Friday, November 2, 2018

The Discovery of Radioactivity


The discovery of radioactivity has truly changed the world as many useful applications have been developed to take advantage of this property of matter. Radioactivity is being used in nuclear power plants to produce electricity, in the field of medicine to sterilize medical instruments, and as tracers within the human body to help doctors diagnose and treat patients.


The discovery of X-rays by the German physicist Wilhelm Roentgen in November 1895 led to much activity in the scientific community as this new form of energy was capable of piercing through matter to see what was inside. X-rays could “look” inside the human body and see the inner workings of the skeleton and organs. The French physicist Antoine Becquerel was one of the scientists caught up in the frenzy to investigate the properties of the new discovered X-rays. Born in 1852, Becquerel was a third-generation physicist and had been investigating the nature of florescence and phosphorescence. Phosphorescent minerals have the property that they absorb light and re-emit light some time after the exciting light has been switched off – they appear to glow in the dark!

Becquerel’s Discovery

Becquerel heard about Roentgen’s discovery in January 1896 and began wondering if there was a connection between the phosphorescence he had already been investigating with the newly discovered X-rays. He wondered if any florescent material might be emitting X-rays. This was reasonable since Roentgen discovered X-rays by the fluorescence they produced. He began to follow up on Roentgen’s work on X-rays and started testing various fluorescing materials to see if they also emitted X-rays. He tested various materials for ten days without success and then decided to try a uranium salt, uranyl potassium sulfate. This time his experiment succeeded, finding that uranium salt emitted radiation and appeared to glow or fluoresce. He had sealed a photographic plate in black paper, sprinkled a layer of uranium salt onto the paper and “exposed the whole thing to sun for several hours.” When he developed the photographic plate “I saw the silhouette of the phosphorescent substance in black on the negative.” He mistakenly interpreted the result and thought that sunlight activated the uranium salt to emit X-rays, much like in Roentgen’s experiment where the X-rays flogged a photographic plate that was shielded from light by a dark paper. Becquerel took his experiment as evidence that he was correct and the phosphorescent uranium salts absorbed sunlight and emitted a penetrating radiation similar to x-rays. Confident in his discovery, he reported the results at the February 24, 1896 meeting of the French Academy of Science.

Now serendipity steps into the story for Paris was cloudy and overcast for the next two days which did not allow Becquerel to repeat his experiment. Being forced to wait for a sunny day, he put the covered photographic plate away in a dark drawer with the uranium salt next to the plate. A few days later he decided to go ahead and develop the photographic plate, “expecting to find the images very feeble. On the contrary, the silhouettes appeared with great intensity. I though at ounce that the action might be able to go on in the dark.” Apparently energetic rays were being emitted from the uranium salt that did not require sunlight to stimulate the emission of the energy. This was very usual as normally; a fluorescent material requires a strong source of light such as sunlight to “charge” up the material so that it then again fluoresce and emit the light once the sunlight was removed. The next day, March 1, 1896, Becquerel reported at the Academy of Sciences that the uranium salts emitted radiation without any stimulation from sunlight. The strange new rays became known as Becquerel or uranium rays.


Figure - Image of Becquerel's photographic plate which has been fogged by exposure to radiation from a uranium salt. The shadow of a metal Cross placed between the plate and the uranium salt is clearly visible.

Becquerel began to study the radiation emitted from the uranium salt and found it quite like X-rays, since it penetrated matter and ionized air. The radiation came from the salt in an unending stream and seemed to come from all directions within the material. Marie Curie named this new phenomenon “radioactivity” – a name that would stick for generations to come.

Figure - Henri Becquerel, Pierre Curie, and Marie Curie

The Curies and Rutherford’s Work on Radioactivity

Becquerel initially though his new rays were similar to X-rays, but with further experimentation he was able to show that his rays could be bent by a magnet, whereas, X-rays were not affected by a magnet. The young graduate student in physics, Marie Curie, read Becquerel’s paper on these new rays and decided that she would study the rays as part of her Ph.D. thesis. She began her research immediately and with the help of her husband, Pierre, undertook a systematic study of the strange uranium rays. The couple devised a sensitive apparatus to measure the intensity of the radioactivity, and soon discovered other radioactive elements: polonium, thorium and radium.

