Jung il LEE for KIMS collaboration Sejong University A measurement of nuclear recoil with Am-Be neutron source in CsI(Tl) crystal Jung il LEE for KIMS collaboration Sejong University

Motivation 암흑물질 탐색 실험을 위한 핵 되튐측정. Previous measurement with mono-energetic neutron beam in accelerator. WIMP-nucleus recoil study with neutron-nucleus recoil. Studies on Pulse Shape Discrimination (PSD). 중성자 소스(Am-Be)를 이용하여 지속적이고, 체계적인 연구 가능.

Previous test with neutron beam at KIGAM Results of pulse shape discrimination 6keV< E <7keV E=2.62MeV

KIMS Am-Be neutron source의 특성 9Be(α,n)12C : 수 MeV neutrons α + 9Be -> 12C*(12C)+ n 12C + γ(4.4MeV) 300 mCi Am-Be source 재활용 (NETEC)  1.1 x 1010 Bq  total 7 x 105n/sec 예상 (70 neutrons/106 alphas)  수백 neutrons/sec hit 3cmX3cm crystal  limited by slow decay time of CsI(Tl) We can use it to study recoil signal systematically.

Experimental setup at SNU Source + 20cm Liquid Scintillation Counter (LSC) 5cm Pb shielding 10cm Borated Paraffin 2cm Fe shielding and structure 46o CsI BC501a 34cm 37cm 29cm n LSC Am-Be 90o 17.4o

Electronics diagram detector2 CsI down detector1 detector3 up Linear fan In/out Pre AMP Oct.DFD CF8000 Oct.CFD DF8000 D.G.G Dicrimi nator Oct. CFD trigger or Osc.ext Adc.partial Adc.full LSC Oct CFD DGG Tdc.stop Adc.gate Tdc.start Osc ch1 Osc ch2 Adc Dlming

(Am-Be neutron source) BC501A from source Gamma gamma neutron Partial charge Full charge

Timing spectra : T(BC501A) – T(LSC) gamma n

60Co calibration spectrum 60Co timing Am-Be timing n gamma

Neutron energy spectrum of Am-Be source

Calculation of neutron energy spectrum Lower than the total energy spectrum due to 4.4 MeV gamma coincidence requirement counts En (MeV)

Calculation of Nuclear recoil 10MeV 5MeV θ E0 ER m M 1MeV 17 46 90

Neutron & gamma separation Preliminary data with low statistics with only 17 degree Neutron Detector PID neutron Bc501a gamma Timing(BC501a-LSC) PID=(partial charge-55)/fullcharge

Pulse shape discrimination of CsI(Tl) 137Cs source Compton signals Am-Be neutron source signals Results : 137Cs mean= 1.818+-0.019 Sigma=0.5 Neutron (recoil) mean=1.509+-0.052 Sigma=0.675 Neutron Recoil signal is shorter than gamma signal !!

137Cs gamma-recoil Discrimination 2~6keV 6~10keV 10~14keV

Conclusion & future Demonstrated using Am-Be soure to study recoil with 4.4 MeV gamma tagging. The pulse shape discrimination is shown for nuclear recoil events with short decay time. Plan 1: increase # of neutron detector (~ 10) Plan 2 : measure En accurately from Am-Be Plan 3 : measure the quenching factor of CsI(Tl). Plan 4 : Use the setup for general recoil measurements

Gamma-recoil discrimination E(keV)

Cs137 gamma-recoil discrimination E(keV)

60Co source data 2 gamma coincidence T(BC501A) – T(LSC) 60Co Full vs partial graph Sigma=1.95ns Quenching Factor (=Emeas / Erecoil)를 측정하기 위하여는 약 1 ns 의 Resolution 필요

Gamma-recoil discrimination

Neutron energy spectrum of 239Pu/Be source

Pulse shape discrimination of CsI(Tl) Cs137 mean= 1.818+-0.019 Sigma=0.5 Neutron (recoil) mean=1.509+-0.052 Sigma=0.675 Gamma=1.509+-0.030 sigma=0.525