The Versatile Array of Neutron Detectors at Low Energy

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1 The Versatile Array of Neutron Detectors at Low Energy S. V. Paulauskas, R. Grzywacz, M. Madurga, D. Miller, S. Padgett, W. A. Peters, and the VANDLE Collaboration

2 Why use the time-of-flight technique? Pros: A common technique to measure neutron energies; used at many facilities. Works well with low count rates Well suited to use with digital electronics Can be used to measure neutrons with energies ranging from.1-2 MeV Cons: Scattering can be an issue Requires large arrays to maximize efficiency

3 Measuring Neutron Energy via Time-of-Flight Maximize solid angle for exotic nuclei There is a trade off - resolution for efficiency. Using a small VANDLE bar with d = 6 cm, the bar thickness (3cm) gives 6% error in energy. d n Emission Point t 1 t 2

4 VANDLE A highly modular array of plastic scintillators Can be used to measure b-delayed neutrons and for reaction studies. Bar Sizes: Small : 3x3x6 cm 3 Medium : 3x6x12 cm 3 Large : 5x5x2 cm 3 Neutron Energies Covered: Small/Med. :.1-3 MeV Large : 1-2 MeV

5 Intrinsic Module Efficiency Courtesy of W. Peters Measurement performed using 252 Cf and a calibrated liquid scintillator High efficiency due to combination of electronics and PMTs.

6 Electronics XIAs Pixie digitizers Time stamps each event Records digitized signals Low trigger threshold Coupled with VANDLE yields a unique system, using "slow" digitizers with fast scintillators

7 Electronics Schematic Analog ~15 MB/s/channel Digital Total Load : ~ 3 GB/s Sig Amplitude (arb) -15 Amplitude (mv) 1 Amplitude (mv) Amplitude (mv) Energy Time Time (ns) Time (ns) Nyquist Filter Time (ns) Digitization Time (ns) FPGA Shaping

8 Custom Triggering Start() Start(n max =16) Start-Trigger VANDLE( left ) VANDLE( right ) VANDLE-Trigger() VANDLE(n left ) VANDLE(n right ) VANDLE-Trigger(n) Handles upto 16 starts and n VANDLE modules Reduces count rates Allows for acquisition in PMT noise System allows for 99.9% live time.

9 High Resolution Timing 3 25 f(t)=αe -β(t-φ) (1-e -γ(t-φ)4 ) 6 5 Amplitude (arb) FWHM (ps) Time (4ns/ch) Voltage (mv) Studies done with a pulser signal. Left : Function fit to the digitized signal. Right : Resolution as a function of input voltage.

10 Timing with PMTs A small 1x1x.5 in 3 EJ-2 chip between 2 PMTs 6 Co provides gammas Counts 15 1 FWHM =.713 ns Time (2 ps/bin) The resolution is consistent with PMT specifications. Electronics are "invisible"

11 Simulated Energy Resolutions Courtesy of S. Ilyushkin 14 n Arbitrary Units 1 6 Full detector modules built in Geant4 Includes scintillator and wrapping materials Assumes a constant time resolution of 1 ns Peaks widen due to bar thickness Arbitrary Units Neutron Energy (MeV)

12 Simulation of Experimental Setup Full experimental setup coded into Geant4 Currently simulating: Time-of-flight for neutrons Efficiency of entire setup Effects of scattering Ceiling I-Beam I-Beam Floor and Ceiling Frame High Purity Ge Courtesy of S. Ilyushkin

13 Simulation of Time of Flight Courtesy of S. Ilyushkin Uses full experimental setup Neutron energies.3, 1, 5 MeV Tails from the scattering from frame

14 Decay of 77 Cu Plot displays the kinematic curve for neutrons We can gate (red line) on the neutrons and project into the Time-of-Flight axis.

15 Low-energy Neutron Detecton Counts Energy (kev) Gamma detection essential to determine if gamma dexcitation competes with neutron decay. Brown spectrum gated on the 2 + state (6 kev) in b-n daughter Can observe neutrons at ~8 kev Counts Energy (MeV) 1 Preliminary Time of Flight (3ns).5 Brown Counts x15

16 VANDLE at ANL - Setup We learn from the past Using new medium bars 14x 6cm VANDLE bars Redesigned frame Clovers no longer mask VANDLE modules and are essential to experimental campaigns. Courtesy of N. Brewer Potential to add end caps to the new design

17 Summary VANDLE has achieved Over 5% intrinsic efficiency at 1 MeV Low neutron detection thresholds High resolution timing is lynch pin for system Simulation efforts critical to analysis Beginning experimental campaigns world wide