i will join an “measurement of d-p elastic scattering at 300 MeV/nucleon” experiment.

this experiment is going to study the 3-nuclear force, which is the force connects 3 body at same time. since the nuclear force is polarization dependence, or spin dependence, we have to measure the polarization of the beam.

the way to do is measuring the asymmetry of scattering, by spin-orbital coupling. for a spin up particle incident on left, the spin-orbital coupling strength is different from the incident on the right. thus, we will install a plastic scintillator on both side, left and right, up and down, to determine the polarization.

the scintillator was installed at particular angle such that the different is biggest. ( i don’t know how to calculate this angle ) the optimal angle for proton and deuteron are different, so, we use 8 detector in total.

after installation, we put a Co-60 gamma ray source in front of it, and connect the photomultipler tube (PMT) with about 1000V to 2000V, depend on the sensitivity of each PMT. The signal was displayed on CRO, and it shoen a typical signal pattern. although the gamma ray energy is fixed, the detection process in the plastic scintillator is via Compton scattering of electron, that make fluctuation of the signal. Thus, we take count average of about 60 to 100 counts. the typical signal depth is 200mV and fall time is 3uS, raise time is 5 to 7 uS.

footnote:

Co-60 has 1 gamma ray decay of 0.058MeV, then it goes 2 channels beta decay of 0.31MeV with 99.88% and 1.48MeV with 0.12% to Ni-60, the excited Ni-60 will emit 2 gamma ray, of 1.17MeV and 1.33MeV.

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