Cross-section s of Neutron Threshold Reactions Studied by Activation Method

Cross-sections of Neutron Threshold Reactions Studied

by Activation Method

Nuclear Physics Institute, Academy of Sciences of Czech RepublicDepartment of Nuclear Reactors, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague

NEMEA-6, Krakow, 25.-28.10.2010NEMEA-6, Krakow, 25.-28.10.2010

J. Vrzalová, O. Svoboda, A. Krása, M. Majerle, A. Kugler, A. Laredo,

M. Suchopár, V. Wagner

2

Outline- Motivation

- Cross - section measurements

- Neutron sources

- Background subtraction

- NPI Řež

- TSL Uppsala

- Comparison NPI, TSL

- Conclusion

Motivation Cross-section measurements Neutron sources in NPI and TSL Background subtraction Experiments on Cyclotron in Řež TSL Uppsala experiments Comparison Conclusion

3

Motivation measurement of spatial distribution of neutrons

is important part of studies by means of set-ups based on spallation neutron source

the activation detectors are very useful tool for neutron field determination in this case

for neutron detection are used threshold reactions on Au, Al, Bi, In, Ta, Co, Y

almost no experimental cross-section data for most of observed threshold reactions are available for higher neutron energies (E>30MeV)→it is necessary to perform new cross-section measurements

- Motivation• Detection of neutrons• Evaluation• Corrections


- Neutron sources


- NPI Řež

- TSL Uppsala


- Conclusion

4

Detection of neutrons-Motivation• Detection of neutrons• Evaluation• Corrections


- Neutron sources


- NPI Řež

- TSL Uppsala


- Conclusion Al Au Bi Co In Ta

ReactionE thresh [MeV]

Half-life

197Au (n,2n) 196Au 8.1 6.183 d197Au (n,3n) 195Au 14.8 186.1 d197Au (n,4n) 194Au 23.2 38.02 h

209Bi (n,3n) 207Bi 14.42 31.56 y209Bi (n,4n) 206Bi 22.55 6.243 d

115In (n,2n) 114In 9.12 1.2 min

5

Evaluation - DEIMOS- Motivation• Detection of neutrons• Evaluation• Corrections


- Neutron sources


- NPI Řež

- TSL Uppsala


- Conclusion

6

Spectroscopic corrections



- Neutron sources


- NPI Řež

- TSL Uppsala


- Conclusion

Detector efficiency Self-absorption

Real γ-γ cascade coincidences decay during cooling

decay during irradiation

unstable irradiation

non-point like emitters

detector dead time

7

Evaluation - total yield- Motivation• Detection of neutrons• Evaluation• Corrections


- Neutron sources


- NPI Řež

- TSL Uppsala


- Conclusion

)()(

)(

11

1

)(

)( 0

irrreal tirr

t

t

foillive

real

areaP

aabspyield e

t

e

e

mt

t

CCoiEI

BECSN

Peak area Self-absorption correction

Beam correction

Dead time correction

Decay during cooling and measurement

γ line intensity

Detector efficiency

Correction for coincidences

Square-emitter correction

Weight

normalization

Decay during

irradiation

8

Cross-section measurements



- Neutron sources


- NPI Řež

- TSL Uppsala


- Conclusion

Requirements for -measurements by activation method:

high energy neutron source with good intensity

monoenergetic (quasi-monoenergetic) neutrons or well known spectrum

pure monoisotopic samples

good spectroscopic equipment – and X-rays detectors

Then we can calculate Nyield and finally :An

yield

NN

ASN

Evaluation process:

Irradiation→HPGe→Deimos→Yield →Corrections →Cross-section

Number of neutrons

in peak

foil size relative mass

Avogadro´s

number

9



- Neutron sources


- NPI Řež

- TSL Uppsala

- Comparison NPI, Uppsala

- Conclusion

Neutron sources

Neutron source on cyclotron U-120M

Blue Hall, UppsalaQuasi-monoenergetic neutron source

BeamBeam-line

Li-target

Graphite stopper

Samples

NPI ASCR Řež: Energy range 10 – 37 MeV, neutron intensity ~ 108 n.cm-2.s-1

TSL Uppsala: Energy range 20 – 180 MeV, neutron intensity ~ 105 n.cm-2. s-1

10



- Neutron sources


- NPI Řež

- TSL Uppsala

- Comparison NPI, Uppsala

- Conclusion

Neutron spectra from p/Li source in NPI

0.0E+00

2.0E+14

4.0E+14

6.0E+14

8.0E+14

1.0E+15

1.2E+15

4 9 14 19 24 29 34 39

Neutron energy [MeV]

Num

ber

of n

eutr

ons

(1/s

r M

eV C

)

E=25 MeV

E=20 MeV

E=32.5 MeV

E=37 MeV

uncertainty in spectrum determination - 10%

proton beams of energies 20, 25, 32.5, 37 MeV were used

11



- Neutron sources


- NPI Řež

- TSL Uppsala


- Conclusion

Background subraction

background contribution was determined by folding of the neutron source spectrum and calculated cross-sections (TALYS 1.0)

we calculated ratio between production in neutron peak and total production and with this ration we multiplied the yields to subtract background production

