Publications

An assessment of fundamentals of neutron porosity interpretation: Americium-beryllium source versus neutron generator-based alternatives

Badruzzaman, Ahmed; Schmidt, Andrea; Antolak, Arlyn J.

Basics of ratio-based porosity response of four proposed generator-based neutron tools are studied using Monte Carlo simulation of the radiation transport to examine, at a fundamental level, their potential to replace Americium-Beryllium (Am-Be) sources. Accelerator-based sources considered include a dense plasma focus (DPF) alpha-particle accelerator, Deuterium-Tritium (D-T), Deuterium-Deuterium (DD), and Deuterium–Lithium (D-Li7) neutron generators. The DPF alpha-particle accelerator utilizes the (-Be) reaction generating a neutron spectrum that is nearly identical to that from an Am-Be source. D-T and D-D neutron generators utilize compact linear accelerators and emit, respectively, 14.1 and 2.45 MeV neutrons. The D-Li7 neutron spectrum resembles the Am-Be spectrum at lower energies, and has a neutron peak at 13.3 MeV. In the present work, simple spherical geometry models that do not include tool and borehole are first used to explore the basic physics. A tool-borehole-formation configuration is then utilized to briefly explore key observations from the simpler model. In both models, the responses at various detectors are examined to understand the behavior of the ratios constructed. Sensitivity to formation conditions such as low porosity and presence of thermal absorbers, and operational conditions, such as tool standoff are examined. The state of neutron generator technology is also discussed in terms of neutron yield, target properties, power demands, etc., which would be important considerations in actually utilizing generators in nuclear logging tools.