WIRSCHAFFENWISSEN– HEUTEFÜRMORGEN

Shielding – High Energy Neutrons – Spallation vs. Fission

UweFilges, PaulScherrer InstitutPhilBentley,EuropeanSpallationSource

20th September 2018,

Neutron Energy Classification

Page2

thermal

epithermal

fast

High energy neutrons

<0.15to 0.625eV

> 0.1– 1MeV

Page3

Spallation vs Fission

Spallation

Neutron energy average: 1.2MeVWatt-Fission Spectrum

Neutron energy distribution: depends from proton energy and target !!!

Neutron production – Proton energy

Page4

Goal: Increasing the proton energy

PSI

ESS

Pulsed spallation sources

Page5

ISISTS2– 800MeV proton beam

SNS– 1GeV proton beam

ESS– 2 GeV proton beam

Released Neutron Spectra

Page6

Bigdifference inshielding efforts !!!

Moderation ?

Page7

• Reactor facilities: bigvolumes – basedonhydrogen(heavywater &lightwater)

Goal: slowing downneutrons tothermal energy (notimedependency)

• Spallation sources: efficiently doneonlyinsmallvolumese.g.H2-ModeratorsBeryllium usedas reflector (moderation is50times worseasD2O)

Goal:keeping the timestructure of thereleased neutrons– minimizeabsorption/scattering between targetandsmallmoderator volume

Bigdifference inshielding efforts !!!

Continuous neutron flux

Pulsed neutron flux

Effects on Neutron Scattering Experiments

Page8

How you can shield high energy neutrons ?

Page9

Depends from the Material Cross Sections (Absorption & Scattering)

Goodscattering materials areworkingwell upto1MeV(scattering isdominating)

GEM applications outside high energy physics - Duarte Pinto, Serge Mod.Phys.Lett. A28 (2013)

Fast Neutrons > 10 MeV

Page10

Density of the materials becomes more and more important.

Tungsten – around4-5barn

Hydrogenhascross sections <1barn!!!

Datacanbefoundon: http://www.nndc.bnl.gov/sigma/

Copper – around2-3barn

Resonances !!!

Page11

Ironis nota„good“ shielding material for epithermal neutrons !!!!

High Energy Neutron Shielding

Page12

Shielding Design

Page13

Collimators along the beamline &Layeredstructure(repetition oflayers)ofshielding material

• McStas,aMonteCarloray-tracingcodeforneutronscatteringinstrumentation,simulatesveryefficientevents(neutrons)fromasourcesurfacetothedetectorposition(alternatives:VITESS&Restrax)

SINQ MCNPX-Model

Simulations-Tools• MCNPX (anadvancedMonte-CarloCodeforparticlephysics)isaperfecttoolto

describea3Dneutronsource,includingmoderator&shieldingmaterials …(alternatives:GEANT4&PHITS)

Input:protonbeamorreactorcoremodel

Input:neutron source description

SINQ CATIA-Model SINQ McStas-Model

( )λλ

λ

λλλ λ

λdIdf

iT

iTi

i

i

2

exp241

0

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

=⎟⎟⎠

⎞⎜⎜⎝

⎛∗∗=∑

n- Maxwellian distribution

Examples – PSI & ESS

Page15

ICON– Imaging beamlineHowgoodwecan describe asource?

Eiger– thermal triple axes instrumentNon-magnetic /compact shielding

MAGiC – Single crystal diffractometer

ODIN– TOinvestigations

Zebra– thermal single crystal diffractometer ESTIA– Reflectometer

Cold Source Simulations/Measurements at SINQ

4.7 m7.2 m

11.8 m16.8 m

McStas

MCNPX

no supermirrors are installed, different pinhole geometries are possible,measurement positions are closed to the source with direct view

L.Giller, U.Filges, G.Kuehne, M.Wohlmuther, Nucl. Instr. and Meth. 586 (2008) 59-63

Measurement positions

ICONbeamline

-4 -3 -2 -1 0 1 2 3 4-4

-3

-2

-1

0

1

2

3

4

width [cm]

heig

ht [c

m]

