Research And Application Of High Performance Diamond Radiation Detectors

With the rapid development of the magnetic confinement fusion technology,the requirements on nuclear radiation detection also become higher.In particular,the plasma parameters in fusion reaction can be well determined by diagnosing the loss of high-energy particles.Due to the unique physical properties of diamond,the detector based on it will have the characteristics of high temperature resistance,radiation resistance and fast response comparing to other semiconductor detectors.This motivate us to carry out the research in this work.Uniform diamond radiation detectors with high performance were fabricated using II_a electronic grade CVD diamond samples and its responses to various irradiation are also studied thoroughly.Firstly,for the growth of diamond,the growth parameter and procedure of single crystal diamond by MPCVD was carefully studied and improved.A new groove substrate platform was designed and using it the method for growing single crystal diamond was optimized.It can effectively overcome the disadvantages of low flatness and higher growth rate on the edge of the crystal than in the middle when using the traditional substrates to grow single crystal diamond.In addition,the common characterization methods of diamond are summarized and the characterization results of our sample and those grown domestically or abroad are compared.The fabrication details of CVD diamond detectors are introduced in the form of four steps:selection of the electronic grade sample,selection of circuit board and design of circuit,fabrication of electrode,connection of each component and encapsulation of the detector.The fabricated detectors were tested for their dark current and X-ray photocurrent.The dark current density of single crystal detector per unit electric field intensity is 9.2[pA/mm²]/[V/um]and the polycrystalline diamond detector is20.5[pA/mm²]/[V/um].At the X-ray tube voltages of 10keV and 40keV,the signal to noise ratio?SNR?of the single-crystal detector can reach about 2000 and 7000respectively,and the SNR of the polycrystalline detector can reach about 550 and 2000,indicating that the fabricated detectors have good basic electrical characteristics.The pulse signal response of diamond detectors irradiated by Alpha particle source was studied,and the test results of commercial single crystal diamond detectors abroad were compared under the same test environment.The order of the response time of a single Alpha pulse signal is about 1ns.In terms of energy resolution,the fabricated single crystal diamond detector is 3.7%,while that of commercial single crystal diamond detector is 3.9%.The Hecht model was used to fit the charge collection efficiency of the detector by integrating the height pulse spectrum.For the fabricated single-crystal detector,when the external bias reaches above 200V,the collection efficiency is more than 97%,1-2%higher than the result of the commercial detector under the same voltage.For the polycrystalline detector,it can also detect a single Alpha pulse signal well,but its pulse height spectrum is continuously decreasing.This spectrum is attributed to polarization effect caused by the internal trap in the polycrystal.In addition,the response difference between single and polycrystalline detector to a single pulse signal confirms that how the free electron hole pairs generated by the external incident particles drift to the two electrodes of the detector will ultimately determine the shape of the pulse signal.CVD diamond neutron detector was also fabricated by evaporation of the ⁶LiF conversion layer,and its pulse responses under ²⁴¹Am-Be and ²⁵²Cf neutron sources were tested.The corresponding neutron signals were collected,under the irradiation of the two neutron sources,and the gamma signals were also found at the low energy level.Finally,the ¹⁵²Eu and ¹³⁷Cs gamma sources were used separately to confirm that the diamond detector was responsive to the gamma pulse signals.