12

TALYS 1.0 – nuclear models



- Neutron sources


- NPI Řež

- TSL Uppsala


- Conclusion

Bi-207

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

1,8

2

15 20 25 30 35 40

E [MeV]

XS

[ba

rn]

ld1 ld2 ld3 ld4 ld5 EXFOR MENDL-2

ld1 - Fermi model

ld2 – backshifted Fermi model

ld3 - superfluid model

ld4 - Goriely table

ld5 - Hilairey table

models with different nuclear level density change the shape of cross-section dependency on neutron energy

13

TALYS 1.0 – nuclear models- Motivation• Detection of neutrons• Evaluation• Corrections


- Neutron sources


- NPI Řež

- TSL Uppsala


- Conclusion

Difference between cross-sections models with different nuclear level density and default Fermi model, reaction 209Bi(n,3n)207Bi

Bi-207

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

15 20 25 30 35

Energy [MeV]

Dev

iatio

n [-]

Fermi model

backshifted Fermi model

superfluid model

Goriely table

Hilairey table

it is necessary to analyze influence of this faktor on determination of radioactive nuclei number in the future

14



- Neutron sources


- NPI Řež

- TSL Uppsala


- Conclusion

Uncertainty analysis HPGe detector calibration uncertainty: less than 3%

Gauss-fit of the gamma peaks: > 1% (usually less than 10%)

spectroscopic corrections uncertainty: less than 1%

neutron spectra determination: 10%

neutron beam intensity determination: 5% at NPI, 10% at TSL

uncertainty of background subtraction - will be analyzed in the future

15



- Neutron sources


- NPI Řež

- TSL Uppsala


- Conclusion

Experiments in NPI four measurements in

years 2008-2009

proton beam energies 20, 25 MeV (August 2008), 32.5 (April 2009) and 37 MeV (Mai 2009)

irradiation time about 20 h.,irradiated foils: Ni, Zn, Bi, Cu, In, Al, Au, Ta, Fe and I

the sample distances from the lithium target – 11 to 16 cm

16



- Neutron sources


- NPI Řež

- TSL Uppsala


- Conclusion

Experiments in TSL proton beam energies 25, 50, 100 MeV (June 2008); 62, 70, 80, and 93 MeV (February 2010)

irradiation time about 8 h.,irradiated foils: Au, Bi, In, Al, Ta, Co, Y and I

17



- Neutron sources


- NPI Řež

- TSL Uppsala


- Conclusion

NPI and TSL results

197Au(n,2n)196Au

0

0.5

1

1.5

2

2.5

3

0 10 20 30 40 50 60 70 80 90

Energy [MeV]

Cro

ss-s

ectio

n [b

arn]

EXFOR

TALYS

NPI Řež

TSL Uppsala

PRELIMINARY

Comparison of cross-section reaction (n,2n) 197Au with EXFOR and TALYS

18



- Neutron sources


- NPI Řež

- TSL Uppsala


- Conclusion

NPI and TSL results

197Au(n,4n)194Au

0

0.3

0.6

0.9

1.2

1.5

20 30 40 50 60 70 80 90

Energy [MeV]

Cro

ss-s

ectio

n [b

arn]

EXFOR

TALYS

NPI Řež

TSL Uppsala

PRELIMINARY


19



- Neutron sources


- NPI Řež

- TSL Uppsala


- Conclusion

NPI and TSL results

197Au(n,6n)192Au

0

0.2

0.4

0.6

0.8

40 50 60 70 80 90

Energy [MeV]

Cro

ss-s

ectio

n [b

arn]

TALYS

TSL Uppsala

PRELIMINARY


20



- Neutron sources


- NPI Řež

- TSL Uppsala


- Conclusion

NPI and TSL results

209Bi(n,4n)206Bi

0

0.3

0.6

0.9

1.2

1.5

1.8

20 30 40 50 60 70 80 90 100

Energy [MeV]

Cro

ss-s

ectio

n [b

arn]

EXFOR

TALYS

NPI Řež

TSL Uppsala

PRELIMINARY

Comparison of cross-section reaction (n,4n) 206Bi with EXFOR and TALYS

21



- Neutron sources


- NPI Řež

- TSL Uppsala


- Conclusion

Conclusion eleven cross-section measurements were performed in years 2008-2010

energy region from 17 MeV to 94 MeV was covered

good agreement between our data and other experimental data and code TALYS was observed in many cases

previous measurements in NPI and TSL are now completely processed and were published at scientific workshop EFNUDAT – Slow and Resonance neutrons in 2009 in Budapest and at International Conference on Nuclear Data for Science and Technology in April 2010 in South Korea

only preliminary cross-section data from the last measurement are presented

by the means of this new measurement we covered energy range 59-89 MeV, where no data were available so far

Thanks for attention

Documents

Cross-section s of Neutron Threshold Reactions Studied by Activation Method