Journal of Physics: Conference Series PAPER • OPEN ACCESS Study of exotic decay of Cs isotope close to the proton drip line To cite this article: P. Das et al 2020 J. Phys.: Conf. Ser. 1643 012127   View the article online for updates and enhancements. You may also like Search for Multimessenger Sources of Gravitational Waves and High-energy Neutrinos with Advanced LIGO during Its First Observing Run, ANTARES, and IceCube A. Albert, M. André, M. Anghinolfi et al. - Electron and photon reconstruction and identification with the CMS experiment at the CERN LHC The CMS collaboration, A.M. Sirunyan, A. Tumasyan et al. - Performance of the ATLAS RPC detector and Level-1 muon barrel trigger at (s)=13 TeV The ATLAS collaboration, G. Aad, B. 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Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd 27th International Nuclear Physics Conference (INPC2019) Journal of Physics: Conference Series 1643 (2020) 012127 IOP Publishing doi:10.1088/1742-6596/1643/1/012127 1 Study of exotic decay of Cs isotope close to the proton drip line P.Das1,2, Ushasi Datta1,2†0, S.Chakraborty1,3, A.Rahman1,4, M.J.G.Borge5,6, O.Tengblad5, A. N. Andreyev7, A.Becerril5, P.Bhattacharya1, A.Bhattacharyya1,2, J.Cederkall8, H. De Witte9, L. M. Fraile10, A.Gottberg6,11, P. T. Greenlees12,13, L.J.Harkness-Brennan14, M. Huyse9, D.S. Judson14, J. Konki12,13, J.Kurcewicz6, M.Kowalska6, I. Lazarus15, R. Lica 6, S.Mandal16, M. Madurga6, N. Marginean17, R. Marginean17, C. Mihai17, I.Morroquin5, E. Nacher5, A. Negret17, R. D. Page15, S.Pascu17, A. Perea5 V. Pucknell15, P. Rahkila12, E. Rapisarda6, F. Rotaru17, J.Ray1, C. O. Sotty9, P. Van Duppen9, V. Vedia10, N. Warr18, T. Stora6, R.Wadsworth7 1Saha Institute of Nuclear Physics, Kolkata, India 2Homi Bhabha National Institute, Mumbai, India 3University of Engg. and Management, Kolkata, India 4Jalpaiguri Govt. Engg. College, Jalpaiguri, West Bengal, India 5Inst. de Estructura de la Materia, CSIC, Madrid, Spain 6ISOLDE, CERN, Geneva, Switzerland 7University of York, Department of Physics, York YO10 5DD, North Yorkshire, United Kingdom 8University of Lund, Sweden 9KU Leuven, Instituut voor Kern- en Stralingsfysica, Celestijnenlaan 200D, 3001 Leuven, Belgium 10Grupo de Fisica Nuclear, and IPARCOS, Facultad de CC. Fsicas, Universidad Complutense, CEI Moncloa, 28040 Madrid, Spain 11TRIUMF, Vancouver, Canada 12University of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, Finland 13Helsinki Institute of Physics, University of Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland 14Department of Physics, Oliver Lodge Laboratory, University of Liverpool, Liverpool L69 7ZE, United Kingdom 15STFC Daresbury, Daresbury, Warrington WA4 4AD, United Kingdom 16University of Delhi, Delhi, India 17University of Bucharest, Faculty of Physics, Atomistilor 405, Bucharest-Magurele, Romania 18Institut fur Kernphysik, Universitat zu Koln, Zulpicher Strasse 77, D-50937 Koln, Germany Abstract. The neutron-deficient 115Cs was produced at ISOLDE, CERN by spallation reaction using 1.4 GeV proton on LaC2 target. The exotic decay modes were studied by using a charged particle array (DSSD and pad detectors) and a γ-detector array (four Clovers) at the ISOLDE decay station (IDS). In this report, results on observed β-delayed particle emission from 115Cs, a nucleus close to proton drip line, is presented. By measuring the time distribution in the delayed proton spectrum, the half-life of the ground state of 115Cs was extracted. The 0 † : Corresponding author : ushasi.dattapramanik@saha.ac.in 27th International Nuclear Physics Conference (INPC2019) Journal of Physics: Conference Series 1643 (2020) 012127 IOP Publishing doi:10.1088/1742-6596/1643/1/012127 2 obtained half-life is in agreement with previous reported value. For the first time, the p-unbound states of 115Xe, obtained by measuring beta-delayed protons from 115Cs is reported. 