summary of niels bohr experiment

Bohr Model of the Atom Explained

Planetary Model of the Hydrogen Atom

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The Bohr Model has an atom consisting of a small, positively charged nucleus orbited by negatively charged electrons. Here's a closer look at this planetary model.

Overview of the Bohr Model

Niels Bohr proposed the Bohr Model of the Atom in 1915. Because the Bohr Model is a modification of the earlier Rutherford Model, some people call Bohr's Model the Rutherford-Bohr Model. The modern model of the atom is based on quantum mechanics. The Bohr Model contains some errors, but it is important because it describes most of the accepted features of atomic theory without all of the high-level math of the modern version. Unlike earlier models, the Bohr Model explains the Rydberg formula for the spectral emission lines of atomic hydrogen .

The Bohr Model is a planetary model in which the negatively charged electrons orbit a small, positively charged nucleus similar to the planets orbiting the sun (except that the orbits are not planar). The gravitational force of the solar system is mathematically akin to the Coulomb (electrical) force between the positively charged nucleus and the negatively charged electrons.

Main Points of the Bohr Model

• Electrons orbit the nucleus in orbits that have a set size and energy.
• The energy of the orbit is related to its size. The lowest energy is found in the smallest orbit.
• Radiation is absorbed or emitted when an electron moves from one orbit to another.

Bohr Model of Hydrogen

The simplest example of the Bohr Model is for the hydrogen atom (Z = 1) or for a hydrogen-like ion (Z > 1), in which a negatively charged electron orbits a small positively charged nucleus. Electromagnetic energy will be absorbed or emitted if an electron moves from one orbit to another. Only certain electron orbits are permitted. The radius of the possible orbits increases as n 2 , where n is the principal quantum number . The 3 → 2 transition produces the first line of the Balmer series . For hydrogen (Z = 1) this produces a photon having wavelength 656 nm (red light).

Bohr Model for Heavier Atoms

Heavier atoms contain more protons in the nucleus than the hydrogen atom. More electrons were required to cancel out the positive charge of all of the protons. Bohr believed each electron orbit could only hold a set number of electrons. Once the level was full, additional electrons would be bumped up to the next level. Thus, the Bohr model for heavier atoms described electron shells. The model explained some of the atomic properties of heavier atoms, which had never been reproduced before. For example, the shell model explained why atoms got smaller moving across a period (row) of the periodic table, even though they had more protons and electrons. It also explained why the noble gases were inert and why atoms on the left side of the periodic table attract electrons, while those on the right side lose them. However, the model assumed electrons in the shells didn't interact with each other and couldn't explain why electrons seemed to stack irregularly.

Problems With the Bohr Model

• It violates the Heisenberg Uncertainty Principle because it considers electrons to have both a known radius and orbit.
• The Bohr Model provides an incorrect value for the ground state orbital angular momentum .
• It makes poor predictions regarding the spectra of larger atoms.
• The Bohr Model does not predict the relative intensities of spectral lines.
• It does not explain fine structure and hyperfine structure in spectral lines.
• The Bohr Model does not explain the Zeeman Effect.

Refinements and Improvements to the Bohr Model

The most prominent refinement to the Bohr model was the Sommerfeld model, which is sometimes called the Bohr-Sommerfeld model. In this model, electrons travel in elliptical orbits around the nucleus rather than in circular orbits. The Sommerfeld model was better at explaining atomic spectral effects, such the Stark effect in spectral line splitting. However, the model couldn't accommodate the magnetic quantum number.

Ultimately, the Bohr model and models based upon it were replaced Wolfgang Pauli's model based on quantum mechanics in 1925. That model was improved to produce the modern model, introduced by Erwin Schrodinger in 1926. Today, the behavior of the hydrogen atom is explained using wave mechanics to describe atomic orbitals.

• Lakhtakia, Akhlesh; Salpeter, Edwin E. (1996). "Models and Modelers of Hydrogen". American Journal of Physics . 65 (9): 933. Bibcode:1997AmJPh..65..933L. doi: 10.1119/1.18691
• Linus Carl Pauling (1970). "Chapter 5-1".  General Chemistry  (3rd ed.). San Francisco: W.H. Freeman & Co. ISBN 0-486-65622-5.
• Niels Bohr (1913). "On the Constitution of Atoms and Molecules, Part I" (PDF). Philosophical Magazine . 26 (151): 1–24. doi: 10.1080/14786441308634955
• Niels Bohr (1914). "The spectra of helium and hydrogen". Nature . 92 (2295): 231–232. doi:10.1038/092231d0
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Niels Bohr Atomic Model Theory Experiment

Niels Bohr Education & Life

Niels Bohr is a well-known Danish physicist that spent the majority of his life studying the atomic model. The atomic model is a theory that holds that the atoms in an element are different from one another and contain protons, electrons, and neutrons.

What Was Niels Bohr Experiment? What Did Niels Bohr Discover?

The Niels Bohr Atomic Model theory is a model that was introduced by Niels Bohr in 1913 to describe the atom. It was a postulation of Bohr that the electrons rotated in a circular orbit around the nucleus of the atom.

Niels Bohr’s atomic model was created based on previous research by Rutherford, Rutherford’s gold foil experiment, and Ernest Rutherford’s model of the atom.

In his model, Bohr postulated that electrons were placed in orbits that are referred to as orbitals. Atoms consist of a central nucleus, surrounded by electrons in orbital shells.

The electrons sit in energy levels around the nucleus, with the lowest possible energy level being electron number one and the highest being electron number eight.

The Bohr atomic model theory states that atoms are composed of a nucleus, which consists of one or more protons and neutrons that are held together by nuclear forces.

It is also known as a hydrogen atom model or the Rutherford-Bohr Atomic Model Theory.

Niels Bohr was a Danish physicist who had a theory about atoms that he called the “atomic model”. Bohr’s atomic model had a nucleus with a certain number of positively charged particles that were held together by negatively charged particles. The electrons would orbit around the nucleus of the atom.

Atomic Model Theory is the idea that the electrons orbiting the atom don’t orbit around a stationary nucleus like they were on the earth in a solar system. Instead, the electrons orbit around the nucleus of the atom, which is constantly moving.