In 1899 the British physicist Ernest Rutherford identified two types of radiation: alpha radiation, which produces significant ionization in the surrounding air (ionization is the removal of one, or more, electrons from an atom, leaving it positively charged), but can be absorbed by a single sheet of paper; and the second type known as beta radiation produces less ionization but is capable of penetrating a sheet of metal a few milli-meters thick. In 1900 a third type of radiation, called gamma radiation, was discovered by Paul Villard who found that Radium emitted an extremely penetrating electromagnetic radiation much like X-rays.

Figure - Three types of radiation emitted from a radioactive atom.

Nobel Prizes

In recognition of the work of the Curies and Becquerel the Nobel Prize in Physics for 1903 was divided, one half awarded to Antoine Henri Becquerel "in recognition of the extraordinary services he has rendered by his discovery of spontaneous radioactivity", the other half jointly to Pierre and Marie Curie, "in recognition of the extraordinary services they have rendered by their joint researches on the radiation phenomena discovered by Professor Henri Becquerel." Ernest Rutherford would continue his research on radioactivity and win the 1908 Nobel Prize in Chemistry for "for his investigations into the disintegration of the elements, and the chemistry of radioactive substances."

References


Asimov, Isaac. Asimov’s Biographical Encyclopedia of Science and Technology. 2nd edition. Doubleday & Company, Inc. 1982.

Brain, Denis. The Curies: A Biography of the MostControversial Family in Science. John Wiley & Sons, Inc. 2005.

Rhodes, Richard. The Making of the Atomic Bomb. Simon & Schuster, Inc. 1988.

“March 1, 1896: Henri Becquerel Discovers Radioactivity.” APS Physics. https://www.aps.org/publications/apsnews/200803/physicshistory.cfm     Accessed November 11, 2018.
“The Nobel Prize in Physics 1903.” https://www.nobelprize.org/prizes/physics/1903/summary/    Accessed November 1, 2018.

Monday, October 22, 2018

Free as a Bird: The First Manned Balloon Flights


Since ancient times, man has dreamed of flying through the air like a bird. It was during the 13-th century that the Franciscan monk, Roger Bacon, would make one of the first contributions to the history of aviation. In his book (ca 1250) Secrets of Art and Nature he visualizes something very similar to the 20th century airplane.  Bacon described “Engines for flying, a man sitting in the midst thereof, by turning only about an instrument, which moves artificial wings made to beat the air, much after fashion of a birds flight.” Other creative minds would follow the dream of man flying through the air such as the 15th century Italian inventor, Leonardo da Vinci, who designed several “flying machines.” However, it would not be until the late eighteenth century in France when two inventive brothers would put a man aloft in a hot air balloon.

Figure - Joseph-Michel Montgolfier and Jacques-Étienne Montgolfier.

The Montgolfier Brothers


The French paper maker, Joseph Montgolfier, sitting in front of his fireplace wondered why the smoke, sparks, and more solid matter were disappearing up the chimney. He questioned if it would be possible to capture this “gas” and lift a man-made object into the air. Joseph began to experiment while living in Avignon, France, in 1782 and made a bag of fine silk and lit a fire under it. To his delight, the bag rose to the ceiling.

Inspired, Joseph wasted no time and enlisted the help of his brother Etienne. They constructed a large envelope or bag to trap the hot air and built a fire underneath it which caused it to rise to about 70 feet in the air. The brothers continued to experiment and built even larger “aerostatic machines”, a name the brothers gave to their balloons. They were now able to construct balloons that could rise to 1000 feet and float for a mile before the gas cooled and the balloon crashed to the ground. To show the world their new invention, the two men built a balloon made of linen and lined with paper that was more than 100 feet in diameter.

To bolster their claim as the inventors of flight the brothers made a large balloon for a public demonstration. This balloon was globe-shaped and made of sackcloth tightened with three thin layers of paper inside. The balloon weighted around 500 pounds and was constructed in four pieces, the dome and three lateral bands, and held together by 1,800 buttons. A reinforcing fish net was used to contain and strengthen the outside of the envelope. On June 4, 1783, they demonstrated their balloon to a large crowd of spectators at the market place in Annonay. As the balloon filled with the hot air, it took eight men to hold it to the ground. Once released the large balloon rose to a height of about a mile.