1. Introduction The study of properties of nuclei near and beyond the drip lines provides unique information on n-n interaction that is important in understanding the limits of existence of the quantum many body systems i.e. atomic nuclei [1]. The experimental data close to the drip line may validate the nuclear models and nucleon-nucleon interaction [2, 3, 4]. Many interesting properties are observed in these nuclei; the disappearance of the magic numbers [5, 6], appearance of PIGMY resonance [7, 8], exotic decay [9, 10, 11, 12], exotic cluster structure [13] etc. In this article, the study of exotic decay mode of neutron deficient nucleus, A∼ 115 close to the proton drip-line is reported. Due to large difference in the binding energies of proton(s) and neutron(s) in the nuclei around drip-line, the Q-value for decay of the nucleus is large enough to populate the excited states of the daughter nucleus above the particle threshold. The study of these exotic decays may provide information on a rich variety of properties as spin, parity, energy and lifetime of the unbound states above particle threshold. Comparing the properties of those states, one access to the component of n-n interaction due to coupling to the continuum. Moreover, the effect of the proton-skin thickness on decays properties of neutron-deficient nuclei still needs further investigation. The mass region A∼ 100-120 around the proton drip line is known as Island of cluster emitter, which yet need experimental verification. We have initiated an experimental investigation to study exotic decay for the nuclei Cs, Xe, Ba, near proton drip line. In this article, experimental observation of the decay of 115Cs is presented. 115Cs is located close to the proton drip line with a half-life of 1.4(8)sec according to latest evaluation [14]. Due to the large Q-value ( QEC) for electron capture many different decay channels are open in the daughter nucleus. Thus after electron capture of 115Cs, the daughter nucleus, 115Xe can be populated in excited states above the proton threshold and it may further decay by proton or alpha emission. According to previous measurement [14] the delayed proton branch for this isotope is 0.07% . In case of 115Xe, the one proton separation (Sp), two proton separation (S2p), alpha separation energy (Sα) are (-3.15(15)) MeV, (-4.89(3) ) MeV and 2.506(14) MeV [15], respectively. Fig. ?? represents schematic diagram of part of the exotic decay of 115Cs. 2. Experiment The radioactive Cs, Ba beam were produced by bombarding a tailored Lanthanum Carbide (LaC2) target with 1.4 GeV protons, obtained from CERN PS booster, followed by spallation/fragmentation reaction in the target. The radioactive beams were produced, ionized, extracted by a hot rhenium surface ion source, and separated using the ISOL method. The extraction and ionization efficiencies of Cs isotopes exceed the ones for Ba isotopes significantly. Therefore, in-target fluorination was used in order to extract Ba as fluoride molecules on a mass with greatly reduced isobaric contaminations. Particular beam of mass (A) with energy of 60 keV was mass-separated and transferred to the experimental hall and implanted on a 20 µg/cm2 carbon foil located in the middle of the detector setup. At IDS, a compact particle detection system consisting of four DSSDs (Double Sided Silicon Strip Detectors), stacked in telescope configuration with 4 PAD detectors. A fifth DSSD (1500 µm thick was placed below the setup for beta counting, see Fig.3. Four High-Purity Germanium(HPGe) clover detectors surround the chamber to provide better resolution and high γ-ray detection efficiency (see Fig.2). The detector setup is therefore able to detect both charged particles and γ-rays with high efficiency. The DSSDs are of different thickness. The thin DSSDs (65 and 67 µm) are insensitive to β radiation but they stop low energy protons, alphas etc. The thick DSSDs can fully stop high 27th International Nuclear Physics Conference (INPC2019) Journal of Physics: Conference Series 1643 (2020) 012127 IOP Publishing doi:10.1088/1742-6596/1643/1/012127 3 115Cs55 115Xe54 114I53 p 8.9MeV Figure 1. Schematic diagram of the part of exotic decay mode. energy protons, while a fifth thick horizontal DSSD is mainly used for detection of β radiation. The PADs have been used for β detection. Figure 2. Photograph of the experi- mental setup at IDS, ISOLDE, CERN during experiment IS545. DSSD1: 295μm PAD1: 1483 μm DSSD2: 524 μm PAD3: 1473 μm Target DSSD4: 67μm PAD4: 505μm DSSD6: 65μm PAD6: 500μm DSSD5: 1000μm Incoming beam of 115Cs Figure 3. Arrangements of Double sided silicon detector (DSSD) and PAD detector setup used during IS545 experiment at IDS, ISODE, CERN. The distance of each of the DSSDs from the target is ∼ 4.0 cm. Each of the DSSD is made of 5cm×5cm silicon wafer. There are 16 strips in each of the front layer and back side 27th International Nuclear Physics Conference (INPC2019) Journal of Physics: Conference Series 1643 (2020) 012127 IOP Publishing doi:10.1088/1742-6596/1643/1/012127 4 layer of the DSSD. The width of each strip is 3.0 mm, where the front strips are vertical and back strips are horizontal. The Solid angle coverage of of the silicon strip detectors is nearly 43%. For the calibration of silicon detectors long-lived calibrated standard alpha sources were used: 148Gd64(T1/2=71.1 years), 241Am95(T1/2=432.6 years),239Pu94(T1/2=24110 years),249Cf98(T1/2=351 years). For the calibration of HPGe a standard calibrated gamma source 152Eu was used. 3. Data Analysis After calibration and validating the events the data analysis has been performed using the CERN-ROOT platform. For the first time detailed study of exotic decay mode of delayed proton(s), alpha, γ-rays and exotic clusters of 115Cs, beyond proton drip line is reported and the delayed bound and resonance states of daughter nuclei have been identified. Fig.4 [left] shows the thin DSSD energy spectrum which contains the energy loss of β-particles, proton and alphas. By performing coincidence and anti-coincidence with consecutive PAD detector spectrum, these spectra can be separated into each component. Fig. 4 [right] shows two dimensional particle energy-loss spectrum obtained in coincidence with the thin DSSD and consecutive pad detector. Clearly, proton and beta related parts have been separated (see Fig.4[right]). The proton spectrum is shown in the fig. 4 [right] by a banana-plot. Where as the alpha spectrum can be obtained from the energy loss spectrum in the thin DSSD in anti-coincidence mode with consecutive PAD detector. Figure 4. [left] The energy loss spectrum obtained from thin DSSD detector of this experiment. [right] Two dimensional coincidence spectrum for dE-E telescope where dE was obtained from above thin DSSD and E was obtained from consecutive PAD detector. For more details see text. 4. Results and discussion 4.1. Determination of Half-life The half-life of 115Cs has been obtained from the time distributed protons spectrum. Fig.5 shows time distributed proton obtained from the proton banana-plot condition as shown in Fig 4. To obtain the decay half-life of 115Cs, the time distributed proton spectrum was fitted with the function N=N0e −λt as shown in Fig. 5. The obtained half-life of 115Cs is 1.03(10) sec. The previous reported value is 1.4(8) sec [14]. 