This is what Bohr called his quantum leap. Bohr’s theory helped to explain the interference experiment and helped to create quantum theories, like the wave-particle duality

Niels Bohr came up with a model of the atom that was entirely radical for its time. It contradicted much of what was previously believed about atoms and electrons.

He believed that an electron orbits a nucleus, which is made up of a group of subatomic particles. Bohr received the Nobel Prize in 1922 for his theory.

Niels Bohr As A Physicist

Niels Bohr is considered to be one of the greatest physicists in history. He worked for many years on physics, teaching, and management. This work led him to become a professor at the University of Copenhagen for thirty years.

In 1912, he was offered a professorship at the Institute of Theoretical Physics in Stockholm. However, there was a problem with his salary because he was not on an equal footing with his counterpart at Uppsala University.

In 1920, Bohr returned to the Institute of Theoretical Physics in Copenhagen. To this day, Bohr remains one of the most celebrated people in Danish history.

Niels Bohr as a Father and a Husband

In 1908, Niels Bohr married Margrethe Nørlund. They had two sons, Aage Nørlund (1909) and Harald Bohr (1911). In 1920, they moved to King’s Gate No.1.

They remained there for the rest of their lives. Bohr was a caring husband and father, who did not like to leave home too often because he missed his family.

Bohr also liked to play classical music, and he was a good enough pianist to give concerts in Copenhagen.

Niels Bohr’s Death

In 1942, Niels Bohr became increasingly ill and was diagnosed with an incurable muscle disease, which caused him great pain and robbed him of his ability to walk.

In September 1948, Bohr became very ill. He developed a blood clot in his leg and he could no longer move around on his own. On October 17, he suffered a severe stroke. He passed away on 18 November.

After his death, the Danish king said about Bohr: “I know of no one who has contributed more to the knowledge and to the progress of mankind than Niels Bohr”.

Niels Bohr’s Legacy

One of the most important things that Niels Bohr did was to create a new model of the atom. He realized that electrons could exist in ‘allowed’ orbits, but they could also ‘jump’, or transition, to higher energy orbits.

One way that people continued to think about Bohr’s ideas was through the use of his concept of quantum jumps.

Bohr also believed that the electron didn’t exist in any particular orbit, but instead was found in all orbits all at the same time, and that only when we looked at an atom would it ‘decide’ which orbit to be in.

He was awarded the Nobel Prize for physics in 1922 for this work.

The Bohr Model of The Atom

Bohr’s model of the atom was one of the most important contributions of his career because it helped us to understand why atoms didn’t collapse.

However, Bohr’s model didn’t explain all the properties of an atom. For example, in the ‘old model of the atom, electrons were stationary (always in the same orbit), and they were at a fixed distance from their nucleus. In other words, they orbited at a fixed distance from their nucleus.

Now, with Bohr’s model, this wasn’t true anymore – electrons could jump around to different orbits. It’s easy to understand that if electrons can jump around, then they can’t have a fixed distance from the nucleus. They would also have to be influenced by the nucleus.

So, when you measure any of the properties of an atom (e.g. the position of an electron), you can never measure it as if it were in ‘absolute space’, but only as how things are relative to each other (relative motion).

What Is Niels Bohr Known For?

The physics community remembers Niels Bohr for his work with the Bohr model of the atom. He was able to explain and interpret vast amounts of experimental data in terms of his atomic model.

The Bohr atomic model consists of one positively charged nucleus surrounded by electrons, which are negatively charged.

The positive charge in the nucleus is balanced by negative charge in the electron. Bohr argued that electrons move around the atom by radially oscillating, which wiggles their position in space.

Bohr also thought that atoms could be described as a series of stationary orbitals. An orbital can be considered a “shell” around an electron and “is filled” with electrons.

Energy can be transferred between an orbital and the electron by oscillations. Bohr provided the mathematical description of his model by applying quantum mechanics.

For example, the electron orbits are given by Schrödinger wave equations. The radius of the orbits is related to energy levels in a very simple way.

These are the most basic atomic model equations ever published. All other models have been derived from these basic ones.

Bohr himself made sure that the model could be applied to spectroscopy and other measurements.

What Is Niels Bohr Famous For?

Niels Bohr was a physicist who made fundamental contributions to the theory of the atom, quantum mechanics, and chemical bonding.

He is also known as the father of modern quantum physics. Bohr was one of the first to apply mathematics to physics. He was able to think in terms of waves and positions instead of just particles and points.

Niels Bohr’s Influence On Chemistry

Bohr’s influence also extended beyond physics. In fact, he made some interesting contributions to chemistry.

For example, he correctly predicted that helium atoms would absorb high-frequency light in a series of elements (helium, neon, argon, and krypton).

He also predicted that they would emit light in a series of elements (for example sodium). But perhaps his most important contribution to chemistry was helping to explain why certain chemical reactions occur.

Bohr’s ideas about quantum jumps also helped us to understand how hydrogen, which has a very large atomic mass, could be broken up into its component atoms.

He explained that a hydrogen atom consists of only one electron which moves around the nucleus. The electron orbits the nucleus and then jumps to a new energy level.

Another of Bohr’s greatest contributions was his work in spectroscopy. He correctly predicted that the frequency of light would increase when light passed through a series of metals (such as helium and sodium).

He also predicted that these elements would emit photons at visible frequencies when heated.

The Bohr Model And Quantum Mechanics

While the basic idea behind Bohr’s model (the atom is made up of electrons that move around a nucleus) is still in use today, it was eventually superseded by quantum mechanics .

However, Bohr’s ideas were very important for understanding how atoms worked. He showed how the strangeness of quantum physics explained why atoms didn’t collapse.

He also showed how the strangeness of quantum physics could be used to explain how atoms absorb and emit light.

While Bohr’s model did not explain some of the properties of atoms (mass, charge, or size), it had a major influence on the way that we think about and study atoms today.

Niels Bohr And Experimental Data

Bohr was a physicist who was very important to experimentalists. His contributions helped to explain how electrons could jump from one orbit to another in an atom.

It also helped explain why different atoms have different masses and predicted light emission colors for various kinds of spectroscopy.

In addition, Bohr was one of the first to suggest that the cathode rays (later to be called electrons) do not actually have a definite trajectory but instead travel in a broad wave with peaks and troughs. The wave theory described the behavior of electrons much better than the Newtonian particle model, which had been used up until then.