-4 -3 -2 -1 0 1 2 3 4-4

-3

-2

-1

0

1

2

3

4

width [cm]

heig

ht [c

m]

first collimationsection

cold source

9x9 tally grid at collimation entrance

9x9 tally grid 50 cm inside offirst collimation

energy range: 1eV - 0.3 meV (200 bins) – 3000 h computing time

moderator

Simulated Neutron Flux Distribution at the ICON beamport

NEWInputforMcStas

Thermal flux distributionMCNPX results

-20 -15 -10 -5 0 5 10 15 20

0.0

0.2

0.4

0.6

0.8

1.0

Vertical Profile - 20 mm Setup

norm

aliz

ed in

tens

ity

vertical position [cm]

measurement simplified model improved model McStas-MCNPX model

-20 -10 0 10 20-20

-10

0

10

20

-15 -10 -5 0 5 10 15-20

-15

-10

-5

0

5

10

15

20

Comparison of horizontal and vertical beam profils at middle position (11.8m)

using the McStas-MCNPX model - 20 mm aperture

-20 -15 -10 -5 0 5 10 15 200.0

0.2

0.4

0.6

0.8

1.0

Horizontal Profile - 20 mm Setup

norm

aliz

ed in

tens

ity

horizontal position[cm]

measurement simplified model improved model McStas-MCNPX model

measurement

simulation

heig

th

[cm

]he

igth

[c

m]

width [cm]

width [cm]

Neutron flux distribution at ICON middle position

Measurement/simulation of cold source brightness at SINQ

Experiment – TOF setup with collimator system

- chopped : 0.15% duty cycle

- beam size : ø1 mm

- solid angel : 0.693 mStr

peak factor

simulation(detailed) 1.0

measurement(efficiency by MCNP)

1.2

collimator

Detector shielding with sapphire crystal

Cold source

ICON Beamline (MCNP model)

TOF-Setup

NIMAinpreparation

Background measurements with Bonner Sphere Spectrometer

Bonner spheres spectrometer (BSS) Response matrix of the Bonner spheres system

standard Bonner sphere system consists of a He-3 neutron detector and a set of 10 polyethylene spheres

of diameters from 2 to 15 inches (each sphere has a different energy response)

measurementposition

EPFL – Lausanne

Extension of BSS System

Page21

Extended energy range: >2GeV (interesting also for SwissFEL, ESS...)

Shielding Design for the Triple Axes Spectrometer EIGER

Thermal spectrometer EIGER at SINQ

EIGER Monochromator shielding design

water scatterer

MCNPX model

SINQ

target

Primary beamline layout

- Design of anon-magnet shielding with amaximum thickness of 85cm

Page23

• dose rate < 10 µSv/h with a shielding thickness of 85 cm

Calculated gamma and neutron dose rate distribution at the outer surface of monochromatorshielding – 17° position

MCNPX geometry layout for the shielding

calculations – 17° position

• developing/simulations of different compositions of heavy concrete (non-magnetic) with a density of approx. 5.1 g/cm3

• developing a special material composition (tungsten/paraffin) for absorbing (slowing down) fast neutrons

Gamma and Neutron Dose Rates behind the Shielding

Heavy concrete developments

Page24

• 7 different concrete compositions were tested and simulated (all are special PSI compositions)

• non-magnetic / magnetic samples for different applications

• Sample 1: special efforts - stainless steel balls with different sizes and thermal treatment

• In addition Sample 1 includes as mineral Barite – very good gamma shielding material

Comparison: normal concrete: < 0.13 cm-1

Heavy concrete Measurements

Page25

0 100 200 300 400 5001E-3

0.01

0.1

1

10

100

1000

10000

100000

1000000

˚

˚DoseRate˚(!Sv/h)

Thickness˚(mm)

˚E˚Measured˚Data˚B˚Fits˚to˚I0*exp(-bx)

M1(baryte+1.4301)

I0=52200˚˚b=0.313˚cm-1

Incoming spectrum at ICON beamlineAttenuation for the fast Neutrons

Sample with strong steel collimator (1m)

Shielding for background

reduction was needed

12 inch sphere detector

Page26

• design reduces the background by around a factor of 2

triangular spike-surfaces

Optimized neutron trap

neutron trap with flat surfaces

point of

interest

Original neutron trap proposal

Neutron Trap Design for Eiger

- triangular volume is filled with B4Cpowder

- inaddition Eiger uses aSapphire filter for background reduction

Neutron Filter Data for MCNPX/McStas

Page27

Sapphire crystals

within shielding

- Dimension: 26 mm x 26 mm x 10 mm

- Orientation: c-plan

- Precision of orientation: 1 deg

Sapphire filter setup on BOA

A.Freund NIMA 213(1983)495-501

Samples from three different suppliers(Stettler – 4crystals;Korth– 4crystals;Kyburz – 4crystals)

Page28

Sapphire - Neutron Filter Measurements at BOA

fast neutron flux can be reduced by a factor of 12.5 (120 mm sapphire) – Peak Intensity

fast neutrons (1eV - 1 MeV)

cold neutron flux is reduced by 30 –60% (120 mm sapphire)

Comparison MCNPX simulations and Measurements

Resonances ?

