Intensities of the γ -ray emissions following the 111 Sn decay determined via photonuclear reaction yield measurements
A. Chekhovska, Ye. Skakun, I. Semisalov, S. Karpus, V. Kasilov
IIntensities of the 𝛾 -ray emissions following the 𝑆 𝑛 decaydetermined via photonuclear reaction yield measurements
A. Chekhovska a,b , Ye. Skakun a , I. Semisalov a , S. Karpus a and V. Kasilov a a National Scientific Center Kharkiv Institute of Physics and Technology, 1 Akademicheskaya St., Kharkiv, 61108, Ukraine b V. N. Karazin Kharkiv National University, 4 Svobody Sq., Kharkiv, 61022, Ukraine
A R T I C L E I N F O
Keywords :Radioactive decayPhotonuclear reactionsBremsstrahlung 𝛾 -Ray emissions A B S T R A C T
The intensities of the ten strongest 𝛾 -ray transitions following the 𝑆𝑛 ( 𝑇 =35.3 m) decayhave been determined via comparison of the two sets of the experimental photonucleon reac-tion yields driven using the traditional activation equation and the activation equation for thegenetically coupled radioactive nuclei. The found absolute intensities of the 𝛾 -ray transitions inquestion were happened to be noticeably different from the currently recommended values.
1. Introduction
Nucleus decay data are important for both nuclear spectroscopy theories and experimental techniques determiningnuclear reaction cross sections or yields by means of residual activity measurements. The tin-111 ( 𝑆𝑛 ) nucleusdecaying by ( 𝜀 + 𝛽 + ) -process with the half-life of 35.3 m populates a large array of excited levels of the indium-111( 𝐼𝑛 ) daughter nuclide among which there is an isomeric state with the excitation energy 537.2 keV and the half-life 𝑇 𝑚 = 7 . 𝑚 (Fig. 1). The ground state of the 𝐼𝑛 nuclide ( 𝑇 𝑔 = 2 . 𝑑 ) decays to the stable 𝐶𝑑 one followingthe strong 𝛾 -ray transitions of 171.2 keV and 245.3 keV. The last evaluated decay data for the A=111 nuclear masswere recommended by publication [1] and involved to NuDat 2.8 base [2]. Meanwhile the intensity values of the 𝛾 -raytransitions between the 𝐼𝑛 excited levels following the 𝑆𝑛 decay are based on the relatively old experimentalmeasurements, mostly performed at the 1970-1980s (see references of [1]), and taken with detectors of relatively lowefficiencies and poor resolutions compared with the current 𝛾 -ray spectrometry techniques.A large quantity of experimental measurements of activation cross sections and yields of different nuclear reactionsinduced by various incident particles, which lead to the formation of the 𝑆𝑛 nuclide, have been carried out for basicand applied purposes to date [3]. The correct values of the 𝛾 -ray emissions following the residual nuclei are needed forthe correct determination of the nuclear reaction cross sections or yields using a 𝛾 -ray spectrometry activation tech-nique. We have met this problem determining the bremsstrahlung activation yields of the near-threshold photonuclearreactions on the 𝑆𝑛 nuclide as a target which are partly of interest as input data for studying the 𝛾 -scenario of thestellar nucleosynthesis of the so-called 𝑝 -nuclei [4, 5].
