Precision imaging of 4.4 MeV gamma rays using a 3-D position sensitive Compton camera

TL;DR

This paper demonstrates high-precision imaging of 4.4 MeV gamma rays using a novel 3-D position sensitive Compton camera, with applications in proton therapy dose verification and gamma-ray astronomy.

Contribution

Introduction of a new 3-D position sensitive Compton camera capable of high-precision imaging of 4.4 MeV gamma rays in nuclear applications.

Findings

Gamma-ray images sharply concentrate near the Bragg peak.

The 3D-PSCC effectively identifies nuclear lines in proton-irradiated samples.

The system can distinguish 4.4 MeV gamma rays from background.

Abstract

Imaging of nuclear gamma-ray lines in the 1-10 MeV range is far from being established in both medical and physical applications. In proton therapy, 4.4 MeV gamma rays are emitted from the excited nucleus of either 12^C^* or 11^B^* and are considered good indicators of dose delivery and/or range verification. Further, in gamma-ray astronomy, 4.4 MeV gamma rays are produced by cosmic ray interactions in the interstellar medium, and can thus be used to probe nucleothynthesis in the universe. In this paper, we present a high-precision image of 4.4 MeV gamma rays taken by newly developed 3-D position sensitive Compton camera (3D-PSCC). To mimic the situation in proton therapy, we first irradiated water, PMMA and Ca(OH)_2 with a 70 MeV proton beam, then we identified various nuclear lines with the HPGe detector. The 4.4 MeV gamma rays constitute a broad peak, including single and double escape peaks. Thus, by setting an energy window of 3D-PSCC from 3 to 5 MeV, we show that a gamma ray image sharply concentrates near the Bragg peak, as expected from the minimum energy threshold and sharp peak profile in the cross section of 12^C(p,p)12^C^*.