PPTX GEANT4 Simulation of the New C6D6 Detectors - IFIC Indico Server (Indico)

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XXXVI Reunión Bienal RSEF, 17-21 June 2017, Santiago de Compostela

Radiative neutron capture on 242 Pu in the resonance

region at n_TOF-EAR1

J. Lerendegui-Marco (U. Sevilla), C. Guerrero (U. Sevilla),

E. Mendoza (CIEMAT), K. Eberhardt (U. Mainz), A. Junghans (HZDR)

and the n_TOF Collaboration

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Outline

1

•

²⁴²

Pu (n,γ): Motivations and goals

• Experimental set-up at n_TOF-EAR1

• Analysis towards capture yield

• Resonance analysis and average parameters

• Conclusions & outlook

XXXVI Reunión Bienal RSEF, 17-21 June 2017, Santiago de Compostela

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Introduction and motivations

242

Pu for MOX Fuels

• Use of Pu in spent fuels + depleted U: MOX Fuels ( + fast reactors)

• Capture on

²⁴²

Pu highest cross section and large uncertainties in the previous data Required reduction uncertainties

Goals of the measurement

• RRR: Provide experimental data: 3

^rd

in history, 2

^nd

in the last 40 years!

Extract individual and average resonance parameters up to at least 1keV

• URR: Provide experimental data up to (at least) 75 keV. Hopefully 200-500 keV Test consistency of Avg. Res. Par. from the RRR at higher energies

Nuc. System Energy range Present accuracy (%) Required accuracy (%)

SFR 2-500 keV 35 8

ADMAB (ADS) 9-25 keV 35 10

NEA/HPRL 0.5 -2 keV 14 8

FIRST AND MAIN GOAL

2

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4

Flux (Φ) (neutrons/cm

²

)

n

_at

(atoms/cm

²

) Reaction products

Transmission Scattering

t0 γ

L= 184 m t

PS Proton pulses

(20 GeV/c) σ = 7 ns

Pb Spallation MeV-GeV Neutrons

n_TOF-EAR1 at CERN:

Time-of-flight technique

BEAM LINE EAR1

Time-of-Flight to E

_n

relation (non-rel.):

5cm water moderator

Neutrons (meV to GeV)

E

n

t L t

ToF   0 

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 γ-rays from neutron capture : 4 Deuterized Benzene (C

₆

D

₆

) detectors (BICRON)

 Sample: 95 mg

²⁴²

Pu (>99.9%)-> 7 x 45mm ø targets

 Neutron flux monitor: 4 x Si detectors:



5

Neutron Beam

242

Pu Sample

Experimental set-up at n_TOF:

detectors & sample

COLLABORATION

WITHIN CHANDA:

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6

Solution: Give to each signal a amplitude-dependent weight: PHWT

AX Sn

En

A+1 X

s

_g

+n

E

_c

� � =� ∑

�=�

E  i =��

Efficiency independent of the cascade path! 

e

_gi

E

_gi

After PHWT:

(ε

_c

)

_Weighted

=

g g g

Efficiency to detect a cascade UNKNOWN: depends on

the cascade path

SOLUTION: TED

Total Energy Detection with C 6 D 6 detectors

 TED: Based in two principles

 Condition I : Low efficiency detectors e

_gi

<<1

Detecting a cascade: e

_c

=1-P(1- e

_gi

)

 Condition II: The efficiency is proportional to E

_γ

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Total Energy Detection with C 6 D 6 detectors

7

 TED: Based in two principles

 Condition I : Low efficiency detectors e

_gi

<<1

Detecting a cascade: e

_c

=1-P(1- e

_gi

)

 Condition II: The efficiency is proportional to E

_γ

Solution: Give to each signal a amplitude-dependent weight: PHWT

� � =� ∑

�=�

E  i =��

e

_gi

E

_gi

After PHWT:

(ε

_c

)

_Weighted

=

PHWT requires response of the detectors :

MC simulations (Geant4)

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8

242 Pu and backgrounds

• Counts normalized to “nominal” pulse intensity 7x10

¹²

protons

• Beam-off background dominates below 1eV

• Neutron induced background dominates above few keV

• This work focused: Resonance Region 1eV- 4keV Threshold in

energy deposited:

