Refinement of Present-Day Neutron Flux Distribution and Production Rates
Current geographical scaling formulations are largely based on neutron counting surveys conducted ~50 years ago for cosmic-ray research. These need to be supplemented with measurements performed using modern technology and directed toward linking neutron fluxes with production rates.
- Direct neutron flux measurements: In order to tie together historical neutron counting data, current cosmic-ray fluxes, and proposed artificial target experiments, we propose to install a neutron-monitor network along altitude transects in high, mid-, and low latitudes. We plan to install fixed neutron monitors at the lowest and highest points of the transects, and use mobile monitors in between.
- Direct measurement of 3He, 10Be, and 21Ne production using artificial targets: Water and silicon targets will be placed at points on the neutron monitoring transects, exposed for some years, and retrieved and analyzed to establish production rates under known neutron flux conditions.
- Measurement of "proxy nuclides" using artificial targets: Short-lived nuclides produced at similar energies to those of geological interest (e.g., 32P from S and Cl targets) can be measured by decay counting with much less time and labor than for artificial target experiments involving the actual nuclides of interest. These exposure experiments can therefore be done over a wider geographical range, and shorter time resolution.
- Altitude transects on lava flows: Altitude-latitude scaling formulations derived using the experiments described above can be related to those over geological time scales by measurement of nuclide accumulation in lava flows that extend over large altitude ranges, such as at Mauna Loa or Mount Etna.
