Neutron Depth Profiling

Neutron Depth Profiling (NDP) is a nondestructive analytical technique for measuring the concentration profile of certain light elements as a function of depth. The concentration profile in the first few micrometers of a surface is determined by analyzing the energy spectrum of charged particles promptly emitted following neutron capture by the element.

For an overview, see:

Downing, R.G., and Lamaze, G.P., Langland, J.K., and Hwang, S.T., “Neutron Depth Profiling: Overview of the NIST Facilities” NIST Journal of Research, 98(1) (1993) 99. (PDF)

Additional publications available upon request.

Technique: Neutron Depth Profiling (NDP) measures elemental concentration profiles up to a few micrometers in depth for elements that emit a charged particle following neutron capture.

Elements Analyzed: boron, lithium, helium, nitrogen and several additional light elements with less sensitivity.

Sample Environment: In an evacuated chamber, samples are irradiated with a beam of low energy neutrons. A small percentage of the emitted reaction particles are analyzed by surface barrier detectors to determine their number and individual energies.

Principles: The emission intensity is compared to a known standard to quantitatively determine the elemental concentration. The emitted particles lose energy at a predicable rate as they pass through the film; the total energy loss correlates to the depth of the reacting nucleus.

Advantage: NDP is non-destructive. NDP analysis allows repeatedly determinations of the sample volume following different treatments.

Neutron beam flux at sample: 7.5x10⁸ n/cm²-s

Beam area: from a few mm² to 110 mm²

These are the primary reactions potentially available for NDP applications.

Fusion Reactor Wall Annealing Study by NDP

The primary tungsten enclosure wall of a fusion reactor receives a large flux of energetic He ions during the fusion process. Accumulation of He leads to bubble formation that increase in number and size leading to the release of W metal particles into the chamber. An annealing protocol is needed to avert wall damage and maintain fusion efficiency.

ORNL, ONR, UNC, & NIST are developing an annealing protocol to release implanted He preventing damage to the tungsten containment wall.

Tungsten coupons are implanted at energies comparable to the expected "threat" conditions in a fusion chamber. Some coupons were provided "as is," others are subjected to various heat-time cycles. NDP is being used to assess the implantation energy, dose, and affect of annealing. The figure shows NDP determinations of ³He profiles used to calibrate the process