Distance and direction-sensitive cosmogenic neutron sensors
A cosmogenic neutron sensor includes a hydrogen-sensitive neutron detector orientable above a measurement surface. A neutron shield is positionable on the hydrogen-sensitive neutron detector. The neutron shield is positioned to interact with at least a portion of cosmogenic neutrons propagating in a direction of the hydrogen-sensitive neutron detector.
1. A local area cosmogenic neutron sensor for detecting moisture within a measurement surface, the local area cosmogenic neutron sensor comprising:
a neutron detector positionable above the measurement surface, wherein a moderator material is positioned around at least a portion of the neutron detector to form a moderated neutron detector which is sensitive to hydrogen, wherein the moderator material is substantially 2.5 cm thick;
a neutron shield positioned around a portion of the moderated neutron detector, whereby the neutron shield substantially covers lateral sides of the moderated neutron detector and substantially an entirety of a top of the moderated neutron detector, wherein the neutron shield is positioned to interact with cosmogenic neutrons propagating to the lateral sides or the top of the moderated neutron detector, thereby substantially blocking fast, epithermal and thermal cosmogenic neutrons propagating to the lateral sides or the top of the moderated neutron detector from reaching the moderated neutron detector, and wherein the neutron shield is not positioned on a bottom side of the moderated neutron detector; and
a stand structure holding the moderated neutron detector and the neutron shield in a position a spaced vertical distance above the measurement surface with the bottom side of the moderated neutron detector facing the measurement surface,
wherein local area cosmogenic neutrons propagating from the measurement surface below and near the moderated neutron detector travel through an air space before arriving at the bottom side of the moderated neutron detector.
2. The local area cosmogenic neutron sensor of claim 1 , wherein the neutron shield positioned to interact with cosmogenic neutrons propagating from above the moderated neutron detector has an area larger than an area of an upper surface of the moderated neutron detector.
3. The local area cosmogenic neutron sensor of claim 1 , wherein the neutron shield has an area larger than an area of the lateral sides of the moderated neutron detector.
4. The local area cosmogenic neutron sensor of claim 1 , wherein the neutron shield is positioned to interact with cosmogenic neutrons that have not interacted with the measurement surface.
5. The local area cosmogenic neutron sensor of claim 1 , wherein the neutron shield is positioned on an entirety of the lateral sides of the moderated neutron detector.
6. The local area cosmogenic neutron sensor of claim 1 , wherein the measurement surface is an area extending substantially 5 meters from a point below the moderated neutron detector.
7. The local area cosmogenic neutron sensor of claim 1 , wherein the measurement surface is an area substantially below the moderated neutron detector.