J. Nig. Soc. Phys. Sci. 2 (2020) 166–169 Journal of the Nigerian Society of Physical Sciences Original Research Measurement of the Excited Energies Identified in 42Ca using the ROSPHERE Gamma-ray Arrays T. Daniela,∗, A. A. McAsuleb aDepartment of Physics, Benue State University, P. M. B. 102119, Makurdi, Benue State bDepartment of Physics, Federal University of Agriculture, P. M. B. 2373, Makurdi, Benue State Abstract Excited energy states totalling 11 in number identified to be associated with the 42Ca were detected via the ROSPHERE gamma-ray array detec- tors of IFIN-HH Bucharest from a 28Si(18O, 2p2n), where a multi-particle of 2 protons and 2 neutrons were evaporated in a fusion reaction. The excited energies were identified using γ-ray coincidences. All detected gamma energies (γ) recorded were compared with various literatures from NNDC and this shows an excellent agreement with each and the results are presented together with their calculated relative intensities. Keywords: Absolute relative error, accuracy, comparative study, stability. Article History : Received: 05 February 2020 Received in revised form: 20 April 2020 Accepted for publication: 03 May 2020 Published: 01 August 2020 c©2020 Journal of the Nigerian Society of Physical Sciences. All rights reserved. Communicated by: W. A. Yahya 1. Introduction Calcium-42 is one of the isotopic-nucleus of calcium with 22 neutrons and 20 protons. The two excess neutrons present in the nucleons distinguish it from the first stable nucleus of 40Ca with either protons or neutrons being magic. The heaviest of the isotopes is 48Ca with 8-neutrons higher than 40Ca [1]. The measured gamma energies of the nucleus have been reported in several articles with some of them showing the relative inten- sities of the measured gamma transitions. In this, the relative intensities of these gamma energies have been measured after they were identified to be associated with 42Ca through the in- strumentalities of Coincidence analysis [2]. ∗Corresponding author tel. no: +2348167598988 Email address: tdaniel@bsum.edu.ng, terver.daniel@yahoo.co.uk (T. Daniel ) 2. Experimental Details In the Coulomb unsafe reaction of 192Os target with the 18O beam at 80 MeV using the 9 MV tandem accelerator of the Horia Hulubei National Institute of Physics and Nuclear Engi- neering (known as IFIN-HH) in Bucharest [3], a fusion multi- particle of 2n2p was evaporated from the fusion of 28Si target with 18O – beam. 28Si was found to be one of the impurities in the 192Os target foil material bought from the Trace company in USA. This contaminated percentage of 42Ca and other chem- ical impurities from the target were observed to have reacted during the experiment when the 18O beam delivered the labora- tory energy of 80 MeV on the 192Os target in the chamber of the accelerator. Details of the purity composition of the 192Os are as shown in Table 1. This nuclear fusion evaporation reaction produced 42Ca as 166 Daniel & McAsule / J. Nig. Soc. Phys. Sci. 2 (2020) 166–169 167 the product of the reaction after evaporating 2n2 p particles from the compound with the beam current of 20 pnA with a hardware trigger condition of either LaBr3(Ce) – LaBr3(Ce) or HPGe – HPGe [4, 5]. The predicted fusion-evaporation cross-section for the observed channels (that is, from 60 MeV to 100 MeV) have 42Ca nucleus dominating the entire laboratory energy re- gion as chosen in this work. The relative cross-section mea- sured for the 42Ca nucleus is ≤ 100 mb [4, 5]. The experiment for the 18O beam on 192Os target was con- ducted for a period of 9 consecutive days at IFIN-HH Bucharest within which an approximate count of 1,200,000.00 was recorded using the ROmanian SPectroscopy in HEavy REactions, RO- SPHERE gamma-ray array of 14 High Purity Germanium, HPGe and 11 Lathanum-Bromide doped Cerium , LaBr3(Ce) detec- tors [4, 5, 6]. Table 1. The 192Os Target with the Observed Chemical Impurities [5] Element Symbol Impurity Measurement (ppm) Aluminium Al 500 Calcium Ca 100 Copper Cu 70 Iron Fe 500 Magnesium Mg 50 Manganese Mn 50 Nickel Ni 100 Lead Pb 50 Platinum Pt 50 Silicon Si 500 Tungsten W 100 3. Data Analysis Coincidence analysis was performed on the detected gamma energies from the ROPSHERE gamma-ray array detectors of the IFIN-HH Bucharest and these were identified to be associ- ated with 42Ca. Doing this, a gating condition was used where a particular gamma transition was selected as a reference en- ergy and all other energies that were seen to be in coincidence, that is, appearing with the selected gate at the same time were recorded. This was to further confirm that the measured gamma transitions were indeed associated with 42Ca [1, 7, 8]. Table 2 shows all the measured gamma transitions in the current work. The partial energy level scheme of 42Ca was obtained as shown in Figure 1 using RADware. Table 2. Details of the Observed Transitions in the Current Work as Detected from the 28Si(18O,2n2p)42Ca Eγ(keV ) Energy Level (keV) Relative Intensity Transition Ei → E f Iγ 146 6555 → 6409 23 9− → 8− 264 6409 → 6146 7 8− → 7− 437 3190 → 2752 50 6+ → 4+ 810 6555 → 5747 28 9− → 7− 815 7369 → 6555 20 10− → 9− 910 4099 → 3190 36 5− → 6+ 917 6409 → 5492 18 8− → 6− 1227 2752 → 1525 78 4+ → 2+ 1347 4099 → 2752 7 5− → 4+ 1525 1525 → 0 100 2+ → 0+ 1645 5745 → 4099 28 7− → 5− Figure 1. Symmetrical HPGe γ – γ matrix showing gates on 1227 keVand 1525 keV (left panel). The right panel of the figure shows the same gates on 1227 keV and 1525 keV gamma energies but with a different folding coincidence condition of γ – γ - γ (triple) trigger in HPGe detectors using RADware and GASPware softwares. 