Ion Beam Analysis
An assessment of surface heating during ion beam analysis.
Surface heating is an inevitable consequence of ion beam analysis and results in damage to some thermally insulating materials. Reducing beam current to a low value limits temperature rise, at the expense of data collection time.
Heating effects on biological specimens were assessed via a physical model using typical operating parameters for PIXE. In this way it was possible to decide whether pellets would be lightly charred, or taken to temperatures at which the matrix was destroyed by the heat generated. A 2 mm diameter temperature-regulated probe placed against the front surface of a specimen simulated the interaction of a 2 mm diameter proton beam. Heating the front surface of the pellet through a range of temperatures, whilst monitoring rear surface temperatures, allowed a calibration curve for front and rear surface temperatures to be constructed. Front surface temperatures during normal PIXE operating conditions were established by cross referencing to a similar calibration curve constructed whilst monitoring rear surface temperatures for a range of beam currents.
Results suggest a beam current of 20 nA induces a surface temperature rise of 80 C in pellets of compressed powdered human hair (GBW 09101), and differential scanning calorimeter measurements suggest there is no significant destruction of the sample.
An assessment of surface heating during ion beam analysis - Application to biological materials.
Surface temperature rise can have a significant affect on biological specimens through the loss of volatile species and charring, which can alter the gross chemical composition.
In this study the equilibrium temperature rise on the surface of animal ‘soft tissue’ and plant specimens were measured during ion beam analysis by PIXE. Pellets of compressed powdered human hair, bovine liver and apple leaves were irradiated with a range of proton beam currents at energies of 1 and 2.5 MeV, and a beam diameter of 2 mm. The effects of the observed temperature rise were assessed by differential scanning calorimeter measurements and scanning electron microscopy.
Comparisons are made to our previously published results for human hair and suggestions for operating parameters are given below.