This is not a particle at all. In fact, it's an electro-magnetic wave even more dangerous than ultra violet, or even X-rays.
Gamma rays have no mass, and travel at the speed of light - about 300,000 km/s in a vacuum, and not much slower in air. This makes them very penetrating, and they will pass right through paper or aluminium. It takes several centimetres of lead to noticably reduce their strength, and still some get through! [More on gamma rays]
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