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