Preliminary results of n f measurements at cern n tof with fic0 and fic1 detectors
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Preliminary Results of (n,f) Measurements at CERN n_TOF with FIC0 and FIC1 Detectors. P.Cennini 1 , A.Goverdovski 2 , W.Furman 3 , V.Ketlerov 2,1 , V.Konovalov 3,1 , V.Vlachoudis 1 1 CERN, 2 IPPE, 3 JINR and n_TOF Collaboration. With a lot of help of:. A.Doroshenko 2 S.Girod 1

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Preliminary Results of (n,f) Measurements at CERN n_TOF with FIC0 and FIC1 Detectors

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Preliminary Results of (n,f) Measurements at CERN n_TOF with FIC0 and FIC1 Detectors

P.Cennini1,

A.Goverdovski2,

W.Furman3,

V.Ketlerov2,1,

V.Konovalov3,1,

V.Vlachoudis1

1CERN, 2IPPE, 3JINR

and n_TOF Collaboration


With a lot of help of:

A.Doroshenko2

S.Girod1

D.Kolokolov2

V.Mitrofanov2

B.Samylin2

M.Sedysheva3

1CERN, 2IPPE, 3JINR


Motivation

n_TOF Collaboration scientific program

Nuclear data for ADS:

fission cross-section measurements

Fundamental nuclear physics:

study of vibrational fission resonances


Fast Ionization Chamber Design

  • Gas – Ar 90%+CF4 10%

  • Pressure – 600 mbar

  • Distance – 5 mm

  • HV – 300 V

  • 17 targets in the beam

  • “noise” electrode

  • 2 targets out of the beam


FIC1 Photo


FIC1 and FIC0 Photo


Inside FIC1 Photo 1


Inside FIC1 Photo 2


FIC0 Main Electronics


Basic Equations

For single channel i of given isotope X

TDC data

Flash ADC data

If there is some impurity nucleus Y


Extraction of cross-section

Flash ADC data

Kiis obtained from MC simulation

is calculated with accounting for dead time and

from an analysis of pulse-height histogram

is really measured (see below for more detail)

From reference 235U channel one can extract F(E(t))

So it is possible to extract fission cross-section

from counting rate of each (X,i) channel


Isotopic Dilution Method

Definitions:

m5 , m6 – masses of 235U and 236U targets

 - content of 235U in 236U target

5, 6 – fission cross-sections

5, 6– registration efficiencies of FF

(6 is valid for FF from 235U admixture to 236U target!)

n5, n6 – count rates


Isotopic Dilution Method

  • Master equation

  • R = n6 / n5 = (6/5)(m66 +  m65)/ (m55)

  • Around resolved resonances En=8 – 20 eV 5 is very high

  • (up to 710 b) while 6 = 0, then

  • R0 =  (m66)/( m55 )

  • For other energies where 5 << 6 and due to  << 1

  • R(En) = R0 (6 / 5 )/ 

  • There are no 6,5 or m6 , m5 ratios. We have only  and count rates.

  •  = 0.00047 ± 0.00002 – measured by mass-spectrograph


  • Isotopic Dilution Method

    U-235, 0.047%


    List of Targets

    ----FIC0----

    235U- 47mg (3 targets)

    238U- 110mg (3 targets)

    232Th- 80mg (2 targets)

    236U- 20mg (2 targets)

    237Np- 10mg (1 target)

    234U- 34mg (6 targets)

    ----FIC1----

    235U- 30mg (1 targets)

    238U- 90mg (2 targets)

    241Am- 2mg (4 targets)

    243Am- 10mg (4 targets)

    245Cm- 2mg (2 target)

    233U- 20mg (2 targets)


    Targets

    Backing - 100 microns aluminum foil

    Substance is painted on both sides

    Spot diameter is 80mm

    Thickness from 5mkg/cm2 to 450mkg/cm2

    Number of painted layers 100-200

    Uniformity is 5% - 10%


    Painting Technique


    Target analysis

    For mass, impurities, uniformity with

    Ionization chamber with Frisch grid

    For low radioactive targets

    232Th, 238U, 235U, 237Np, 236U

    Si detector

    For high radioactive targets

    233U, 245Cm, 243Am, 241Am


    Ionization Chamber


    Alpha Spectrum of 235U


    Alpha Spectrum of 232Th


    Si Detector

    S = 1 cm2


    Alpha Spectrum of 241Am


    Alpha Spectrum of 243Am

    (2.6%)


    Alpha Spectrum of 245Cm


    Alpha Spectrum of 237Np


    235U Contamination

    Even impurity of 10e-5 – 10e-4

    which is impossible to determine by a-analysis

    is essential for neutron induced fission experiments


    235U Contamination of 236U and 238U

    1e-5 of 235U

    238U

    236U

    4e-4 of 235U

    235U


    Noise Filtering 238U


    Noise Filtering 237Np


    Noise Filtering (Low Energy)


    Noise Filtering 237Np (res)


    Neural Network Filtering


    Pulse Height Histogram 236U


    T-E Calibration from Capture


    235U Resonances


    T-E Calibration from Fission


    Energy Resolution 234U


    Preliminary Results Below 1MeV

    234U, 236U

    237Np, 245Cm


    237Np Resonances 1


    237Np Resonances 2


    237Np Resonances 3


    237Np Resonances 4

    present

    ENDF pointwise


    237Np Resonances 5


    245Cm with a-background


    245Cm


    245Cm Resonances 1


    245Cm Resonances 2


    245Cm Resonances 3


    234U Resonances 1


    234U Resonances 2


    234U Resonances 3


    234U Resonances 4


    234U Resonances 5


    234U Resonances 6


    234U Vibrational Resonances


    236U Resonances 1


    236U Resonances 2


    236U Resonances 3


    236U/ 235U Ratio


    Present Status of Data Analysis

    Flash ADC raw data analysis with neural network

    TDC and FADC data comparison and adjustment

    T-E calibration for En>0.5MeV

    Completion of full MC simulation

    Neutron flux determination

    Extraction of neutron induced fission cross-sections


    Thank You Very Much

    Good luck!


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