What Did Niels Bohr Think About The Atom And Quantum Mechanics?

According to Bohr, an atom is composed of a charged nucleus and a cloud of electrons. The nucleus is fixed in space, while the electrons can move around inside the atom.

This movement happens very quickly but is maintained by electromagnetic forces. It is also maintained by the energy which keeps the electrons in their orbits. Ionization occurs when an electron jumps from one orbit to another – or when light from a specific wavelength enters an atom.

Bohr was very conscious of the fact that he was a ‘complementary’ physicist. This means that he accepted quantum theory, but also believed in the classical view (which has all particles having definite locations).

In his day, this challenged the idea of quantum mechanics, since it meant that Bohr himself did not believe in quantum theory.

This is because Bohr did not equate the accuracy of his predictions with the validity of theoretical physics.

However, since he never really discussed these views with his colleagues, and because the laws of quantum mechanics were absolutely consistent with all of his predictions, Bohr did not suffer any significant criticism.

What Was Niels Bohr’s Contribution To Quantum Mechanics?

In 1913 Bohr began working on what we now call the “old” model of an atom. Before this time, it was thought that electrons orbited the nucleus in evenly spaced orbits.

It was also thought that electrons jumped to a new orbit when they gained or lost energy. Bohr changed this view completely by introducing the idea of stationary, allowed orbits.

This meant that electrons had a certain angular momentum inside the atom, which was ever-changing.

An electron could jump to another orbit by losing or gaining energy but did not jump because of an external push or pull. In other words, electrons jump because they are excited by the electromagnetic radiation of an atom.

The idea of stationary allowed orbits was revolutionary. It meant that atoms could emit and absorb energy in a continuous way, rather than in individual packets (which is what happened when people used the Bohr-Ellsberg-Slater theory).

In 1914, Bohr suggested that electrons could exist only in certain orbits inside the atom. This meant that there was a mathematical connection between atomic orbitals and wavelengths or frequencies of light.

Later, in 1916, Bohr suggested that the atom is mainly made of neutrons. He also introduced the idea of electron jumping. This was significant because it was one of the first models to combine quantum theory and classical physics.

In 1918 Bohr published an explanation for atomic structure based on a “postulate” about what happened when electrons jumped from one orbit to another.

According to Bohr, electrons could exist only in certain orbits (i.e., certain energy levels). Electrons could also jump from one orbit into another.

This was an important development in quantum mechanics because it helped to explain why the atom would not collapse.

What Did Niels Bohr Contribute To Society?

Bohr was one of the founders of quantum mechanics. This theory is still in use today. In addition, Bohr was one of the first people to think about atoms – what they might be like and how we can observe them.

He developed models which are still used today.

Besides this, Bohr was a very successful teacher and mentor. Many young scientists (including future Nobel Prize winners) studied with him in Copenhagen and benefited from his advice and guidance.

Niels Bohr was one of the first people to suggest that the laws of classical physics could be thought of as being the same as the laws of quantum physics.

This was a revolutionary idea, and it showed that everything in our world is quantifiable. In other words, nothing in our world can escape quantification – or measurement.

This view of reality – or what we would call ‘the scientific method’ – has had a huge influence on modern thinking about how our society works.

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What Is Bohr’s Atomic Theory?

Rutherford’s failed model, the hydrogen spectrum, bohr’s atomic model, shortcomings.

Niel Bohr’s Atomic Theory states that – an atom is like a planetary model where electrons were situated in discretely energized orbits. The atom would radiate a photon when an excited electron would jump down from a higher orbit to a lower orbit. The difference between the energies of those orbits would be equal to the energy of the photon.

Niels Bohr was a Danish physicist and is considered one of the founding fathers of quantum mechanics , precisely old quantum mechanics. For his exemplary contributions to science, the Carlsberg brewing company decided to give him a house situated right next to one of their breweries. The house was connected to the brewery by a pipeline. Bohr was rewarded with a lifetime supply of free beer that would pour out of a tap at his whim. What extraordinary feat did Niels Bohr accomplish to deserve this prestigious honor, and well, a Nobel Prize?

Quite simply, Niels Bohr illuminated the mysterious inner-workings of the atom. Although he arrived at his model and its principles in collaboration with the august founder of the atomic nucleus, Ernest Rutherford, the model is only credited to Bohr. Originally called the Rutherford-Bohr atomic model, it is now commonly referred to as Bohr’s atomic model.

To understand Bohr’s theory, we must first understand what prior discoveries led him to pursue his revolutionary ideas.

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It was Sir J.J. Thomson who first discovered that the atom wasn’t indivisible after all, a notion believed to be true for centuries. However, the subatomic particle he discovered was negatively charged. If atoms were merely a cluster of negative charges, then chairs, tables, you and I would be anything but stable. He immediately realized that to account for matter’s stability, there must be a net positive charge to neutralize the negativity.

Thomson devised what became the very first model of an atom. He suggested that the negative particles, which he called electrons, were like seeds embedded in a positively charged watermelon. The model is popularly known as the  plum or raisin pudding model . I’m sure the analogy is obvious.

This view held true until Ernest Rutherford showed that when positive particles are shot at an atom, most of them pass straight through, but a few are observed to be deflected at a large angle. Rutherford realized that most of the atom was filled with empty space, but at the center was a dense, point-like concentration of positive charge. He called this the atom’s nucleus. The volume of empty space between an atom’s electrons and its nucleus is so huge that if the atom were expanded to the size of a baseball stadium, its nucleus would be the size of a baseball.

Rutherford suggested that perhaps the atomic system was analogous to our Solar System, where the electrons revolve around the nucleus like planets revolving around the Sun. The crucial difference was, of course, that the electrons were captivated by electrostatic force, rather than gravity. However, Maxwell and Hertz would have vehemently disagreed.

Maxwell’s laws of electromagnetism had recently established that the motion of a charged particle, such as an electron, comes at the expense of energy. Thus, a revolving electron, like the circus men on motorbikes racing around inside a sphere, would soon spiral and collapse as it ran out of fuel. In fact, physicists calculated that it would take just 16 picoseconds for an electron to radiate all its energy and collapse into its nucleus. That is one-trillionth of a second. A new atomic model that would explain matter’s profound stability had yet to be discovered.