27th International Nuclear Physics Conference (INPC2019) Journal of Physics: Conference Series 1643 (2020) 012127 IOP Publishing doi:10.1088/1742-6596/1643/1/012127 5 0 2 4 6 8 10 12 0 1 2 3 4 5 6 Half-Life = 1.03(10)sec C o u n ts p e r 0 .1 s e c Time(sec) Figure 5. The time distribution of delayed proton events obtained from 115Cs of present experiment. The time distributed spectrum has been fitted with the function N=N0e −λt. Figure 6. The energy spectrum of unbound resonance states of nucleus 115Xe, populated after decay of 115Cs. 4.2. Unbound resonance states After electron capture or positron decay of 115Cs, the daughter nucleus 115Xe, was populated with energy upto 8.0 MeV and the unbound states above one proton threshold (Sp = 3.15 MeV for 115Xe) can be reconstructed from delayed proton energy measurement. From the preliminary data analysis, it has been observed that the delayed proton branch for this isotope is much larger than previous reported value[14]. Fig.6 shows reconstructed excited states (preliminary) of 115Xe, populated after decay of 115Cs. It is evident from Fig.6 that the populated states are sharp resonance closely spaced states in the energy-range energy 5.5 MeV to 8.0 MeV. More investigations are ongoing to study the properties of those p-unbound states which may allow to constrain the component of coupling to the continuum in the n-n interaction of nuclei around proton drip line. Thus for the first time p-unbound states (preliminary) of 115Xe obtained by measuring delayed proton from 115Cs is reported. 5. Summary The neutron deficient Cs isotope close to the proton drip line was studied at ISOLDE using IDS facility. Details of the exotic decay mode i.e. decaying delayed proton, alpha, γ-rays and exotic clusters from the neutron deficient nuclei near proton drip line was measured using a compact dE-E telescope and a clover array. The half life (t1/2) of 115Cs was obtained from the data analysis of time distributed delayed proton events that is in agreement with previous reported value within error. We report for the first time on the p-unbound excited states of 115Xe obtained by studying the delayed protons from 115Cs. Further data analysis are going on to understand the background from different sources. Further investigation to identify multi-particles or cluster decaying unbound states in this mass region will be performed. 27th International Nuclear Physics Conference (INPC2019) Journal of Physics: Conference Series 1643 (2020) 012127 IOP Publishing doi:10.1088/1742-6596/1643/1/012127 6 6. Acknowledgement The authors would like to thank the technical members of accelerator and target development group of ISOLDE, CERN for delivering the beam and production target of ISOL facility. One of the authors, Ushasi Datta acknowledges with thanks to SERB, India for the financial support (travel) for attending and presenting the paper in the conference (INPC2019). Authors of SINP deeply acknowledge the SEND (XI th plan, DAE, India) and IENP/HENPP (XII th plan, DAE, India) project grant. This project has received funding from the European Union’s Horizon 2020 ENSAR2 project under grant agreement no 654002 and the Spanish research council under contract FPA2015-64969-P. The authors (P.Das and A.Bhattacharyya) acknowledge with thanks the financial support provided by the CSIR vide file number 09/489(0111)/2019EMR-I and 09/489(0115)/2019EMR-I respectively. References [1] J.Erler et al., Nature 486, 509 (2012). [2] A.Miller et al., Nature physics 15, 432 (2019). [3] G.A.Lalazissis, D.Vretenar, P.Ring, arxiv:nucl-th/9905019v1 (1999). [4] P.J.Woods and C.N.Davids Ann.Rev. Nucl. Part.Sc. 47, 541 (1997). [5] C.Thibault et al., Phys.Rev.C 12, 644 (1975). [6] U.Datta et al., PRC 94, 034304 (2016). [7] A.A.Leistenschneider, et al., Phys.Rev.Lett. 86, 5442 (2001). [8] P.Adrich et al., Phys.Rev.Lett. 95, 132501 (2005). [9] M J G Borge,Phys.Scr. 014013 (2013). [10] M.Pfuetzner et al., Rev. Mod. Phys. 84, 567 (2012). [11] I.Marroquin et al., Acta Physica Polonica B, vol. 47 (2016). [12] J.Ray et al., EPJ66, 02089 (2014). [13] U.Datta et al., AIP 2038, 020020 (2018). [14] J.M.D’auria et al., Nuclear Physics A301 397-410 (1978). [15] nndc.bnl.gov.