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A-level物理知识点梳理系列(七)

点击量:     发布日期:2017-03-02 13:17    作者:四老师

1.Characteristics of the three kinds of emission

2. Radioactive decay

Radioactive decay:A radioisotope (an unstablearrangement of neutrons and protons in a nucleus) is altered to make a morestable arrangement. The parentnucleus becomes a daughter nucleusand a particle (decay products).

Words andsymbol equations using examples:

Alpha decay:

An elementwith a proton number 2 lower and nucleon number 4 lower, and an alpha particleis made (2p + 2n) e.g.

Words:Radium-226 nucleus (parent nucleus) → Radon-222 (daughter nucleus) + helium-4nucleus (alpha particle)

Symbols:  

Beta decay:

A neutronchanges into a proton, an electron and an antineutrino so an element with thesame nucleon number (just 1 neutron is now a proton but the mass is the same)but with a proton number 1 higher e.g.

Words:iodine-131 nucleus → xenon-131 nucleus + antineutrino + beta particles(electron)

Symbols:     (antineutrino symbol = v with a horizontal line on top of it)

Gamma emission:

With someisotopes, the emission of an alpha or beta particle from a nucleus leaves the protonsand neutrons in an “excited” arrangement. As the protons and neutrons rearrangeto become more stable, they lose energy. This is emitted and the mass andatomic number are uncharged.

Gammaemission by itself causes no change in mass number or atomic number.

 

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