found that the internal structure of a caesium-137 nucleus is consistent with that put together from older studies and theoretical calculations.
The physicists have demonstrated a femtoscope.
Just as a light microscope can probe things that are around a micrometre in size, a femtoscope is a machine that can probe the femtometer scale (1 / 100000 0000000000) of atomic nuclei.
With the femtoscope, the hope is that a unifying theory of nuclear structure will be found somewhere in the gaps between expected and unexpected shapes.
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