Batch measurements of wood density on intact or prepared drill cores usingx-ray microdensitometry

The performance of a batch scanning x-ray densitometer for measuring wood d ensity without sample preparation, i.e., on intact drill cores, or on recta ngular samples prepared from drill cores, was analysed. Effects of x-ray in tensity, sample thickness and fiber direction, as well as extractives conte nt, were evaluated for young (mainly sapwood) and old (mainly heartwood) wo od from Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L. ) Karst.). The x-ray power level used as standard (1.4 kW; 40 kV and 35 mA) seemed appropriate for the tested species and specimen thickness. The dens ity of intact drill cores could be determined with a mean standard deviatio n of 1.6% for each sample, with a single machine run, if the cores were mou nted with a fixed fiber direction and calibrations were made for each wood type. The corresponding precision for rectangular samples was 1.0%. Further improvements are attainable by using standard reference samples in each ma chine run and batch-wise analysis. For the chosen wood types and measuremen t technique, a sample thickness of 5 mm should give the best precision. How ever, for species with very narrow rings, thinner samples would improve the spatial resolution when ring boundaries are angled or curved. Extractives should be removed, especially for pine, but possibly also for spruce, if hi gh precision in density determination is required.