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1Mechanical, Aerospace and Nuclear Engineering The Gaerttner LINAC Center

Experimental Fission Research at the GaerttnerLINAC Center at Rensselaer Polytechnic Institute

LANL FIESTA Fission Workshop, Sep. 10 - 12, 2014

Y. Danon, Z. Blain

Gaerttner LINAC Center, Rensselaer Polytechnic Institute, Troy, NY 12180


Collaboration (fission related)• RPI

– PI: Y. Danon, Professor, Director Gaerttner LINAC Center, Nuclear Engineering Program Director

– Graduate Students: Z. Blain, N. Thompson, D. Williams, A. Daskalakis, B. McDermott, A. Youmans

– Undergraduate students: K. Mohindroo, Amanda Lewis

• KAPL

– Dr. T. Donovan, Dr. G. Leinweber, Dr. D. Barry, Dr. M. Rapp, Dr. R. Block, B. Epping

• LANL (fission / LSDS)– Dr. R. Haight, Dr. P. Talou

• ORNL (sample for LSDS measurements)– Dr. Romano

The authors thank the Stewardship Science Academic Alliance for their funding of this research, grant

numbers: DE-NAOOO1814, DE-FG03-03NA00079, DE-FG52-06NA26202, DE-FG52-09NA29453


The Nuclear Data Program at the Gaerttner LINAC Center at RPI

• Driven by a 60 MeV pulsed electron LINAC ~ 1013 n/s

• Neutron transmission

– Resonance region: 0.001 eV- 1000 keV,

– High energy region: 0.4- 20 MeV

• Neutron Capture

– Resonance region: 0.01-1000 eV

• Neutron Scattering

– High energy region: 0.4 MeV- 20 MeV

• LSDS

– Assay of used nuclear fuel

• Prompt Fission neutron spectrum

• LSDS

– Fission cross section and fission fragment spectroscopy.

– (n,a), (n,p) and (n,g) cross sections on small (radioactive) samples.

• Support from various DOE offices

• Started a major refurbishment project ( ~$10M)


Focus on• Historical Perspective

• Lead Slowing Down Spectrometer (LSDS)– Simultaneous measurements of fission cross section and fission

fragment mass and energy distributions of small samples.

• Time-of-Flight and gamma tagging– Measurements of fission neutron spectra ( also < 1 MeV) as a

function of the incident neutron energy using a gamma tag.

– Fission cross section using a gamma tag.


Early Fission Related Work at RPICross Section Measurements and PFN multiplicity

• 232Th– Nakagome, Y., Block, R.C., Slovacek, R.E. and Bean, E.B., “Neutron-Induced Fission Cross Section of 232Th from 1 eV to 20 keV,”

Physical Review C, Vol. 43, No. 4, April, 1991.

• 233U– Weston, L.W., Gwin, R., de Saussure, G., Ingle, R.W., Todd, J.H., Craven, C.W., Hockenbury, R.W. and Block, R.C., “Neutron Fission and

Capture Cross-section Measurements for Uranium-233 in the Energy Region 0.02 to 1 eV,” Nuclear Science and Engineering, 42, 143-149, 1970.

• 235U– Kaushal, N.N., Malaviay, B.K., Becker, M., Burns, E.T. and Gaerttner, E.R., “Measurement and Analysis of Fast Neutron Spectra in

Uranium Depleted in the Uranium-235 Isotope,” Nuclear Science and Engineering, Vol. 49, n 3, p. 330-48, November, 1972.

• 238U– Slovacek, R.E., Cramer, D.S., Bean, E.B., Valentine, J.R., Hockenbury, R.W. and Block, R.C., “238U(n,f) Measurements Below 10 keV,”

Nuclear Science and Engineering, 62, 455-462, 1977.

• 239,240,241Pu– Weinstein, S. and Block, R.C., “Neutron Multiplicity-Spin State Correlations for 239Pu Resonances,” Physical Review Letters, Vol. 22,

No. 5, 195-198, February, 1969.– Gwin, R., Weston, L.W., Saussure de, G., Ingle, R.W., Todd, J.H., Gillespie, F.E., Hockenbury, R.W. and Block, R.C., “Simultaneous

Measurement of the Neutron Fission and Absorption Cross Sections of Plutonium-239 Over the Energy Region 0.02 eV to 30 keV,”Nuclear Science and Engineering, 45, 25-36, 1971.

