A  study  of  Gamma  produc0on    from  neutron  capture  on  

gadolinium    

Takatomi  Yano  Kobe  University

11th Geant4 Space Users Workshop 28th Aug. Hiroshima Institute of Technology  

Collaborators: M.Sakuda, K.Hagiwara, Y.Yamada, P.Das, I.Ou, T.Mori, Y.Koshio (Okayama), A.Kimura, H.Harada, N.Iwamoto, S.Nakamura (JAEA)

1.  Introduction •  Gd(n,g) reaction •  Application in neutrino experiments •  Gd(n,g) models

2. Experiment •  Measuring gamma-ray from Gd(n,g)

3. Analysis •  Geant4 detector modeling •  A new code for Gd(n,g)

4. Summary

Outline

Introduction

Reaction Cross-section (barn)

n+p àd+γ (2.2MeV) 0.3326 n+6Li àα+3He 940 n+10B àα+7Li 3837 n+155Gdà156Gd+γ 60,900 n+157Gdà158Gd+γ 254,000

Gd(n,g) reaction •  Among all stable nuclei, Gd-157 has the largest thermal neutron capture cross-section.

•  Gd-155 also has large cross-section. •  Both capture interaction emits total ~8MeV gamma-rays.

Frequently used neutron absorbers

×15 ~ ×250 Cross-section!

n+155Gd → 156Gd+γs [8.5 MeV] n+157Gd → 158Gd+γs [7.9 MeV]

Introduction (2) Application of Gd(n,g) in neutrino experiments •  To identify anti-neutrino interactions from other reactions, Gd(n,g) reaction is used. → Lowering backgrounds, better analysis.

Experiments •  Neutrino mixing angle measurements (θ13)

•  D-CHOOZ, Daya-Bay, RENO… •  Supernova Relic Neutrino search

•  Super-Kamiokande + Gd (GADZOOKS, SK-GD)

e+

p Gd

νe

γ

Delay n

Super Kamiokande detector n 50kton  water  n ~2m  OD  viewed  by  8-­‐inch  PMTs  

n 32kt  ID  viewed  by  20-­‐inch  PMTs  

n 22.5kt  fid.  vol.    (2m  from  wall)  

n SK-­‐I:  April  1996~  n SK-­‐IV  is  running  n Trigger  efficiency    >99%@4.0MeVkin    ~86%@3.5MeVkin  

SK  

2km  3km  

1km  (2700mwe)  

39.3m  

41.4m  

Atotsu  Mozumi  

Ikeno-­‐yama  Kamioka-­‐cho,  Gifu  Japan  

Inner  Detector  (ID)  PMT:      ~11100  (SK-­‐I,III,IV),    ~5200  (SK-­‐II)  Outer  Detector  (OD)  PMT:  1885  

ID  

OD  

Figures are taken from Neutrino 2014 presentations.

Reactor neutrino exp. Double-Chooz (France) Daya Bay (China) RENO (Korea) Target channel : νe → νe Liquid scintillator detector

Double-Chooz

Daya-Bay

Daya-Bay

SRN search with SK

SRN includes the information of: •  Eν spectrum •  Star Formation Rate •  Black hole, dim supernova (extra-ordinary supernovae)

Factor 2-4

K.Bays et al., Phys.Rev.D85, 052007 (2012)

A search for SRN (supernova relic neutrino) •  Diffused neutrinos coming from all past supernova. •  It is showering and always detectable. •  Current upper limit at SK is about ~×2 of a model.

•  Background limited. •  If we can lower the background, SK will discover SRN. (10~60 events in 10 years.)

Detection of Gd(n,g) Detection of Gd(n,g) events •  With liquid scintillator detector, total energy of gamma-rays is measured well.

•  With water Cherenkov detector, we will lose some of energies. Because we have Cherenkov threshold of ~1 MeV for scattered electron. •  Number of Gamma-ray × ~1MeV will be missed. Gd(n,g) in Liquid Sci. Gd(n,g) in SK Yano, 2013 JPS

BLK：data RED：MC total PNK：Gd(n,γ) Geant 4 no FSMF6 GRN：p(n,γ) BLU: background

0 1 2 3 4 5 6 7 8 9

4-5MeV

8MeV

[MeV]

Original Gd(n,g) MC + Geant4

+G3 base Detector MC

Gd(n,g) models •  Several algorithm for computing gamma-ray emission exists.