Also Read: What Is J.J. Thomson’s Plum Pudding Model?

Another absurdity that perplexed physicists at that time was Planck’s black body radiation and the “emission spectrum” given off by different atoms. The word ‘spectrum’ was first coined by Newton to describe the rainbow of colors that sprang from his prism.

Similarly, when a body is heated, it radiates a spectrum of electromagnetic energy. If you burn a bar of iron with a blowtorch, you will observe that as the temperature of the bar increases, the color it assumes will also change gradually. First, it’s red, then orange, and then bright white before veering towards violet.

This is because the electromagnetic energy radiated by that iron bar falls in the range of visible light – light that our eyes can detect. If you were to heat the bar to 20,000 Kelvin, the energy radiated would be in the ultraviolet (UV) range. In fact, every object in the Universe radiates such a spectrum of energy, including human beings, but since the temperature of our body is so low, the energy emitted is also meager, somewhere in the range of infrared light. Our eyes are equipped with sensors that can only identify one member amongst the several members of the electromagnetic spectrum.

Max Planck called this phenomenon black body radiation. If you were to plot the heat’s intensity with the wavelength of light radiated, you would observe a peak at a certain range of wavelengths. The peak for the Sun’s core burning at 6,000K lies partly in the visible range, while for a star burning at 20,000K, it lies completely in the UV range, and for a stellar explosion, such as the birth of a black hole , it lies in the gamma range.

Furthermore, the graph depicts that as the temperature of a body declines, the wavelength of light it radiates increases. For instance, the radiation from the Big Bang may have started out as gamma rays, but as it cooled down over more than 13 billion years, the wavelengths elongated to microwaves. If you were to plot these waves on a black background, you would witness a beautiful, hazy mélange of colors – a continuous spectrum.

However, the major implication of Planck’s finding was that the radiated energy traveled in discrete packets, like rigid particles, which Einstein later called photons. The energy of a single quantum is inversely proportional to its wavelength or directly proportional to its frequency. With a fundamental constant of proportionality called Planck’s constant,  h , the energy E for a frequency v   can be expressed as E = hv.

Now, if you were to heat a volume of gas of a single element in this way and plot the colors on a black background, you would observe something of an anomaly. The spectrum is no longer a beautiful or continuous mixture of colors. Instead, it comprises a series of definite, single-colored lines intermittently separated by chunks of the absolutely black background. For instance, take a look at the ever-famous spectrum of hydrogen.

In fact, each and every element in the Universe paints its own unique, discontinuous spectrum. While hydrogen’s spectrum lies in the visible range, certain elements produce a spectrum that lies in the ultraviolet or infrared range. For this reason, an element’s spectrum is considered its fingerprint. The knowledge of its uniqueness allows us to study the composition of stars and has even aided scientists in discovering new elements!

Looking at the spectrum of hydrogen, it was obvious that only certain colors appeared because only certain frequencies – those associated with these colors – were radiated. Given that, why would atoms exhibit this peculiar behavior? What atomic structure would restrict them so severely to express themselves so laconically? Niels Bohr, in 1913, finally realized why.

Bohr went ahead with Rutherford’s Solar System model, but added a small tweak. He rectified its failing aspect by suggesting (for a reason yet to be known) that electrons revolve around a nucleus in fixed or definite orbits. He claimed that in these orbits, the electrons wouldn’t lose any energy, therefore ensuring that they didn’t collapse into the nucleus.

Bohr called these fixed orbits “stationary orbits”. He claimed that the orbits weren’t randomly situated, but were instead at discrete distances from the nucleus in the center, and that each of them was associated with fixed energies. Inspired by Planck’s theory, he denoted the orbits by n, and called it the quantum number .

However absurd the theory might have appeared, it predicted the spectrum of hydrogen splendidly. According to it, when a gas is heated, its energized electrons jump from an orbit of lower energy to an orbit of higher energy (in the case of hydrogen, from n =1 to n = 2). However, to regain stability, they must jump back down to the lower energy orbits. While undergoing this transition, the electron must lose some of its energy, and it is this energy that is radiated in the form of light!

The discrete nature of orbits provides a concise explanation for the discrete nature of photons. Bohr found that the energy of an emitted photon is equal to the difference of energies of the two levels between which the electron makes its jump. For instance, infrared is radiated when the electron makes a short leap, while ultraviolet is radiated when it makes a much larger leap. This relation can be simply expressed as E2 – E1 = hv. Conversely, an electron jumps to a higher orbit when it absorbs a photon.

The spectrum of an atom is restricted to particular colors because its concrete, organized structure allows its electrons to only certain energy transitions – and therefore certain frequencies of light. Now, if an atom of hydrogen only contains a single electron, why does its spectrum consist of multiple colors? Well, this is because the gas is composed of millions and billions of atoms with electrons raised to different orbits that are higher or lower than those nearby.

So, this was Bohr’s model – a planetary model where electrons were situated in discretely energized orbits. The atom would radiate a photon when an excited electron would jump down from a higher orbit to a lower orbit. The difference between the energies of those orbits would be equal to the energy of the photon.

Also Read: Protons And Electrons Have Opposite Charges, So Why Don’t They Pull On Each Other?

Unfortunately, Bohr’s model could only explain the behavior of a system where two charged points orbited each other. This meant the hydrogen atom, in particular. It also included ionized helium (helium has two electrons, so ionization would seize one of those, leaving it with only one) or double-ionized lithium (lithium has three electrons… you do the math). His theory couldn’t explain the behavior of any other atom except hydrogen.

Furthermore, his theory dictated that electrons align in the stationary orbits like beads on a thread, meaning that he had assumed a non-interactive system of electrons. This horribly discounts the violently repulsive electrostatic force between not just two, but multiple electrons clustered together that would thrust each other miles away. Eventually, we discovered that electrons do not just revolve, but also rotate or spin on their axis. Bohr’s model couldn’t explain why this didn’t lead to a loss of energy.

It is speculated that part of the reason why Bohr’s theory was so readily accepted is that it made successful theoretical predictions of multiple spectra that hadn’t been observed. Still, it is widely lauded, as it revolutionized modern physics by paving the way for modern quantum mechanics. Eventually, modern quantum mechanics perfectly explained the true nature of energy shells, how electrons would inhabit each of them, as well as the problem of spin.