4. The Measured Energy Levels Associated with 42Ca in the Current Work The 1525-keV Level. The 1525 keV level is fed with a 1227 keV transition from the yrast Iπ = 4+ state to the Iπ = 2+. This energy level is assigned a spin of 2 with a positive parity. It decays to the ground state 0+ with the gamma energy of 1525 keV. The relative intensities of the gamma transitions have been determined in this current work as shown in Table 2. The 2752-keV Level. This energy level is populated by 437 keV gamma transition which is a decay from the 3190 keV level to a spin and positive parity of 4+. The relative intensity is cal- culated to be 50 (even though the directional correlations from 167 Daniel & McAsule / J. Nig. Soc. Phys. Sci. 2 (2020) 166–169 168 oriented states DCO’s calculation is not shown here). The mul- tipolarity is dominantly an E2, but can possibly be an M3 tran- sition using the expression in equation (1):∣∣∣Ii − I f ∣∣∣≤ ∆L ≤ ∣∣∣Ii + I f ∣∣∣ , (1) where the largest possible value of ∆L is Ii + I f and the lowest possible value Ii − I f . The parity change in the transition is given by the selection rules [9]. The 3190-keV Level. As shown in Figure 2 of the current work, more than two gamma transitions populated this energy level but with different experimental branching ratios, B(M1)/B(M2) (not determined here). Apart from 910 keV transition energy populating this state, both 2956 keV and 2302 keV gamma tran- sitions are not observed in this current work. This also forms the basis for which the gamma transitions are shown as bro- ken lines and under brackets. The observed multipolarity is M1 which is the likely dominant one. This is so because there is a strong dependence of the transition rate on multipolarity where the lowest multipolarities are most likely to occur [9]. The rel- ative intensity of the 910 keV gamma transition is calculated as 18 and this is shown in Table 2. 5. Discussion and Conclusion The coincidence spectra on selected gamma transition ener- gies in the left panel of Figure 1 is a double fold: that is, γ – γ matrix sorting condition in the master trigger of ROSPHERE. In this sorting, the gamma energy generally has more counts as recorded for same gates in triple fold gating condition. On the 1227 keV gate, gamma transitions of 145-, 264-, 382-, 437- , 810-, 815-, 910-, 917-, 1347-, 1525-, and 1645-keV were observed to be in coincidence with one another with 437-keV having the highest counts of approximately 2000 counts/keV. Looking at both Figures 1.0 and 2.0, 1227 keV and 1525 keV are coincident with each other. This implies that, a gate on ei- ther one should produce the other one in coincidence. On 1525 keV gate, gamma transitions found to be in coincidence are the 145-, 437-, 507-, 810-, 910-, 1227-, and 1645-keV [7, 8, 5, 10]. The coincidence analysis performed in Figure 1 further af- firms the assigned nucleus of 42Ca in the current work where the gamma transitions have already been reported by other re- searchers [1]. Acknowledgments TD thanks in a special way his PhD supervisors, Profs. Patrick Regan and Zsolt Podolyak for their mentorship during his programme at the University of Surrey, Guildford, UK. TD thanks Dr. Stanimir Kisyov of the IFIN-HH Bucharest and all other staff of the Institute for their various contributions during the 192Os(18O,16O)194Os experiment late 2015. Figure 2. Partial Energy Level Scheme of 42Ca Showing the Measured Gamma Transitions up to Higher Spin and Parity of Iπ = 10-- in the Current Work. References [1] Evaluated Nuclear Data File (ENSDF), http://www.nndc.bnl.gov/ensdf. Retrieved (2020). [2] N. Marginean, D. I. Balabanski, D. Bucurescu, S. Lalkovski, L. Atanasova, I. Cata-Danil, G. Cata-Danil, J. M. Daugas, D. Deleanu, P. Detistov, G. Deyanova, D. Filipescu, G. Georgiev, D. Ghia, K. A. Gladnishki, R. Lozeva, T. Glodariu, M. Ivacu, S. Kisyov, R. Mihai, R. Marginean, A. Negret, S. Pascu, D. Radulov, T. Sava, L. Stroe, G. Suli- man, & N. V. Zamfir, “In-beam Measurements of Sub-nanosecond Nu- clear Lifetimes with A Mixed Array of HPGe and LaBr3(Ce) Detectors”, Europium Physics Journal A 46 (2010) 329. [3] T. Daniel, S. Kisyov, P. H. Regan, N. 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