2. Experimental procedure and analysis
The 𝑆𝑛 radioisotope was produced by the 𝑆𝑛 ( 𝛾, n) 𝑆𝑛 photonuclear reaction at the 30 MeV electron linearaccelerator located at the National Scientific Center Kharkiv Institute of Physics and Technology (NSC KIPT). Theelectron beam of ∼ 𝜇 A current and 15 MeV and less energies impacted to the 100 𝜇 m tantalum foil to be convertedto a bremsstrahlung photon flux irradiating the investigated target placed along the electron beam axis while non-converted electrons were deflected with a permanent magnet. Four self-supporting tin metallic foils having the squareshape with side 18 mm and total weighing 77 mg enriched with the 𝑆𝑛 isotope to 80% level were used as theunified target. At every irradiation the gold foil of 20 mm in diameter weighing 120 mg was placed with the studiedtin target in the close geometry in order to use the 𝐴𝑢 ( 𝛾, n ) 𝐴𝑢 reaction as the standard one to determine the ∗ Corresponding authors [email protected] (A. Chekhovska); [email protected] (Ye. Skakun); [email protected] (I.Semisalov); [email protected] (S. Karpus); [email protected] (V. Kasilov)
ORCID (s):
Chekhovska A. et al.:
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Page 1 of 7 a r X i v : . [ nu c l - e x ] M a y -Ray emissions of the 𝑆𝑛 decay − + + + ; 𝟗𝟐 + IT . . . . . . . . . . . . + + + + ; 𝟏𝟏𝟐 + + 𝐂𝐝 + ; 𝟗𝟐 + + + + + 𝐈𝐧 𝐒𝐧 Figure 1:
Simplified scheme of the 𝑆𝑛 → 𝑚,𝑔 𝐼𝑛 → 𝐶𝑑 radioactive chain. bremsstrahlung flux. The cross sections of the last reaction were earlier measured and evaluated by several experimentalteams [6, 7, 8, 9] in the giant resonance region the results of which are consistent each with other well and the 𝐴𝑢 residual radioactive decay has the very suitable properties [2] for its activity measurement. The ionization chamberplaced along the beam axis was monitoring the photon flux crossing both targets during irradiations. Several exposuresof such the combined target (the target sandwich) were carried out over a range of bremsstrahlung endpoint energiesbetween the threshold of the 𝑆𝑛 ( 𝛾 ,n) 𝑆𝑛 reaction (10.79 MeV) and 15 MeV to obtain the energy dependence ofthe photoactivation yield.After each irradiation lasting usually ∼
100 m the targets were delivered to a low-background room far from theaccelerator as soon as possible in order to begin to measure the energy spectra of 𝛾 -rays following the radioactive decayof the 𝑆𝑛 and its daughter 𝐼𝑛 using a coaxial Canberra High Purity Germanium detector with relative efficiencyof 30% in comparison to the efficiency of (3 in.ÃŮ3 in.) 𝑁𝑎𝐼 ( 𝑇 𝑙 ) -detector and 1.8 keV resolution for the 1332 keV 𝛾 -line of the 𝐶𝑜 isotope source. To reduce ambient radioactivity the detector was contained in a lead shield, withwalls 12 cm in depth and degraders of 3 mm 𝐶𝑑 and 5 mm 𝐶𝑢 line the inside of the shield to reduce the interference ofthe 𝑃 𝑏 fluorescence X-rays. The 𝛾 -ray spectra of the 𝐴𝑢 ( 𝑇 = 6.16 d [2]) residual nucleus of the standard reactionwere measured secondarily. The irradiated targets were mounted along the vertical axis of the spectrometer on severalsample-to-detector distances between 5 and 10 cm. The measurements of the detector full-energy-peak efficiencywere performed at the (50-1500) keV 𝛾 -ray energy region using 𝑁𝑎, 𝐶𝑜,
𝐵𝑎,
𝐶𝑠,
𝐸𝑢,