– Hockenbury, R.W., Moyer, W.R. and Block, R.C., “Neutron Capture, Fission, and Total Cross Sections of Plutonium-240 from 20 eV to30 keV,” Nuclear Science and Engineering, 49, 153-161, 1972.

– M. S. Moore, O. D. Simpson, and T. Watanabe, J. E. Russell and R. W. Hockenbury, Fission Cross Section of Pu-241, Phys. Rev. 135,B945–B952 (1964).

• 244,246,247,248Cm, 254Es– Maguire, Jr., H.T., Stopa, C.R.S., Block, R.C., Harris, D.R., Slovacek, R.E., Dabbs, J.W.T., Dougan, R.J., Hoff, R.W. and Lougheed, R.W.,

“Neutron-Induced Fission Cross-Section Measurements of 244Cm, 246Cm and 248Cm,” Nuclear Science and Engineering, 89, 293-304,1985.

– Danon, Y., Slovacek, R.E., Block, R.C., Lougheed, R.W., Hoff, R.W. Moore, M.S., “Fission Cross-Section Measurements of 247Cm, 254Esand 250Cf from 0.1 eV to 80 keV,” Nuclear Science and Engineering, 109, 341-349, 1991.


RPI Old Gd Loaded Scintillator -1969• S. Weinstein, R. Reed, R.C. Block ,Neutron Multiplicity Measurements for 233U, 235U and 239Pu

Resonance Fission, Second IAEA Symposium on Physics and Chemistry of fission,IAEA-SM-122/113, 1969.

• Measured neutron multiplicity in a short slowing down time window following a fission event.

Multi plate fission chamber

Gd loaded Scintillator tank


Results - 1969

• Observed fluctuations in 239Pu neutron multiplicity were used to infer resonance spin states.

Weinstein, S. and Block, R.C., “Neutron Multiplicity-Spin State

Correlations for 239Pu Resonances,” Physical Review Letters, Vol. 22,

No. 5, 195-198, February, 1969.


Lead Slowing Down Spectrometers in the US

LANL – Proton Driven RPI –Electron Driven

Dr. Jason ThompsonGraduated

Dr. Catherine RomanoGraduated

Ezekiel Blain

LINAC Staff


VacuumTi Window

ElectronBeam

Air Filled Drift Section

Neutron Source

Air cooled Ta Target

LEAD

Crossed I beam + Li2CO3

180 cm

18

0 c

m

Detector

Flux Monitor

Flux Monitor

Flux Monitor

•Tantalum target in the center produces neutrons.

•Neutrons scatter elastically with the Pb.

•Neutrons can pass through the same position several times.

•About 103-104 times higher flux than an equivalent neutron TOF experiment.

(60 cm from corner)

Why Use a Lead Slowing-down Spectrometer Showing - Lead Slowing-down Spectrometer at RPI

67 tons of Pb


Slowing -Down-Time vs. Energy RelationLANL LSDS

1E-7 1E-6 1E-5 1E-4 1E-3 0.01 0.1 1

0.0

0.2

0.4

0.6

0.8

1.0

1.2

MCNPX Calculation

E

/Em

ea

n

Energy (MeV)

E

E

E

20tt

KE

10-1

100

101

102

103

104

105

103

104

105

106

107

108

Ne

utr

on F

lux [

#/c

m2/s

ec/e

V]

Neutron Energy [eV]

RPI LSDS I=15 uA, P=825 W

LANL LSDS I=1 uA, P=800 W

For En>50 KeV

detector recovery of <1 ms

is required


MCNPX Calculations LANL LSDS 1 proton

-60 -40 -20 0 20 40 60

-60

-40

-20

0

20

40

60

-60 -40 -20 0 20 40 60

-60

-40

-20

0

20

40

60

Y A

xis

(cm

)

X Axis (cm)

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

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-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

Y A

xis

(cm

)

X Axis (cm)

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

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-60

-50

-40

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-10

0

10

20

30

40

50

60

Y A

xis

(cm

)

