Nucleus and electrons are held together by the electric attraction between positive (+) and negative (-) charges. In any atom, the two charges are exactly balanced, so that to the outside world the atom is electrically neutral.
Nucleus and electrons are held together by the electric attraction between positive (+) and negative (-) charges. In any atom, the two charges are exactly balanced, so that to the outside world the atom is electrically neutral.
Ion types
Hydrogen, the simplest atom, has one electron. When that electron is removed, we get the simplest positive ion, the "proton"; like the electron, it is a fundamental particle, but 1836 times heavier. The chemical symbol for hydrogen is H, but for the proton it is H+.
The next heavier atom is that of helium (chemical symbol He) and it contains two electrons. Its nucleus consists of two protons and also two neutrons, particles similar to the proton but with no electric charge. The Sun gets its energy by combining protons (some of which convert to neutrons in the process) into helium, deep in the Sun's core; since the helium nucleus is an unusually stable combination of particles, energy is released in the process.
In addition it released a barium cloud in the solar wind to produce an "artificial comet". Soon after the cloud formed, the magnetic field embedded in the solar wind picked it and made it share the wind's flow, a process similar to the one which creates the ion tails of comets (see solar wind, history).
This section starts with the words "Matter is made of atoms." Actually it took about a century, many experiments and some clever deductions to arrive at that conclusion! It would be completely impossible to tell the entire story here, but you might want to look at a brief sketch of the steps which led to the atomic theory, part of material prepared for teachers in a different course.
This leakage was used, around 1900, to detect radioactive emissions and measure their intensity. The drawing below shows a simple instrument for performing such measurements. It is called an electroscope and contains two parallel leaves
of metal foil, protected from wind inside a metal box with transparent windows and attached to a metal rod insulated from the box and leading outside (drawing).
Typically the release is done after sunset or before sunrise, so that while the canisters explode in full sunlight, observers on the ground can watch the cloud against the dark sky: soon a bluish ion cloud separates from the green one, usually elongated or striped in the direction of the magnetic field lines, which guide the ions.