Word spread through France of the Montgolfier’s flying machine and they were asked to perform a demonstration before the French Academy of Sciences. This very successful flight brought on a request for a demonstration before the king and queen, Louis XVI and Mary Antoinette. To make the event even more spectacular, the brothers put aloft a cage with a sheep, a rooster, and a duck. To everyone’s delight, the flight lasted eight minutes and brought the bewildered passengers safely to rest over a mile away. King Louis awarded the brothers the Order of Saint Michel and from then on, all hot-air balloons became known as montgolfieres.


Figure: The first manned hot-air balloon, designed by the Montgolfier brothers, takes tethered off at the garden of the Reveillon workshop, Paris, on October 19, 1783.

First Manned Balloon Flight


The obvious next step was to put a man aloft in a balloon. On the afternoon of November 21, 1783, in a courtyard on the outskirts of Paris, a balloon constructed by the brothers Montgolfier, made history as two men floated through the air as a bird. The historic flight was piloted by the young scientist Jean-Francois Pilatre de Rozier and an army officer, the Marquis d’Adlandes. The twenty-five-minute flight carried the two men over the city of Paris and they landed safely ten miles from where they started. The early balloon flights made a sensation with the public. To commemorate the event, numerous engravings were made, chairs were designed with balloon backs, mantel clocks were made with the dial that looked like a balloon, and much more.

Video:

Lighter Than Air: Man’s First Balloon Flight


Hydrogen Balloons


Twenty years before the Montgolfier brothers stated flying their balloons, the British chemist Henry Cavendish had isolated a new and extremely light gas, hydrogen. In December 1783, the French chemist, J.A.C. Charles mixed a large quantity of iron filings and sulfuric acid, which produced hydrogen gas. Charles used the gas to fill a large balloon which allowed him to make a two hour flight for a distance of 27 miles. If Mr. Charles would have fully understood the explosive nature of hydrogen, he may not have decided to make a balloon filled with such a highly combustible material. It quickly became apparent that the use of hydrogen was superior to filling a balloon with hot-air as a lifting agent. The hot-air filled balloons constantly needed a source of fuel, such as burning straw to stay aloft. Hydrogen became the gas of choice for balloons and their development spread rapidly all over Europe. The first balloon flight in America was made by the Frenchman, Francois Blanchard, in early 1793. President George Washington was present at this first balloon demonstration.
Hydrogen would remain the gas of choice for balloons until after World War I, when helium was substituted in the United States. Though helium was less efficient than hydrogen as a lifting agent, it would not burn or explode.

References


Taylor, John W.R. and KennethMunson. History of Aviation. Crown Publishers, Inc. 1977.

Challoner, Jack (editor) 1001 Inventions That Changed the World. Quintessence Books. 2009.


Wednesday, February 28, 2018

Jocelyn Bell Burnell – Astronomer who helped discover the Pulsar

Introducion

Jocelyn Burnell entered into the world of astronomy with more fanfare that most astronomers receive in their careers. As a 24-year-old graduate student she was part of the team that observed the first known pulsar, which is a star that emits rapid pulses of radio signals. Her work was key to the discovery and soon lead to a Noble Prize. Even though Burnell didn’t receive the Nobel Price, this put her on the map in the astronomy community and lead to much publicity for herself and her group of astronomers.
Figure - Susan Jocelyn Bell (Burnell) in 1967.

Early Years

Susan Jocelyn Bell, also known as Jocelyn Bell Burnell and Susan Jocelyn Bell Burnell, was born on July 15th, 1943 in Belfast, Northern Ireland. She was the daughter of M. Allison Bell and Amagh Observatory architect G. Philip Bell. Her father was an avid reader and encouraged Jocelyn to be one as well. It was through her father's book collection that Jocelyn was first introduced to the world of astronomy. While she was born in Belfast, Jocelyn spent much of her childhood in Lurgan, Ireland.

Her parents encouraged her new found love of astronomy with the help of the staff at the nearby Armagh Observatory. Her parents believed adamantly that women should be educated. So when Jocelyn failed the '11 plus' examination, which was required for children of the UK in order to attend secondary school, her parents opted to send her to a boarding school to further her education. The exam was crucial for children in order to get to a 'grammar' school, which is the next step towards a university education.

