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Compare the size of the nucleus of calcium with that of potassium.

Explanation:

Atomic radius increases as you move down a group and to the left across a period.

Calcium has a more dense nucleus than that of potassium because it has more protons in its nucleus.  The positive charge from the protons pulls the electron cloud around it closer in, making for a smaller atomic radius.

Because potassium has less protons, the atomic radius is larger.

it is to be noted that an alpha particle is an helium nucleus. so it contains 2 protons 2 neutrons and has a mass number of 4. when alpha decay particles are ejected from the nucleus it gets transformed into an atom which has atomic number less than 2 and a mass number less than 4.

an equation that could represent alpha decay is radium 226 decay of alpha particle forms radon 222.

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