In target chamber Ⅱ of the BEPCII-LINAC Test Beam

radiation field of mixed particles(mainly proton

neutron

gamma

pion

positron and electron) of consecutive energy is generated from the object target bombarded by the 1.89 GeV pulsed electron beams from the linear accelerator.This mixed radiation field is ideal for irradiating materials or biological samples.However

these experiments need to know the dose of various particles delivered to the samples.In light of this

a mixed radiation detector(phoswich detector) was developed.In this paper

the basic process of the detector development and its key properties are reported.The basic structure of detector and principles of detection are given.GEANT4 simulation results of detection efficiency of different particle and performance of n-γ discrimination are given.The results show that the mixed radiation detector

with the design specifications being achieved

satisfies the measurements of mixed field in the Test Beam.