Abstract: Particle detector comprising a vacuum envelope in which there are provided a thin planar target made from a material which can emit secondary electrons when a given particle of sufficient energy strikes the target and an electron multiplier comprising a plurality of thin planar amplifying plates made from a material able to emit secondary electrons when struck by electrons with a sufficient energy, said plates being parallel to the target and spaced from one another, the secondary electrons emitted by the target and by each of the plates being accelerated by an appropriate potential difference established between the target and the closest plate and between the various plates, wherein the materials forming the target and the amplifying plates are porous.