𝑅𝑎, and 𝐴𝑚 calibrated point sources. Fig. 2 shows the energy dependences of the detector efficiency for the two distances betweenthe source and crystal end-cup. Chekhovska A. et al.:
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Page 2 of 7 -Ray emissions of the 𝑆𝑛 decay Figure 2:
The full-energy peak detection efficiency curves of the HPGe 𝛾 -ray spectrometer for sample-to-end-cap distances5 and 10 cm. The two typical 𝛾 -ray spectra of the 𝑆𝑛 target irradiated with 15 MeV bremsstrahlung are shown in Fig. 3. Ashorter-live fraction of the induced radioactivity is given in the upper panel, a longer-live one in the lower one. Thearrows of the upper panel indicate the 10 strongest gamma-ray transitions in the 𝐼𝑛 nucleus following the 𝑆𝑛 decay. The energy of each transition is indicated in kiloelectron-volt units above the arrow. Figure 3:
Short (upper panel) and long (lower panel) fractions of the typical 𝛾 -ray spectrum measured after irradiation ofthe 𝑆𝑛 target with 15 MeV bremsstrahlung.Chekhovska A. et al.: Preprint submitted to Elsevier
Page 3 of 7 -Ray emissions of the 𝑆𝑛 decay The 𝛾 -ray spectrum measured one day later irradiation (the lower panel of Fig. 3), except weak background, containsonly 2 strong peaks (171 keV and 245 keV, indicated with arrows), which are correspond to the 𝛾 -rays following thedecay of the 𝑔 𝐼𝑛 nucleus ( 𝑇 𝑔 = 2.80 d) being the daughter of the 𝑆𝑛 nucleus (see Fig. 1) and on the otherside can be additionally produced via the 𝑆𝑛 ( 𝛾, p) 𝑚 + 𝑔 𝐼𝑛 reaction (the 7.55 MeV threshold) in appliance with thescheme:The energies and intensities of the mentioned 𝛾 -ray transitions of the 𝑆𝑛 → 𝐼𝑛 → 𝐶𝑑 radioactive chainborrowed from NuDat 2.8 base [2] are presented in Table. 1. Table 1
Energies and intensities of the 𝛾 -ray transitions following the 𝑆𝑛 , 𝑚 𝐼𝑛 , and 𝑔 𝐼𝑛 decays [2] 𝐸 𝛾 [keV] 𝐼 𝛾 [%] 𝑆𝑛 → 𝐼𝑛 𝑚 𝐼𝑛 → 𝑔 𝐼𝑛 𝑔 𝐼𝑛 → 𝐶𝑑 The radioactive decay curves derived analyzing the two most intense 𝛾 -ray transitions (761.9 and 1152.9 keV) ofthe 𝐼𝑛 daughter nucleus are depicted in Fig. 4. The half-life values (indicated in the plot) of the 𝑆𝑛 radionuclidedetermined from the time dependencies of the intensities of these two 𝛾 -lines are in good agreement with the the NuDat2.8 base value 35.3 (6) m [2]. The remaining gamma lines following the 𝑆𝑛 decay obey the same consistent patternof exponential decay.The bremsstrahlung activation yield 𝑌 of the 𝑆𝑛 ( 𝛾, n ) 𝑆𝑛 reaction can be determined solving the traditionalactivation equation (1) 𝑆 𝛾 𝜀 ⋅ 𝐵𝑟 ⋅ 𝑛 ⋅ 𝜙 = 𝑌𝜆 ⋅ ( 𝑒 − 𝜆𝑡 ) ⋅ 𝑒 − 𝜆𝑡 ⋅ ( 𝑒 − 𝜆𝑡 ) (1)in which 𝑆 𝛾 is the experimental area of any 𝛾 -ray peak of the 𝑆𝑛 decay, 𝜀 the full-energy peak detection efficiency, 𝐵𝑟 = 𝐼 𝛾 ∕100 branching coefficient of the same 𝛾 -ray transition, 𝑛 the number of nuclei in the target being irradiated, 𝜙 the flux of the bremsstrahlung photons covering the target, 𝜆 radioactive decay constant, 𝑡 , 𝑡 , and 𝑡 the irradiation,cooling and measurement times of the target activity respectively.De-excitation of the 𝐼𝑛 states (including the 𝑚 𝐼𝑛 isomer) populated by the decay of 𝑆𝑛 leads to the 𝐼𝑛 ground state. The experimental areas 𝑆 𝛾 of the 171.2 keV and 245.3 keV 𝛾 -ray peaks of the 𝑔 𝐼𝑛 decay at the Chekhovska A. et al.:
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Page 4 of 7 -Ray emissions of the 𝑆𝑛 decay Figure 4:
