Institute of Radiation Physics Dr. Evert Birgersson Member of the Leibniz Association The nELBE...

Institute of Radiation Physics Dr. Evert Birgersson www.fzd.de Member of the Leibniz Association

The nELBE neutron source

Dr. Evert Birgersson, Institute of Radiation Physics, FWKK

Institute of Radiation Physics Dr Evert Birgersson www.fzd.de Svenskt Kärnfysikmöte XXIX, 17-18 november 2009, Örebro universitet, Örebro

Overview

• Introduction• nELBE – neutron facility at ELBE• Total cross section measurements • Inelastic scattering cross section measurements • Summary


nELBE – neutron facility at ELBE(Electron Linear accelerator with high Brilliance and low Emittance)


Liquid lead loop

Collimator

Ø = 2 cm Ø = 3 cm

electronsLead flow

• Small liquid lead volume (1 cm3) and short electron pulse (10 ps) gives a neutron energy resolution of E/E 1 % when ToF is used to determine neutron energies

• Stable operation for more than 800 hours

• The ELBE electron beam hits liquid lead and creates neutrons from the bremsstrahlung by (,n) reactions

• Ee- = 30 - 40 MeV, Bunch charge 77 pC, repetition rate 100 or 200 kHz


Absorbers or transmission targets

0 3 6 9

0.01

0.1

1

neutrons gamma

Rel

ativ

e in

ten

sity

red

uct

ion

I/I

0

lead absorber length (cm)

Absorption is higher for gammas than neutrons

1E-5 1E-4 1E-3 0.01 0.1 1 101E-14

1E-13

1E-12

1E-11

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

neutrons gammas

(c

m-2 e

lect

ron

-1)

Energy (MeV)


PTB ionization chamber

• Parallel plate ionisation chamber• well-characterized U layers• 201.6 mg 235U• 10 layers • Diameter 7.2 cm


Neutron energy spectra• The ToF spectrum in the Fission chamber is converted to energy and by

using the 235U fission cross section and target material the flux is determined, 3.8•104 n/cm2s at 19 A at 5.55 m from the lead radiator.

• A factor of two neutron yield is still missing, compared to MCNP simulations and cathode current measurement

– was 60 in August 2008– Was 6 in December 2008

• Improved beam tuning, alignment of beam line

0.01 0.1 1 10

10

100

1000

10000

neutrons through fission chamber

MCNP (1/2.1) Experiment

ne

utr

on

s (

n/s

)

En (MeV)

0 5 10

50000

100000

150000

neutrons through fission chamber

MCNP (1/2.1) Experiment

ne

utr

on

s (

n/s

/ Me

V)

En (MeV)


Beam profile scanVertical scan

Main neutron and gamma beam well described

Experiment show more neutrons and gammas in the halo

Scans can be performed vertically and horizontally with a movable plastic scintillator

-40 -20 0 20 40

1E-3

0.01

0.1

1

Experiment MCNP

Yie

ld (

arb

. u

nit

)distance from centre (cm)


12 n

12 Shutter

open

Shutter closed

Gammas through the door

n

Concrete wallLead


Less radiation adjacent room

• The extra shielding is necessary

12

200 220 240 260 280 300 320 340 360 380 400100

101

102

103

104

105

106

Yie

ld (

cts)

ToF (Ch)

No extra wallWith extra wall


Transmission measurement

•

• ch->ToF->En

•

• Only one event per accelerator bunch can be used due to after pulsing in the photomultiplier, large gamma flash reduces the efficiency

•

• Tlive_daq is the time the dataacquisition is readyfacc is the accelerator repetition rate

)(

)(ln)(

0

1

EI

EI

N

xME

a

1

0__

1)()(

i

j accjdaqliveichlive f

chNTchT

)(/)()( _ chTchCchI chlive

Every Channel has its own live time


nELBE – inelastic scattering detector Setup

4 plastic scintillatorsfor neutron detection(1 m, 11 x 43 mm2)Beyer et al., NIMA 575 (2007) 449

neutron beam

BaF2 array for gamma detection(42 crystalls, 29 cm, Ø 5.3 cm

sample: natFe (99.8%) 91.754% 56Femass: 19.82 g 18.15 g 56Fe

flight paths:source – sample:600 cmsample – BaF2:30 cmsample – Plastics:100 cm

235U fission chamberfor neutron flux determination

VME-based electronics setup All detectors have time resolutions of about 600 ps


Experimental method

Fe)n'Fe(n, 5656 n'FenFe *5656 γFeFe 56*56

Integral at target: 2x104 n/s/cm2

En,out = En,in - Ex


Tof and energy from 2 MeV neutrons

• 2 MeV mono energetic neutrons were simulated to understand additional background. Flux determined 1m from the side of the beam.

• Gamma-neutron coincidence not possible in MCNP

0.0 0.5 1.0 1.5 2.0300

350

400

450

500

En (MeV)

To

F (

ns

)

2.0E-17

1.3E-16

8.9E-16

5.9E-15

3.9E-14With Iron target

0.0 0.5 1.0 1.5 2.0300

350

400

450

500

En (MeV)

To

F (

ns

)2.0E-17

1.3E-16

8.9E-16

5.9E-15

3.9E-14

No Iron target

Elastic scattering in the collimator

Elastic scattering on Fe

Inelastic scattering on Fe


Preliminary Result, neutron Inelastic scattering on iron


Conclusions

• The nELBE neutron ToF facility has been operational since November 2007

• Background conditions are continously improving• Operation of the liquid lead loop is extremely stable• Transmutation relevant cross section are measured

• From 2010: Superconducting RF-injector (bunch charge 2nC (77pC) 1mA at 500 kHz, which is the design criterion for the lead loop

• New larger measurement room planed in conection to the extention ELBE

Outlook


Thanks to all CollaboratorsFZD, Institute of Radiation Physics:

A.R. Junghans, D. Bemmerer, R. Beyer, The ELBE Crew, M. Erhard, E. Grosse, R. Hannaske, A. Hartmann, K. Heidel, M. Kempe, K. Kossev, U. Lehnert, M. Marta, R. Massarczyk, A. Matic, P. Michel, C. Nair, K.-D. Schilling, R. Schurig, R. Schwengner, M. Sobiella, A. Wagner

FZD, Institute of Safety Research:

E. Altstadt, C. Beckert, V. Galindo, K. Noack, F.-P. Weiss

FZD, Department Radiation Protection and Safety:

B. Naumann

FZD, Department Research Technology:

R. Schlenk, S. Schneider

TU Dresden:

H. Freiesleben, M. Greschner, A. Klix, K. Seidel

Physikalisch Technische Bundesanstalt Braunschweig:

M. Mosconi, R. Nolte, S. Röttger

Others:

J. Klug, C. Rouki, G. Rusev

Institute of Radiation Physics Dr. Evert Birgersson Member of the Leibniz Association The nELBE...

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