Alpha, Beta and Gamma particles: the great discovery of Rutherford and Soddy

Rutherford and Soddy had been trying for some time to understand the phenomenon of radioactivity, discovered by Becquerel and described by Marie and Pierre Curie. And finally they had managed to show that in radioactive materials the atoms disintegrate, so that the atoms of a radioactive element are transformed into another element.

So the transmutation, which alchemists had sought for so many centuries, occurred spontaneously and naturally. The idea was so groundbreaking that Rutherford and Soddy avoided adding prejudices and spoke of transformation instead of transmutation when in 1902 they published "The Cause and Nature of Radioactivity", which condensed their experiments into the theory of atomic disintegration. With it they broke the scientific dogma that the atom was indivisible (which is what atom means in Greek).

Ernest Rutherford (1871–1937) identified the three main types of radioactivity: alpha rays, beta rays, and gamma rays. And he continued to study transmutation. He saw how stable lead atoms appeared in the middle of a radioactive uranium ore. There was no way of knowing when an individual atom would transform, but Rutherford noted that any sample (larger or smaller) of the same radioactive element took exactly the same time to halve. That time, called a half-life, made radioactive elements perfect timers.

Knowing that constant speed with which uranium is transformed into lead and measuring the amount of lead in a pitchblende rock (uranium ore), Rutherford and his colleague Boltwood calculated in 1907 that some of those stones had at least 1,000 million. of years: It was much older than Earth was then thought to be!

In addition to thoroughly understanding radioactivity, Rutherford gave it its first practical use (long before medical, warfare, or energy applications): calculating the age of the Earth. For all this he received the Nobel Prize in Chemistry in 1908. Although he could well have received two more Nobels for the following discoveries of his:

Rutherford used radioactivity to explore the interior of atoms. Along with his student Geiger, he shot alpha rays at a very thin sheet of gold and watched in amazement as some of those alpha particles bounced back. Recovered from the impact, in 1911 he deduced that this was only possible if the atoms had a tiny nucleus, with a positive charge, which concentrated almost all their mass. Rutherford's model of the atom was born, later perfected by his student Bohr: that familiar image of the atom, with the electrons revolving around that nucleus.

In his laboratory he continued bombarding atoms with alpha rays, until in 1919 he succeeded in transforming nitrogen atoms into oxygen: thus becoming "the first successful alchemist in history." That transmutation of nitrogen into oxygen was the first artificial nuclear reaction; and, among its remains, Rutherford found the proton, a new positively charged subatomic particle.

Meanwhile, Frederick Soddy (1877–1956) had continued to study the natural decay of radioactive elements and discovered in 1913, at the same time as Kazimierz Fajans, the rules of transmutation: when an atom spontaneously emits an alpha particle, it moves back two squares on the periodic table (eg, uranium-238 becomes thorium); when an atom emits a beta particle, it moves forward one square (eg carbon-14 becomes nitrogen).

Following these rules, known as the Fajans-Soddy law, natural decay chains are produced, such as the one that begins with radioactive uranium-238 and ends in stable lead, passing through intermediate products such as radium or uranium-234. . And by studying those chains step by step, Soddy discovered isotopes along the way: different versions of the same element, with atoms that weigh differently but have the same chemical properties.

The 1921 Nobel Prize in Chemistry recognized Soddy's discoveries, in which the writer H.G. Wells had been inspired to write his science fiction novel "World Liberation" (1914). That book, which Wells dedicated to Soddy, anticipated the danger of nuclear weapons, almost 20 years before Leó Szilárd conceived the chain reaction idea.