I read to you a short biography of Ernest Rutherford

Ernst Rutherford is a direct heir of French leading scientists:

  • Henri Becquerel, who in 1896 had highlighted the existence of a then unknown radiation from uranium atoms and he called  »  the uranium radiation  « ;
  • Marie and Pierre Curie who, from the beginning of the twentieth century showed that the radiation Beckerel resembled radioactivity (name given by Marie Curie ) natural: the ability of certain atoms (such as uranium, radium or thorium) emitting radiation whose nature, however, remained unknown.

I read to you a short biography of Ernest Rutherford

Ernest Rutherford wanted to understand the nature of this radiation. He has the idea for this position gold leaf growing between thick uranium sample and a target. He realizes that the radiation decreases with increasing thickness, but only from a certain thickness, it decreases more. Part of the radiation is stopped and another continuous perforating gold leaf. There would be two different types of radiation! He named the most penetrating and least penetrating Alpha Beta.

By repeating the experiment with Thorium, he showed that the disintegration decreases over time depending on a formula. It thus highlights the principle of half-life: the time required for half of the sample disintegrates. This half-life is specific to each radioactive element.

An atom can turn into another!

It also shows, and it is revolutionary that the thorium in its emitting alpha radiation gives rise to another particle, itself radioactive.

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Example of the decay of radium: losing an alpha particle it turns into Radon

This result challenges an old dogma of 2500 years: the impossibility of dividing an item. Those who claimed to provide far turn lead into gold were called quacks. Rutherford therefore destroyed a certainty stated by the old Democritus . He had also given the last grain of indivisible matter the atom name (Greek: we can not divide).

A disintegration that emits a lot of energy

The energy released by the decay is promising as much greater than the energy that can be generated by a traditional chemical reaction. Atoms therefore contain a certain energy that would ensure their cohesion. The break would be to release this energy!

Alpha radiation: this is the « helium

In 1903, it seeks to characterize the nature of alpha radiation. He places a radioactive sample in electric and magnetic fields. It measures the speed, load and the ratio load / mass. He deduces that this is helium.

Atoms: is the empty!

We did not know much about the nature of the atom. We only knew he was electrically neutral (it contained many positive charges as negative charges) and had a mass. Rutherford then continues bombarding gold foil with alpha radiation. Some particles are deflected but most crosses the barrier unhindered as if the gold leaf does not exist. Rutherford gold leaf consists of a constellation of tiny dots separated by a vacuum. These items contain the bulk of the mass of the atom: its core. He deduced the modern model of the atom: a tiny central nucleus surrounded by a cloud of electrons.


However, was a mystery that will lift Niel Bohr : for what (s) reason (s) the negatively charged electrons from falling, after some time, the positively charged nucleus?

A tall man

Rutherford was therefore a major element in the chain of science that helped to understand the nature of matter. With Rutherford began the golden age of physics that will Bohr and Einstein and many others.