Experimental Evidence: Unraveling The Arom Model

The AROMA project is a European initiative that aims to harness the full potential of NeuroSpin's 11.7T scanner, the highest field strength for magnetic resonance imaging (MRI) to date. This technology will enable the non-invasive exploration of the human brain at an unprecedented scale, with a focus on cognitive functions and disorders such as schizophrenia, autism, and depression.

One of the key objectives of the project is to maximise the signal-to-noise ratio and obtain in vivo images in under 2 seconds. This will be achieved through innovative RF coil designs and radiofrequency pulse sequences. Another challenge that the project aims to address is the correction of subject-related, non-thermal noise, such as that induced by head motion, respiration, and cardiac pulsation, which can compromise the targeted functional sensitivity.

The AROMA project has received funding from the European Union's Horizon 2020 research and innovation programme, reflecting the significance and potential impact of this endeavour.

John Dalton's experiments with gases in the early 19th century led to his atomic theory

John Dalton is known as the father of atomic theory. In the early 19th century, he conducted experiments with gases that led him to propose a modern theory of the atom.

Dalton's interest in atmospheric pressures and gases led him to examine the nature and chemical makeup of air. He discovered that air was not a chemical solvent but a mechanical system composed of small individual particles. This led him to formulate Dalton's Law of Partial Pressures, which states that the total pressure of a mixture of gases is equal to the sum of the partial pressures exerted by each individual gas.

Dalton's work with gases also led him to discover that certain gases could only be combined in certain proportions, even if they shared a common element or group of elements. This observation, along with his study of the laws of conservation of mass and definite proportions, led him to develop his law of multiple proportions. This law states that if two elements can form multiple compounds, the ratios of the masses of the second element that combine with a fixed mass of the first element will be in ratios of small whole numbers.

Dalton's atomic theory, first presented in 1803, was based on the following assumptions:

• Matter is made up of atoms that are indivisible and indestructible.
• All atoms of an element are identical.
• Atoms of different elements have different weights and chemical properties.
• Atoms of different elements combine in simple whole numbers to form compounds.
• Atoms cannot be created or destroyed; they can only be combined, separated, or rearranged.

Dalton's atomic theory and his law of partial pressures have had a significant impact on the fields of chemistry and physics. His work laid the foundation for many other scientific discoveries and contributed to the progression of chemistry into a modern science.

J.J. Thomson's cathode ray tube experiments in the 19th century discovered the electron

J.J. Thomson's cathode ray tube experiments in the 19th century were pivotal in discovering the electron. His work in this area earned him the Nobel Prize in Physics in 1906.

In the late 19th century, physicists were attempting to understand the nature of cathode rays. They knew that an electric charge passed across a glass tube with wires inserted at both ends would create a fluorescent glow. This was known as a cathode ray tube or 'electron gun'. The cathode ray tube was invented in 1897 by German physicist Karl Ferdinand Braun.

J.J. Thomson, an English physicist, conducted a series of experiments to determine the nature of cathode rays. He first set out to prove that the negative charge and the ray were intertwined. He did this by building a cathode ray tube with a metal cylinder on the end with two slits leading to electrometers, which could measure small electric charges. By applying a magnetic field across the tube, he found that the charge had been bent away by the magnet, proving that the negative charge and the ray were inseparable.

In his second experiment, Thomson aimed to prove that the rays carried a negative charge. He constructed a cathode ray tube with a fluorescent coating at one end and a near-perfect vacuum. Halfway down the tube were two electric plates, producing a positive anode and a negative cathode, which he hoped would deflect the rays. As expected, the rays were deflected by the electric charge, proving that the rays were made up of charged particles carrying a negative charge.

In his third experiment, Thomson attempted to work out the nature of the particles. He found that the charge-to-mass ratio was so large that the particles either carried a huge charge or were a thousand times smaller than a hydrogen ion. He decided on the latter, concluding that the cathode rays were made of particles that came from within atoms. This was a very bold and innovative idea.

Thomson's cathode ray tube experiments led to a greater understanding of the atom and its internal structure. His work also inspired future generations of physicists, including his student Ernest Rutherford, who developed Thomson's ideas and theorised that the atom consisted of a positively charged nucleus surrounded by orbiting tiny negative particles, which he called electrons.

Ernest Rutherford's gold foil experiment in 1909 discovered the atomic nucleus

In 1909, Ernest Rutherford directed a landmark series of experiments known as the Rutherford scattering experiments, which provided crucial insights into the structure of atoms. Rutherford's student, Ernest Marsden, reported unexpected results that Rutherford described as the most incredible event of his life.

In the now-famous gold foil experiment, alpha particles were fired at a thin gold foil, and their scattering was observed. To Rutherford's astonishment, some alpha particles scattered backwards. This observation contradicted the prevailing model of the atom, the "plum pudding" model proposed by J.J. Thomson, which envisioned electrons embedded in a positively charged sphere.

