A scintillation detector for neutrons below 1 MeV with gamma-ray rejection Scintillators are 3 mm BC408, 10 layers total Adjacent layers are optically isolated Active scint. area approx. 10 cm x 10 cm in this prototype Each PMT discriminator triggered near top of 1 photoelectron distribution L-R and T-B thresholds approx. 10 keVee; Coincidence requirement removes noise

The light response of BC-418 plastic scintillator to protons with energies from 60 keV to 5 MeV

Motivation primary interest in n+p=>d+γ for Big-Bang Nucleosynthesis models Important neutron kinetic energies: 50 – 500 keV => produced deuteron kinetic energy 25 – 250 keV we used fast plastic scintillator BC-418 as active target (AT) AT in coincidence with NE-213 liquid scintillator used to test limits of the detector and observe low energy proton recoils from n-elastic scattering in BC-418

Motivation data on relative light response of plastic scintillators to heavy charged particles scarce and/or non-existent below 350 keV => Determination of neutron detector efficiency depends on the threshold, big systematic errors for detection of low energy neutrons => Cross calibration with γ-sources difficult general applications: - (not so) fast neutron, proton detection - nuclear safeguards (search for 3 He substitute(s)) - modeling of detector response - etc…

light response The only information from Bicron (aka Saint-Gobain) is for BC-400, or semi-generic for high energy only. => what about BC-418 ?

Smith et al., NIM64(1968) 300 keV Same as BC-400 light response data scarce and/or nonexistent for E proton < 300 keV

Experiments at WNR proton beam (E p =800 MeV) impinges on bare tungsten spallation target 4FP15R – neutron beam line 15° on the right of the proton beam axis – neutron energies ~450 keV – 800 MeV (with 1.8 μs beam pulses) – neutron energies ~120 keV – 800 MeV (with 3.6 μs beam pulses)

Experimental setup neutron beam impinges on the active target (BC-418; 2mm thick) energy of beam particles is determined from their time-of-flight when neutron is elastically scattered in the active target (AT) the recoil proton (E p = f E beam ) is detected in AT in coincidence with elastically scattered neutron detected in neutron detector (NE-213 2x2 inch cylinder) (E n = (1-f) E beam ) f is function of scattering angle (=0.11 for Θ=20°; =0.5 for Θ=45°; ) analog signal from AT integrated by LeCroy 4300B FERA QDC

most of the beam neutrons with energies ~ 1-5 MeV time-of-flight to AT for 1 MeV neutron is ~ 1.2 us time resolution ~ 2ns => high energy-resolution events of neutron elastic scattering in AT selected from 2D- plot of ToF (AT=>ND) vs. E beam => defined by complete kinematics E beam [MeV] ToF (AT=>ND) [ns] counts elastic scattering

Experimental results E p-recoil [MeV] counts light respons [A.U.] high gainlow gain E p-recoil = 100 ±10 keVE p-recoil = 250 ±25 keV light respons [A.U.]

241 Am (59.54 keV) 133 Ba (~31 keV) Smith et al. (68) Experimental results measurement of the BC-418 light response to both protons and electrons reaches new low energy limits for plastic scintillators

Experimental results BC-418 light response data seem to confirm that light response to protons increases with respect to light response to electrons below ~ keV p/β ratios:

November 4, 2010 DNP Fall Meeting, 2010 Brian Daub Massachusetts Institute of Technology 13 Of 16 Measurement of Neutron-Proton Total Scattering Cross Section by Neutron Transmission Brian Daub, Vladimir Henzl Massachusetts Institute of Technology Michael Kovash, Khayrullo Shoniyozov University of Kentucky

November 4, 2010 DNP Fall Meeting, 2010 Brian Daub Massachusetts Institute of Technology 14 Of 16 Motivation There are numerous fields which would benefit from precise n-p total cross section data.  Two Body Nucleon Interactions  Nuclear Reactors  Detector Efficiencies  Particle Astrophysics

November 4, 2010 DNP Fall Meeting, 2010 Brian Daub Massachusetts Institute of Technology 15 Of 16 Motivation However, there are few measurements of the n-p total cross section below 500 keV.

