On scaling cosmogenic nuclide production rates for altitude and latitude using cosmic-ray measurements

Desilets, D Zreda, M

D. Desilets et M. Zreda, On scaling cosmogenic nuclide production rates for altitude and latitude using cosmic-ray measurements, EARTH PLAN, 193(1-2), 2001, pp. 213-225

60

INGLESE

Article

Earth Sciences

EARTH AND PLANETARY SCIENCE LETTERS

0012-821X → ACNP

193

1-2

2001

213 - 225

ISI

0012-821X(20011130)193:1-2<213:OSCNPR>2.0.ZU;2-1

The wide use of cosmogenic nuclides for dating terrestrial landforms has pr ompted a renewed interest in characterizing the spatial distribution of ter restrial cosmic rays. Cosmic-ray measurements from neutron monitors, nuclea r emulsions and cloud chambers have played an important role in developing new models for scaling cosmic-ray neutron intensities and, indirectly, cosm ogenic production rates. Unfortunately, current scaling models overlook or misinterpret many of these data. In this paper, we describe factors that mu st be considered when using neutron measurements to determine scaling formu lations for production rates of cosmogenic nuclides. Over the past 50 years , the overwhelming majority of nucleon flux measurements have been taken wi th neutron monitors. However. in order to use these data for scaling spalla tion reactions, the following factors must be considered: (1) sensitivity o f instruments to muons and to background, (2) instrumental biases in energy sensitivity, (3) solar activity, and (4) the way of ordering cosmic-ray da ta in the geomagnetic field. Failure to account for these factors can resul t in discrepancies of as much as 7% in neutron attenuation lengths measured at the same location. This magnitude of deviation can result in an error o n the order of 20% in cosmogenic production rates scaled from 4300 in to se a level. The shapes of latitude curves of nucleon flux also depend on these factors to a measurable extent. thereby causing additional uncertainties i n cosmogenic production rates, The corrections proposed herein significantl y improve our ability to transfer scaling formulations based on neutron mea surements to scaling formulations applicable to spallation reactions, and. therefore. constitute an important advance in cosmogenic dating methodology . (C) 2001 Elsevier Science BN. All rights reserved.