Development Of BGO Detector For Jinping Underground Nuclear Astrophysics Lab

JUNA(Jinping Underground Nuclear Astrophysics lab)project has planned several direct measurement of key(?,?),(?,n)reactions in stellar hydrostatic helium burning stage and(p,?),(p,?)reactions in hydrostatic hydrogen burning in CJPL(China Jinping Underground Laboratory).A 4? detector array and extremely low background experimental environment is essential.Considering the high detection efficiency,high stop capability,low radioactive background and liable to deliquesce of BGO,we will manufacture a 4? BGO detector array to detect ?-rays emitted in(?,?)and(p,?)reaction measurements.We designed two schemes for the BGO detector array,and after analyzing the energy spectrum simulation of 12C(?,?)16O experiment of the two schemes,we adopt the array scheme consisting of eight trapezoid.In order to test whether the BGO crystal produced by Shanghai Institute of Ceramics,Chinese Academy of Sciences to meet the requirements of our experiment,we installed a prototype of BGO,using a 6 cm×8 cm×25 cm BGO crystal and the energy resolution of the prototype was test.The test results show that the energy resolution and stability of the BGO crystal produced by the Shanghai Institute of Ceramics,Chinese Academy of Sciences reach the advanced level in the world,fulfilling our requirements.Basing the requirement of extremely low background experimental environment of JUNA project,we used the prototype to make a background test,and then according to the test results,the shields used in the experiment were improved.Finally,we designed a shielding scheme which can meet the experimental requirements.Due to the temperature sensitivity of the light yield of BGO crystal,the variation of temperature will lead to peak drift when a BGO detector is used to detect ?-ray.To study this effect,a 4 cm×4 cm×3 cm BGO crystal and a 6 cm×8 cm×25 cm BGO crystal were cooled down.A 137 Cs source is used to study the influence of temperature on peak drift of the ?-ray spectrum and the change of energy resolution.The result shows that peak position of ?-ray spectrum is linearly correlated with temperature within the range of our experiments and the energy resolution of BGO improves with the decrease of temperature.