•  Geant4, EBITEM(PHITS), CCONE, etc.

•  Any of them does not reproduce the gamma-ray emission sufficiently.

Geant4 no FSMF6 GLG4sim (a package for liquid scintillator neutrino detector.)

natural Gd

EBITEM (PHITS276) Gd157(n,g) CCONE

Gd157(n,g)

0 1 2 3 4 5 6 7 8 [MeV]

0.014

0.012

0.010

0.008

0.006

0.004

0.002

0

104

103

102

10

0 0 1 2 3 4 5 6 7 8 [MeV]

An experiment to measure Gd(n,g) Purpose p To study the fundamental information of Gd(n,g) reaction. (Multiplicity and energies of gamma-rays)

p To provide more precise information for the neutrino experiments using Gd(n,g).

Experimental method p We use a neutron beam line at J-PARC/MLF (Tokai, Japan).

p We have ANNRI detector there that is a array of Ge detector. → High energy resolution (ΔEγ = 9keV at 1.3MeV)

Ge

Ge

n

ANNRI detector

Experimental Setup Flight L=21.5m

Neutron Beam

JPARC/MLF/BL04 (ANNRI) Ge Specrometer Hg target

Proton(3GeV)

•  n beam: 1.3x1011n(/s/m2) at En=1.5-25 meV at Power 300kW.•  Spectrometer (ANNRI)： two Ge clusters with BGO veto shields. •  Each cluster : an array of 7 Ge crystals, arranged in hexagon.

Acceptance (Coverage) •  Ge: 22％ •  BGO VETO 55％

Analysis of Gd(n,g) data

Strategy of Gd(n,g) analysis 1.  To construct a Reliable MC (Geant4 base) 2.  To construct a gamma-emission model of Gd(n,g) 3.  To compare MC and Gd(n,g) data.

Experimental period : 2013/Mar/14-17 Target : Natural Gd(99.99% 5mm×5mm×10,20µm) Total event : 3×109events Calibration source :60Co,137Cs

Experimental period : 2014/Dec/11-16 Target : Enriched Gd(A=155(91.65%),157(88.4%)), Gd2O3Powder Total event : 8×109events Calibration source :22Na, 60Co,137Cs, 152Eu, NaCl

2014 B0124 -enriched Gd (155Gd, 157Gd) targets

2012 B0025 -natural Gd target Data sets

Detector Monte Calro Geant4 Monte Calro : made by Yamada, Hagiwara (Okayama), Yano (Kobe)

BGO veto detector

Ge detector

Beam pipe

LiH, Pb, B discs

4-1. MC calibration with 60Co, 152Eu, NaCl(n,γ)

•  An absolute peak detection efficiency at ~1 MeV is measured with 60Co (1.17, 1.33MeV gamma-rays). –  Detection efficiency: 2.4% (0.11%@1.17MeV for 1 crystal)

•  Relative peak detection is measured with 152Eu source and NaCl(n,γ) reaction. MC reproduce the experimental result within 20% for 0.5 - 9 MeV.

•  We will improve MC, to reproduce ± 10%.

0.0E+00%2.0E'04%4.0E'04%6.0E'04%8.0E'04%1.0E'03%1.2E'03%1.4E'03%1.6E'03%1.8E'03%

0% 1000% 2000% 3000% 4000% 5000% 6000% 7000% 8000% 9000%10000%

Peak

det

ectio

n ef

ficie

ncy�

Energy [keV]�

60CoNaCl152EuGeant4MC

Comparison of Data & MC Gd(n,g)

•  4meV  <  En  <  25meV  (Thermal  neutron  capture)  is  selected.  •  Background  contamina>on  is  ~1%.  •  Data,  Geant4.9.6p02  (w/o  FSMF6),  Geant4.9.6p02  +  

GLG4sim  Gd(n,g)  subrou0ne  are  shown.

Even

ts (

arbi

trar

y un

it)

BLK  :    Data  BLU  :  Geant4.9.6p02  (w/o  FSMF6)  RED  :  GLG4sim  

Comparison of Data & MC Gd(n,g)

•  Geant4.9.6p02  (w/o  FSMF6)  •  Several  extra  peaks  between  3  〜  5MeV  

•  Geant4.9.6p02  +  GLG4sim  Gd(n,g)  subrou0ne  •  Good  peaks  >  5MeV  (manually  wricen  branch  in  the  code.)

