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Experimental%20Nuclear%20Physics

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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 ... – PowerPoint PPT presentation

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Title: Experimental%20Nuclear%20Physics


1
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
2
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
3
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
4
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.
5
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.
6
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).
7
In-Beam Tests _at_ WNR/15R August, 2010
Pulse height
Low Energy Neutrons Cut on TOF for Elt1.4 MeV
Cut on single-plane events

8
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 (Ep f
    Ebeam) is detected in AT in coincidence with
    elastically scattered neutron detected in neutron
    detector (NE-213 2x2 inch cylinder) (En (1-f)
    Ebeam )
  • f is function of scattering angle (0.11 for
    T20 0.5 for T45 )
  • analog signal from AT integrated by LeCroy 4300B
    FERA QDC

9
  • 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 gt high
    energy-resolution

counts
Ebeam MeV
  • events of neutron elastic scattering in AT
    selected from 2D-plot of ToF(ATgtND) vs. Ebeam
  • gt defined by complete kinematics

elastic scattering
ToF(ATgtND) ns
Ebeam MeV
10
Experimental results
light respons A.U.
light respons A.U.
high gain
low gain
Ep-recoil MeV
Ep-recoil MeV
Ep-recoil 100 10 keV
Ep-recoil 250 25 keV
counts
counts
light respons A.U.
light respons A.U.
11
Experimental results
Smith et al. (68)
241Am (59.54 keV)
NEW!
133Ba (31 keV)
  • measurement of the BC-418 light response to both
    protons and electrons reaches new low energy
    limits for plastic scintillators

12
Measuring n-p Scattering at Low Energy
  • There are few measurements of the n-p total cross
    section below 500 keV.

13
Transmission Measurement
  • Setup for Transmission Measurement at UKy

85 cm from LiF to Sample
287 cm from LiF to Neutron Detector
14
Transmission Measurement
  • Neutron time of flight spectra, showing deficit
    of neutrons.

?-flash from LiF target
neutrons produced from LiF target
15
First Results - Hydrogen
  • Total n-p scattering cross sections with Endf
    tabulation and other data in range. Most results
    10-15 difference with Endf.
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