However, for its simplicity, Bohr’s ideas still continue to exist and dominate high school physics. The textbooks are replete with concentric circles filled with electrons surrounding a nucleus, which resembles the beads-in-a-thread model. For his contribution, Bohr surely deserved that free beer after all. And of course… a Nobel Prize.

• Bohr Atomic Model.
• Rutherford and Bohr describe atomic structure.
• How are Spectra Produced?.
• Bohr model.

Akash Peshin is an Electronic Engineer from the University of Mumbai, India and a science writer at ScienceABC. Enamored with science ever since discovering a picture book about Saturn at the age of 7, he believes that what fundamentally fuels this passion is his curiosity and appetite for wonder.

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Niels Bohr: Biography and contributions to atomic energy

Biography of niels bohr, birth and early years, bohr's atomic model, copenhagen institute of theoretical physics, contribution to atomic energy, nobel prize in physics, niels bohr's contributions to atomic models, niels bohr's contributions to nuclear energy, nuclear fision, development of nuclear reactors, legacy and conclusion.

Niels Bohr: Biography & Atomic Theory

Niels Bohr was one of the foremost scientists of modern physics, best known for his substantial contributions to quantum theory and his Nobel Prize -winning research on the structure of atoms.

Born in Copenhagen in 1885 to well-educated parents, Bohr became interested in physics at a young age. He studied the subject throughout his undergraduate and graduate years and earned a doctorate in physics in 1911 from Copenhagen University.

While still a student, Bohr won a contest put on by the Academy of Sciences in Copenhagen for his investigation into the measurements of liquid surface tension using oscillating fluid jets. Working in the laboratory of his father (a renowned physiologist), Bohr conducted several experiments and even made his own glass test tubes. 

Bohr went above and beyond the current theory of liquid surface tension by taking into account the viscosity of the water as well as incorporating finite amplitudes rather than infinitesimal ones. He submitted his essay at the last minute, winning first place and a gold medal. He improved upon these ideas and sent them to the Royal Society in London, who published them in the journal Philosophical Transactions of the Royal Society in 1908, according to Nobelprize.org . 

His subsequent work became increasingly theoretical. It was while conducting research for his doctoral thesis on the electron theory of metals that Bohr first came across Max Planck's early quantum theory, which described energy as tiny particles, or quanta.

In 1912, Bohr was working for the Nobel laureate J.J. Thompson in England when he was introduced to Ernest Rutherford, whose discovery of the nucleus and development of an atomic model had earned him a Nobel Prize in chemistry in 1908. Under Rutherford's tutelage, Bohr began studying the properties of atoms.

Bohr held a lectureship in physics at Copenhagen University from 1913 to 1914 and went on to hold a similar position at Victoria University in Manchester from 1914 to 1916. He went back to Copenhagen University in 1916 to become a professor of theoretical physics. In 1920, he was appointed the head of the Institute for Theoretical Physics.

Combining Rutherford's description of the nucleus and Planck's theory about quanta, Bohr explained what happens inside an atom and developed a picture of atomic structure. This work earned him a Nobel Prize of his own in 1922.

In the same year that he began his studies with Rutherford, Bohr married the love of his life, Margaret Nørlund, with whom he had six sons. Later in life, he became president of the Royal Danish Academy of Sciences, as well as a member of scientific academies all over the world.

When the Nazis invaded Denmark in World War II, Bohr managed to escape to Sweden. He spent the last two years of the war in England and the United States, where he got involved with the Atomic Energy Project. It was important to him, however, to use his skills for good and not violence. He dedicated his work toward the peaceful use of atomic physics and toward solving political problems arising from the development of atomic weapons of destruction. He believed that nations should be completely open with one another and wrote down these views in his Open Letter to the United Nations in 1950.

Atomic model

Bohr's greatest contribution to modern physics was the atomic model. The Bohr model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons. 

Bohr was the first to discover that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element.

The chemical element bohrium (Bh), No. 107 on the periodic table of elements , is named for him.

Liquid droplet theory

Bohr's theoretical work contributed significantly to scientists' understanding of nuclear fission . According to his liquid droplet theory, a liquid drop provides an accurate representation of an atom's nucleus.

This theory was instrumental in the first attempts to split uranium atoms in the 1930s, an important step in the development of the atomic bomb.

Despite his contributions to the U.S. Atomic Energy Project during World War II, Bohr was an outspoken advocate for the peaceful application of atomic physics.

Quantum theory

Bohr's concept of complementarity, which he wrote about in a number of essays between 1933 and 1962, states that an electron can be viewed in two ways, either as a particle or as a wave, but never both at the same time.

This concept, which forms the basis of early quantum theory, also explains that regardless of how one views an electron, all understanding of its properties must be rooted in empirical measurement. Bohr's theory stresses the point that an experiment's results are deeply affected by the measurement tools used to carry them out.

Bohr's contributions to the study of quantum mechanics are forever memorialized at the Institute for Theoretical Physics at Copenhagen University, which he helped found in 1920 and headed until his death in 1962. It has since been renamed the Niels Bohr Institute in his honor.

Niels Bohr quotations

"Every great and deep difficulty bears in itself its own solution. It forces us to change our thinking in order to find it."

"Everything we call real is made of things that cannot be regarded as real."

"The best weapon of a dictatorship is secrecy, but the best weapon of a democracy should be the weapon of openness."

"Never express yourself more clearly than you are able to think."

Additional reporting by Traci Pedersen, Live Science contributor

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Elizabeth is a former Live Science associate editor and current director of audience development at the Chamber of Commerce. She graduated with a bachelor of arts degree from George Washington University. Elizabeth has traveled throughout the Americas, studying political systems and indigenous cultures and teaching English to students of all ages.

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Introduction

Niels Henrik David Bohr was born on October 7, 1885, in Copenhagen, Denmark. His father was a professor at the University of Copenhagen. Niels was a good student. He was even better at sports. He and his brother were excellent soccer players. In high school, Niels showed a talent for mathematics and physics. In 1903 he went to the University of Copenhagen to study physics. He earned a Ph.D. in 1911.

