Figure 8
Relationship between the elemental concentration, the mass irradiated and the prompt gamma production. (a) Prompt gamma energy spectra resulting from the irradiation of 12 tissue surrogate inserts by helium beams. A windowing over the region where oxygen and carbon reactions predominate is shown. (b) The measured grams of oxygen irradiated in the tissue surrogate inserts and the total prompt gammas (PGs) detected within the 5.2 MeV peak are linearly related. The linear fit excluded the PMMA outlier. The average uncertainty in the irradiated oxygen mass is Δ\({m}_{O}=35.6\,\text{mg}\). (c) A windowing over the 1.66 MeV energy line shows clear differences in prompt gamma production attributable to calcium reactions. (d) The data points relating the calcium concentrations and the prompt gamma production from the irradiation of the tissue surrogates by helium and carbon beams are shown for two detectors and one detector placed at 15 cm and 20 cm from the beam axis, respectively. The minima for calcium correspond to adipose and brain surrogates. It is clearly distinguishable from breast surrogate (0.95%) and from solid water, muscle and liver surrogates (2.3%). The maximum concentration appears in cortical bone. The average statistical uncertainty is 1.72 × 10−7 for helium ions and 2.74 × 10−7 for carbon ions. The uncertainty in the calcium concentration ranges from Δ\([Ca]=0.14 \% \) ([Ca] = 0.95%) to Δ\([Ca]=0.28 \% \) ([Ca] = 26.8%) for helium ions and the detector at 15 cm. For carbon ions, it ranges from Δ\([Ca]=0.15 \% \) ([Ca] = 2.31%) to Δ\([Ca]=0.25 \% \) ([Ca] = 26.8%).
