One can deduce the mass from the ionization range of the particles that left the trace in the cloud chamber. I will only copy a bit, but if you are interested read the article
. Since the mass of the proton or alpha particle is much greater than that of the electron, there will be no significant deviation from the radiation's incident path and very little kinetic energy will be lost in each collision. As such, it will take many successive collisions for such heavy ionising radiation to come to a halt within the stopping medium or material. Maximum energy loss will take place in a head on collision with an electron.
In this particular exposure there are faint struggling tracks making large scatters, and they can classified as electrons, there are straight tracks with minimum ionization ( same as electrons) which must be muons, and thick tracks with high ionization. Particularly the ones you point out are good candidates for an alpha since they have such high ionization are straight and stop.
It may be that they have placed a radiation source close by, one needs more information of the exposure. It is clear in the photo in the main article that they have a radiation source there.
The bubble chamber, with a magnetic field allowed real particle identification by the ionization of the tracks per cm and the curvature in the magnetic field which gave the momentum, thus complete interactions could be identified with the particle content known for large accumulated statistics.
This has the disadvantage of needing a lot of scanning of pictures by eye.
The advance of electronics and material science allowed the identification by ionization to be carried out digitally and with more accuracy for high energies.
The method of particle identification by ionization digitally is till in use in time projection chambers , TPCs.