Page29

Sapphire - Neutron Filter Measurements at BOA

• Quality of the crystal are comparable between suppliers

• Signal-to-noise can be chosen depending from the application

• Performance of the crystals is relative non-sensitive to the alignment (< 5% within 1 deg)

Application at TRICS/Zebra

Page30

-40 -20 0 20 40-80

-60

-40

-20

0

20

40

60

80after optimisation of TRICS beam path

x [mm]

y [m

m]

-40 -20 0 20 40-80

-60

-40

-20

0

20

40

60

80

x [mm]

y [m

m]

present state at TRICS right after monochromator

NEU

39 cm2

47.5 cm2

(120 cm2)

Monochromator

additional beam reduction

OLD

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0-5

0

5

10

15

20

25

30

35

40 sapphire 55 mm sapphire 57 mm sapphire 59 mm sapphire 61 mm

loss

es [p

erce

nt]

wavelength [Å]

intensity loss if Si-Filter (120mm) is replaced by a Sapphire Filter

improved beam reduction

new sapphire filter

Sapphire-Filter vs. Si-Filter

used neutrons

background

- fast neutron background reduced by a factor of 3

(only primary instrument)

- minimal intensity loss for the used thermal neutrons (1.2 & 2.4 Å)

TRICS to Zebra

Page31

Reference model (TRICS)

ZEBRA upgrade modelPoint of Interest

(entrance to secondary beam opening)

n-flux(n/s/cm2/mA)

n-DR(mSv/h/mA)

g-DR(mSv/h/mA)

2.4*105 4.2+/- 0.7 0.55+/- 0.1

A B Cn-flux

(n/s/cm2/mA)

n-DR(mSv/h/mA)

g-DR(mSv/h/mA)

1.25*105 1.39+/- 0.3 0.57+/- 0.2

Dose Rates (DR) are valid for 1500 μA – SINQ power

A – new Sapphire filter

B – new insert for the nitrogen-tank

C – new insert within Monochromator shieldingCollimator: B4C/borated PE/borated Steel

Comparison – Source Spectra

Page32

ESS – April 2016 (bunker report)

neutronspectruminsidecoldmoderator

Comparison SINQ / ESS – Nov. 2013

neutronspectruminfrontofthebeamports

Energy region

0.5 eV – 600 MeV

SINQ ratio: 8:1 (thermal to fast)

ESS ratio: 1:1 (thermal to fast)

ESS ratio: about 1:5 (thermal to fast)

MAGiC Beamline Layout

• polarizedsinglecrystaldiffractometer atbeamport W6

• Cold&thermalbeamextraction

• Ellipticguidesystemwithakinkat80m

Partners: LLB,FZ-Jülich and PSI

0.00E+00

2.00E+06

4.00E+06

6.00E+06

8.00E+06

1.00E+07

1.20E+07

1.40E+07

1.00E-01 1.00E+00 1.00E+01

-2.00E+07

0.00E+00

2.00E+07

4.00E+07

6.00E+07

8.00E+07

1.00E+08

1.20E+08

1.40E+08

1.60E+08

1.00E-09 1.00E-07 1.00E-05 1.00E-03 1.00E-01 1.00E+011.00E+03W6 – beam exit 30 mm x 38 mm

Energy (MeV)

Gamm

a dos

e rate

(muS

v/h)

Total: 27 Sv/h

Energy (MeV)

Neutr

on do

se ra

te (m

uSv/h

)

Total: 447 Sv/h

W6 – beam entrance 30 mm x 124 mm

Incomparison SINQ:around15Sv/h

Neutron and Prompt Gamma Dose Rate at 5.5 m

Neutron flux spectrum

Neutron flux: 8.4*E9 n/s/cm2

0.00E+00

5.00E+04

1.00E+05

1.50E+05

2.00E+05

2.50E+05

3.00E+05

1.00E-01 1.00E+00 1.00E+01

Page35

0.00E+00

2.00E+05

4.00E+05

6.00E+05

8.00E+05

1.00E+06

1.20E+06

1.40E+06

1.60E+06

1.00E-09 1.00E-07 1.00E-05 1.00E-03 1.00E-01 1.00E+01 1.00E+03

W6 – vacuum channel 10 cm x 10 cm (0.5 deg tilt)

Dose rates @ 24.5m

Energy (MeV)

Gamm

a dos

e rate

(muS

v/h)

Total: 0.79 Sv/h

Energy (MeV)

Neutr

on do

se ra

te (m

uSv/h

)Total: 13.8 Sv/h

New SDEF-card defined for guide shielding calculations

Neutron dose rate

Gamma dose rate

Neutron and Prompt Gamma Dose Rate at 24.5 m

High Energy Shutter

Page36

6 drums are positioned within the neutronbunker wall.

