The Study On The Performance Of X-ray CCDs

The main method of X-ray astronomy is the observation of X-ray radiation. There are several X-ray radiation mechanisms as follows, thermal radiation, non-thermal bremsstrahlung, synchrotron radiation, and inverse Compton scattering.The Hard X-ray Modulation Telescope is an astronomy satellite of high sensitivity and good spatial resolution, which is designed and manufactured independent by the direct demodulation imaging principle that is put forward by Chinese scholars. HXMT will complete the sky survey image of the full energy paragraph from1keV to250keV. High sensitivity and spatial resolution will be achieved in the hard X-ray segment.CCD236is an X-ray CCD detector with two-phase. The signals can be read-out quickly without the position information.The CCD’s performance parameters include energy linearity, energy resolution, read out noise, and so on.The proton irradiation affects the performance of the CCD236. The dark current increases significantly when it is above-60℃. While the dark current can be ignored when the CCD236is below-60℃. The dark current of the proton-irradiated CCD236increases faster than not irradiated. When it is below-30℃, the CTI dominates the energy resolution. When it is below-90℃, both the CTI and the dark current contributes little to the energy resolution.The experiment of proton energy response evaluates the energy loss and the collision times during the interaction between the protons and the silicon. The energy loss of protons depends a lot on the thickness of the depletion layer, which means protons will lose more energy in the thicker depletion layer. For the same thickness of the depletion layer, the relationship between the energy of incoming protons and their energy loss is not linear. Abandoning the events which split times are more than3will be helpful to decrease the background.As the amplitude, the energy resolution and the readout noise of the CCD236is all stabilized, which coincides within the error range, CCD236have high credibility in the measurement. The amplitude of the CCD236decreases with the rate about1‰/℃, when the operating temperature increases. The tendencies of the energy resolution and the readout noise are similar. In detail, it changes little when the operating temperature is below-60℃, while it increases significantly when the operating temperature is above-60℃.The calibration test was carried out to evaluate the energy linear and the relationship between the energy resolution and the energy. Both the linear and the consistency of the CCD236are very good below8keV. However, there is some nonlinear above8keV. The theoretic results and the measurements of the relationship between the energy resolution and the energy fit well. In the end, the outlook of the future work is mainly carried out around the LE calibration, including the response matrix functions, the quantum efficiency and so on.