X Axis (cm)

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

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-60

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-40

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-10

0

10

20

30

40

50

60

Y A

xis

(cm

)

X Axis (cm)

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

Y A

xis

(cm

)

X Axis (cm)

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

Y A

xis

(cm

)

X Axis (cm)

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

Y A

xis

(cm

)

X Axis (cm)

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

Y A

xis

(cm

)

X Axis (cm)

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

Y A

xis

(cm

)

X Axis (cm)


LSDS Applications• Assay of use nuclear fuel

– The slowing down spectrum induces fission in the fissile material such as 235U and 239Pu

– To first order the reaction rate as a function of time is a linear combination of the of U and Pu content.

– Use threshold fission detector with 238U (indicated some problems in the sub threshold fission of 238U).

• Fission cross section measurements

• Fission fragment spectroscopy

• (n,a) and (n,p) cross section measurements

• Capture cross section measurements

The LSDS is a high flux environment which requires

appropriate detector development


LSDS - Fission cross section measurement example

254Es

247Cm

Hemispherical fission ion chamber

reduces alpha particle pileup

Danon, Y., Slovacek, R.E., Block, R.C., Lougheed, R.W., Hoff, R.W.

Moore, M.S., “Fission Cross-Section Measurements of 247Cm, 254Es and 250Cf from 0.1 eV to 80 keV,” Nuclear Science and Engineering, 109,

341-349, 1991.


Simultaneous Measurements of Fission Cross Section and Fission Fragment Mass and Energy Distributions of

Small Samples• Use a double gridded fission chamber with the

RPI LSDS• Use kinematics to compute

– Fragment angle relative to the normal to the sample– Fragment energy distribution– Fragment mass distribution

• Future improvements– Improve by converting to digital electronics (next

slide)• Enables more flexibility in the data analysis

• Advantages – Low mass samples <40mg)– High data throughput (<8h for above mass)

Anode

Grid

Guard Ring

Guard Ring

Cathode

Grid

Anode

d=0.8mm r =0.05 mmH=35 mm

h=6mm

+ ++

+

+

+

++

C. Romano, Y. Danon, R. Block, J. Thompson, E. Blain, E. Bond, “Fission Fragment Mass And Energy Distributions As A Function of Neutron Energy Measured In A Lead Slowing Down Spectrometer”, Phys. Rev. C, 81, 014607 (2010).


Electronics and DAQ• VME based system with preamplifiers near the LSDS


Thin Samples

Sample Frame• 2500 A thick polyimide• 1.5 cm aperture• Made by Luxel Corporation

Actinide Sample is made by dissolving actinide in acid and dropping measured amounts on the film

• 25 mg 235U sample made at LANL• 0.41 ng 252Cf made at RPI

34 mg sample of 239Pu made at INL


Fragment Mass and EnergyIterative procedure to find the preneutron and postneutron mass and energy

( )i i iT T Tm m m

i

i i

i

T

T T

T

mE E

m

F.J. Hambsch, H.H. Knitter and C. Budtz-Jorgensen, Fission Mode Fluctuations

in the Resonances of 235U(n,f), Nuclear Physics A491 (1989) 56-90

**

*

i

i

i i

i i

i i

B

T

T B

T B

B T

Em A

m mE E

m m

Initial guess:

* * / 2i iT Bm m A

( )i i iT T TE E PHD m

1 1

* * 0.25 0.25i i i iT T B Bif m m and m m then done

( )i i iB B Bm m m

( )i i iB B BE E PHD m

**

*

i

i

i i

i i

i i

T

B

B T

B T

T B

Em A

m mE E

m m

i

i i

i

B

B B

B

mE E

m


252Cf Contour Plot of TKE vs Fragment Mass


Results – Fission Fragment Mass distribution En<0.1 eV235U 239Pu

80 100 120 140 160 1800.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09252

Cf Preneutron Emission Mass

Yie

ld

Mass [amu]

Hambsch

Current Data

252Cf

60 80 100 120 140 160 1800.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

235U Preneutron Emission Fission Fragment Mass

Yie

ld

Mass [amu]

Hambsch Data

Current Data

60 80 100 120 140 160 1800.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09239

