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postgraduate thesis: [Beta]-delayed neutron emission measurement of neutron-rich Sn to Cs isotopes

Title[Beta]-delayed neutron emission measurement of neutron-rich Sn to Cs isotopes
Authors
Advisors
Advisor(s):Lee, HCJXie, MH
Issue Date2019
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
Citation
Liu, J. [劉嘉健]. (2019). [Beta]-delayed neutron emission measurement of neutron-rich Sn to Cs isotopes. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR.
Abstractβ-delayed neutron emission probabilities (Pn values) and β-decay half-lives T1/2 of neutron-rich nuclei are important properties for understanding the formation of the heavy elements in the universe. It has been known for years that T1/2 and Pn values have key factors to determine rapid neutron-capture process (r-process) model calculation which is believed to be responsible for the creation of about half of the stable isotopes beyond iron. In r-process solar abundance distribution, there are three main peaks locating in mass number A ~ 80, 130 and 195. Especially, the second abundance peak of r-process at mass number A$\sim$130 is of great interest since its shape and distribution could help to pin down the astronomical environments. However, lacking experimental T1/2 and Pn values gives large uncertainties to astrophysical conditions in r-process nucleosynthesis. Although there are many theoretical models to predict the T1/2 and Pn, including shell model and gross theory, there is still a large discrepancy between experimental values, especially for very neutron-rich nuclei. $\beta$-delayed neutron emission measurement (BRIKEN) experiments have been carried out to measure T1/2 and Pn values of neutron-rich Sn to Cs (Z = 50 to 55, N >82)isotopes , aiming to improve and constrain astrophysical conditions for r-process nucleosynthesis calculations and provide benchmark points for theoretical nuclear models. The measurements were performed at Radioactive Isotope Beam Factory (RIBF) in RIKEN, Japan where can produce the most intense ion beam in the world. The nuclei of interest with averaged mass number A around 130 were produced by in-flight fission of a 238U beam colliding on a 5-mm-thick $^9$Be target with an energy of 345 MeV/u. The fragments were separated and identified by BigRIPS spectrometer using Bρ-ΔE-TOF method. The selected ions were transported through ZeroDegree spectrometer (ZDS) and stopped by a highly-compacted silicon array called AIDA which consisted of six double-sided strip silicon detectors for heavy ion and $\beta$ particle measurement. Total 140 $^3$He tubes surrounded around AIDA, forming a high-detection-efficiency neutron counter array called BRIKEN. On both sides of BRIKEN array, two Clover detectors were placed for $\gamma$ measurement. In order to reduce effects of background, an ancillary detection system including a single-sided strip detector (SSD) and different thickness of plastic scintillation detectors surrounded around BRIKEN and AIDA. The experiment resulted in new T1/2 and Pn values of a large range of neutron-rich Sn to Cs isotopes. Totally, 13 new T1/2 and 14 new Pn values, including 141Sb, 139-143Te, 142-146I, 148Xe and 149-151Cs were determined for the first time. The Pn values of 133-138Sn, 136-140Sb and 146-147Xe have been revised with better uncertainty. The comparison between experimental values and current different theoretical results of T1/2 and Pn values was carried out which indicates that a few experimental T1/2 and Pn can be reproduced by theoretical calculations. A network nucleosynthesis calculation for r-process isotopic abundance based on neutron star merger scenario with new T1/2 and Pn values has been performed to study the effects on the final isotopic abundance. Compared with the abundance calculated without new T1/2 and Pn values, it is shown that the new experimental values have increased about 20% calculated abundance closer to r-process abundance in mass 130~140. However, the calculated abundance with new experimental results is about one order magnitude smaller than the one without new values in mass 140~160 since the r-process path within this mass region lies on more neutron-rich nuclei, which still no experimental T1/2 and Pn values is known. The new experimental T1/2 and Pn values reported here are expected to improve theoretical models to predict more reliable β decay properties of more neutron-rich nuclei that experimental technique could not reach now. These predicted values will also help improving the r-process nucleosynthesis calculations.
DegreeDoctor of Philosophy
SubjectAntimony - Decay - Isotopes
Isotopes - Decay - Cesium
Isotopes - Iodine - Decay
Isotopes - Decay - Tellurium
Decay - Isotopes - Tin
Isotopes - Decay - Xenon
Dept/ProgramPhysics
Persistent Identifierhttp://hdl.handle.net/10722/278416

 

