samples were mounted hermetically in weld-sealed aluminium containers. ... reaction cross sections (partial excitation function) taken from JEFF-3.1 [7].
ARIA 2008 1 Workshop on Accelerator Radiation Induced Activation October 13-17, 2008 Paul Scherrer Institut, Switzerland st
Transmutation of 129I and 237Np in the secondary neutrons of graphite-lead setup exposed to deuterons with kinetic energy 2.33 GeV J. Adam1,2, V.S. Pronskikh1, V.M. Tsoupko-Sitnikov1, V.G. Kalinnikov1, A.A. Solnyshkin1, V.I. Stegailov1, V.M. Golovatiouk1, N.M. Vladimirova1, M.I. Krivopustov1, V.A. Babkin1, A.D. Kovalenko1, W. Westmeier3, H. Robotham3, A.M. Khilmanovich4, B.A. Martsynkevich4, T.N. Korbut4, I.V. Zhuk5, A.S. Potapenko5, A.R. Balabekyan6, M.Majerle2 1
Joint Institute for Nuclear Research, Dubna near Moscow, 141 980 Russian Federation Phone: +07-49621-62175, FAX: +07-49621-66666, E-mail: iadam@ jinr.ru 2 Czech Academy of Science, Nuclear Physics Institute, Řež near Prague, 250 68 Czech Republic 3 Kernchemie Institute, Phillips-Universität, Marburg, Germany 4 Institute of Physics of National Academy of Sciences, Minsk, Belarus 5 Joint Institute of Power and Nuclear Research, Sosny, Minsk, Belarus 6 Yerevan State University, Yerevan, 1 Alex Manoogian, Republic of Armenia
Introduction Accumulation of large amount of long-lived radioactive isotopes is one of the most significant lacks of the present-day nuclear industry, which is an unavoidable option of electric energy production, and accelerator-driven systems not containing fissile isotopes and achieving high neutron fluxes seem to be feasible for transmutation of selected dangerous radioisotopes. An experiment using a setup consisting of a graphite moderator with the sizes 110x110x60 cm and a 8 cm in diameter 60 cm long lead target installed in the center of it, a reactor core model with total weight 1200 kg) was carried out in March of 2007 [1]. The graphite-lead block has been exposed to extracted deuteron beam with kinetic energy 2.33 GeV. Radioactive waste samples of 239Pu, 238Pu, 237Np, 129I as well as a number of threshold detectors, 139La samples, and other counters were installed in the holes drilled within the setup and than exposed to the secondary neutron flux generated by deuteron beam in the lead target. In this work we discuss experimental and calculated transmutation rates for 129I and 237Np isotope.
Experimental setup Described in this work setup (see Figure 1), with the total weight approximately 1200 kg, was mounted on a rail-based table which allows arbitrary movement of the setup in the irradiation position at the F3N focus. The block's position was adjusted so that the extracted beam from the Nuclotron hit the centre of the lead target. A number of levelling screws allowed a fine adjustment of the setup on the table. Proper positioning of the setup with respect to the beam was achieved with the use of a laser sight and checked during the run with Polaroid film. The front of the lead target from the accelerator pipe line beam exit window was approximately seven meters. Formerly, several experiments were performed using a 60 cm in length and 8 cm in diameter cylindrical lead target surrounded by a 6 cm thick paraffin moderator and was used for transmutation studies at the LPHE JINR accelerator complex proton beams in the energy range 0.53 — 4.15 GeV [2]. Despite paraffin has rather high neutron slowing down cross section, which makes it suitable for activation experiments, its obvious lack is that this material is not technologically feasible for an industrial transmutation Figure 1. Graphite-lead setup consisting of a 8 cm in facility.
diameter lead target surrounded with the 110x110x60 cm graphite moderator.
The transmutation samples of radioactive isotopes 129I (+127I), 237Np, 239Pu and 238Pu were installed in the graphite cylinders which mounted into the channels in the graphite sections. In addition to the 129I ( +127I) isotopic mix, samples of the stable isotope 127I were also prepared and attached to each of the mixed iodine ones in order to estimate its contribution to the transmutation rate. The order of samples is the same in all cylinders and defined (from right to left) as 238Pu, 239Pu, 237Np and 129I (the rightmost sample is not visible in the picture). In the course of the experiment the samples were exposed to neutrons generated by the deuteron beam in the lead target.
