`""_(90)Th^(232) to ""_(83)Bi^(212)`
Decrease in mass number `=232-212=20`
number of `alpha`-partices emitted due to the above decrease in
Mass number `=(20)/(4)=5`
Expected decresase in atomic number due to emission of 5`alpha`-particles `=5xx2=10`
Expected atomic number of the nucleus formed `=90-10=80`
but the atomic number of the nucleus formed =83
increase in atomic number `=83-80=3`
Number Of `beta^(-)` -particles emitted =3.
thus , 5`alpha`-particles and `3beta^(-)` particles are emitted .
(iii) Electron capture is competitive with positron emission since bth processed lead to the neutrino.
`""_(Z)X^(A)+e^(-1)to ""_(Z-1)Y^(A)+v`
in most caes , it is a K- shell electron that is captured , and for this reason the process i sreferred to as K- Capture ,One example is the capture of an electron by `""_(4)Be^(7)`
`""_(4)Be^(7)+e^(-)to ""_(3)Li^(7)+v`
Note,-
1. Electron capture occures in those nuclides on which `(N)/(2)` ratio is too small for stability but `beta ^(+)` emission is not energetically possible .
2. After an electron ,a vacancy is created in the atomic shell and hence X- rays are emitted.