Bohr Atomic Model

Bohr made his own model of the atom. He claimed that electrons could only occupy particular orbits around the nucleus. He also explained that when an electron jumped from an outer orbit to an inner orbit, energy would be given off. An electron would absorb energy if it jumped from an inner orbit to an outer orbit.

In 1916 Bohr returned to the University of Copenhagen to work as a professor. There he became director of the Institute for Theoretical Physics in 1920. He won the Nobel Prize in physics in 1922.

A Refuge for Jewish Scientists

When Adolf Hitler and the Nazi Party took power in Germany in 1933, many Jewish scientists were no longer allowed to work in their German homeland. Bohr used his connections in Denmark to help scientists get out of Germany and to work at his institute at Copenhagen University. From there, scientists would obtain permanent appointment elsewhere, most often in the United States.

The Atomic Bomb

Bohr himself was of Jewish descent. Eventually the Nazis occupied his country. He was warned that the Nazis were planning to arrest him. He escaped Copenhagen in 1943. After that, he moved to England and then the United States. At that time, World War II was going on. Scientists in Europe and the United States were afraid that Germany was trying to develop an atomic bomb. Bohr helped scientists in the United States develop their own atomic bomb.

After the war, Bohr returned to Denmark. He continued to direct the institute at Copenhagen University. His son Aage worked there as well. Bohr died in Copenhagen on November 18, 1962. Aage became director of the institute after that and later won a Nobel Prize as well.

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Among physicists working at Bohr’s institute between the World Wars, the “Copenhagen Spirit” came to denote the very special social milieu there, comprising a completely informal atmosphere, the opportunity to discuss physics without any concern for other matters, and, for the specially privileged, the unique opportunity of working with Bohr.

Notwithstanding the important experimental work performed by Hevesy, Coster, and others, it was the theorists who led the way. In 1925 Werner Heisenberg of Germany developed the revolutionary quantum mechanics , which, in contrast to its predecessor, the so-called “old quantum theory” that drew on classical physics, constituted a fully independent theory. During the academic year 1926–27, Heisenberg served as Bohr’s assistant in Copenhagen , where he formulated the fundamental uncertainty principle as a consequence of quantum mechanics. Bohr, Heisenberg, and a few others then went on to develop what came to be known as the Copenhagen interpretation of quantum mechanics, which still provides a conceptual basis for the theory. A central element of the Copenhagen interpretation is Bohr’s complementarity principle , presented for the first time in 1927 at a conference in Como , Italy. According to complementarity, on the atomic level a physical phenomenon expresses itself differently depending on the experimental setup used to observe it. Thus, light appears sometimes as waves and sometimes as particles. For a complete explanation, both aspects, which according to classical physics are contradictory, need to be taken into account. The other towering figure of physics in the 20th century, Albert Einstein , never accepted the Copenhagen interpretation, famously declaring against its probabilistic implications that “God does not play dice.” The discussions between Bohr and Einstein, especially at two of the renowned series of Solvay Conferences in physics, in 1927 and 1930, constitute one of the most-fundamental and inspired discussions between physicists in the 20th century. For the rest of his life, Bohr worked to generalize complementarity as a guiding idea applying far beyond physics.

In the early 1930s Bohr found use once more for his fund-raising abilities and his vision of a fruitful combination of theory and experiment. He realized early that the research front in theoretical physics was moving from the study of the atom as a whole to the study of its nucleus. Bohr turned to the Rockefeller Foundation , whose “experimental biology” program was designed to improve conditions for the life sciences. Together with Hevesy and the Danish physiologist August Krogh , Bohr applied for support to build a cyclotron —a kind of particle accelerator recently invented by Ernest O. Lawrence in the United States—as a means to pursue biological studies. Although Bohr intended to use the cyclotron primarily for investigations in nuclear physics, it could also produce isotopes of elements involved in organic processes, making it possible in particular to extend the radioactive indicator method, invented and promoted by Hevesy, to biological purposes. In addition to the support from the Rockefeller Foundation, funds for the cyclotron and other equipment for studying the nucleus were also granted to Bohr from Danish sources.

Just as the close connection between theory and experiment had proved fruitful for atomic physics , so now the same connection came to work well in the study of the nucleus. Thus, after the German physicists Otto Hahn and Fritz Strassmann in late 1938 had made the unexpected and unexplained experimental discovery that a uranium atom can be split in two approximately equal halves when bombarded with neutrons , a theoretical explanation based on Bohr’s recently proposed theory of the compound nucleus was suggested by two Austrian physicists close to Bohr— Lise Meitner and her nephew Otto Robert Frisch ; the explanation was soon confirmed in experiments by Meitner and Frisch at the institute. By that time, at the beginning of 1939, Bohr was in the United States , where a fierce race to confirm experimentally the so-called fission of the nucleus began after the news of the German experiments and their explanation had become known. In the United States, Bohr did pathbreaking work with his younger American colleague John Archibald Wheeler at Princeton University to explain fission theoretically.

Bohr had felt the consequences of the Nazi regime almost as soon as Adolf Hitler came to power in Germany in 1933, as several of his colleagues there were of Jewish descent and lost their jobs without any prospect of a future in their home country. Bohr used his connections with well-established foundations—as well as the newly set up Danish Committee for the Support of Refugee Intellectual Workers, in which he sat on the executive board from its creation in 1933—to get physicists out of Germany in order for them to spend some time at Bohr’s institute before obtaining permanent appointment elsewhere, most often in the United States.

(1885-1962)

Who Was Niels Bohr?

Niels Bohr was an accomplished physicist who came up with a revolutionary theory on atomic structures and radiation emission. He won the 1922 Nobel Prize in physics for his ideas and years later, after working on the Manhattan Project in the United States, called for responsible and peaceful applications of atomic energy across the world.

Niels Bohr was born on October 7, 1885, in Copenhagen, Denmark, to mother Ellen Adler, who was part of a successful Jewish banking clan, and father Christian Bohr, a celebrated physiology academic. The young Bohr eventually attended Copenhagen University, where he received his master's and doctorate in physics by 1911. During the fall of the same year, Bohr traveled to Cambridge, England, where he was able to follow the Cavendish Laboratory work of scientist J.J. Thomson.

In 1912, Bohr wed Margrethe Nørlund. The couple would have six children; four survived to adulthood and one, Aage, would become a well-known physics scientist as well.