150 keV

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9

Capture yield:

Theoretical

 Capture yield = Probability for an incident neutron to undergo a capture reaction

Total cross section

� � h ( � � ) =( 1 − � − ��

^��

) � �

� ��

Capture cross section

Thin target approximation

<<1

� �� ( � � ) ≈ � � �

Sample’s areal

density

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10

Capture yield:

Experimental & corrections

 Capture yield = Probability for an incident neutron to undergo a capture reaction

� �� ( � � ) = �� ( � � ) − � ( � � )

� . � � ( � � )

Efficiency -> TED + PHWT:

Absolute Normalization:

Saturated Resonance Method

Efficiency corrections:

mainly loss below threshold (F

_thr

) Efficiency corrections:

mainly loss below threshold (F

_thr

)

Simulation capture cascades

Flux = Neutrons per pulse Total counts –

background (per pulse)

Fit of 4.9 eV saturated

resonance

¹⁹⁷

Au

(ancillary measurement)

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11

Efficiency corrections:

Simulation of capture cascades

 PHWT: Detection efficiency (numerically) = energy of the capture cascade

 Main correction:

 Fraction of counts lost below the detection threshold (F

_thr

)

Corrections extracted from realistic simulations of capture cascade

Large correction

& nuclei- dependent

E

_thr

= 150 keV F

_thr

= 1.09

E

_thr

= 150 keV

F

_thr

= 1.05

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12

Summary of

systematic uncertainties

ACHIEVED SYSTEMATIC UNCERTAINY WELL BELOW THE

8% REQUIRED BY THE NEA-HPRL

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XXXVI Reunión Bienal RSEF, 17-21 June 2017, Santiago de Compostela 13

Resonance analysis in brief

Resonance analysis with the SAMMY code:

Extraction of parameterized resonant cross sections from the fit of time-of-flight yields

Includes experimental effects:

Resolution and Doppler broadenings, self-shielding, etc…

�

�_�

�

_�

�_�

Breit Wigner

Width:

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Doublet

@ 504eV

• Good general agreement or slightly above JEFF 3.2 and ENDF/B VII.1

• E

_n

<1.3 keV: Confirmed: 75 + Rejected: 7 (NOT seen) + New: 17 (most p-waves)

• E

_n

>1.3 keV: Resonances beyond current high energy limit RRR: up to 4KeV

Resonance analysis:

242 Pu(n,γ) @ n_TOF-EAR1

FIRS T RE QUI REM ENT OF THE HPR L:

RES ONA NCE S UP TO 2Ke V

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15

Comparison to evaluations:

Radiative Kernels

• Average ratio: 1.07(2) (1.040(4) if weighted with the stat. uncertainties)

• Energy dependence: Largest deviation (12-13%) 400 - 800 eV

• Current uncertainty in the evaluations 500 eV-2keV: 14%

Radiative Kernel Resonance

Area

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Avg. Radiative Width <Γγ>

Avg. Level Spacing D

₀

Neutron Strenght Function S

₀

Bias: p-wave resonances D

₀

=12.5 ± 0.7 eV

S

₀

=0.89 ± 0.09

<Γγ>=25.4 ± 0.5 meV

Average Resonance Parameters (s-waves)

D

₀

=14.3 ± 1.0 eV

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 Innovative nuclear systems using MOX Fuels require a reduction of uncertainties.



²⁴²

Pu(n,g) with C

₆

D

₆

was successfully carried out @ n_TOF – EAR1 in Sept. 2015.

 Resonance region:

• Final results have been presented.

• Analysis towards a final yield in the RRR with 3.5-4% syst. Uncertainty.

• Resonance analysis: Extended up to 4 keV & more accurate Avg. Res. Parameters.

• Draft ready to be published soon.

 Outlook:

• Finalize the analysis of the n_TOF data with the URR up to >200 keV.

• Measurement of the thermal cross section at Budapest Research Reactor (Fall 2017) by means of the Prompt Gamma Activation Analysis (CHANDA).

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Conclusions & outlook

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THANK YOU

FOR YOUR ATTENTION!