Though the school in Lurgan agreed to keep her on for a few years, until she went to boarding school in England, the failure stuck with her for many years. In fact, she kept her low exam score a secret until later when she attained the status of Professor.

Looking back today, Jocelyn believes that the 11 plus curriculum at the time didn’t suit her, as there wasn’t any science in it. She was attending school in the 1950s, and while her scientific ability was recognized during her first year at Lurgan Grammar School when she took first in her class, the pending segregation of the sexes was disheartening. During her first year of secondary school, the boys were taken to the science lab and the girls were put into domestic science education classes, the UK equivalent of 'Home Economics'.

Women, at every age, were not encouraged to do science during this point of time in Northern Ireland, so while Jocelyn was geared for it the school was giving her a resounding "no." Her parents 'kicked up a fuss,' and Jocelyn, along with two other girls, were permitted to join the boys in the lab. Jocelyn attended Lurgan for two more years before she went to England.

The Bell family belonged to the Quaker faith and, as was tradition, she attended a Quaker School called Mount School, in York, England. Though it was initially traumatic, Jocelyn did well in her studies and eventually felt good about being away from home. England did not discourage girls from doing science, as they did in Northern Ireland, but, there was still a mixed standard of science education.

Education and Early Professional Work

The early years of uncertainty in Jocelyn's education paid off when she got accepted to Glasgow University to study science. She did well at Glasgow University and completed her B.S. in physics in 1965. She had high enough scored to be accepted to the University of Cambridge, which was and is a top of the line university full of Nobel Prize winnings scientists. It was during her time as a graduate student at the University of Cambridge, while working under Antony Hewish, that she first discovered pulsars.

It was quite by accident that pulsars were even discovered, as the goal of the research project she was working on was to find quasars. Quasars, short for Quasi-Stellar Radio Source, are basically star like objects that give off radio signals. Quasars are now believed to be the centers of distant galaxies, about 2.6 to 16 billion light years away. Quasars are very bright, brighter than our entire galaxy which consists of 200 billion stars, and since each quasar is only about one light year across, they give off an immense amount of energy. It is also believed that quasars surround a supermassive black hole. It is interesting to note that scientists now know that only 10% of quasars give off radio signals.

At the time, Jocelyn Bell described quasars as "big, big things like galaxies, but they are incredibly bright and they send out a lot of radio waves." The project Jocelyn and Hewish were working on had them using a telescopic array to search the cosmos for sources of natural radio waves.

The work was not all the glamour often associated with astronomers, at least not for Jocelyn. A special array of linked telescopes had to be designed and constructed on a four acre site at the Mullard Astronomy Observatory close to Cambridge. Jocelyn was in charge of the nitty-gritty aspects of getting the 81.5 megahertz project up and running. This meant that she connected miles of wire, banged stakes into the ground and dug much of it herself.

The hard manual labor paid off when the array was complete in July 1967. She immediately began the monumental task of looking for the interplanetary scintillation of compact radio sources. Jocelyn couldn't wait to get started on the research and analysis of the data. It was during the first few months of the array's operation that she found unusual signals in the miles of print-outs. She deemed these anomalies "scruff." An analysis of the areas of "scruff" indicated radio signals that were too fast and to regular to be from quasars. She also determined that these radio signals were coming from a fixed location outside of our solar system.

The first mysterious signal they detected was called "Little Green Man 1" (LGM-1), sort of an inside joke, it is now known as PSR B1919+21. Later documentation of the pulsar was later presented in the BBC Horizon series.

Jocelyn and Hewish began looking into the causes of the repeated signals. They were able to rule out orbiting satellites almost immediately. They then looked into, and eventually ruled out, radar, television signals and even alien communication. The questioned remained... what could be causing the fast recurring signals? Over the next few months, she discovered three more distinct signals.

The first publication to report on these unknown signals was a renowned scientific journal called Nature, in 1968. The lab she worked for also did a series of publications and interviews on the discovery. Reading some of the research papers they wrote, specifically those pertaining to the world of theoretical physics, determined that these signals must be coming from super-dense, rapidly spinning, collapsed stars. The media deemed these pulsars and the story was published world-wide. The four pulsars she discovered, are the first four known pulsars in human history.

