Month: March 2019

1938: Nuclear Fission

Posted on by Dan

The discovery of nuclear fission, a process that releases an enormous amount of energy by splitting the nucleus of an atom, was an explosive moment in the history of science and technology. This incredible discovery directly led to the development of nuclear weapons and nuclear energy production, both of which would become world changing events.

The Birth of Atomic Physics

1979 German postage stamp depicting a diagram of splitting uranium atoms
1979 German postage stamp depicting a diagram of splitting uranium atoms

The discovery of nuclear fission began with the birth of atomic physics and its related research into the components of the atom.  In 1897, J. J. Thomson discovered the first subatomic particle, the electron, while working on experiments with cathode ray tubes.  This discovery prompted further research into the structure of the atom.  Fourteen years later, Ernest Rutherford discovered the nucleus of the atom when to his surprise alpha particles were occasionally reflected straight back to the source when directed at a thin sheet of gold foil.  At this point, the nucleus was thought to only contain positively charged protons, however in the 1920s Rutherford hypothesized the existence of neutrons, a theoretical neutral subatomic particle in the nucleus with no electric charge, to account for certain observed patterns of radioactive decay.

The neutron was quickly discovered by James Chadwick, a colleague and mentee of Ernest Rutherford, in 1932.  The discovery of the neutron proved to be a critical step for the development of nuclear fission technology.  Scientists soon realized that they could use the neutron to split heavier atomic nuclei.  Since the neutron have a lack of electrical charge, they are not repelled by the positively charged nucleus in the way alpha particles are repelled, and they can penetrate and be absorbed by the nucleus.  This makes the nucleus unstable and causes it to split into two or more smaller nuclei, releasing a tremendous amount of energy in the process.  

The Discovery of Nuclear Fission

Shortly after the discovery of the neutron scientists began using it to probe the structure of the atom further.  In 1934 Enrico Fermi began using the neutrons to bombard uranium atoms.  He thought he was producing elements heavier than uranium, as was the conventional wisdom of the time.  

The first experimental evidence for nuclear fission occurred in 1938 when German scientists Otto Hahn, Fritz Strassmann, Lise Meitner, and their team began also bombarding uranium atoms with neutrons.  As was so often the case in the early days of atomic physics, their results were completely unexpected.  Instead of creating heavier elements, the neutrons split the nucleus to produce smaller, lighter elements such as barium among the radioactive decay.  At the time it was thought improbable that a neutron could split the nucleus of an atom.  The experiments were quickly confirmed, and the first instance of nuclear fission had been achieved.  

It was quickly realized that if enough neutrons were emitted by the fission reaction it would create a chain reaction, and an enormous amount of energy would be released in the process.  By 1942 the first sustained nuclear fission reaction had taken place in Chicago.  Hann was awarded the Nobel Prize in Chemistry in 1944 “for his discovery of the fission of heavy nuclei”. 

An Explosive Impact on Civilization

Nuclear fission is the process of splitting an atom into smaller fragments.   The mass of the sum the fragments is slightly less than the mass of the original atom, usually by about 0.1%.  The mass that had gone missing is actually converted into energy according to Albert Einstein’s E=mc^2 equation.  

The discovery of nuclear fission ushered in the atomic age, leading to inventions such as nuclear power and the atomic bomb with world changing consequences.  Almost immediately after its discovery, scientists realized the immense power that could be unleashed by splitting the atom.  In 1939, a group of influential scientists including Albert Einstein drafted a letter to President Frankling D. Roosevelt warning at the potential military applications of nuclear fission and urging the United States government to initiate its own nuclear research program.  They speculated that Nazi Germany may be developing nuclear weapons of their own.  

Cooling reactors of a nuclear power plant
Cooling reactors of a nuclear power plant
(Credit: Wikimedia Commons)

In response, an Advisory Committee on Uranium was formed which eventually led to the creation of the Manhattan Project. The Manhattan Project was officially launched in 1942 and led by J. Robert Oppenheimer at a secret facility in Los Alamos, New Mexico.  The result of the massive scientific and engineering project was the development of the world’s first atomic bomb, which was ultimately used against Japan at the end of World War II.

