Experimental Determination of Neutron Cross Sections of Yttrium by Activation Method by Barbara Geier Supervisors: Assoc. Prof Dr. Wolfgang Sprengel RNDr. Vladimír Wagner Csc. Ing. Ondřej Svoboda

Internship at the Nuclear Spectroscopy Department of Nuclear Physics

Internship Organized by IAESTE Graz 6 weeks Departement of Nuclear Spectroscopy in Řež

Summary 1. Irradiation of the yttrium foil by neutrons to produce radioactive isotopes 2. 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 N yield out of the peak area 5. Determination of the cross section for the single isotopes out of N yield

Introduction Cross section: probability of nuclear reaction Depends on the neutron energy – excitation function Example:

Activation Method Reaction 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 Beam E Protons : 35 MeV Reaction: 7 Li(p,n) 7 Be E Neutrons : ~32 MeV Yttrium sample was irradiated for 22 h Quasi- monoenergetic neutron spectrum for a 7 Li(p,n) 7 Be reaction, with protons at an energy of 35 MeV

Experiment Gamma 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 Deimos32 Determination of area and uncertainty of area for gamma peaks

Corrections N yield : Number of produced nuclei in a given foil

Corrections Weighted average : Uncertainty of weighted average: 2 –test:

Possible Reactions

Radioactive potassium isotope 40 K Gamma peak at an energy of 1460 keV Analysed for reference to see if the measurement went smoothly The ratio between the area of the gamma peak and the life time of the detector should be constant

Number of produced nuclei N yield for the isotope 88 Y Reaction: 89 Y(n,2n) 88 Y Half liveT 1/2 = d Comparison between the different measurements of the 23 mm distance between sample and detector for the gamma line at an energy of keV keV 1836 keV Gamma lines

Number of produced nuclei N yield for the isotope 88 Y 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.

N yield for the isotope 88 Y Comparison between the different measurements at different distances for the keV gamma line:

N yield for the isotope 87 Y Reaction: 89 Y(n,3n) 87 Y Half liveT 1/2 = 79.8 h keV keV Gamma lines Comparison between the different measurements of 23 mm distance between sample and detector for the gamma line at an energy of keV

N yield for the isotope 87 Y Nearly 100% decays from the isomeric state 87m Y to 87 Y The equation for the change of radioactive nuclei after irradiation for 87 Y is:

Cross section

Cross section for 88 Y 1 barn = m 2 Cross section for the 89 Y(n,2n) 88 Y reaction: (0.41±0.05) barn

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

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

Cross section for 87 Y Cross section for the 89 Y(n,3n) 87 Y 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