Bohr’s own research led him to theorize in a series of articles that atoms give off electromagnetic radiation as a result of electrons jumping to different orbit levels, departing from a previously held model espoused by Ernest Rutherford. Though Bohr's discovery would eventually be tweaked by other scientists, his ideas formed the basis of future atomic research.

After teaching at Manchester’s Victoria University, Bohr settled again at Copenhagen University in 1916 with a professorship position. Then, in 1920, he founded the university’s Institute of Theoretical Physics, which he would head for the rest of his life.

Wins Nobel Prize

Bohr received the 1922 Nobel Prize in Physics for his work on atomic structures, and he would continue to come up with revolutionary theories. He worked with Werner Heisenberg and other scientists on a new quantum mechanics principle connected to Bohr's concept of complementarity, which was initially presented at an Italian conference in 1927. The concept asserted that physical properties on an atomic level would be viewed differently depending on experimental parameters, hence explaining why light could be seen as both a particle and a wave, though never both at the same time. Bohr would come to apply this idea philosophically as well, with the belief that evolving concepts of physics deeply affected human perspectives. Another physicist, by the name of Albert Einstein, didn’t fully see eye to eye with all of Bohr's assertions, and their talks became renowned in scientific communities.

Bohr went on to work with the group of scientists who were at the forefront of research on nuclear fission during the late 1930s, to which he contributed the liquid droplet theory. Outside of his pioneering ideas, Bohr was known for his wit and warmth, and his humanitarian ethics would inform his later work.

Fleeing Europe

Atoms for peace.

After the end of the war, Bohr returned to Europe and continued to call for peaceful applications of atomic energy. In his "Open Letter to the United Nations," dated June 9, 1950, Bohr envisioned an "open world" mode of existence between countries that abandoned isolationism for true cultural exchange.

He helped to establish CERN, a Europe-based particle physics research facility, in 1954 and put together the Atoms for Peace Conference of 1955. In 1957, Bohr received the Atoms for Peace Award for his trailblazing theories and efforts to use atomic energy responsibly.

Bohr was a prolific writer with more than 100 publications to his name. After having a stroke, he died on November 18, 1962, in Copenhagen. Bohr’s son Aage shared with two others the 1975 Nobel Prize in Physics for his research on motion in atomic nuclei.

QUICK FACTS

• Name: Niels Bohr
• Birth Year: 1885
• Birth date: October 7, 1885
• Birth City: Copenhagen
• Birth Country: Denmark
• Gender: Male
• Best Known For: Niels Bohr was a Nobel Prize-winning physicist and humanitarian whose revolutionary theories on atomic structures helped shape research worldwide.
• Science and Medicine
• Astrological Sign: Libra
• Copenhagen University
• Nacionalities
• Danish (Denmark)
• Death Year: 1962
• Death date: November 18, 1962
• Death City: Copenhagen
• Death Country: Denmark

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• Every great and deep difficulty bears in itself its own solution. It forces us to change our thinking in order to find it.
• An expert is a man who has made all the mistakes which can be made, in a very narrow field.
• Never express yourself more clearly than you are able to think.

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Niels Bohr (1885 - 1962)

Niels Henrik David Bohr was born in Copenhagen in 1885 to Christian Bohr, a professor of physiology at the University of Copenhagen and a Nobel Prize winner, and Ellen Adler Bohr, who came from a wealthy Sephardic Jewish family prominent in Danish banking and parliamentary circles. Bohr received his doctorate from Copenhagen University in 1911 and then studied under Ernest Rutherford in the Victoria University in Manchester, England.

In 1911, Bohr visited Cambridge, where he followed the experimental work occurring in the Cavendish Laboratory under Sir J.J. Thomson's guidance and pursued his own theoretical studies. In 1912, he worked in Professor Rutherford's laboratory in Manchester. Based on Rutherford's theories, Bohr published his model of atomic structure in 1913, which is still commonly used and taught today as an educational simplification. The model introduced the theory of electrons traveling in orbits around the atom's nucleus, the chemical properties of the element being largely determined by the number of electrons in the outer orbits. Bohr also introduced the idea that an electron could drop from a higher-energy orbit to a lower one, emitting a photon (light quantum) of discrete energy. This became the basis for quantum theory.

Following in his father's footsteps, in 1916, Bohr became a professor at the University of Copenhagen. In 1920, he became director of the newly constructed "Institute of Theoretical Physics" and was awarded the Nobel Prize in Physics in 1922 "for his services in the investigation of the structure of atoms and of the radiation emanating from them."

After 1930, Bohr's activities in his Institute were focused on research on the constitution of the atomic nuclei and of their transmutations and disintegrations. He also contributed to the clarification of the problems encountered in quantum physics, which is discussed in several essays written between 1933 and 1962.

In 1943, shortly before he was to be arrested by the German police, Bohr escaped to Sweden and then traveled to London. He worked at Los Alamos on the Manhattan Project, where he was allegedly known by the assumed name of Nicholas Baker for security reasons. However, his role in the project was minor, as he was seen as a knowledgeable consultant. After the war, he returned to Copenhagen, advocating for a peaceful use of nuclear energy. In 1955 he organized the first Atoms for Peace Conference in Geneva, Switzerland.

Bohr and his wife Margrethe had six children, one of whom, Aage Niels Bohr, became a very successful physicist and also won a Nobel Prize in Physics. Bohr died in Copenhagen in 1962. The element bohrium is named in his honor.

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• Niels Bohr - Biographical

Biographical

N iels Henrik David Bohr was born in Copenhagen on October 7, 1885, as the son of Christian Bohr, Professor of Physiology at Copenhagen University, and his wife Ellen, née Adler. Niels, together with his younger brother Harald (the future Professor in Mathematics), grew up in an atmosphere most favourable to the development of his genius – his father was an eminent physiologist and was largely responsible for awakening his interest in physics while still at school, his mother came from a family distinguished in the field of education.

After matriculation at the Gammelholm Grammar School in 1903, he entered Copenhagen University where he came under the guidance of Professor C. Christiansen, a profoundly original and highly endowed physicist, and took his Master’s degree in Physics in 1909 and his Doctor’s degree in 1911.