A more positive benefit to civilization than atomic weapons is the development of nuclear energy.  Nuclear energy produces extremely low amounts of greenhouse gases, making it a much cleaner alternative form of energy from fossil fuels.  If humanity it to solve its climate crisis in the coming century, nuclear energy may prove to be the saving technology. 

Continue reading more about the exciting history of science!

Marie Curie

Posted on by Dan
Marie Curie
Marie Curie

Marie Curie (1867 – 1934) was a Polish physicist and chemist who overcame a gender discrimination in the sciences to conduct groundbreaking work on radioactivity. Her incredible scientific career awarded her two Nobel Prizes in two different fields and earned her the distinction of being the first woman to win the award.

Marie Curie was born in Warsaw to the parents of two teachers who were very interested in science.  She was the top student in her high school, passionate about science, and wanted to peruse a higher education however there were obstacles in her way.  She was unable to enroll in traditional higher education institutions because she was a woman and her family had little money to support her.  To earn money for herself and to help support her sister’s studies she worked as a tutor.  In her free time she read books on physics, chemistry and mathematics.  In 1891 she departed Poland for Paris, France to join in studies with her sister.  There she studies physics, chemistry, and mathematics, and once again was the top student in her class.  She earned her Ph.D. in physics and in 1985 she married Pierre Curie.  That same year Wilhelm Roentgen discovered x-rays.  The following year Henri Becquerel discovered a new type of ray, resembling that of x-rays yet different, emitting from Uranium.

Curie decided to study these new rays emitting from Uranium and made a handful of remarkable discoveries.  Her husband became interested in her work and joined her.  Their joint work resulted in the discovery of new two elements – Polonium, named for Curie’s home country Poland, and Radium, named for the word ray.  They discovered that Radium would continuously produce heat without any chemical reactions occurring that it emitted rays in far greater quantity than Uranium.  They term they coined for this phenomenon they were observing was radioactivity.  The term stuck.

In December 1903 Marie Curie was the first woman ever to be awarded a Nobel Prize.  Along with her husband Pierre, Marie won the prize in physics for her work in the field of radiation.  The award brought recognition and money for the two scientists, however they would not be able to enjoy it for long.  Pierre was killed in a tragic accident in 1906 when he was hit by a horse-drawn carriage while crossing the street.  Marie Curie continued her scientific work after her husband passed away and was awarded a second Nobel Prize in 1911, this time in the field of chemistry.  By now she had cemented her reputation as one of the elite scientists alive.

Curie continued to work up until her death in 1934 when she died from a rare bone marrow disease.  The disease was likely cause by her long-term exposure to radiation without proper protection.  Her legacy was that of one of the greatest scientists of the time and her work broke barriers for other woman to pursue work in the scientific fields of their choosing.

1913: Bohr Model of the Atom

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In 1913 Niels Bohr proposed a model of the atom based on quantum mechanic physics which helped solve problems of previous atomic models that were based on classical physics. His proposal came to be know as the Bohr model of the atom. 

Earlier Models of Atomic Structure

Bohr Model of the Atom
Bohr’s Model of the Atom

Prior to Bohr’s model of the atom there were various competing models being used.  In 1897 J.J. Thomson discovered the electron through his experiments with cathode ray tubes, setting the stage for the development of his plum pudding model.  In this model electrons were embedded in a positively charged sphere, akin to plums scattered in a pudding.   

Shortly afterwords, Ernest Rutherford announced the surprising discovery of the atomic nucleus which instantaneously and radically transformed our understanding of the structure of the atom.   The discovery of the nucleus paved the way for Rutherford’s nuclear model of the atom, placing the nucleus in the center with electrons orbiting around it, akin to planets orbiting the Sun in our Solar System.  Unfortunately, both of these models had shortcomings because they were entirely based on classical physics.

