If a type of radiation is attracted to the negative electrode, then it must have a positive charge. Beta particles are electrons and are negative. X-rays and gamma rays are essentially the same thing and are electromagnetic energy. They have no charge. The difference between X-rays and gamma rays is how they are produced*. Your answer is alpha radiation. An alpha particle is the nucleus of a helium atom and carries a +2 charge.
* Gamma rays are a product of the random nuclear decay of unstable nuclei. X-rays are produced when high speed electrons are caused to stop or slow down. The kinetic energy of the electron is converted to electromagnetic energy. X-rays and gamma rays are not particles and do not carry a charge, and cannot be attracted or deflected from charged electrodes.
