| CPC G01N 33/0055 (2013.01) | 15 Claims |

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1. An alpha radiation detector for measuring radon concentration in ambient air, the alpha radiation detector comprising:
a housing having a base on which there is arranged a hood having a chamber which is located therein, the housing being configured in such a way that ambient air can penetrate into the chamber from outside, and
an optical sensor;
the hood having a first portion having an inner wall, which is provided with a scintillation material which generates light pulses upon impingement of alpha particles, which light pulses are sensed by the optical sensor, wherein the hood has a second portion formed as a ring which is made of a material that is impermeable to light but permeable to gas, so that radon gas can penetrate into the chamber from outside through a wall of the ring in a direction that is transverse to a circumferential direction of the ring, wherein the first portion and the second portion are arranged on top of each other.
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