Nuclear medicine injects radioisotopes into the body to diagnose organ function. radioisotopes with short half lives are used so they completely degrade quickly leaving harmless chemicals behind in the body. check the two isotopes are most likely to be used in nuclear medicine.

yttrium-90 has a half life of 7.3 x 10^- 3 years
uranium 238 has a half life of 4.5 x 10^6 years
iodine-131 has a half life of 2.2 x 10^- 2 years
plutonium - 239 has a half life of 2.4 x 10^4 years
cobalt-60 has a half life of 5 years

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

            and  

since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.