To understand what a pulsar is, you must first understand, in laymen's terms, what a neutron star is. A Neutron star is comprised of a liquid mantle and a solid core. They have a crust which is only about an inch thick. However, due to their liquid mantle, they have a gravitational pull stronger than that of the earth by about one trillion times. When a Neutron star, which emits electromagnetic radiation in the form of radio waves from it's north and south poles has either of it's poles pointing toward earth, it will appear to pulse on a radio telescope.

Figure - The Vela Pulsar, a neutron star corpse left from a titanic stellar supernova explosion, shoots through space powered by a jet emitted from one of the neutron star's rotational poles. Now a counter jet in front of the neutron star has been imaged by the Chandra X-ray observatory.

Now, this means that all pulsars are a type of Neutron star, but not vice versa. Imagine if you will, a figure skater. They begin to spin with their arms outstretched. As they pull their limbs in and squat down, they will pick up speed, spinning faster and faster. This is an example of the Low of Angular Momentum, which states that as something spins and shrinks in size, but maintain the same mass, it will spin faster. This is seen with pulsars which are very compact and fast spinning, with rotations from as little as one rotation in 4.308 seconds to 1,122 rotations per second.

Career and Personal Life

Soon after her discovery of pulsars, but before completing her Ph.D. in radio astronomy, Jocelyn Bell became Jocelyn Burnell when she married an English government worker by the name of Martin Burnell in 1968. His job took them all across the country. The birth of their son, Gavin Burnell, limited her career in some aspects, but she did manage to still work part-time while raising their son.

On her own, Jocelyn continued to study astronomy. She began learning everything she could about every electromagnetic wave spectrum, gaining much experience along the way. This led to a fellowship, junior teaching, at the University of Southampton. She taught there for three years, from 1970 to 1973. During her time teaching at Southampton, Jocelyn developed and calibrated a 1-10 million electron volt gamma-ray telescope.

After her period of teaching with Southampton University, she held a research and teaching position at Mullard Space Science Laboratory in London. Her focus there was on x-ray astronomy. She also studied infrared astronomy in Edinburgh.

Because of the fame Jocelyn had found in her early 20's it was never very difficult for her to find new work when her husband's job made them move. The downside to her early fame was that people kept expecting her to discover something new. She was expected to come up with amazing discoveries all of the time. She said in a later interview that "A discovery such as finding pulsars comes only about once per decade in the astronomical community as a whole, and so it is a bit hard to live up to such expectations."
Figure - Anthony Hewish - 1974 Nobel Prize Laureate.

Her work at Cambridge, in which she discovered the first pulsars, led to Antony Hewish and Martin Ryle receiving a Nobel Prize in 1974. Despite all of her brilliance, Jocelyn was left off of the Nobel Prize list, a discredit which many of her friends, fans, and fellow astronomers consider a discredit to her service. The fact that Hewish and his senior supervisor, Ryle, refused to demand that Burnell get recognized for her part in the discovery of pulsars added insult to injury. The Nobel Prize society got around the controversy by claiming the prize was presented to Ryle and Hewish was for cumulative contribution.

Burnell stated in a later interview that she was not upset about being left off of the Nobel Prize. She gives three reasons for this. The first is that demarcation disputes between a student and their supervisor are nearly impossible to resolve. Second, the supervisor is held responsible if the project should fail. She feels it should serve that the supervisor gets the benefit of the successes as well as the fault of failures. The third reason, and probably the one that says the most about her character is that she believes it would be disrespectful and demeaning to the status of the Nobel Prize itself if it was awarded to research students. She says she is, after all, in good company.

While it was short of the Nobel Prize, Burnell did receive the American Tentative Society Award for her work with pulsars in 1978.

Since her time at Cambridge, Jocelyn Burnell has studied every ground breaking field of astronomy she could get access too. This includes gamma-ray studies and x-rays. Over the course of her professional career, Burnell was a professor at Open University, dean of the sciences as the University of Bath, and VP of the Royal Astronomical Society, then later as president from 2002-2004.

Burnell was made the Commander of the Order of the British Empire (CBE) in 1999 and the Dame (DBE) in 2007. The following year, she served two terms as the president of the Institute on Physics. She also found the time to be a member of the Royal Society.

Her divorce in 1989 did not deter Burnell from her pursuit of the sky and the access women have to the scientific fields. A portion of her life has been devoted to campaigning for the improved status of women in the academic and professional fields of astronomy. She is still active in the field of astronomy and is the patron of Burnell House at Cambridge Grammar School in Ballymena. She also still works as a research scientist at the Mullard Space Science Laboratory of the University College in London.

Unlike many who take the path of the sciences, Jocelyn remained active in the Quaker faith throughout her childhood and into adult life. In 1995, 1996 and 1997 she served as the clerk for the Quaker British Yearly Meeting. She delivered a lecture at Swathmore titled Broken for Life. She was also the plenary speaker at the U.S. Friends General Conference Gathering of 2000.

Jocelyn kept her beliefs separate from her science and out of the public eye until an interview with Joan Bakewell in 2006. As recently as 2007, she served on the Quaker Peace and Social Witness Testimonies Committee and helped create Engaging with the Quaker Testimonies: A Toolkit.

Her religion has become mostly a moot point to those who have worked with her in a scientific capacity. Her days are filled with being a visiting professor of Astrophysics at Oxford University where she is allowed to freely conduct whatever research fascinates her without the extra responsibilities being thrust upon her. Her legacy, Nobel Prize or not, is clearly secure. This was made apparent in a pulsar conference held in Sardinia in 2010 , which honored Jocelyn for her 45 years of contributions to the scientific community. She was also given the honor of christening their new radio telescope. Her long-time friend and fellow scientist, Dick Manchester, delivered a speech detailing all of her many contributions.

Her Contributions to the Next Generation

Her legacy will not stop with her. Jocelyn's son, Gavin Burnell has followed in his mother's footsteps and is now a physicist making his own marks on the scientific world. From 2008 until 2011, Gavin Burnell was a lecturer on Condensed Matter Physics. He has published over 85 articles and has a specific interest in understanding the physics of electron transport in materials through the fabrication and characterization of nanoscale devices.

Beyond her blood lineage, many women who are working in various scientific fields today, be it astronomy, physics, biology, chemistry or one of the other fields once exclusively for men, owe their very careers to Jocelyn Bell Burnell. It is the determination of her and other women in science like, Annie Jump Cannon, Williamina Fleming, and Ellen Dorrit Hoffleit, that dared to do what society dictated they weren't equipped to do that has opened up the doors to women today. Jocelyn Burnell started by failing, but rose to monumental heights by her own brilliance, perseverance and will.

References

Burnell, Jocelyn Bell. AQuaker Astronomer Reflects: can a scientist also be religious? (The James Backhouse Lectures) (Volume 23). The James Backhouse Lectures. 2013.

Thursday, February 1, 2018

Dr. Robert Goddard Launches First Liquid Propellant Rocket

Dr. Robert Goddard’s experiments became increasingly more sophisticated. First he worked with solid fuel rockets and started experimenting with liquid-fueled engines. Despite the lack of funding, after numerous attempts, he finally launched the first liquid-fueled rocket on March 16, 1926, on his aunt's farm in Auburn, Massachusetts. The rocket used gasoline and liquid oxygen as fuel and it was the important demonstration that Goddard needed for proving that liquid propellant rockets were indeed possible. The 10-foot long rocket reached an altitude of 41 feet and stayed aloft for 2.5 seconds.

By 1929, Goddard’s work gained national notoriety again, with each rocket launch bringing him more attention from the public. Goddard disliked attention and thought it interfered negatively in his research, but the popularity of his work finally brought him a generous sponsor. Financier Daniel Guggenheim showed his willingness to fund Goddard’s research for a period of four years. The Guggenheim family continued to support Goddard in his work for many more years. The money from the Guggenheim Foundation and the Smithsonian allowed Goddard and his team to set up a research station in a remote desert location near Roswell, New Mexico. There, Goddard made significant advances in rocketry that eventually lead to the space program.

Learn more about Dr. Goddard's history first powered rocket flight at: https://owlcation.com/stem/Dr-Robert-H-Goddard-Father-of-American-Rocketry


References:

Carey, Charles W. Jr. American Scientists. Facts on File, Inc. 2006.