Experiment The experiment was started on March 17 and finished on March 18 of 2007, the total irradiation time amounted to 25 hours and 17 minutes. The setup was exposed to the accelerator extracted deuteron beam with kinetic energy of 2.33 GeV. The average beam intensity showed a significant increase during the irradiation and gradually became rather stable, about 8·109 deuterons per burst. Several pre-arranged beam interruptions were made to exchange SSNTD detectors or to adjust or exchange the 3 He and 4He neutron detectors that were mounted on top of the moderator block. The deuterons have been monitored using the 27 24 129 Al, 3p2n) Na reaction [3]. An aluminum foil (with d( I 237 Np thickness 6.7 mg/cm2 and diameter ∅ = 20 cm each) was installed at a distance of 3.1 meters from the center of the lead target in order to determine profile of the beam and the number of deuterons hit the lead target. Two covering foils of the same sides were attached to the monitor foil from both sides to protect from escape of the residual product nuclei. After the irradiation the protecting foils were detached and the monitor foil was cut into four concentric rings, the inner ring was a circle with the diameter 2.1 cm, the three following ring had the outer diameters 8.0, 12.0, Figure 2. Placement of 129I and 237Np and 16.0 cm respectively. These rings were compressed into four small compact disks and measured at the HPGe samples in the graphite-lead setup. detectors, three spectra of each of the rings. To control how uniformly the deuteron beam was distributed over the target, two innermost foils were divided into two parts – 1) from r = 0 mm to r = 10.5 mm; and 2) from r = 10.5 mm to r = 40 mm – and their induced activity was measured. The first piece of the monitor has acquired less induced activity than the second one. For additional control on the number of deuterons on target the ionization chambers were also used. The displacement of the deuterons was not very significant because the integral number of particles measured on the two inner monitor rings was 92 ± 4% of the total beam which means that only 7.8% of the beam is not on the lead target, the total number of projectiles on the monitor foils is measured as (1.848 ± 0.154) * 1013 particles (approximately 1.7·1013 deuterons on the lead target). The significant contribution to the total uncertainty of beam on target comes from the cross section of the monitor reaction d(27Al, 3p2n)24Na reaction with the only known published value [3] of the cross section in this energy range was used. Three sets of 129I samples (82.9% of 129I and 17.1% of 127I) as well as three respective samples of pure 127I isotope, used to subtract the 127I isotope admixture contribution, were placed in the channels within the graphite block at 13.8, 24 and 51.3 cm distances from the symmetry axis (Z) of the lead target, respectively. Also three sets of 237Np samples were mounted in the positions shown in the Figure 2. Except the 129I (+127I) isotopic mix, samples of the stable isotope 127I were also prepared and attached to each of the mixed iodine ones in order to estimate its contribution to the transmutation rate. Position of the 239Np sample in the cylinder No. 4 is shown in Figure 3. Four samples are placed in each cylinder, the leftmost one is 237Np, and rightmost sample of 129I is not shown. The weights of the three 129I samples (82.9% of 129I and 17.1% of 127I) used in the experiments were 0.591, 0.339 and 0.218 grams. The 237Np samples weighted 1.115, 1.085 and 1.011 grams respectively. All the samples were mounted hermetically in weld-sealed aluminium containers. These containers are regularly checked by the producer (Institute of Physics and Power Engineering) for integrity, while the radiation safety service checks integrity of all samples before each experiment. The sample's containers are 35 mm in diameter and have the 15 mm high walls. Radioactive material in all containers put in a hollow in the double walled bottom 21 mm in diameter and about 0.5 mm height. In the course of the experiment the samples were exposed to neutrons generated by the deuterons in the lead target. Three sets of 129I samples (82.9% of 129I and 17.1% of 127I) as well as three respective sets of pure 127I samples, used for the 127I isotope admixture subtraction, were placed in the holes within the graphite at 19, 29 and 55 cm from the center of the lead target, respectively, and irradiated by secondary neutrons generated in the target media by primary deuterons. After irradiation the radioactive samples were taken to the spectroscopy complex of Laboratory of Nuclear Problems for gamma-spectrometric measurements with the set of high efficiency and energy resolution High Purity Germanium spectrometers. Several spectra from each sample were measured over an interval of several weeks, the spectra were analyzed and the transmutation reaction rates for the production of the
neutron-induced reaction products were calculated with account of detector efficiencies, decay during irradiation, decay between end of irradiation and start of measurement as well as decay during the counting time using program codes [4, 5]. Comparison of the transmutation rates for the isotope 129I in the reaction 129I(n, γ)130I by secondary neutrons in the experimental conditions and setup described above in this paper with those obtained in the earlier experiments with lead target and paraffin moderator [2] (where the 129I sample was placed on surface of the moderator) showed that the B-factors at that setup are approximately 200 times lower as compared at the 19 cm position of the setup, about 150 times lower at 29 cm and about 3 times higher at 55 cm distance from the target center; this comparison is made at similar energy of protons. Results of the data analysis can be presented in the form of B-parameter (d-1 g-1), showing number of nuclei transmuted in a gram of initial isotope by a projectile particle, or also reaction rate R (d-1 at-1), representing the number of nuclei transmuted by a projectile particle per atom of initial isotope: B=
N at m⋅ Np
[proton −1 ⋅ gram −1 ]
R=
Emax B⋅ A = σ ( E )Φ ( E )dE [proton -1atom-1 ] N A ∫Emin
These parameters also can be calculated using theoretical models and used for comparison with the experimental ones.