Even

ts (

arbi

trar

y un

it)

BLK  :    Data  BLU  :  Geant4.9.6p02  (w/o  FSMF6)  RED  :  GLG4sim  

1.

2.

Comparison of Data & MC Gd(n,g)

•  Geant4.9.6p02  (w/o  FSMF6)  •  Several  extra  peaks  between  3  〜  5MeV  

•  Geant4.9.6p02  +  GLG4sim  Gd(n,g)  subrou0ne  •  Good  peaks  >  5MeV  (manually  wricen  branch  in  the  code.)

Even

ts (

arbi

trar

y un

it)

BLK  :    Data  BLU  :  Geant4.9.6p02  (w/o  FSMF6)  RED  :  GLG4sim  

0"

0.2"

0.4"

0.6"

0.8"

1"

1.2"

1.4"

1.6"

0" 1000" 2000" 3000" 4000" 5000" 6000" 7000" 8000"

Energy[keV]

±0.4

Dat

a/M

C r

atio

1.4

1

0.6

0 2000 4000 6000 8000

•  The energy spectrum of natural Gd and MC (Geant4 + GLG4sim) agrees within 40%. (If we ignore small structures.)

•  99% of decay has continuum spectrum for Gd(n,g).

•  Some discrete branches should be enough to reproduce discrete spectrum.

•  How can we tune the continuum?

A new code for Gd(n,g) reaction A new algorithm for reproducing neutron capture gamma-ray (0.1-8.5 MeV) is written. •  I greatly own and thank for CCONE codes and Iwamoto-san(JAEA), the developer, for coding.

The code calculates the gamma emission probability, considering the residual energy in the excited nuclei. It will chase whole gamma-ray emission and provide the number of gamma-rays and these E. •  Gamma-ray strength function : Enhanced Generalized Lorentzian (Kopecky et.al Phys.Rev.C32 1993)

•  Nuclear Temperature : Fitting function with RIPL-3 data

•  Level Density : Fitting function with RIPL-3 data

E1  Resonance  M1  Resonance  E2  Resonance

EGLO,  Gd156

Energy  Spectrum  Gd156(n,g)  Kopecky  et.al  Phys.Rev.C  Vol47-­‐1,  p312

Energy  Spectrum  Gd155(n,g)  My  model  calcula>on

MeV MeV

Calculation with new code

It reproduces shape of single gamma energy spectrum.

Gd  Data  

GLG4SIM  

GLG4SIM Kopecky (3MeV E1,sig=0.35) (3MeV E1,sig=0.1)

0 　 2000 　 4000 　 6000 　 8000 (MeV)      

0 　 2000 　 4000 　 6000 　 8000 (MeV)       p  Eγ spectrum data

Comparison MC vs MC p  Eγ spectrum MC (before detector MC)

Gd  Data  

GLG4SIM  

GLG4SIM Kopecky (3MeV E1,sig=0.35) (3MeV E1,sig=0.1)

0 　 2000 　 4000 　 6000 　 8000 (MeV)      

0 　 2000 　 4000 　 6000 　 8000 (MeV)       p  Eγ spectrum data

Comparison MC vs MC p  Eγ spectrum MC (before detector MC)

We see positive tendency when we compare the spectrum. Now we are running with detector MC.

The new model can be tuned by changing parameters, e.g. GSF.

•  We will reproduce the continuum spectrum of Gd(n,g) with new code. Discrete spectrum will be defined by known energies and our measured intensity.

•  We can clearly separate these peaks of 155Gd and 157Gd by comparing enriched Gd and natural Gd.

Energy[keV]

arbi

trar

y

Energy spectrum

Analysis for Discrete Gamma-rays

natGd 157Gd 155Gd

•  Gd(n,g) reaction is applied for several ν experiments. –  A detailed information of Gd(n,g) is needed.

•  e.g. number of gammas and each energies.

•  We perfumed experiments to measure Gd(n,g) [nat. Gd, 155Gd and 157Gd] with large statistics. (~109 events ) –  A MC of detector is made. By source calibration, the characteristics between E=0.5 and 8MeV is understood in 20%.

•  A new gamma-ray emission code is written. Better reproducibility is expected.

•  With a continuum spectrum based on the algorithm and precise measurement result of discrete spectrum, we will make a new Gd(n,g) gamma-emission model.

Summary