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Progress on Table Top Neutron Source for the Calibration of Nuclear Recoil Detectors Dante Nakazawa with Prof. Juan Collar For Physics 335 with Prof. Mark.

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Presentation on theme: "Progress on Table Top Neutron Source for the Calibration of Nuclear Recoil Detectors Dante Nakazawa with Prof. Juan Collar For Physics 335 with Prof. Mark."— Presentation transcript:

1 Progress on Table Top Neutron Source for the Calibration of Nuclear Recoil Detectors Dante Nakazawa with Prof. Juan Collar For Physics 335 with Prof. Mark Oreglia

2 Reminder of Project Facility of Table Top Neutron Source : Calculation of neutron response of scintillating crystals. Ability to discern the direction of recoil. Proof of Principle Calculate neutron energy spectrum of 252 Cf neutron source with time-of-flight spectroscopy. Using this initial neutron energy scattering angle to calculate the energy of the recoiling atom (Na or I). Measure the known scintillation response of a NaI(Tl) crystal to neutron recoils w.r.t. gamma recoils.

3 Experimental Setup 252 Cf Shielding Pb Polyethylene Borated Silicone 60 cm NaI(Tl) Coupled to Photomultiplier Tube 60 cm NaI(Tl) Crystal 6 LiI Crystal D1B D1A D2 D3

4 Experimental Setup D3 D2 D1BD1A

5 When does a fission occur? Each fission from 252 Cf emits 20 gammas and 4 neutrons PNNL solution : try to cover at least 3 of the source with gamma detectors (also NaI in our case) and trigger from a coincidence. NaI(Tl) Coupled to Photomultiplier Tube 252 Cf shielding

6 Coincidences D1A D1B time PMT voltage

7 Event Rate Estimation 252 Cf source :  Decay Rate GBq (10 9 decays per second)  3.1% into fissions, MBq Measured :  kBq, roughly 10% of events. This seems fine considering not all gammas, incident on the phototubes, will be above triggering threshold.

8 Logic Electronics D1AD1B discriminator AND Logic Unit 10x Amp

9 Coupled the 2 nd and 3 rd Detectors NaI(Tl) Crystal Fast PMT (response < 1 ns) High Speed Amplifier D2 D3 6 LiI Crystal

10 6 LiI : Ideal for 3 rd Detector Do not need PSD to discriminate neutrons from gammas. Use the (n,alpha) reaction.

11 Measured 6 LiI Spectrum with a multi channel analyzer Y-88 gamma lines at 898 keV and MeV Co-60 gamma lines at 1.1 and 1.3 MeV Am-Be gamma line at 4.4 MeV, neutrons at 4-8 MeV Cf : 80% of gammas are below 1 MeV. (n,alpha) reaction in 6 Li peaks at 3 MeV so pulse height discrimination will work.

12 Problems Shifting baseline from Timing PMTs (D1A and D1B). Probably need to look for coincidences offline in the data analysis phase. 6 LiI Detector we have may not have the efficiency necessary for nanosecond timing needed for 252 Cf spectrum measurements. Need to build a liquid or plastic scintillator and use pulse shape discrimination. EnergyTime-of-flight in 60cm (ns) 10 keV keV137 1 MeV43 5 MeV19

13 To do : Once we have timing coincidence nailed down and another scintillator, we can acquire spectrum of 252 Cf. Develop the Data Acquisition Software (LabVIEW):  Trigger from 3 rd detector once well shielded against background neutrons. Store waveform of D2 and coincidence detectors.  Check timing information from D3, D2, and coincidence logic for energy conservation per event.  Calculate nuclear recoil energy from initial energy (time-of-flight) and scattering angle.  Integrate the pulse of 2 nd detector.  Acquire NaI(Tl) gamma response and calculate the scintillation efficiency.


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