| CPC G21F 5/02 (2013.01) | 14 Claims |

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1. A gauge comprising:
a detector;
a base that carries the detector;
a source housing carried by the base and defining a shield material circumferentially extending inwards; and
a source rod positioned within the housing and carrying a source that is translatable between a shielded position within the housing and a measuring position external of the housing, the source rod having a source shield on the top thereof and a shield material positioned-downwardly from the source such that the source is encapsulated when in the shielded position,
wherein an actuator is provided for translating the source from the shielded position to the measuring position and wherein the actuator is biased in a locked position in which the source is in the shielded position.
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