Development of a thimble ionization chamber for high-energy x-ray dose distribution measurement in water

In order to accurately measure the dose distribution of high-energy X-ray in water, in this paper, based on the analysis of the requirement of high-energy X-ray dose distribution measurement in water, the manufacturing process of the ionization chamber is studied, the structure design of the ionization chamber is completed, and a thimble ionization chamber with a small sensitive volume is developed in the end. It can be seen from the test experiment that the fingertip ionization chamber has good angular response, directivity, repeatability, time linearity and saturation characteristics. The angular response, directivity and repeatability are 2.3%, 0.4% and 0.09%, respectively. The time linearity test shows that the measured values of the developed thimble ionization chamber remain well linear with the cumulative time over the cumulative time of 200 seconds. Through the saturation characteristic test, it can be determined that the saturation region of the developed thimble ionization chamber is 100V~300V, the plateau length is 200V, and the maximum change rate of absorbed dose rate in the saturation region is 0.70%. Through the comparison and verification experiment of the percentage depth dose measurement between this thimble ionization chamber and PTW's thimble ionization chamber, the results show that the maximum dose point depth and X-ray radiation quality of the two kinds of thimble ionization chamber are in good agreement. So the thimble ionization chamber developed in this paper can be applied to the high energy X-ray dose distribution measurement in water, and its technical level is equivalent to that of foreign products such as PTW Company.