Experimental Determination of Neutron Cross Sections of Yttrium by Activation Methodby Barbara Geier

Supervisors: Assoc. Prof Dr. Wolfgang Sprengel RNDr. Vladimír Wagner Csc. Ing. Ondřej Svoboda

Internship at the Nuclear Spectroscopy Department of Nuclear Physics

InternshipOrganized by IAESTE Graz6 weeksDepartement of Nuclear

Spectroscopy in Řež

Summary1. Irradiation of the yttrium foil by neutrons

to produce radioactive isotopes2. Analysing of the gamma emission of the

daughter nuclei by a germanium semiconductor detector

3. Determination of the area of a gamma peak with the program DEIMOS32

4. Determination of the number of produced nuclei Nyield out of the peak area

5. Determination of the cross section for the single isotopes out of Nyield

IntroductionCross section: probability of

nuclear reactionDepends on the neutron energy –

excitation functionExample:

Activation MethodReaction of a neutron beam with

nuclei to produce radioactive isotopes

Daughter nuclei start to decay by gamma emission

Semiconductor detector (for analysing gamma emission)◦ Compton scattering◦ Photoeffect◦ Production of electron-positron pairs

Experiment: Production of the Neutron BeamEProtons: 35 MeVReaction: 7Li(p,n)7BeENeutrons: ~32 MeVYttrium sample was irradiated for

22 hQuasi- monoenergetic neutron spectrum for a 7Li(p,n)7Be reaction, with protons at an energy of 35 MeV

ExperimentGamma emission of yttrium sample

was measured in a germanium semiconductor detector for different distances: 15, 23, 53, 70, 93, 173 mm

Evaluation of measured gamma spectrum with Deimos32Determination of area and uncertainty of area for gamma peaks

CorrectionsNyield: Number of produced nuclei in a given foil

CorrectionsWeighted average:

Uncertainty of weighted average:

2 –test:

Possible Reactions

Radioactive potassium isotope 40KGamma peak at an energy of

1460 keVAnalysed for reference to see if

the measurement went smoothlyThe ratio between the area of the gamma peak and the life time of the detector should be constant

Number of produced nuclei Nyield for the isotope 88YReaction: 89Y(n,2n)88Y Half liveT1/2 = 106.95 d

Comparison between the different measurements of the 23 mm distance between sample and detector for the gamma line at an energy of 898.0 keV

898.0 keV

1836 keV

Gamma lines

Number of produced nuclei Nyield for the isotope 88Y

The sample was turned to the other side after each measurement. There is a slight influence on the results between side (a) (left) and side (b) (right) of the sample.

Nyield for the isotope 88YComparison between the different measurements at different distances for the 898.0 keV gamma line:

Nyield for the isotope 87Y

Reaction: 89Y(n,3n)87YHalf liveT1/2 = 79.8 h

388.5 keV484.8 keV

Gamma lines

Comparison between the different measurements of 23 mm distance between sample and detector for the gamma line at an energy of 388.5 keV

Nyield for the isotope 87Y

Nearly 100% decays from the isomeric state 87mY to 87YThe equation for

the change of radioactive nuclei after irradiation for 87Y is:

Cross section

Cross section for 88Y

1 barn = 10-28

m2

Cross section for the 89Y(n,2n)88Y reaction: (0.41±0.05) barn

Cross section for 87mYCross section for the 89Y(n,3n)87mY reaction: (0.56±0.07) barn

Cross section for 87Y +87mYCross section for the 89Y(n,3n)87Y + 89Y(n,3n)87mY reaction: (0.77±0.08) barn

Cross section for 87YCross section for the 89Y(n,3n)87Y reaction: (0.21±0.03) barn

Thank you for your attention!

Questions?

Calculation of the peak efficiency correction factor for the distance of 173 mm