Decay curves of the 𝑆𝑛 radioactive nucleus constructed from the 761 keV and 1152 keV 𝛾 -line intensities. 𝑡 cooling time much more 7.7 m (the 𝑚 𝐼𝑛 isomer half-life) obey the equation (2) [10] for genetically-coupledradioactive nuclides 𝑆 𝛾 𝜀 ⋅ 𝐵𝑟 ⋅ 𝑛 ⋅ 𝜙 = 𝑌 𝑝 ⋅ 𝜆 𝑝 ⋅ 𝜆 𝑑 𝜆 𝑑 − 𝜆 𝑝 ⋅ [ 𝑒 − 𝜆𝑝𝑡 𝜆 𝑝 ⋅ 𝑒 − 𝜆 𝑝 𝑡 ⋅ ( 𝑒 − 𝜆 𝑝 𝑡 ) − 𝑒 − 𝜆𝑑𝑡 𝜆 𝑑 ⋅ 𝑒 − 𝜆 𝑑 𝑡 ( 𝑒 − 𝜆 𝑑 𝑡 )] + 𝑌 𝑑 𝑒 − 𝜆𝑑𝑡 𝜆 𝑑 ⋅ 𝑒 − 𝜆 𝑑 𝑡 ⋅ ( 𝑒 − 𝜆 𝑑 𝑡 ) (2)where in our case 𝑌 𝑝 and 𝑌 𝑑 are the yields of the p arent ( 𝑆𝑛 ) and d aughter ( 𝐼𝑛 ) nuclei, 𝜆 𝑝 and 𝜆 𝑑 the decayconstants of the parent and daughter nuclei respectively.The curves of the 𝐼𝑛 nucleus accumulation and decay plotted according to the experimental 𝛾 -line intensities171.2 keV and 245.3 keV, measured after the end of irradiation of the tin target, are shown in Fig. 5. These timedependences obey equation (2) and their forms are due to the differences of the half-lives of the parent and daughtermembers of the radioactive chain and the values of the yields ( 𝑌 𝑝 and 𝑌 𝑑 in the equation (2)) of the 𝑆𝑛 ( 𝛾 ,n) 𝑆𝑛 and 𝑆𝑛 ( 𝛾 ,p) 𝐼𝑛 reactions respectively. The growing pieces of the 𝐼𝑛 activity curves at the left part of Fig. 5are explained by the feeding of the longer-living nucleus by the shorter-living one decay. Fitting the equation (2) forgenetically-coupled activities by least squares method we were able to determine the values of the both yields andobtained an unexpected result: the values of 𝑌 𝑝 (i. e. of the 𝑆𝑛 ( 𝛾 ,n) 𝑆𝑛 ) reaction turned out to be noticeablyless than those determined using the traditional activation equation (1). Both data sets for different bremsstrahlungenergies are shown in Fig. 6. The decay features of the long-lived 𝐼𝑛 nucleus are investigated quite well to date andthe only reason for this observation may be large uncertainties of the experimental values of the 𝛾 -ray emission valuesof the radiation transitions following the 𝑆𝑛 isotope decay.The circles of Fig. 6 represent the experimental weighted average values of the photonuclear 𝑆𝑛 ( 𝛾 ,n) 𝑆𝑛 reaction yields calculated applying the traditional activation equation (1) and the current [2] 𝛾 -ray emission values ofthe 10 strongest 𝛾 -ray transitions of the 𝑆𝑛 → 𝐼𝑛 decay. The set of the triangles was obtained applying equation(2) for genetically coupled activities and the database [2] emission values of the 171.2 keV and 245.3 keV 𝛾 -rays ofthe 𝐼𝑛 → 𝐶𝑑 decay.The numerous measurements and analysis of the decay 𝛾 -ray energy spectra at different bremsstrahlung energiesand cooling times of the irradiated target enable us to recalculate the new values of the 𝛾 -ray emission values for the10 strongest radiation transitions following the 𝑆𝑛 nucleus radioactive decay. The intensities of the 9 transitions,excluding the 537.2 keV one, were happened to be lower those of NuDat 2.8 base [2] at the average factor of 1.64 Chekhovska A. et al.:
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Page 5 of 7 -Ray emissions of the 𝑆𝑛 decay Figure 5:
Accumulation and decay curves of the 𝐼𝑛 isotope nuclide. Figure 6:
The 𝑆𝑛 ( 𝛾 ,n) 𝑆𝑛 reaction yields determined using the traditional activation equation (circles) and equationfor genetically coupled activities (triangles). (0.10). The 537.2 keV 𝛾 -ray intensity recalculating taking into account different contributions of the ( 𝛾 ,n) and ( 𝛾 ,p)reactions is lower at the factor of 1.92 (0.16).In addition the solid and dashed curves in Fig. 6 represent the integral bremsstrahlung yields of the 𝑆𝑛 ( 𝛾 ,n) 𝑆𝑛 reaction calculated from the cross sections predicted by the statistical theory of nuclear reactions implemented in theNON-SMOKER computer code [11] and TENDL-2019 data library [12] respectively. Further interpretation of the 𝑆𝑛 ( 𝛾 ,n) 𝑆𝑛 and 𝑆𝑛 ( 𝛾 ,p) 𝑚,𝑔 𝐼𝑛 activation yields are currently underway. Chekhovska A. et al.:
