Presentation on theme: "Dante Nakazawa with Prof. Juan Collar"— Presentation transcript:
1Progress on Table Top Neutron Source for the Calibration of Nuclear Recoil Detectors Dante Nakazawawith Prof. Juan CollarFor Physics 335 with Prof. Mark Oreglia
2Reminder of ProjectFacility of Table Top Neutron Source : Calculation of neutron response of scintillating crystals. Ability to discern the direction of recoil.Proof of PrincipleCalculate neutron energy spectrum of 252Cf 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.
5When does a fission occur? Each fission from 252Cf emits 20 gammas and 4 neutronsPNNL 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 toPhotomultiplier Tube252Cfshielding
7Event Rate Estimation 252Cf source : Measured : Decay Rate GBq (109 decays per second)3.1% into fissions, MBqMeasured :337.5 kBq, roughly 10% of events. This seems fine considering not all gammas, incident on the phototubes, will be above triggering threshold.
8Logic Electronics D1A D1B 10x Amp 10x Amp discriminator discriminator AND Logic Unit
9Coupled the 2nd and 3rd Detectors 6LiI CrystalNaI(Tl) CrystalFast PMT (response < 1 ns)High Speed Amplifier
106LiI : Ideal for 3rd Detector Do not need PSD to discriminate neutrons from gammas. Use the (n,alpha) reaction.
11Measured 6LiI Spectrum with a multi channel analyzer Y-88 gamma lines at 898 keV and MeVCo-60 gamma lines at 1.1 and 1.3 MeVAm-Begamma line at 4.4 MeV, neutrons at 4-8 MeVCf : 80% of gammas are below 1 MeV. (n,alpha) reactionin 6Li peaks at 3 MeV so pulse height discrimination will work.
12Time-of-flight in 60cm (ns) ProblemsShifting baseline from Timing PMTs (D1A and D1B). Probably need to look for coincidences offline in the data analysis phase.6LiI Detector we have may not have the efficiency necessary for nanosecond timing needed for 252Cf spectrum measurements. Need to build a liquid or plastic scintillator and use pulse shape discrimination.EnergyTime-of-flight in 60cm (ns)10 keV433100 keV1371 MeV435 MeV19
13To do :Once we have timing coincidence nailed down and another scintillator, we can acquire spectrum of 252Cf.Develop the Data Acquisition Software (LabVIEW):Trigger from 3rd 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 2nd detector.Acquire NaI(Tl) gamma response and calculate the scintillation efficiency.