September 24, 1945 - Death of Hans Geiger, German physicist who developed the counter that bears his name

D. in physics and mathematics from the University of Erlangen (Germany), he collaborated with Ernest Rutherford at the University of Manchester (England).

In 1908, he built the first version of the particle detector and counter that bears his name, indispensable in Rutherford's and his own identification of the nature of alpha particles as helium nuclei.

This first Geiger counter consisted of a cylinder filled with gas at reduced pressure and a wire looped through its axis, establishing a high potential difference between the two. When an ion or electron penetrates the tube, electrons are released from the atoms of the gas filling the tube. Due to the positive voltage of the center wire, they are attracted to it, and in doing so gain energy, collide with the gas atoms and release more electrons, until the process continues and a detectable current pulse is produced. With the right gas, the flow of electricity stops by itself or even the electric circuit can help stop it.

Why is it called a counter? This is because each particle passing through it produces an identical pulse, allowing the particles to be counted. In the case of the Geiger counter, it only detected alpha particles.

In 1911, Geiger and Jon Mitchell Nuttall developed the Geiger-Nuttall Law and carried out a series of experiments that led to Rutherford's atomic model. This law establishes the relationship between the decay constant of a radioactive isotope and the energy of the alpha particles they emit, i.e., it is established that short-lived isotopes emit more energetic alpha particles than long-lived ones.

In 1912, already in Germany, he held the position of director of the Physics Research Laboratory in Berlin, and between 1925 and 1929, he became a professor at the University of Kiel (Germany), where his first graduating student was precisely Walther Müller. In 1928, the two of them developed a counter that could detect various types of ionizing radiation. It was a practical and relatively inexpensive instrument, the output signal from the tube required very little electronic processing (an advantage over other devices) so it achieved great popularity as a portable radiation detector.

The current version of the counter was developed by physicist Sidney H. Liebson in 1947. This device has a longer lifetime than the original Geiger instruments and requires a lower voltage.