# What is the electron capture reaction for astatine-200 in terms of the individual steps?

Sep 4, 2017

Electron capture is when an inner-core electron (""_(-1)^(0) e) combines with a proton (""_1^1 p) in a nucleus to spit out a neutron (""_(0)^(1) n) and a neutrino (a neutral fermion, denoted $\nu$):

${\text{_(-1)^(0) e + ""_1^1 p -> }}_{0}^{1} n$

A neutron can then combine into an isotope to give:

${\text{_(Z)^(A) X + ""_(0)^(1) n -> }}_{Z}^{A + 1} X$

And a proton that was used up in the process is lost as follows:

${\text{_(Z)^(A+1) X -> ""_(Z-1)^(A) X + }}_{1}^{1} p$

Astatine-200, $\text{At} - 200$, has atomic number $Z = 85$ and mass number $A = 200$, so its isotope notation is:

$\text{_(85)^(200) "At}$

So, this isotope takes in an electron to lose a proton and gain a neutron as described above:

""_(-1)^(0) e + cancel(""_1^1 p) -> cancel(""_(0)^(1) n)

""_(85)^(200) "At" + cancel(""_(0)^(1) n) -> cancel(""_(85)^(201) "At")

$\cancel{{\text{_(85)^(201) "At") -> ""_(84)^(200) "Po" + cancel(}}_{1}^{1} p} + \nu$

Overall, we then get...

$\textcolor{b l u e}{\underline{\text{_(85)^(200) "At" + ""_(-1)^(0) e -> ""_(84)^(200) "Po} + \nu}}$

And with $Z = 84$, the element becomes a polonium-200 isotope.