Radium-226 does not decay by beta decay. It decays by alpha decay to radon-222.
Today radium-226 is not used for radiotherapy.
This is the isotope radium-226.
The density of radium is 5,5 g/cm3.
Radium-226--------------------Radon-222 + alpha
When radium-226 decays to form radon-222, the radium nucleus emits a alpha particle.
Radium-226 does not decay by beta decay. It decays by alpha decay to radon-222.
radium-226 isa radioactive element and has the form of a pellet or solution housed with in a ceramic outer housing
Radium 226--------alpha particle-------- Radon 222
Today radium-226 is not used for radiotherapy.
This is the isotope radium-226.
1.875g
The density of radium is 5,5 g/cm3.
When Radium-226 decays to form Radon-222, the Radium nucleus emits an alpha particle. The atomic number goes down by 2, and the mass number goes down by 4, matching the atomic number and mass number of the alpha particle.
The density of radium at about room temperature is 5.5  g·cm−3. That's 5.5 grams per cubic centimeter, or 5.5 grams per milliliter. A link to the Wikipedia article on radium is provided.