Patent Number: 
Section: claims

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; anda 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 the housing defines a failure zone about a bottom thereof, such that in a failure where the base separates from the source housing, the source remains shielded within the source housing. 2. The gauge according to claim 1, wherein the failure zone defines a circumferentially extending recess along the circumference of the source housing. 3. The gauge according to claim 1, wherein the failure zone is defined at a portion of the housing that is downward of an end of the source. 4. The gauge according to claim 1, wherein the shield material spaced-downwardly from the source comprises an end cap having one of tungsten or carbide. 5. The gauge according to claim 1, wherein an actuator is provided for translating the source from the shielded position to the measuring position. 6. The gauge according to claim 5, wherein the actuator is biased in a locked position in which the source is in the shielded position. 7. The gauge according to claim 6, wherein the actuator remains biased in the locked position unless unlocked by an operator. 8. The gauge according to claim 7, further comprising an electronic access module that must be activated in order to advance the actuator from the locked position to the unlocked position. 9. The gauge according to claim 8, further comprising an electromechanical source rod lock in communication with the electronic access module. 10. The gauge according to claim 1, further including an accelerometer for measuring shock or stress to the gauge. 11. The gauge according to claim 1, wherein the shield material positioned-downwardly from the source is fixedly secured thereto. 12. The gauge according to claim 1, further including an orientation detector for determining the orientation of the gauge. 13. The gauge according to claim 12, wherein, when the orientation detector determines that the gauge is not generally horizontal, a control module directs an electromechanical lock to lock the source into the shielded position. 14. A neutron source for use in determining one or more characteristics of a construction material, the source comprising a source shield on the top thereof and a shield material fixedly secured on the bottom thereof. 15. A gauge comprising:a detector; anda source having a shield fixedly secured to the top and bottom thereof, and being further encapsulated around a periphery thereof when in a shield position and configured such that the source is not shielded about a periphery thereof when in a measuring position,wherein the gauge defines a failure zone about a bottom thereof, such that in a failure where a bottom portion of the gauge separates from a remainder of the gauge, the source remains shielded.