Measurement of excitation yields of low energy prompt - ray

1. National Scientific Centre Kharkov Institute of Physics and Technology Measurement of excitation yields of low energy prompt -ray from proton bombardment of 48Ti foil V.N. Bondarenko, A.V. Goncharov a, I.M. Karnaukhov, V.I. Sukhostavets, A. G. Tolstolutskiy, S.N. Utenkov, K.V. Shebeko NSC KIPT, Kharkov, Ukraine a Chief scientific investigator 1-st Technical Meeting on Development of Reference Database for Particle-Induced Ray Emission (PIGE) Spectroscopy, 16-20 May 2011, IAEA Headquarters, Vienna

2. Kharkov on a map

3. Kharkov Institute of Physics and Technology • 1928 – founded with aim of developing urgent fields of research. • 1931 – the cryogenic laboratory first in the USSR was organized. • 1932 – 1937 Landau formed an internationally known school of theoretical physics. • 1934 – the first in the world radar was constructed. • 1937 – Van de Graaff accelerator (2.5 MeV) first in the USSR was built. • Post-war years – activity in the field of atomic energy including investigations of thermonuclear fusion. • 1960-1970 – many unique experimental facilities, namely, a number of electron and ion accelerators, including the largest in the USSR electron linear accelerator were built. • 1972 – 1991 the Institute executed functions of a main organization in the USSR in the field of radiation materials science and radiation technologies. • 1991 - present time – the Institute constitutes an essential part of research complex of Ukraine, especially in the field of atomic industry, material science, accelerator equipment and new sources of energy for civil and defense purposes.

4. The basic fields of research work at NSC KIPT • Solid-state physics. Physics of radiation effects and radiation materials science. Technologies of materials. • Plasma physics and controlled fusion. • Nuclear physics, physics of electromagnetic interactions, physics and engineering of electron accelerators. • Plasma electronics and physics of high-current beams. Physics and engineering of heavy charged particle accelerators. New methods of acceleration. • Theoretical physics.

5. Motivation The PIGE technique is widely used for quantitative analysis. For example, the technique can be used for determination of Ti in the strengthened by fine dispersed TiO2ferritic steels which are developing for fast reactors. PIGE measurements can be simultaneously performed with PIXE ones using HPGe detector. In comparison with the PIXE technique the PIGE one is characterized by larger depth of analysis in steels. That is only one of reasons why the experimental cross-sectionvalues of 48Ti(p,)49V, 48Ti(p,)49V+49Ti(p,n)49V reactions are necessary for PIGE database.

6. NSC KIPT “ESU 5”Van de Graaff accelerator - Acceleration voltage0.5 … 3.5 МeV; - Energy spread  0.07%; - Ion beam current of the direct output  90 μА; - Ion beam current after the bendingmagnet 20 μА; - Accelerated ions – H+, He+

7. NSC KIPT “Sokol” Van de Graaff accelerator - Acceleration voltage0.2 … 2 МeV; - Energy spread  0.07%; - Ion beam current of the direct output50 μА; - Ion beam current after the bendingmagnet 10 μА; RF source of gas ions : H+, He+, N+

8. Experimental beam lines of the“SOKOL” facility 3 4 1 2 5 6 • High pressure vessel of the accelerator • Beam-bending magnet (analysis of energy and mass) • Beam line #1(PIXE, PIGE) • Beam line #2(beam in air, biological materials, PIXE, PIGE) • Beam line #3(for implantation) • Beam line #4(“universal chamber”, PIXE, RBS, NRA, PIGE, ERD) • Beam line #5(microbeam, PIXE, PIGE, RBS). • Diameter of ion beam ≈ 3 µm. 7

9. Experimental setup for low energy -emission measurements Experimental chamber with 100 m Be-window HPGe detector (20 mm26 mm)

10. Necessity of proton energy averaging at the cross-section measurements. The choice of target thickness for the averaging. (p,) – reactions on medium nuclei are usually followed with a large number of very narrow resonances corresponding to excited states of residual nuclei. Typical level widths of the 49V nucleus (product of the 48Ti(p,) reaction) range from several to several tens electron-Volts. (T.W. Burrows. Nuclear Data Sheets for A=49). So detail measurements of “true” energy dependences for the cross sections of such reactions are practically impossible under conditions when a primary beam has a finite energy spread and a target has a finite thickness. But from standpoint of practical use in PIGE technique, such detailed measurements are not necessary because energy spread of beam rises quickly in analyzing substance. In this connection cross-sections measured with some averaging on proton energy are more useful. Obviously, averaging interval would be larger than distances between resonances. In practice this interval is determined by thickness of a target used at cross section measurement. On the other hand the target thickness would not be too large to avoid indistinctness of resonance structure of the measured cross-sections, at least near strong resonances. At the preliminary measurements we used the Ti target with 97.8 % enrichment of the 48Ti isotope. Thickness of the target was equal to about 0.65 m.