While still a student, the announcement by the Academy of Sciences in Copenhagen of a prize to be awarded for the solution of a certain scientific problem, caused him to take up an experimental and theoretical investigation of the surface tension by means of oscillating fluid jets. This work, which he carried out in his father’s laboratory and for which he received the prize offered (a gold medal), was published in the Transactions of the Royal Society , 1908.

Bohr’s subsequent studies, however, became more and more theoretical in character, his doctor’s disputation being a purely theoretical piece of work on the explanation of the properties of the metals with the aid of the electron theory, which remains to this day a classic on the subject. It was in this work that Bohr was first confronted with the implications of Planck ‘s quantum theory of radiation.

In the autumn of 1911 he made a stay at Cambridge, where he profited by following the experimental work going on in the Cavendish Laboratory under Sir J.J. Thomson’s guidance, at the same time as he pursued own theoretical studies. In the spring of 1912 he was at work in Professor Rutherford’s laboratory in Manchester, where just in those years such an intensive scientific life and activity prevailed as a consequence of that investigator’s fundamental inquiries into the radioactive phenomena. Having there carried out a theoretical piece of work on the absorption of alpha rays which was published in the Philosophical Magazine , 1913, he passed on to a study of the structure of atoms on the basis of Rutherford’s discovery of the atomic nucleus. By introducing conceptions borrowed from the Quantum Theory as established by Planck, which had gradually come to occupy a prominent position in the science of theoretical physics, he succeeded in working out and presenting a picture of atomic structure that, with later improvements (mainly as a result of Heisenberg ‘s ideas in 1925), still fitly serves as an elucidation of the physical and chemical properties of the elements.

In 1913-1914 Bohr held a Lectureship in Physics at Copenhagen University and in 1914-1916 a similar appointment at the Victoria University in Manchester. In 1916 he was appointed Professor of Theoretical Physics at Copenhagen University, and since 1920 (until his death in 1962) he was at the head of the Institute for Theoretical Physics, established for him at that university.

Recognition of his work on the structure of atoms came with the award of the Nobel Prize for 1922.

Bohr’s activities in his Institute were since 1930 more and more directed to research on the constitution of the atomic nuclei, and of their transmutations and disintegrations. In 1936 he pointed out that in nuclear processes the smallness of the region in which interactions take place, as well as the strength of these interactions, justify the transition processes to be described more in a classical way than in the case of atoms (Cf.  »Neutron capture and nuclear constitution«, Nature , 137 (1936) 344).

A liquid drop would, according to this view, give a very good picture of the nucleus. This so-called liquid droplet theory permitted the understanding of the mechanism of nuclear fission, when the splitting of uranium was discovered by Hahn and Strassmann, in 1939, and formed the basis of important theoretical studies in this field (among others, by Frisch and Meitner).

Bohr also contributed to the clarification of the problems encountered in quantum physics, in particular by developing the concept of complementarity . Hereby he could show how deeply the changes in the field of physics have affected fundamental features of our scientific outlook and how the consequences of this change of attitude reach far beyond the scope of atomic physics and touch upon all domains of human knowledge. These views are discussed in a number of essays, written during the years 1933-1962. They are available in English, collected in two volumes with the title Atomic Physics and Human Knowledge and Essays 1958-1962 on Atomic Physics and Human Knowledge , edited by John Wiley and Sons, New York and London, in 1958 and 1963, respectively.

Among Professor Bohr’s numerous writings (some 115 publications), three appearing as books in the English language may be mentioned here as embodying his principal thoughts: The Theory of Spectra and Atomic Constitution , University Press, Cambridge, 1922/2nd. ed., 1924; Atomic Theory and the Description of Nature , University Press, Cambridge, 1934/reprint 1961; The Unity of Knowledge , Doubleday & Co., New York, 1955.

During the Nazi occupation of Denmark in World War II, Bohr escaped to Sweden and spent the last two years of the war in England and America, where he became associated with the Atomic Energy Project. In his later years, he devoted his work to the peaceful application of atomic physics and to political problems arising from the development of atomic weapons. In particular, he advocated a development towards full openness between nations. His views are especially set forth in his Open Letter to the United Nations , June 9, 1950.

Until the end, Bohr’s mind remained alert as ever; during the last few years of his life he had shown keen interest in the new developments of molecular biology. The latest formulation of his thoughts on the problem of Life appeared in his final (unfinished) article, published after his death: “Licht und Leben-noch einmal”, Naturwiss ., 50 (1963) 72: (in English: “Light and Life revisited”, ICSU Rev ., 5 ( 1963) 194).

Niels Bohr was President of the Royal Danish Academy of Sciences, of the Danish Cancer Committee, and Chairman of the Danish Atomic Energy Commission. He was a Foreign Member of the Royal Society (London), the Royal Institution, and Academies in Amsterdam, Berlin, Bologna, Boston, Göttingen, Helsingfors, Budapest, München, Oslo, Paris, Rome, Stockholm , Uppsala, Vienna, Washington, Harlem, Moscow, Trondhjem, Halle, Dublin, Liege, and Cracow. He was Doctor, honoris causa , of the following universities, colleges, and institutes: (1923-1939) – Cambridge, Liverpool, Manchester, Oxford, Copenhagen, Edinburgh, Kiel, Providence, California, Oslo, Birmingham, London; (1945-1962) – Sorbonne (Paris), Princeton, Mc. Gill (Montreal), Glasgow, Aberdeen, Athens, Lund, New York, Basel, Aarhus, Macalester (St. Paul), Minnesota, Roosevelt (Chicago, Ill.), Zagreb, Technion (Haifa), Bombay, Calcutta, Warsaw, Brussels, Harvard, Cambridge (Mass.), and Rockefeller (New York).

Professor Bohr was married, in 1912, to Margrethe Nørlund, who was for him an ideal companion. They had six sons, of whom they lost two; the other four have made distinguished careers in various professions – Hans Henrik (M.D.), Erik (chemical engineer), Aage (Ph.D., theoretical physicist, following his father as Director of the Institute for Theoretical Physics), Ernest (lawyer).

Niels Bohr died in Copenhagen on November 18, 1962.

This autobiography/biography was written at the time of the award and first published in the book series Les Prix Nobel . It was later edited and republished in Nobel Lectures . To cite this document, always state the source as shown above.

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