Experimental results and calculations In Table 1 transmutation reaction rates (R-parameters) are shown for the isotopes 124I, 126I, 126I, and 128I formed in the secondary neutrons of the setup in the isotope mix 129I and 127I (128I here can be produced in the 127I(n,γ) reaction). Table 1. Experimental R-parameters for (n, γ) and (n, xn) reactions on 129I and 127I. Distance from Z axis, cm R(127I(n, γ)128I) R(130I) R(124I) R(126I) R(128I) 13.8 8.14E-25 1.09E-27 8.14E-28 4.07E-25 1.90E-3 24.0 6.64E-25 1.07E-28 3.43E-28 2.57E-25 1.20E-3 51.3 1.29E-25 2.78E-29 4.71E-26 2.20E-4 Neutron spectra at places where the samples are installed were calculated using the FLUKA [6] code, and then integrated with respective reaction cross sections (partial excitation function) taken from JEFF-3.1 [7] database to yield transmutation reaction rates (R-parameters). FLUKA code includes a number of fully integrated particle-nucleus and nucleus-nucleus interaction models, of which RQMD (relativistic quantum-molecular dynamic) model was used. Improvement of classical INC by adding dynamical simulation of the nuclear field among nucleons in the course of the reaction, with similar treating of individual nucleon-nucleon scattering/interactions, the model is applicable in the energy region from 0.1 to hundreds GeV/nucleon. calc
exp
R transm utation reaction rate, at^ -1 d^ -1
R transm utation reaction rate, at^-1 d^-1
calc 3.0E-3 2.5E-3 2.0E-3 1.5E-3 1.0E-3 5.0E-4 0.0E+0 0
10
20
30
40
50
distance from target symmetry axis, cm
Figure 4. R-parameters for reaction 127I(n,γ) 129I.
60
exp
1.00E-024 9.00E-025 8.00E-025 7.00E-025 6.00E-025 5.00E-025 4.00E-025 3.00E-025 2.00E-025 1.00E-025 0.00E+000
0
10
20
30
40
50
60
distance from target symmetry axis, cm
Figure 5. R-parameters for reaction 129I(n,γ) 130I.
As compared to experiments with “Energy Plus Transmutation” setup [8], lead target with uranium blanket at 2 GeV protons and 2.52 GeV deuterons R-parameters are very similar for both projectile types. At 19 cm distance from Z-axis (graphite-lead setup) R–parameters are bigger than those measured in [8] for 130I production (R(129I(n, γ)130I) and R for (n, xn) reactions of 124I and 126I formation.
Table 2. Transmutation of 237Np. Fission exper. calc. A – channel B – channel C – channel
exp./calc.
2,81E-28 1,80E-26 4,00E-27 6,33E-26 1,46E-26
Table 2 shows that in the case of satisfactory, within 30 %.
4,51E+00 4,34E+00
(n,g) exper.
calc.
exp./calc.
3,55E-25 3,55E-25 1,00E+00 2,40E-24 3,10E-24 7,73E-01 3,55E-24 5,09E-24 6,98E-01
237
Np(n, γ)238Np reaction calculations agree with experiment rather
Acknowledgement Authors are grateful to the operating crew of the Nuclotron accelerator of LHE, JINR Dubna for irradiation and good beam parameters, and Dr. Vera Bradnova for the experiment’s minutes managing and photographic support. References [1] J.Adam et al., in Abstracts of the 58 International conference on nuclear spectroscopy and structure of atomic nuclei, P.285 Moscow, /S-P / 2008. [2] W. Westmeier, R. Brandt, E.-J. Langrock, H. Robotham et al. Transmutation experiments on 129I, 139 La and 237Np using the Nuclotron accelerator, Radiochem. Acta V. 93, 2005, PP. 65-73. [3] J. Banaigs et al., Nucl. Instr. Meth. V. 95, 1971, P. 307-311. [4] J. Frána, Program DEIMOS32 for gamma-ray spectra evaluation, Journal of Radioanalytical and Nuclear Chemistry, 257 (2003) 583-587. [5] J.Adam et al., Program package and supplements to activation analysis for calculations of nuclear reaction cross sections, JINR Preprint P10-2000-28; Measurement techniques, 44 (2001) 93-100. [6] A. Fasso`, A. Ferrari, J. Ranft, and P.R. Sala, FLUKA: a multi-particle transport code, CERN-200510 (2005), INFN/TC_05/11, SLAC-R-773; A. Fasso` et al. The physics models of FLUKA: status and recent developments, Computing in High Energy and Nuclear Physics 2003 Conference (CHEP2003), La Jolla, CA, USA, March 24-28, 2003, (paper MOMT005), eConf C0303241 (2003), arXiv:hepph/0306267. [7] JEFF-3.1 Joint Evaluated Fission and Fusion File, JEFF Report 21, OECD/NEA, Paris, France, 2006, ISBN 92-64-02314-3. [8] M.I. Krivopustov et al. About the experiment on investigation of 129I, 237Np, 238Pu and 239Pu transmutation at the nuclotron 2.52 GeV deuteron beam in neutron field generated in U/Pb-assembly “Energy+Transmutation”, preprint JINR, E1-2007-7, 2007.