Pu Preneutron Emission Masses

Yie

ld

Mass [amu]

Current Data

Hambsch Data

60 80 100 120 140 160 1800.00

0.02

0.04

0.06

0.08

0.10239

Pu Post Neutron Emission

Yie

ldMass (amu)

Current Data

ENDF/B-VII.0

60 80 100 120 140 160 1800.00

0.02

0.04

0.06

0.08

0.10235

U Postneutron Emission

Yie

ld

Mass (amu)

Current Data

ENDF/B-VII.0

60 80 100 120 140 160 1800.00

0.02

0.04

0.06

0.08

0.10252

Cf Postneutron Emission

Yie

ld

Mass (amu)

Current Data

ENDF/B-VII.0


Results – Fission Fragment Energy DistributionEn<0.1 eV

40 60 80 100 120 40 60 80 100 12040 60 80 100 1200.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

Yie

ld

Energy [MeV]

252Cf, RPI-2008

235

U, RPI-2008

239

Pu, RPI-2008

Hambsch Data


0 1 2 3 4 5 6 7 8 9 10 11-0.5

0.0

0.5

1.0

1.5

2.0

2.5

(V/P

) reso

na

nce/(

V/P

) the

rma

l

Resonance Number

Current Data

Hambsch Data

Faler Data or Nasuhoglu

Fission symmetry in resonance clusters

10-1

100

101

102

103

104

100

101

102

103

Current Data

ENDF/B-VII.0

thermal 1

<0.1 eV

res9res8

res7

res6

res5

res4

res3

res2

high res

f [

ba

rn]

Energy [eV]

thermal

resonance

ratio

PV

PV

PV

K. T. Faler, R. L. Tromp, Phys. Rev. 131, 1746-1748(1963).

R. Nasuhoglu, et al., Phys. Rev. 108, 1522 (1957).


Fitting the fission modesSeveral possibilities can be considered for example:

60 80 100 120 140 160 1801E-4

1E-3

0.01

0.1

235U E<0.1 eV

Yie

ld (

1/a

mu

)

Mass (amu)

60 80 100 120 140 160 1801E-4

1E-3

0.01

0.1

Yie

ld (

1/a

mu

)

235U Resonance Region 9

Mass (amu)

60 80 100 120 140 160 1801E-4

1E-3

0.01

0.1

235U E<0.1 eV

Yie

ld (

1/a

mu

)

Mass (amu)

60 80 100 120 140 160 1801E-4

1E-3

0.01

0.1

Yie

ld (

1/a

mu

)

235U Resonance Region 9

Mass (amu)

S1

S2

SL


Variations In TKE As A Function of Incident Neutron Energy 235U

0 2 4 6 8 100.9

1.0

1.1

1.2

1.3

(W1

/W2

) reso

na

nce/(

W1

/W2

) the

rma

l

Resonance Group Number

Current Data

Hambsch Data

0 2 4 6 8 10-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

1.00

1.04

1.08

1.12

1.16

1.20

Change in TKE

TK

Ere

so

na

nce -

TK

Eth

erm

al

(Me

V)

Resonance Group Number

(W1

/W2

) reso

na

nce/(

W1

/W2

) the

rma

l

Fission Mode Ratios

0 2 4 6 8 10-0.2

0.0

0.2

0.4

0.6

0.8

TK

Ere

so

na

nce -

TK

Eth

erm

al

(Me

V)

Resonance Number

W1,2 weight of S1,2 respectively


239Pu - Results

E<0.1 eV (region 1)

80 100 120 140 160150

160

170

180

190

200

210

Mass [amu]

TK

E [

MeV

]

0.00

0.02

0.04

0.06

0.00

0.02

0.04

0.06

0.00

0.02

0.04

0.06

60 80 100 120 140 160

0.00

0.02

0.04

0.06

60 80 100 120 140 160

0.00

0.02

0.04

0.06

Region 2

Region 3

Region 4

Yie

ld (

1/a

mu

)

Region 5

Region 6

Yie

ld (

1/a

mu

)

Region 7

Mass (amu)

Yie

ld (

1/a

mu

)

Mass (amu)

Region 9

Region 10

high energy

Yie

ld (

1/a

mu

)

Yie

ld (

1/a

mu

)

