1 Measurement of excitation yields of low energy prompt  -ray from proton bombardment of 48 Ti 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 1-st Technical Meeting on Development of Reference Database for Particle-Induced Ray Emission (PIGE) Spectroscopy, May 2011, IAEA Headquarters, Vienna a Chief scientific investigator

2 Kharkov on a map

3 Kharkov Institute of Physics and Technology 1928 – founded with aim of developing urgent fields of research – the cryogenic laboratory first in the USSR was organized – 1937 Landau formed an internationally known school of theoretical physics – the first in the world radar was constructed – 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 – many unique experimental facilities, namely, a number of electron and ion accelerators, including the largest in the USSR electron linear accelerator were built – 1991 the Institute executed functions of a main organization in the USSR in the field of radiation materials science and radiation technologies 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 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 TiO 2 ferritic 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-section values of 48 Ti(p,  ) 49 V, 48 Ti(p,  ) 49 V+ 49 Ti(p,n  ) 49 V reactions are necessary for PIGE database. Motivation

6 - 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 bending magnet  20 μА; - Accelerated ions – H +, He + NSC KIPT “ESU 5” Van de Graaff accelerator

7 RF source of gas ions : H +, He +, N + 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 bending magnet  10 μА;

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

9 Experimental setup for low energy  -emission measurements Experimental chamber with 100  m Be-window HPGe detector (20 mm 2  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 49 V nucleus (product of the 48 Ti(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 48 Ti isotope. Thickness of the target was equal to about 0.65  m.

11 Isotope composition of the used 48 Ti target 46 Ti 47 Ti 48 Ti 49 Ti 50 Ti % NaMgAlSiCaCrFeNiCuPb %       Impurities:

12 Measurement of the target thickness by RBS technique RBS spectra from Ta target and 48 Ti target on Ta backing. E1E1 TiTa-backing  = t kE 0 -  E He +, E 0 =1.6 MeV Ta  = kE 0 He +, E 0 =1.6 MeV

13 Treatment of the RBS spectrometry data Kinematical factor of elastic scattering: M He is 4 He atom mass. M Ta is Ta atom mass. Correct value of the Ti target thickness from RBS spectrometry data was determined from numerical solution of the system of two equations for E 1 and t : t is the Ti target thickness (at/cm 2 ). E 1 is the He ion energy (MeV) on Ti/Ta interface. t =3.7  аt/сm 2  5% 97.8 % 48 Ti S Ti  (E) is the stopping power (MeVcm 2 /at) of He ion in Ti substance vs ion energy E.

14 Beam-target-detector geometry at the excitation function measurement  = 45 0 Ti Ta-backing 100  m Be - window Proton beam HPGe - detector  = 90 0  -rays Guard ring V At the geometry,  -ray absorption in a backing has no influence on measurement results.

15 Calibration of the γ-ray detection system efficiency ε (E γ ) The calibration was carried out with the standard 133 Ba, 152 Eu, and 241 Am sources at the geometry used for the cross-section measurements (here E γ is the γ-ray energy). With that the ordinary expression was used: N γ is the full-energy peak area (counts); n(E γ ) is the quantum yield of used nuclide for the energy E γ (quantum/decay); A is the activity of the source (decay/s); τ live 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. ε absorber ≤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). ε crystal ≤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 Ω e (E γ ) of the detector via equivalent relation

16 Proton energy loss in the Ti target The energy loss ΔE p 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. E op is the primary proton beam energy. The interval of energy averaging at cross-section measurement is equal to the ΔE p

17 7/2 - 5/2 - 3/ V keV 62.3 keV152.9 keV The typical spectrum of low-energy  -ray from the 48 Ti target

18 Data reduction The averaging differential cross-section d σ γ / dΩ of  -ray production from the 48 Ti(p,  ) 49 V reaction was determined from the general expression: N γ is the number of counts in the full-energy peak. k is the ratio between the live time and the exposure time. N p is the number of protons incident upon the target. Ω e =Ω e (E γ ) is the effective solid angle of the detector. f is the relative content of 48 Ti in Ti target substance. t is the Ti target thickness (at/cm 2 ). 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· μC), then we come to the final expression

19 7/2 - 5/2 - 3/ V keV 62.3 keV152.9 keV Differential cross-sections for the production of 62.3 and 90.6 keV  -rays from the reactions 48 Ti(p,  ) 49 V,  lab =90 0. (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 Differential cross-sections for the production of 62.3 and 90.6 keV  -rays from the reactions 48 Ti(p,  ) 49 V for proton energies ranging between 1.0 and 1.6 MeV at the laboratory angle of 90 0 have been measured. Summary

21 Further steps: to prepare thin (  0.1mg/cm 2 ) targets of natural Ti; to measure differential cross-sections for the production of 62.3 keV and 90.6 keV  -rays from the reactions: 48 Ti(p,  ) 49 V at energies < 1412 keV (threshold of 49 Ti(p,n  ) 49 V) and 48 Ti(p,  ) 49 V+ 49 Ti(p,n  ) 49 V at energies > 1412 keV up to 3 MeV. Measurement perspectives

22 7/2 - 5/2 - 3/ V keV 62.3 keV152.9 keV The typical spectrum of low-energy  -ray from the 48 Ti target

23 Thanks for your attention!