CALIBRATION MONITORING OF DIFFRACTOMETERS Giovanni Berti and Mario D’Acunto Universita' di Pisa - Dipartimento di Scienze della Terra, Via S. Maria 53, I-56100, Pisa, Italy berti@dst.unipi.it ABSTRACT The Calibration Monitoring of Diffractometers is a systematic experimental approach to gather information on the actual comparability of data from X-ray Diffraction. The present report synthetically outlines the results obtained by using a commercial sample of Corumdum and specifically designed operative protocols. This experiment aims to find possible characteristic curves of diffraction experiments. These characteristic curves have the potential to check the reproducibility and repeatability of the diffraction measurements and possibly to surpass the stage of observation and result reporting of data, which seems to be the still standing limit of the traditional Round Robin tests. INTRODUCTION In general, most of the Round Robins conducted over the past twenty-five years have given the common result of high internal consistency of data and unexpected low reproducibility; they showed a general low comparability of data without giving effective answers to this long standing problem. A short review of the many Round Robin projects has been reported by Berti (1998) and Berti et al. (2001). This evaluation has the potential to trigger doubts on the comparisons with data taken by others elsewhere and by ourselves before. Because the comparisons of measures from XRPD data are essential tools in many applications, it is mandatory to overcome this quandry if we aim to have the X-ray diffraction measurements included among the disciplines and techniques capable to give reliable scientific information and evidence of facts. We have used here the modelling capability offered by the DIM method (Berti, 1993) to compare our data with data collected by us previously, and with data collected by others. Diffractometers with similar configurations and a number of distinct devices were used to collect data. The experimental Calibration Monitoring of Diffractometers is still in course and we report on the measurements carried out on two diffractometers which have been monitored for three times on the interval of time as long as about three years. This work stemmed as a follow up from the conclusion of the Round Robin on KCl reported by Masciocchi &Artioli, (1996), and by Berti (2001b). 2. CALIBRATION MONITORING OF DIFFRACTOMETERS The three following steps are at the base for starting any x-ray diffraction measurement: 1. the optical and mechanical process of positioning each individual device on the channels of the incident and diffraction beams (the alignment) 2. the alignment verification (e.g. to check the right diffraction location of the spot and the right direction pointing of each individual devices) 3. the calibration (the calculation of not removable residual systematic effects). The objective of the Calibration Monitoring of Diffractometers is to monitor on time the effective values of the parameters describing the devices involved in the diffraction measurement. Here we report on the calibration of two diffractometers of a group of nine Copyright (c)JCPDS-International Centre for Diffraction Data 2002, Advances in X-ray Analysis, Volume 45. 66