Region 1

Thermal

Region 8

10-1

100

101

102

103

100

101

102

103

104

1

10

987

5

64

3

f [

barn

]

Neutron Energy [eV]

2


235U Fission Cross Section Measured at the Same experiment


Results – Measured Fission Cross Section

10-1

100

101

102

103

104

105

100

101

102

103

100

101

102

103

239Pu

This Experiment

Broadened ENDF-7.0

f [

ba

rn]

Energy [eV]

235U

This Experiment

RPI 1993

f [

ba

rn]


Fission and Capure Cross Section Measurement Using a Gamma Tag

16 optically isolated segments NaI(Tl)

Located at 25 m flight station

1.0 cm thick B4C liner enriched in 10B (captures scattered neutrons)

Each event categorized by TOF channel, multiplicity, & total γ energy group (up to four groups)

27


Samples

235U: Multiple ½” discs 93% enriched in 235U

Additional samples: Depleted U & Au (~ 30mil each)Empty sample holder: background subtraction

28


Measurements of 235U Capture & Fission Yields

• Thermal measurement with enriched 235U sample• 16 Segment Multiplicity Detector with 4 Eγ groups

• Good agreement with SAMMY calculations• Extracting Capture Yield from data with mixture of capture

and fission events

• Challenges: Normalization Normalize experimental fission yield to thermal point

Use two equations for a predominantly capture resonance and predominantly fission region (thermal)

Solve the two equations for k2 and k3

Multiplicity ~ 1-8 Multiplicity ~ 3-11

0.0

0.1

0.2

0.3

0.4

0.5

5 10 15 20 25 300.0

0.1

0.2

0.3

0.4

0.5

Yie

ldg

Capture

Experiment

SAMMY ENDF/B 7.0

Normalization

Yie

ldf

Energy [eV]

Fission

Experiment

SAMMY ENDF/B 7.0

1E-3

0.01

0.1

1

0.01 0.1 11E-3

0.01

0.1

1

Yie

ldg

Capture

Experiment

SAMMY ENDF/B 7.0

Normalization

Yie

ldf

Energy [eV]

Fission

Experiment

SAMMY ENDF/B 7.0

f

ENDF

f YkY 1 Solve for k1 @ 0.0253 eV

86.0

g

f

ENDF YkkYkY 222 132 ggf

ENDF YkkYkY 111 132 gg

@ 0.0253 eV@ 11.7 eV res


235U Capture & Fission Yield Data - Epithermal Measurement

• Challenges:• Normalization• False capture due to neutron scattering

Normalize experimental fission yield to resonance

Use two equations for predominantly capture and fission resonances

Solve the two equations for k2 and k3

► Need 2 resonances with known parameters ◄

f

ENDF

f YkY 1

86.0

g

f


63.0

f

f


0.00

0.05

0.10

0.15

0.20

0.25

0.30

10 15 20 25 30 35 40 45 500.00

0.05

0.10

0.15

0.20

0.25

0.30

Yie

ldg

RPI Capture

Sammy CaptureNormalization

Yie

ldf

Neutron Energy [eV]

RPI Fission

Sammy Fission

600 700 800 900 10000.00

0.01

0.02

0.03

0.00

0.01

0.02

0.03

Yie

ldf

Neutron Energy [eV]

RPI Fission

Sammy Fission

Yie

ldg

RPI Capture

Sammy Capture

Solve for k1 @ 19.3 eV res

@ 19.3 eV res@ 11.7 eV res

63.0

f

Provides data to address WPEC subgroup 29 report“Uranium-235 Capture Cross-section in the keV to MeV Energy Region”


500 1000 1500 2000 25000.005

0.010

0.015

0.020

0.025

0.030

Yg

Energy [eV]

RPI - Experiment

JENDL4+MS

SAMMY ENDF7 Capture

END of RRR

in ENDF/B7.0

Comparing 235U Fission and Capture with Evaluations

• Fission is in excellent

agreement with

evaluations

• Capture data has up to 8%

multiple scattering that

must be taken into

account during the

analysis

• Capture yield uncertainty

is about 8%

• 0.4-1 keV capture data

is closer to ENDF/B-7.0

• 1-2 keV ENDF/B7.0 too

high JENDL 4.0 too low.

