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:
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
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.
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
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
Event Rate Estimation 252 Cf source : Decay Rate 0.1737 GBq (10 9 decays per second) 3.1% into fissions, 5.385 MBq Measured : 337.5 kBq, roughly 10% of events. This seems fine considering not all gammas, incident on the phototubes, will be above triggering threshold.
Logic Electronics D1AD1B discriminator AND Logic Unit 10x Amp
Coupled the 2 nd and 3 rd Detectors NaI(Tl) Crystal Fast PMT (response < 1 ns) High Speed Amplifier D2 D3 6 LiI Crystal
6 LiI : Ideal for 3 rd Detector Do not need PSD to discriminate neutrons from gammas. Use the (n,alpha) reaction.
Measured 6 LiI Spectrum with a multi channel analyzer Y-88 gamma lines at 898 keV and 1.836 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.
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 keV433 100 keV137 1 MeV43 5 MeV19
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.