ESR Imaging of Radiation Dose

The spatial distribution of radiation dose can in principle be obtained by measurements on pieces cut from an irradiated sample. The same type of information can also be obtained in a non-destructive way and at higher resolution by ESR imaging (ESRl). The method was proposed already in 1973, but has developed slower than the NMR imaging (MRI) method. The distribution of electron spins in the samples is determined using a magnetic field gradient. Alanine was used in the first application to measure the dose distribution from a radiation source [61]. We refer to 

The dose distribution in potassium dithionate tablets along the beam of C and ions accelerated to 25 MeV was examined using the ESRI methods developed by Schlick et al. [63, 65]. Spectra were collected using an X-band spectrometer equipped with two Lewis coils powered by regulated DC power supplies to produce a variable field gradient up to 20 mT/cm applied along the direction of the tablets. Details of the experimental procedure can be found in an article by Gustafsson et al. [64], Information about the analysis is described in [63, 65]. 

The intensity profiles in potassium dithionate tablets (Fig. 9.10) clearly show Bragg peaks occurring at the end of the range of the particles. Note that no paramagnetic centres were detected beyond the penetration depth (approximately 2.3 mm). 

ESRI spectrometers have been constructed for different purposes, at X-band for small samples, e.g. in ESR dosimetry, at longer wave-lengths for biological applications [62, 63]. Spectrometers at different wave-length bands are also available, commercially. Those spectrometers are of the CW-type. 

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