• E>1 keV data is slightly

higher than evaluations

but within uncertainties.


ORNL SAMMY fit to 235U to RPI fission and Capture Yields


235U (n,g) Low Energy Region

From ORNL 2013 CSEWG presentation


235U (n,g) High Energy Region

From ORNL 2013 CSEWG presentation


Prompt Fission Neutron Spectra


Motivation/Fission Spectra

• Eemission<0.5 MeV and Eemission> 6 MeV– Very little or no

experimental data

– High uncertainty in current models

P. Talou, B. Becker, T. Kawano, M.

B. Chadwick, and Y. Danon,

"Advanced Monte Carlo modeling

of prompt fission neutrons for

thermal and fast neutron-induced

fission reactions on 239Pu", Phys.

Rev. C 83, 064612 (2011).

239Pu, En=Thermal


Fission Spectrum Measurement• Use the double TOF method

• Use a gamma tag for fission (instead of traditional fission chamber)

• Use a combination of Liquid Scintillators and Li-Glass neutron detectors

Electron LINAC

Pulsed neutron source

"2״

Neutron Beam

EJ-301

EJ-301

EJ-301 EJ-301

EJ-301

EJ-

301

Gamma Detectors

Neutron Detectors

Fissile

Material

Sample

energyneutronfission incident,

distanceflightpath

3.72

21

21

2/1

2

2

1

1

,EE

L

m

eVsk

E

kL

E

kLToF

,

m


Gamma Tagging• Advantages

– Eliminated the need to construct a complicated multiplatefission chamber

– Simpler sample preparation

– Can use relatively large samples

– Can increase the detected fission rate

• Disadvantages– False fission detection due to:

• Random coincidence for radioactive decay

• Neutron interactions with the gamma detection

• Beam related:– Gamma capture (no neutron emission)

– Inelastic Scattering (single gamma emitted)

– Increased background (the biggest problem, use simulations to characterize)

Fast neutrons scattering detector array


Experimental Setup

Sample

Position

EJ-301

Detectors

Gamma

Detectors

EJ-204

Detector ＊

E1

L1=30 m

E2

L2=0.5m

4 Gamma Detectors

(top view)

Neutron Detectors

Sample

• Neutron Detectors– EJ-204 Plastic Scintillator

• 0.5” x 5”• 47 cm away from center of sample

– 2 EJ-301 Liquid Scintillators • 3” x 5”• 50 cm away from center of sample

• Gamma Detectors– 4 BaF2 detectors on loan from ORNL– Hexagonal detectors 2” x 5”– 10 cm from center of sample– ¼” lead shield between detectors

• Reducing scattering between detectors

energyneutronfission E

energyneutron incident E

distanceflightpath

3.72

2

1

2,1

2/1

2

2

1

1

L

m

eVsk

E

kL

E

kLToF

m


Gamma Tagging - EJ-204• Gamma tagging method corrected for 30% detection efficiency compared

to 83% detection efficiency with fission chamber

30 100 200 300 35010

2

103

104

105

50 keVBackground

Prompt Neutron Peak

Prompt Gamma Peaks

Co

un

ts

Time-of-Flight [ns]

Gamma tagging method

Fission chamber


Results

Will be shown in Zeke Blain’s talk


Summary• Simultaneous Measurements of Fission Cross Section and Fission

Fragment Mass and Energy Distributions of Small Samples.– Demonstrated the feasibility of this method– Works with small mass sample ~20-40 ug.– Data collection with small sample is very quick (<10 hours)– Fission cross section can also be measured at the same time– Data was obtained for 252Cf, 235U and 239Pu and compares well to other

measurements– Room for improvement in the DAQ system

• Fission and capture measurements from prompt fission gamma– Eliminates the fission detector in the conventional approach– Utilize gamma multiplicity and total energy– Demonstrated on 235Ufrom thermal to 2.5 keV

• Fission spectra– Demonstrated and characterized the concept of gamma tagging with a 252Cf sample.– Studied the effect of a discriminator on measurements with a fission chamber

(applicable to detector calibration with 252Cf).– Performed PFNS measurement 238U


Thank You

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