أكاديميا - كولنز - معاجم الجيب العلمية - الكيمياء - انكليزي - فرنسي - عربي الحرف ٤_ n

Academia - Collins - Pocket Scientific Dictionaries - Chemistry - English - French - Arabic Letter 4_ N


NTP

See STP.

nuclear reactions
Reactions fpl nucleaires

Nuclear reactions. Nuclear reactions differ greatly from ordinary chemical reactions, as new compounds are not formed, changes occur in the nuclei, and new elements may be formed. Most elements have stable and unstable isotopes, such as:

Carbon-12 is stable
Carbon-13 is stable
Carbon-14 is unstable

But some elements do not have stable isotopes, e.g
Uranium and plutonium. Whether an isotope is unstable depends on the numbers of neutrons and protons in the nucleus.

Many reactions can occur when the isotope is not stable:

(a) An isotope can split, meaning it can split, creating two stable isotopes. And then divorced
Neutrons and large amounts of energy.

(b) A neutron can decay into a proton and an electron.

1/0n →1/1p+ - 0/1e

This creates a new element, without changing the
Bloc .

(c) The alpha particle is expelled from the atom, such as:

238/o2U → 234/90Th + 4/2He

(d) An unstable atom can emit gamma rays, which often happens after emitting a beta particle. See half-life.

These nuclear reactions have been used in many ways.

Nuclear power plants use the heat of fission of isotopes of uranium, plutonium, or thorium. The heat generates steam that spins a turbine that produces electricity. This same energy source is used in some countries in the form of bombs that have terrifying destructive capabilities.

Isotopes that produce gamma rays are used to destroy germs in the food industry and cancer cells in the body.
Isotopes are also used in industry for many analytical purposes, such as detecting cracks and fissures in pipelines.

Scientists seek to produce useful energy from fusion reactions, and if this becomes possible, it will provide a source of electricity that does not depend on coal or petroleum.

Radioactive decay products (radioactivity) are dangerous because they can produce harmful effects in the body, including leukemia and cancers. Extreme caution must be taken when using radioactive materials.


nucleus
noyau m

The nucleus of the atom in which the mass is concentrated. The nucleus contains protons and neutrons and is usually depicted as the compact center of a spherical atom.

The electrons move “around” the nucleus, which has a positive charge that is balanced in the neutral atoms by the charges of the electrons.

Hydrogen-1 isotopes are the only atoms whose nucleus does not contain any neutrons.
See nuclear reactions.

Isotopes have different nuclei:

The carbon-12 nucleus contains 6 protons and 6 neutrons

The carbon-14 nucleus contains 6 protons and 8 neutrons


nylon
nylon m

Nylon. Nylon species form a family of polyamide polymers. The most common of these types is “Nylon 6.6”. It is a very strong man-made fibre, and its uses include fabrics (shirts and clothing), yarn for socks, knitting threads, carpets, ropes and nets.

Nylon is useful because it does not spoil or absorb water, but it does stretch, and this is useful in ropes and socks. Nylon is often mixed with other fibers such as wool for the right balance of properties.

6 carbon atoms
6 carbon atoms
Nylon 6.6