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Page 6 of 7 -Ray emissions of the 𝑆𝑛 decay
3. Conclusions
So we can present updated values of the intensities of the 10 𝛾 -ray transitions following the 𝑆𝑛 radioactivedecay. They are presented in the right column of Table 2. Table 2
New intensities of the
𝐼𝑛 𝛾 -ray transitions following the ( 𝜀 + 𝛽 + ) -decay of the 𝑆𝑛 nucleus. 𝐸 𝛾 𝐼 𝛾 [%][keV] NuDat New data372.3 0.42 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± The new intensity values of the 𝛾 -ray emissions following the 𝑆𝑛 nucleus decay will be interest for both nuclearspectroscopy theories and correct calculations of activation cross sections and yields of those nuclear reactions wherethe 𝑆𝑛 radioactive nuclide is a residual one. The numerous relevant data presented in the EXFOR database have tobe revised. References [1] J. Blachot, Nuclear Data Sheets for A = 111, Nuclear Data Sheets 110 (2009) 1239 - 1407. doi:10.1016/j.nds.2009.04.002 .[2] .[3] .[4] T. Rauscher, N. Dauphas, I. Dillmann, C. Fr ̈𝑜 hlich, Z. F ̈𝑢 l ̈𝑜 p, G. Gy ̈𝑢 rky, Constraining the astrophysical origin of the p-nuclei through nuclearphysics and meteoritic data, Reports on Progress in Physics 76 (6) (2013) 066201. doi:10.1088/0034-4885/76/6/066201 .[5] T. Rauscher, Photonuclear reactions in astrophysics, Nuclear Physics News 28 (3) (2018) 12 - 15. doi:10.1080/10619127.2018.1463016 .[6] O. Itoh, H. Utsunomiya, H. Akimune, T. Kondo, M. Kamata, T. Yamagata, H. Toyokawa, H. Harada, F. Kitatani, S. Goko, C. Nair, Y.W. Lui,Photoneutron Cross Sections for Au Revisited: Measurements with Laser Compton Scattering 𝛾 -Rays and Data Reduction by a Least-SquaresMethod, Journal of Nuclear Science and Technology 48 (5) (2011) 834 - 840. doi:10.1080/18811248.2011.9711766 .[7] V. V. Varlamov, B. S. Ishkhanov, V. N. Orlin, S. Y. Troshchiev, New Data for 𝐴𝑢 ( 𝛾 ,nX) and 𝐴𝑢 ( 𝛾 ,2nX) Reaction Cross Sections, Bulletinof the Russian Academy of Sciences: Physics 74 (2010) 842 - 849. doi:10.3103/S1062873810060237 .[8] C. Nair, M. Erhard, A. R. Junghans, D. Bemmerer, R. Beyer, E. Grosse, J. Klug, K. Kosev, G. Rusev, K. D. Schilling, et al., Photoactivationexperiment on 𝐴𝑢 and its implications for the dipole strength in heavy nuclei, Physical Review C 78 (5) (2008) 055802. doi:10.1103/physrevc.78.055802 .[9] C. Plaisir, F. Hannachi, F. Gobet, M. Tarisien, m.-m. Aleonard, V. Meot, G. Gosselin, P. Morel, B. Morillon, Measurement of the 𝑅𝑏 ( 𝛾 ,n) 𝑚 𝑅𝑏 cross-section in the energy range 10-19 MeV with bremsstrahlung photons, The European Physical Journal A 48 (2012)68 - 72. doi:10.1140/epja/i2012-12068-7 .[10] G. Friedlander, J. W. Kennedy, J. M. Miller, Book, Nuclear and radiochemistry 14 (John Wiley and Sons, Inc., New York) (1981).[11] T. Rauscher, F.-K. Thielemann, Astrophysical Reaction Rates From Statistical Model Calculations, Atomic Data and Nuclear Data Tables 75(1-2) (2000) 1 - 351. doi:10.1006/adnd.2000.0834 .[12] https://tendl.web.psi.ch/tendl_2019/tendl2019.html . Chekhovska A. et al.: