My Science School

Have you come across “concrete jungle” in conversations or in your readings? The term is used to refer to a modern city or an urban area that is filled with large buildings, sometimes closely crowded. With little space for trees or grass, the term also carries the connotation of places that are severely competitive, unwelcoming, or even dangerous.

For someone from the past generations, or even those now living in villages with wide open areas, most of our urban cities might feel like concrete jungles. And that might actually include Joseph Aspdin too, an English bricklayer who roamed the Earth 200 years ago and is often credited with the invention of portland cement.

Portland cement

Portland cement is the most common type of cement used these days around the world as a basic ingredient for concrete, mortar, and stucco. A mixture of clay and limestone or other similar materials are heated to a high temperature, just short of fusing. This is then finely pulverised, resulting in portland cement, which sets under water.

Born in Leeds, England in 1778, Joseph Aspdin was the eldest of Thomas Aspdin’s six children. As was common in those days, Joseph followed in his father’s footsteps to become a bricklayer and mason while still in his teens.

Aged 31, Aspdin married Mary Fotherby in 1811, with their marriage certificate stating his occupation as “bricklayer”. By 1816, however, Aspdin had his own business in the field and began tinkering with the hopes of making it big.

Possessed with ambition and curiosity, Aspdin experimented with a number of cement formulas for years before arriving at the one that he patented in 1824. On October 21 that year, Aspdin was granted a patent which was titled “An improvement in the Modes of Producing an Artificial Stone”.

Marketing gimmick

Aspdin called his product portland cement, explicitly mentioning the same in the patent that he received. He coined this name after portland stone, a stone quarried on the island of Portland on the south coast of England that was famous for building work.

Similar in looks and colour and almost as hard when dry, portland cement was a lot like portland stone. And as portland stone was used across Britain in high-status buildings, Aspdin’s naming was a fine marketing technique as it linked his new product in people’s mind with an existing, well-established, and popular product.

Vague? Too lightly burnt?

Even though Aspdin’s patent is vague in certain aspects and his product might have been too lightly burnt to be what we call portland cement now, the invention of portland cement is usually attributed to Aspdin. He certainly gave it its name, something that still remains in common use.

By the time Aspdin died in 1855, portland cement wasn’t famous yet. It took the work of others to get it to the form that we now know it, and its significance became plain only then. Portland cement’s greatest role was in making concrete, which turned out to be the primary building material from the 20th Century onwards.

Whether Aspdin actually invented portland cement will be a point that is up for debate. Nevertheless, members of the British Cement Makers Federation and the American Portland Cement Association cemented his place in history by raising a plaque in Leeds in 1924, 100 years after Aspdin had given “portland cement” in his patent.

Picture Credit : Google

Subatomic particles of the same mass as a proton but having a negative electric charge and oppositely directed magnetic moment, antiprotons are the antiparticles of protons. Even though they are stable, they are typically short-lived as collision with any proton causes both particles to annihilate in a burst of energy.

Even though antiprotons were discovered only in 1955, we will have to go back a few decades further to get our foundations right. For it was in 1928 that Paul Dirac, a brilliant and eccentric English theoretical physicist, formulated an equation to describe the behaviour of relativistic electrons in electric and magnetic fields.

Strong implications

Dirac’s theory, which helped him win the 1933 Nobel Prize in Physics, considered both the special theory of relativity formulated by theoretical physicist Albert Einstein and the effects of quantum physics proposed by physicists Erwin Schrodinger and Werner Heisenberg. Even though the majority of the scientists of the time assumed that a particle’s energy must always be positive, Dirac’s equation permitted negative and positive values for energy.

While the idea went against both common sense and what was observed in physics, the implications were obvious. And when a young physicist, Carl David Anderson, recorded a now historic photograph in a project at the California Institute of Technology in 1932, things changed dramatically. Anderson had discovered an antiparticle that was later named positron, a discovery that made him one of the youngest to win the Nobel Prize for Physics when he received the honour in 1936.

The existence of the positron, the antimatter counterpart of the electron, suggested that the proton too should have an antimatter counterpart. This meant that antiprotons had to exist and the search for them soon got under way.

Bevatron is born

The accelerators available at the time were not powerful enough to produce these particles as two billion electron volts (eV) were required to create proton-antiproton pairs. The best way to do that would be by striking a beam of protons accelerated to an energy of about six billion eV on a stationary target of neutrons.

With these numbers in mind, American nuclear scientist Ernest Lawrence – winner of the 1939 Nobel Prize for Physics for the invention of the cyclotron – commissioned the Bevatron accelerator in 1954 to reach the required energy levels (while billion electron volts is now known as GeV, it was then denoted as BeV, giving the accelerator its name). Even though this wasn’t Bevatron’s officially declared purpose, its energy range – designed to accelerate protons up to 6.5 GeV – wasn’t chosen arbitrarily and it was built to go after the antiproton.

Half the challenge

With a machine at their disposal, two teams were put together to hunt for the antiproton. Edward Lofgren, who managed operations at the Bevatron, headed one team, and the other team was led by physicists Emilio Segre and Owen Chamberlain.

While creating the necessary conditions to produce antiprotons was one huge challenge, devising the means to identify them once they were created was an equally difficult task. Not only would 40,000 other particles be created for every antiproton created, but these antiprotons then annihilated in just microseconds.

It was understood that at least two independent quantities had to be measured for the same particle to identify it as an antiproton. Several possibilities were considered, but they concluded that it had to be momentum and velocity in the end. Apart from putting in place elaborate systems to measure momentum and velocity, an additional experiment to see the signature star image of an annihilation event was also readied to further check if a suspect particle was truly an antiproton.

Segre, Chamberlain, and their group went first in the first week of August in 1955. After their run lasted for five days, Lofgren and his collaborators ran their experiments for the next two weeks. Segre and Chamberlain returned for their next go on August 29, only to see the Bevatron break down on September 5.

60 antiprotons

Even though Lofgren’s crew was scheduled to begin on September 21, a week after repairs had been completed, he generously ceded his time so that Segre and Chamberlain could complete their experiments. It was during that run that they got the first evidence of the antiproton based on momentum and velocity, later confirmed by analysis of images that revealed the signature annihilation star.

The experiments detected 60 antiprotons in all during a run that lasted nearly seven hours. The official announcement of the discovery was made on October 19, and within a couple of weeks, on November 1, a paper titled “Observation of antiprotons” was published in Physical Review Letters.

Segre and Chamberlain won the 1959 Nobel Prize for Physics for their discovery. The Bevatron remained operational for nearly 40 years and the structure was finally demolished in 2011. As for antiprotons, they are now produced in the trillions and are central to high-energy physics experiments.

Picture Credit : Google