November 4, 2010 DNP Fall Meeting, 2010 Brian Daub Massachusetts Institute of Technology 16 Of 16 Transmission Measurement Data taken using the Van de Graaff Accelerator at the University of Kentucky. Neutrons produced by pulsed protons on a LiF target, through the 7 Li(p,n) 7 Be reaction. Detector is placed directly in the beam. Sample is placed in the beam-line upstream of the detector. Neutrons are scattered out of the beam by the sample. Determine total cross section from number of neutrons scattered out.

November 4, 2010 DNP Fall Meeting, 2010 Brian Daub Massachusetts Institute of Technology 17 Of 16 Transmission Measurement Setup for Transmission Measurement 287 cm from LiF to Neutron Detector 85 cm from LiF to Sample

November 4, 2010 DNP Fall Meeting, 2010 Brian Daub Massachusetts Institute of Technology 18 Of 16 Transmission Measurement 2.25 MeV protons pulsed at 1.8 MHz to produce neutrons up to 450 keV. Minimum energy was 200 keV. Neutron detector was 5-inch diameter BC501 liquid scintillator. 287 cm flight path from LiF target to neutron detector.

November 4, 2010 DNP Fall Meeting, 2010 Brian Daub Massachusetts Institute of Technology 19 Of 16 Transmission Measurement Four Samples  1/2 Inch Carbon  1/2 Inch CH 2  1/4 Inch CH 2  Wax Blocker Ratios of normalized target-in to target-out yields give cross section independent of dead time and efficiency.

November 4, 2010 DNP Fall Meeting, 2010 Brian Daub Massachusetts Institute of Technology 20 Of 16 Transmission Measurement γ-flash from LiF target neutrons produced from LiF target Neutron time of flight spectra, showing deficit of neutrons.

November 4, 2010 DNP Fall Meeting, 2010 Brian Daub Massachusetts Institute of Technology 21 Of 16 Transmission Measurement Correlated band in neutron energy (from time of flight) vs. neutron detector pulse height, used to exclude non-neutron background.

November 4, 2010 DNP Fall Meeting, 2010 Brian Daub Massachusetts Institute of Technology 22 Of 16 First Results - Carbon Total n-C scattering cross sections with Endf Tabulation. Data matches Endf within ~2%.

November 4, 2010 DNP Fall Meeting, 2010 Brian Daub Massachusetts Institute of Technology 23 Of 16 First Results - Carbon Our results are consistent with previous measurements.

November 4, 2010 DNP Fall Meeting, 2010 Brian Daub Massachusetts Institute of Technology 24 Of 16 First Results - Hydrogen Total n-p scattering cross sections with Endf tabulation and other data in range. Most results ~10-15% difference with Endf.

November 4, 2010 DNP Fall Meeting, 2010 Brian Daub Massachusetts Institute of Technology 25 Of 16 Results Tabulations match with higher and lower energy range, but deviates in region with our results.

November 4, 2010 DNP Fall Meeting, 2010 Brian Daub Massachusetts Institute of Technology 26 Of 16 Future Measurements γ-ray background-rejecting detector  Discriminates between neutrons and γ-rays  Tested at LANSCE in August 2010 Extending results to  Lower Energies: Lower repetition rate beam at UKY allows for longer times of flight; tested in March  Higher Energies: Increased proton energy yields higher incident neutron energies. Planned run in January 2011 at UKY with these additions.

November 4, 2010 DNP Fall Meeting, 2010 Brian Daub Massachusetts Institute of Technology 27 Of 16 Cross Section Calculation Intensity as a function of Thickness Yield is Intensity times efficiency times livetime. Yield as a function of thickness. Efficiency cancels in ratio.

November 4, 2010 DNP Fall Meeting, 2010 Brian Daub Massachusetts Institute of Technology 28 Of 16 Cross Section Calculation Intensity proportional to beam current.T x J = Q, livetime integrated current. Cross Section is now independent of efficiency and deadtime.