Question

At the time of rutherford's experiment was it known that that an alpha particle is a helium nucleus ?

Answer 1

It was Earnest Rutherford and Paul Villard who first discovered the α-particle in 1899-1900. After some study Rutherford and scientist Thomas Royds, in 1907, proved that ​α-particle were Helium ions. In 1911, Rutherford performed his famous gold foil experiment. So yes, it was known that ​α-particle were Helium ions at the time of the aforesaid experiment.