Drum Sequence:1. Borax (50% epoxy / 50% B4C)2. Standard steel3. Standard steel4. Borax5. Standard steel6. Tungsten/parafin (density 11.8 g/cm3)Effective thickness: each drum 20 cm

n-dose rate: 15.2 µSv/h

g-dose rate: 0.5 µSv/h (only prompt gammas from the drums)

N-Dose rate can be reduced more by replacing steel with tungsten drums.

Neutronic Background at Sample Position

Page37

F

Shielding around guidebehind 77m:

• 2m heavy concretewith vacuum tube belt

• 75m standard concrete(0.5 m thickness)

Neutron dose rates

E

1.00E-08

1.00E-07

1.00E-06

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

1.00E-091.00E-071.00E-051.00E-031.00E-011.00E+011.00E+03

Neutron background at 170 m

@80m ouside guide shielding

tally E: 1.3 µSv/h

@150m inside guide shielding

tally F: 0.2 µSv/h

Fast Neutron flux

4.2 n/s/cm2

T0 – Chopper thickness

TO - Chopper

Page39

Position: @ 6.25 m

Materials:

• Inconel 750

• Tungsten

Thickness:

2 x 15 cm

@ 1 MeV -> reduction factor >100 (Inconel)

@ 1 MeV -> reduction factor >500 (Tungsten)

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

1.00E+07

1.00E+08

1.00E+09

1.00E-08 1.00E-07 1.00E-06 1.00E-05 1.00E-04 1.00E-03 1.00E-02 1.00E-01 1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04

withoutT0

Inconel750

Tungsten

Energy (MeV)

Neutr

on do

se ra

te (m

uSv/h

)

Neutron dose rate

Prompt pulse

Page40

E2 – Estia beamport

• Reflectometer at beamport E

• Cold neutron beam line

• Elliptic guide system (Selene) – only 40 m long

41

Bunker Components – Detailed Simulations

Re-design of the MCNPX model (includes the geometry from CATIA)

42

Collimator Simulations

43

n - Dose Rates

Det.6

Det.7

Det.8

Det.6 – 40 muSv/h

Det.7 – 85 muSv/h !!

Det. 8 – 0.2 muSv/h

Shielding materials for ESTIA

New high-precision Shielding Material – Mineral Cast

Partner: RAMPF Machine Systems GmbH & Co. KG

Mineral cast is used as the base of high-precision machines EpumentEpustone

Epustone has the mechanical properties of granite – interesting for our ESTIA project

Epument has a high hydrogen content – (composition of quartz, basalt and epoxy)

First test series (14 compositions) on BOA@SINQ (activation, attenuation for diff. E) with BSS system

Optimisation: add a thermal neutron absorber (B4C) in the composition.

Comparison 1 – Standard mineral cast

1

10

100

1000

100 200 300 400 500 600 700 800 900

dos

erat

e [m

uSv/

h]

time [s]

mineralcastgranit

normal concrete

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0 20 40 60 80 100 120 140 160

neut

ron

[cou

nts]

material thickness [mm]

mineralcastgranit

heavy concrete

0

5x106

1x107

1.5x107

2x107

2.5x107

3x107

3.5x107

0 20 40 60 80 100 120 140 160

neut

ron

[cou

nts]

material thickness [mm]

mineralcastgranit

normal concrete

Thermal neutron transmission Fast neutron transmission

Activation decay (irradiation time 10 sec)

The tested Granite

includes Thorium!

Mineral cast is better as

standard concrete or granite

12 inch spherebare counter

Comparison 2 – Borated mineral cast – Composition 6

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Thermal neutron transmission Epithermal neutron transmission

Fast neutron transmission

Mineral cast has similar

properties as

heavy concrete !!!

Best samples are: without ash and a high B4C (5%) content -> sample 6 and 9Next Step: increasing hydrogen in sample 6 (was measured in July 2018)

Vacuum tests

03.12.1P Seite48

EPUMENT 130/3 – Gas Treatment

Only for high vacuum environmentmineral cast shows a delayed behaviour, but neutron guides require only 1E-3 mbar

without sample

Page49

Attenuation of Concrete

Neutron Dose rate

Standard concrete: without Boron

Heavy concrete: without Boron, density: 4.4 g/cm3 66 wt% Fe

SINQ Upgrade

Page50

Thank you for your attention.