The most pressing issue was the stability of the atom. According to electromagnetic theory, whenever an electron is accelerated around the nucleus of an atom it should emit radiation resulting in a continuous loss of energy.  This loss of energy would cause the electron to slow down and spiral into the nucleus almost instantly.  Clearly this does not happen in the real world as atoms are stable.  To solve for this problem Bohr used the emerging quantum physics.

Bohr’s Model of the Atom

Bohr’s model resolved this problem by showing the electrons in orbit were consistent with Max Planck’s quantum theory of radiation.  At the turn of the 20th century Max Planck introduced the revolutionary concept of quantized energy to explain the spectrum of black-body radiation.  His key insight was that energy is emitted or absorbed by matter in discrete units, or “quanta,” rather than in a continuous manner as predicted by classical physics.  This insight laid the groundwork for Bohr’s work on the structure of the atom.

In Bohr’s model of the atom electrons would only be able to occupy certain orbits with a specific amount of energy, which he referred to as energy shells or energy levels.  They emit or absorb radiation only when electrons abruptly jump between different orbits.  Using Plank’s constant, the frequency of photons, and some information about the electrons mass and charge, Bohr was able to obtain an accurate mathematical formula for the hydrogen atom.

This was huge improvement on previous models because it incorporated the new quantum physics, however there still were a few problems associated with Bohr’s model.  It was not a particularly useful description for atoms other than hydrogen and it failed to account for the Zeeman Effect in hydrogen.  It was eventually refined and superseded by quantum theory that was consistent the work of Werner Hiesenberg, Erwin Schrodinger, Max Born, and many others.

Impacts of Bohr’s Model of the Atom

Bohr’s model of the atom, with its quantized energy states, was nothing short of revolutionary. It implied several significant impacts on the understanding of atomic structure and on the development of quantum mechanics.  Some of the key impacts of Bohr’s model include:

Bohr's Model of the Atom provided the theoretical framework for understanding the spectral lines of different elements
Bohr’s Model of the Atom provided the theoretical framework for understanding the spectral lines of different elements
(Credit: www.webbtelescope.org)
  • Explanation of atomic spectra: Bohr’s model was successful in explaining the discrete line spectra observed in the emission and absorption of light by atoms.  It provided a theoretical framework for understanding the spectral lines of different elements.
  • Development of quantum theory:  Bohr’s model was crucial in the early development of quantum theory.  It provided one of the first examples of the application of quantum principles to the behavior of electrons in atoms. 
  • Influence on atomic theory: Bohr’s model spurred further research and inspired subsequent scientists, including Werner Heisenberg, Erwin Schrodinger, and Max Born.  These scientists went on the develop more sophisticated quantum mechanical models.
  • Practical technological applications:  Bohr’s model has helped in the development of technologies such as lasers, semiconductors, and nuclear energy.   These technologies depend on an understanding of atomic behavior.  

Overall, Bohr’s model of the atom had a significant impact on physics as a whole.  Its development can be marked as a transition in time between classical physics and quantum mechanics.  While his model has since been superseded by a more comprehensive quantum mechanical model, its significance as a foundational role in the development of atomic theory and quantum mechanics remains important. 

Continue reading more about the exciting history of science.

Niels Bohr

Posted on by Dan

Niels Bohr (1885 – 1962) was a Danish physicist who significantly improved our understanding of the structure of the atom.  His improved model of the atom solved the problems associated with classical physics and was based on the newer quantum mechanic physics.

Early Life and Education

Niels Bohr was born on October 7th, 1885 in Copenhagen, the capital of Denmark.  He was born into an intellectual and supportive family, and his upbringing consisted of a rich educational environment. His father, Christian Bohr, was a professor of physiology at the University of Copenhagen. His mother, Ellen Bohr, came from a prominent Jewish-Danish banking family with influence in parliamentary circles. The combination of his fathers scientific work and his mothers cultural pedigree together created a home environment that nurtured curiosity and scholarly pursuit. It is no surprise that young Niels Bohr grew up strong in mathematics and was naturally attracted to science at a young age. 

