Experimental Nuclear Physics Some Recent Activities 1.Development of a detector for low-energy neutrons a. Hardware -- A Novel Design Idea b. Measure the light response at low energy c. Measure the neutron-proton scattering cross section 2. Measure the electromagnetic polarizability of the neutron Compton scattering of 100 MeV gamma rays

Experimental Nuclear Physics - Some Recent Activities 1.Development of a detector for low-energy neutrons a. Hardware -- A Novel Design Idea Developed in Lexington b. Measure the light response at low energy UKy accelerator/Los Alamos accelerator c. Measure the neutron-proton scattering cross section UKy accelerator 2. Measure the electromagnetic polarizability of the neutron Compton scattering of 100 MeV gamma rays MAX-lab accelerator in Lund, Sweden

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

Low energy neutrons produce recoil protons of very small range, unlike the electrons created by gamma rays. For a 3 mm scintillator thickness, no recoil protons from np scattering cross into adjacent cells. But, some low energy scattered neutrons do rescatter in other cells -- usually not triggering the discriminators. Therefore, NEUTRON TRIGGER: (T and B) or (L and R) Most gamma rays fire all 4 PMTs.

Detector Construction Top Left: The assembled detector. (The bottom PMT is hidden by the table.) Bottom Left: An inside view of five of the scintillators mounted in one light guide. Above: The assembled scintillator box, with five horizontal and five vertical scintillators. Each set is attached to two PMTs operated in coincidence.

Gamma-Ray Rejection These 60Co spectra were gated by all 4 PMTs firing (“Gamma Rays Selected”), and by only 1 pair of PMTs firing (“Gamma Rays Rejected”).

In-Beam WNR/15R August, 2010 “Low Energy Neutrons”: Cut on TOF for E<1.4 MeV; Cut on single-plane events Pulse height

Measure the Light Produced by Recoiling Protons 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 NEW!

November 4, 2010 DNP Fall Meeting, 2010 Brian Daub Massachusetts Institute of Technology 12 Of 16 Measuring n-p Scattering at Low Energy 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 13 Of 16 Transmission Measurement Setup for Transmission Measurement at UKy 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 14 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 15 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.