From left to right, the isotopes are protium ( Isotopes are variants of a particular chemical element which differ in neutron number.
The number of nucleons (both protons and neutrons) in the nucleus is the atom's mass number, and each isotope of a given element has a different mass number.
radioactive elements) between uranium and lead, although the periodic table only allowed for 11 elements from uranium to lead.
Attempts to place the radioelements in the periodic table led Soddy and Kazimierz Fajans independently to propose their radioactive displacement law in 1913, to the effect that alpha decay produced an element two places to the left in the periodic table, whereas beta decay emission produced an element one place to the right.
For example, the alpha-decay of uranium-235 forms thorium-231, whereas the beta decay of actinium-230 forms thorium-230.
Thomson channeled streams of neon ions through a magnetic and an electric field and measured their deflection by placing a photographic plate in their path.