In 1903 he enrolled as an undergraduate at the University of Copenhagen, where he received his master’s and doctorate in physics by 1911.  That same year he traveled to England to work in the Cavendish Laboratory where he met J.J. Thomson. The two scientists didn’t work well together at first, but Bohr soon met another scientist at a different laboratory whom he worked better with. In March 1912 Bohr traveled to Manchester to work with Ernest Rutherford, who had recently won a Nobel Prize in Chemistry for his work on radioactivity.

Scientific Career

Niels Bohr
Niels Bohr

Bohr returned to Denmark in 1912 after having secured a teaching position at the University of Copenhagen.  He brought with him new ideas about the structure of the atom.  It was becoming clear that Rutherford’s model of the atom, based on classical physics, was unstable.  According to classical physics, the electrons moving around the nucleus of an atom in orbit would emit electromagnetic radiation, causing the electron to lose energy and eventually spiral into the nucleus.  The form of electromagnetic radiation being emitted came to be called photons, with each photon having its own precise wavelength and amount of energy.  Quantum physics states that objects emit photons in discrete packets rather than in continuous streams. Using quantum physics, Bohr proposed that electrons are confined to fixed orbits, each with their own distinct energy level.  They only suddenly jump to lower or higher orbits as a precise amount of energy is emitted or absorbed in the atom.  For example to move an electron to a lower energy level it emits a photon of the precise amount of energy that is the difference between the two orbits.  Using Plank’s constant, the frequency of photons, and some information about the electrons mass and charge, Bohr was able to obtain an accurate mathematical formula for the hydrogen atom.  In 1922, Niels Bohr was awarded Nobel Prize in Physics for this work.

Bohr continued to work on quantum physics for the remainder of his life.  He founded the Niels Bohr Institute at the University of Copenhagen.  Later in life he was a part of the Manhattan Project during the Second World War, working with many other great physicists.  He died in Copenhagen at the age of 77.

1781: Discovery of Uranus

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In 1781 Sir William Herschel announced the discovery of a new planet that became named Uranus in the tradition of naming planets after classical mythology. The discovery of Uranus, the seventh planet from our Sun, was a pivotal moment in the history of astronomy. In antiquity, the planets referred to the seven visible points of light that moved across the fixed background of the stars. These included the Sun and the Moon, as well as the classical planets of Mercury, Venus, Mars, Jupiter, and Saturn. The discovery of Uranus marked the first time a new planet was discovered since ancient times and ushered in a new era of exploration within our solar system.

Sir William Herschel Makes a Monumental Discovery

Uranus photo NASA
Photo of Uranus
(Credit: NASA)

Herschel was a German-born astronomer who resided in England.  Born in 1738, Herschel was a polymath with a keen interest in music, mathematics, and of course astronomy.  In 1757 he moved to England where he worked as an organist in Bath. He began his foray into the world of astronomy with a simple, homemade telescope and began observing the stars. He would eventually construct more than 400 telescopes during his lifetime, including a great 40-foot telescope, and most of which were superior to the ones available at the time.

On the night of March 13, 1781, Herschel was conducting a routine survey of the night sky using a 6.2-inch aperture telescope he had constructed himself.  During this survey, he stumbled upon an object that appeared to be a faint, nonstellar object.  Herschel initially reported it as a comet due to its slow movement across the sky and dimness but he continued to observe it over the following nights.  As the months passed by Herschel and the other astronomers he reached out to for input began to suspect differently, as its orbit suggested it was a planet and no tail was visible.  Eventually it became clear the object was a planet as the orbit was calculated by Pierre-Simon Laplace and Alexis Bouvard, two French mathematicians and astronomers.  Their calculations confirmed that Uranus followed a nearly circular orbit around the Sun, consistent with it being a planet.  For the first time in history, our solar system had expanded from the six previously known planets.  

