X-rays and gamma rays are a group of light, but they cannot be seen directly by the human eye. Although imaging methods have been established for X-rays up to 100 keV (kilo electron volt) and high-energy gamma rays exceeding 100 MeV, the 1-10 MeV gamma rays in between are particularly strong in penetrating power and complex reaction. Therefore, imaging is extremely difficult.

　Despite this difficulty, the technology to directly "see" 1-10MeV is eagerly awaited.For example, in advanced medicine, proton beam therapy that promotes the eradication of cancer without inserting a scalpel is attracting attention, and if gamma rays emitted by the reaction of proton beams with elements in the body can be observed, improvement in treatment accuracy can be expected.In addition, gamma rays generated from various excited nuclei (oxygen, carbon, etc.) are concentrated at 1-10 MeV, and if they become observable, it is expected that an important key to unravel the nucleosynthesis of the universe will be obtained.

　This time, the research team has developed a compact high-precision camera specializing in 1-10 MeV gamma rays.Then, as the first demonstration of its usefulness, we focused on the 4.4 MeV gamma ray generated when the proton beam reacts with carbon in the body, and conducted an imaging experiment simulating an online monitor during proton beam therapy.

　As a result, the measured gamma-ray generation distribution was said to be almost exactly the same as the energy loss of the irradiated proton beam, demonstrating its usefulness as an online monitor during treatment for the first time in the world.

　This result not only advances the sophistication of proton therapy, but is also expected to be able to be mounted on satellites due to its successful miniaturization, and it is said that great progress will be made for space science.

Paper information:[Scientific Reports] Precision imaging of 4.4 MeV gamma rays using a 3-D position sensitive Compton camera