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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238 u neutron capture with the tac

238U Neutron Capture with the TAC

Toby Wright

University Of Manchester

n_TOF Analysis Meeting

CERN

October, 2011


Introduction

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

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

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)


238 u neutron capture with the tac

TAC Calibrations - Time


Tac calibrations energy

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 energy1

TAC Calibrations - Energy

Counts

Channel Number


Tac calibrations energy2

TAC Calibrations - Energy

Counts

Channel Number


Tac calibrations energy3

TAC Calibrations - Energy


Detector resolution

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


Counting rate 20 300 ev

Counting Rate (20-300 eV)


Proton beam intensity

Proton Beam Intensity


238 u initial results

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 energy1

TAC Deposited Energy


Tac deposited energy2

TAC Deposited Energy


Tac deposited energy3

TAC Deposited Energy


Tac neutron energy

TAC Neutron Energy


Tac neutron energy1

TAC Neutron Energy


First resonances

First Resonances

Second Resonance

Third Resonance

First Resonance


Statistics

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


Effect of the gamma flash on the tac1

Effect of the gamma flash on the TAC


Conclusions

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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