The discovery of Uranus sparked a debate over its name.  Hershel, the discoverer, felt that he had the right to name the planet and he proposed the name “Georgium Sidus” or “George’s Star,” in honor of King George III.  However this name was not well received in the international community, as it broke with the tradition of naming the planets after ancient Roman Gods.  Several alternative names were suggested, but in the end the name Uranus was chosen and eventually accepted as the planet’s name.  

The Planet Uranus and the Impact of its Discovery

Uranus is the seventh planet from the Sun and approximately 2.6 billion kilometers from Earth.   It takes about 84 years for it to complete a full orbit around the Sun.  Its mass is about fifteen times Earths with a diameter of about four times Earth, making it the third largest planet in our solar system.  Accompanying the planet are thirteen rings and 27 named moons.  Composed mostly of rock and ice, it is one of the coldest planets in the solar system with an average temperature of -216 Celsius.  This is due to its low core temperature – it doesn’t generate much heat unlike Jupiter and Saturn.

The discovery of Uranus marked a new era in the exploration of our Solar System.  Most significantly, it showed that our Solar System was much larger than previously thought.  This provided much motivation for further exploration. Perturbations in Uranus’s orbit could not be explained by Newton’s laws of gravity if the only known planets were considered. This led to a hypothesis that there might be other unknown planets leading to the discrepancies. The discovery of Neptune in 1846 and later Pluto in 1930 confirmed this hypothesis, although Pluto was later reclassified as a dwarf planet in 2006. The discovery of Neptune was a triumph for Newton’s laws of gravity because its position was predicted based on the gravitational influence it had on Uranus.

The discovery of a planet more distant than Saturn provided motivation for advances in telescope technology as astronomers recognized the new for more powerful telescopes to study distant objects.  Lastly, the naming controversy that followed highlighted the significance of tradition in the scientific community.  

Continue reading more about the exciting history of science!

Albert Einstein

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Albert Einstein portrait
Albert Einstein

The scientific career of German-born physicist Albert Einstein (1879 – 1955) was one of the most impactful ever in the history of science.  His work led to significant and meaningful changes in our understanding of several fundamental laws of nature including gravity, light, and time.

Albert Einstein was born on March 14, 1879 in Ulm, Germany.  He became interested in nature and mathematics at an early age.  There were two key moments in his childhood that inspired a wonder of curiosity in him.  The first moment was when he was sick at the age of five.  His father brought him a compass and this device stirred his curiosity and sparked his intellect.  At age twelve he stumbled upon a book of geometry that has much the same effect on him as the compass.

In 1896 Einstein enrolled for a science degree at the Swiss Federal Institute of Technology in Zurich.  He graduated in 1900 with his teachers being largely unimpressed with him.  Two years later he would obtain a post of an examiner in the Swiss Federal patent office where he would go on to make some of his greatest discoveries.

The year 1905 was called the year of miracles for Einstein.  He published four scientific papers each with immense importance for science.  His papers topics were on the photoelectric effect, Brownian motion, the Theory of Special Relativity, and the equivalence of mass and energy.  These four papers gained him international respectability and propelled his academic career.  He won the Nobel Prize for Physics in 1921 for his work on the photoelectric effect.

As Einstein began teaching physics at various institutions he began formulating his General Theory of Relativity, which he finally published in 1915. This theory shows how gravity works as a geometric feature of space and time and how its curvature is directly related to the energy and momentum of the present mass and radiation.

As Einstein aged he still worked in science but became more involved in politics.  He emigrated to the United States in 1933 due to the rise of Nazi power in Germany.  During World War 2 he would work on the Manhattan Project which developed the atomic bomb.  This was a difficult moral decision for him since he was a pacifist, but he was uneasy that Germany would develop the bomb first and ultimately decided to help the US develop it before Germany.  Einstein died in 1955 with the legacy of being one of the most impactful scientists in all of history.