| abstract |
An apparatus for measuring the porosity of earth formations penetrated by a wellbore. The apparatus includes an elongated housing adapted to traverse the wellbore, a controllable source which emits bursts of high-energy neutrons, a near detector primarily sensitive to thermal neutrons and axially spaced apart from the source, a far detector also primarily sensitive to thermal neutrons and axially spaced apart from the source so that the near detector is axially disposed between the source and the far detector. The apparatus includes a neutron shield disposed between the near detector and the far detector, and a neutron scattering insert disposed inside the housing between the source and the near detector. The scattering insert consists of a material selected from the group of aluminum, beryllium, graphite, silicon, potassium, magnesium, lead and sulfur. In a preferred embodiment, the scattering insert consists of aluminum. |