11. Isotope composition of the used 48Ti target Impurities:

12. He+, E0=1.6 MeV  = 1700 kE0 Ta t He+, E0=1.6 MeV E1  = 1700 kE0-E Ti Ta-backing Measurement of the target thickness by RBS technique RBS spectra from Ta target and 48Ti target on Ta backing.

13. Treatment of the RBS spectrometry data Kinematical factor of elastic scattering: MHe is 4He atom mass. MTa is Ta atom mass. Correct value ofthe Ti target thickness from RBS spectrometry data was determined from numerical solution of the system of two equations for E1 and t: t is the Ti target thickness (at/cm2). E1 is the He ion energy (MeV) on Ti/Ta interface. t =3.71018аt/сm2 5% STi(E)is the stopping power (MeVcm2/at) of He ion in Ti substance vs ion energy E. 97.8 % 48Ti

14. Guard ring - 300 V Ti Ta-backing Proton beam  = 450 100 m Be - window -rays  = 900 HPGe - detector Beam-target-detector geometry at the excitation function measurement At the geometry, -ray absorption in a backing has no influence on measurement results.

15. Calibration of the γ-ray detection system efficiency ε(Eγ) The calibration was carried out with the standard 133Ba, 152Eu, and 241Am sources at the geometry used for the cross-section measurements (here Eγ is the γ-ray energy). With that the ordinary expression was used: Nγ is the full-energy peak area (counts); n(Eγ) is the quantum yield of used nuclide for the energy Eγ(quantum/decay); A is the activity of the source (decay/s); τlive is the live time of measurement (s). It is well known that the efficiency may be formally present as the product of several factors: Ω is the solid angle of the detector. εabsorber ≤1 is the factor describing the γ-ray absorption in substance layers between the source and detector crystal (in our case, these absorption layers are the output window of target chamber and the input window of the detector). εcrystal ≤1 is the factor describing the γ-ray absorption in material of the crystal. Using the last equation we may formally introduce the “effective” solid angle Ωe(Eγ) of the detector via equivalent relation

16. Proton energy loss in the Ti target The energy loss ΔEp was determined from numerical solution of the equation: . t is the Ti target thickness. φ is the beam incidence angle taking from normal to the target. Eopis the primary proton beam energy. The interval of energy averaging at cross-section measurement is equal to the ΔEp

17. 3/2- 152.928 62.3 keV 152.9 keV 5/2- 90.639 90.6 keV 7/2- 0 49V The typical spectrum of low-energy -ray from the 48Ti target

18. Data reduction The averaging differential cross-section dσγ/dΩ of -ray production from the 48Ti(p,)49V reaction was determined from the general expression: Nγis the number of counts in the full-energy peak. k is the ratio between the live time and the exposure time. Npis the number of protons incident upon the target. Ωe=Ωe(Eγ) is the effective solid angle of the detector. f is the relative content of 48Ti in Ti target substance. t is the Ti target thickness (at/cm2). φ is the beam incidence angle taking from normal to the target. Since Q is the integrated beam charge (μC) measured during exposition, e is the elementary charge (1.602·10-13 μC), then we come to the final expression

19. 3/2- 152.928 62.3 keV 152.9 keV 5/2- 90.639 90.6 keV 7/2- 0 49V Differential cross-sections for the production of 62.3 and 90.6 keV -rays from the reactions 48Ti(p,)49V, lab=900 . (Preliminary results) Vertical error bar is statistical mean-square error only. Horizontal error bar is equal to a half of proton energy loss in target.

20. Summary Differential cross-sections for the production of 62.3 and 90.6 keV -rays from the reactions 48Ti(p,)49V for proton energies ranging between 1.0 and 1.6 MeV at the laboratory angle of 900have been measured .

21. Measurement perspectives • Further steps: • to prepare thin (0.1mg/cm2) targets of natural Ti; • to measure differential cross-sections for the production of 62.3 keV and 90.6 keV -rays from the reactions: • 48Ti(p,)49V at energies < 1412 keV (threshold of 49Ti(p,n)49V) and • 48Ti(p,)49V+49Ti(p,n)49V at energies > 1412 keV • up to 3 MeV.

22. 3/2- 152.928 62.3 keV 152.9 keV 5/2- 90.639 90.6 keV 7/2- 0 49V The typical spectrum of low-energy -ray from the 48Ti target

23. Thanks for your attention!