Answer 1: The electron is a subatomic particle of an atom. It has a negative charge. Since, it is a sub-atomic particle, it cannot be sub-divided further. Mass of electron is ~ 1/1836 that of a proton.On other hand, positron is an antielectron particle. It has the charge of +1e, a spin of 1⁄2. Positron and electron have same mass. Thus, positron and electron have same mass, but opposite charge.
Answer 2: Positron decay primarily occurs in nuclei possessing heavy mass. Positron emission decreases proton number with respect to the neutron number. Positron undergoes nuclear transmutation reaction. This results in generation of an atom of a different element, as compared to that of parent element. Atomic number of daughter element is less as compared to parent element by 1.
Example: 23 12Mg → 23 11Na + e+ + energy
Answer 3: Electron capture is also called K-electron capture. It involves removal of energy fro atomic shell that is closer to nuclues. This results in loss of electron usually from K or L shell. In this process, following phenomena occurs simultaneously.i) A nuclear proton present in nuclei changes to a neutron, after interacting with an electron which is captured by nucleus, from one of its orbitals (preferentially from K or L)2) Emission of an electron neutrino.Following is an example of K-electron capture.7 4Be + 0 -1e → 7 3Li + energy
Answer 4: Following are the distinct features of transmutations/transformations that is caused by positron emissions and electron capture/K electron capture:i) Positron: A proton is converted into neutron due to radio-active decay process. This results in the emission of positron and neutrino. The process results in decrease in atomic number by one unit, and however atomic mass number remains unchanged.ii) Electron capture: A electron from the low energy level (K-shell or L-shell) falls into the nucleus. Due to this proton is converted into neutron. During this process, neutrino is emitted from the nucleus. As seen in positron emission, the atomic number goes down by one unit, but atomic mass number remains unchanged.