Rutherford's explanation for the unexpected scattering was published in May 1911. He proposed that the atom had a hard, dense core at its center, known as the nucleus, containing a high central charge and most of the atom's mass. This nucleus was much smaller than the atom itself, with Rutherford calculating it to be approximately 1/100,000 the size of the atom. Thus, the atom was mostly empty space.

Rutherford's model of the atom, based on these experimental results, marked a significant departure from Thomson's model. It suggested that the atom consisted of a tiny, dense, positively charged nucleus surrounded by electrons, akin to a planetary system. This discovery laid the foundation for modern nuclear physics and inspired further research into atomic structure.

Niels Bohr's quantum theory in the early 20th century explained the arrangement of electrons

In the early 20th century, Danish physicist Niels Bohr proposed a model of the atom that successfully explained the arrangement of electrons. This model, developed between 1911 and 1918, built upon Ernest Rutherford's nuclear model and was the first to incorporate quantum theory.

According to Bohr's model, electrons travel in distinct orbits around a small, dense nucleus, similar to the structure of the Solar System. However, instead of gravity, the electrons are attracted to the nucleus by electrostatic force. Crucially, Bohr's model introduced the idea that the energy levels of electrons are discrete, meaning they can only occupy certain orbits. This was a significant departure from classical physics, which predicted that electrons would lose energy and spiral into the nucleus due to electromagnetic radiation.

Bohr's model explained why atoms emit light at specific wavelengths, a phenomenon previously observed in late 19th-century experiments with electric discharges. By proposing that electrons could only occupy certain orbits, Bohr was able to account for why atoms emit light in discrete frequencies, forming distinct spectral lines. This model successfully explained the Rydberg formula for hydrogen's spectral emission lines, providing a theoretical basis for previously known empirical results.

Bohr's work had a profound impact on the field of physics, and he is regarded as one of the foremost physicists of the 20th century. His contributions to quantum theory and atomic structure earned him the Nobel Prize in Physics in 1922.

James Chadwick's experiments with beryllium radiation in 1932 discovered the neutron

James Chadwick's experiments with beryllium radiation in 1932 led to the discovery of the neutron, a fundamental particle in the domain of nuclear science. Here is a detailed account of Chadwick's experiments and their significance:

James Chadwick's Background

James Chadwick was born in 1891 in Manchester, England, and graduated from the University of Manchester in 1908. He worked with Ernest Rutherford on various radioactivity studies and obtained his master's degree in 1913. During World War I, Chadwick was interned in Germany but continued his scientific pursuits. After the war, he returned to England and earned his PhD in 1921, working with Rutherford at the University of Cambridge. Chadwick became Assistant Director of Research at the Cavendish Laboratory in 1923 and was elected a Fellow of the Royal Society in 1927.

The Quest for the Neutron

By the 1920s, physicists knew that the atomic nucleus contained protons. However, there seemed to be something more in the nucleus, as the atomic mass was greater than the number of protons. In 1920, Rutherford proposed the existence of a neutral particle formed by the combination of a proton and an electron, but this particle was elusive and difficult to detect.

Chadwick's Experiments with Beryllium Radiation

In 1932, Chadwick's attention was drawn to an experiment conducted by Frédéric and Irène Joliot-Curie. They bombarded beryllium with alpha particles from a polonium source and studied the resulting radiation. This radiation knocked loose protons from hydrogen atoms in a paraffin wax target, and those protons recoiled with very high velocity. The Joliot-Curies interpreted this radiation as high-energy gamma photons.

However, Chadwick disagreed with this interpretation. He reasoned that photons, having no mass, would not knock loose particles as heavy as protons. Chadwick decided to perform similar experiments himself, and he became convinced that the radiation emitted by beryllium was a neutral particle with approximately the same mass as a proton. He conducted experiments with other targets, including helium, nitrogen, and lithium, which helped him refine his understanding of the new particle's mass.

The Discovery of the Neutron

After about two weeks of experimentation, Chadwick published a paper titled "The Possible Existence of a Neutron," favoring the neutron interpretation over gamma ray photons. A few months later, in May 1932, he submitted a more definitive paper, "The Existence of a Neutron." By 1934, it was firmly established that the neutron was a new fundamental particle, distinct from the proton and electron.

The Impact of Chadwick's Discovery

The discovery of the neutron revolutionized the field of atomic physics. It provided scientists with a new tool to probe the atomic nucleus, as neutrons, being uncharged, could penetrate much further into a target than protons. This led to significant discoveries, such as the creation of new radioactive elements by neutron irradiation and the fission of uranium atoms by neutrons. The existence of the neutron also played a crucial role in the development of nuclear weapons and nuclear power.

Recognition for Chadwick's Work

James Chadwick received the Nobel Prize in Physics in 1935 for his discovery of the neutron. His work provided the final piece in understanding the atomic puzzle and sparked a revolution in nuclear science.

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