238 u neutron capture with the tac
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238 U Neutron Capture with the TAC. Toby Wright University Of Manchester. n_TOF Analysis Meeting CERN October, 2011. Introduction. High accuracy (n, γ ) 238 U cross-section measurement Joint future analysis with the same measurement using C6D6 detectors at nTOF and GEEL

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238 U Neutron Capture with the TAC

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238U Neutron Capture with the TAC

Toby Wright

University Of Manchester

n_TOF Analysis Meeting

CERN

October, 2011


Introduction

  • High accuracy (n,γ) 238U cross-section measurement

  • Joint future analysis with the same measurement using C6D6 detectors at nTOF and GEEL

  • Aim of reducing the uncertainty in the cross-section from ~5% to ~2%

  • Currently being measured at nTOF


The Sample

  • 6.125 ± 0.002 Grams

  • Isotopic analysis done in 1984

    • <1 ppm 233U

    • <1ppm 234U

    • ~11ppm 235U

    • <1ppm 236U

  • Wide sample, with perfect alignment it covers ~97% of the beam (53.90 x 30.30 mm)

  • ‘Bonbon’ casing with ~60 microns of Al, ~75 microns Kapton


TAC Calibrations - Time

  • 40 detectors going into 5 different streams

  • Each stream contains 2 digitizers, each with its own clock

  • Clocks have an accuracy to 2ppm therefore each detector must be calibrated to one reference

  • Done using the two gamma rays of Y88

Delta t (ns)

TOF (ns)


TAC Calibrations - Time


TAC Calibrations - Energy

  • Three calibration sources used:

    • 137Cs (661.7 keV)

    • 88Y ( 0.898 and 1.836 MeV)

    • AmBe (4.44 MeV)

  • Gaussians are fitted after the background has been subtracted

  • Routines for the 137Cs and 88Y have been rewritten, but are not completely finished


TAC Calibrations - Energy

Counts

Channel Number


TAC Calibrations - Energy

Counts

Channel Number


TAC Calibrations - Energy


Detector Resolution

  • Resolution = 2.35*FWHM/Energy

  • In this case, we have used channel number instead of Energy

  • Individual detectors resolution determined at the peak of 137Cs (661.7 keV)

2004


Counting Rate


Counting Rate (20-300 eV)


Proton Beam Intensity


238U Initial Results

  • 26 days more running time (20 days completed)

  • Everything seems to be going well!!

  • As of this morning, we have :

    • 268e15protons for 238U (normal nominal and parasitic) (~2e5 events)

    • 21299 ‘events’for beam off

    • 52.8e15protons for sample out (~4e4 events)

    • 14.8e15protons at low intensity (~1.4e4 events)

    • 12.45e16protons at high intensity (~7e3 events)


TAC Deposited Energy


TAC Deposited Energy


TAC Deposited Energy


TAC Deposited Energy


TAC Neutron Energy


TAC Neutron Energy


First Resonances

Second Resonance

Third Resonance

First Resonance


Statistics

  • Aim to have at least 1000 counts per resonance with reasonable binning

  • We already have this for the larger resonances

  • We are well on track for reaching this goal

Plot for runs 12983-13008 (4000 bins between 1 and 2 keV)

Approximately 7% of total statistics


Effect of the gamma flash on the TAC


Effect of the gamma flash on the TAC


Conclusions

  • Measurement is going smoothly

  • Preliminary analysis shows promising results

  • The TAC should be able to be used to measure at higher energies (100keV?) than in the past


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