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Surface exposure dating using TCNs was first attempted in the mid-1950's, but proved to be impractical because of the low sensitivity of the decay counting techniques used at that time. Applications only became possible with the development of accelerator mass spectrometry (AMS) in 1979.

After several years of development a series of papers were published in 1986 demonstrating the practical application of the five commonly used TCNs (3He, 10Be, 21Ne, 26Al, 36Cl). This was the starting point for numerous studies through the early 1990's that aimed to determine the production parameters of these nuclides. However, only rudimentary testing of the fundamental cosmic ray physics that allows calculation and comparison of ages of samples from different latitudes and altitudes was available, with almost complete reliance placed on the calculations made by Devendra Lal (Lal 1991, based on Lal 1958 and Lal and Peters 1967). These pioneering contributions are based on instrumental observations from the 1940's and 1950's which were not intended to provide accuracies better than ± 10% (Lal, 1991). At the turn of last century, the entire TCN dating technique was parameterised with a series of disconnected studies of varying methodology and inter-related by a theoretical framework based on short-term instrumental observations that have never been adequately tested over geological time scales and for geological materials.

Despite its shortcomings the technique has proved adequate for a decade of progress in the field. TCNs have became routinely applied to a wide range of geological, geomorphological and climatological problems, frequently providing answers to long standing scientific questions. The number of studies published worldwide employing TCN has tripled in the past 5 years alone. However, as the precision of analysis has improved and more data has become available for inter-comparison, conflicts and inconsistencies have become apparent and the limitations of the technique were exposed. Consequently several aspects of the theoretical framework were challenged (Dunai 2000; 2001a,b; Stone 2000; Desilets et al. 2001, Desilets and Zreda 2003). The main issues are:

  1. the translation of short term observational data into parameters relevant for time integrated in-situ produced TCNs,
  2. the extent to which observational data, to date mostly neutron-monitor data, can serve as an accurate model for TCN production in geological materials,
  3. the of production rate calibrations of certain TCNs (e.g. 36Cl) at different locations by different investigators appear to be internally consistent but differ from each other by up to 40% (Stone et al. 1996; Phillips et al. 2001; Swanson and Caffee 2001), and
  4. the decay constants of radioactive TCNs are in cases not well known. Discrepancies between published decay constants for 10Be (Hofmann et al. 1987) and activities of certified NIST standard material are as large as 15%, creating a significant ambiguity for age determinations at old sites (consensus at AMS-9 conference, Nagoya 2002).

While the cosmogenic isotope technique has, in principle, the capability to address many important questions in paleoclimatology and other fields that require relatively high accuracy (better than ±5%), the present foundation does not support this quality of results.

Although the shortcomings of the current situation have been apparent to most practitioners for some time, few attempts have been made to rectify the situation. An important reason for this is the sheer size of the task. A complete overhaul of the foundations is out of the reach of a single research team let alone a single researcher. In addition there has been reluctance within the community to abandon and modify systems that have proved useful for the application of the technique in the past. In many ways the current situation resembles that of the radiocarbon community some 20 years ago when it was realized that the use of 'conventional' radiocarbon ages stood in the way of a interdisciplinary communication and externally consistent results and that 'calibrated' radiocarbon ages were required to overcome this. At a workshop on cosmogenic nuclides at Lamont Doherty Earth Observatory in Spring 2002, a community wide consensus about the need of a renovation of the foundations was reached and the CRONUS initiative was launched. CRONUS-EU is part of this initiative, and is a sister programme to CRONUS-Earth, which is funded by NSF.