DC FieldValueLanguage
dc.contributor.advisorLee, HCJ-
dc.contributor.advisorXie, MH-
dc.contributor.authorLiu, Jiajian-
dc.contributor.author劉嘉健-
dc.date.accessioned2019-10-09T01:17:38Z-
dc.date.available2019-10-09T01:17:38Z-
dc.date.issued2019-
dc.identifier.citationLiu, J. [劉嘉健]. (2019). [Beta]-delayed neutron emission measurement of neutron-rich Sn to Cs isotopes. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR.-
dc.identifier.urihttp://hdl.handle.net/10722/278416-
dc.description.abstractβ-delayed neutron emission probabilities (Pn values) and β-decay half-lives T1/2 of neutron-rich nuclei are important properties for understanding the formation of the heavy elements in the universe. It has been known for years that T1/2 and Pn values have key factors to determine rapid neutron-capture process (r-process) model calculation which is believed to be responsible for the creation of about half of the stable isotopes beyond iron. In r-process solar abundance distribution, there are three main peaks locating in mass number A ~ 80, 130 and 195. Especially, the second abundance peak of r-process at mass number A$\sim$130 is of great interest since its shape and distribution could help to pin down the astronomical environments. However, lacking experimental T1/2 and Pn values gives large uncertainties to astrophysical conditions in r-process nucleosynthesis. Although there are many theoretical models to predict the T1/2 and Pn, including shell model and gross theory, there is still a large discrepancy between experimental values, especially for very neutron-rich nuclei. $\beta$-delayed neutron emission measurement (BRIKEN) experiments have been carried out to measure T1/2 and Pn values of neutron-rich Sn to Cs (Z = 50 to 55, N >82)isotopes , aiming to improve and constrain astrophysical conditions for r-process nucleosynthesis calculations and provide benchmark points for theoretical nuclear models. The measurements were performed at Radioactive Isotope Beam Factory (RIBF) in RIKEN, Japan where can produce the most intense ion beam in the world. The nuclei of interest with averaged mass number A around 130 were produced by in-flight fission of a 238U beam colliding on a 5-mm-thick $^9$Be target with an energy of 345 MeV/u. The fragments were separated and identified by BigRIPS spectrometer using Bρ-ΔE-TOF method. The selected ions were transported through ZeroDegree spectrometer (ZDS) and stopped by a highly-compacted silicon array called AIDA which consisted of six double-sided strip silicon detectors for heavy ion and $\beta$ particle measurement. Total 140 $^3$He tubes surrounded around AIDA, forming a high-detection-efficiency neutron counter array called BRIKEN. On both sides of BRIKEN array, two Clover detectors were placed for $\gamma$ measurement. In order to reduce effects of background, an ancillary detection system including a single-sided strip detector (SSD) and different thickness of plastic scintillation detectors surrounded around BRIKEN and AIDA. The experiment resulted in new T1/2 and Pn values of a large range of neutron-rich Sn to Cs isotopes. Totally, 13 new T1/2 and 14 new Pn values, including 141Sb, 139-143Te, 142-146I, 148Xe and 149-151Cs were determined for the first time. The Pn values of 133-138Sn, 136-140Sb and 146-147Xe have been revised with better uncertainty. The comparison between experimental values and current different theoretical results of T1/2 and Pn values was carried out which indicates that a few experimental T1/2 and Pn can be reproduced by theoretical calculations. A network nucleosynthesis calculation for r-process isotopic abundance based on neutron star merger scenario with new T1/2 and Pn values has been performed to study the effects on the final isotopic abundance. Compared with the abundance calculated without new T1/2 and Pn values, it is shown that the new experimental values have increased about 20% calculated abundance closer to r-process abundance in mass 130~140. However, the calculated abundance with new experimental results is about one order magnitude smaller than the one without new values in mass 140~160 since the r-process path within this mass region lies on more neutron-rich nuclei, which still no experimental T1/2 and Pn values is known. The new experimental T1/2 and Pn values reported here are expected to improve theoretical models to predict more reliable β decay properties of more neutron-rich nuclei that experimental technique could not reach now. These predicted values will also help improving the r-process nucleosynthesis calculations. -
dc.languageeng-
dc.publisherThe University of Hong Kong (Pokfulam, Hong Kong)-
dc.relation.ispartofHKU Theses Online (HKUTO)-
dc.rightsThe author retains all proprietary rights, (such as patent rights) and the right to use in future works.-
dc.rightsThis work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.-
dc.subject.lcshAntimony - Decay - Isotopes-
dc.subject.lcshIsotopes - Decay - Cesium-
dc.subject.lcshIsotopes - Iodine - Decay-
dc.subject.lcshIsotopes - Decay - Tellurium-
dc.subject.lcshDecay - Isotopes - Tin-
dc.subject.lcshIsotopes - Decay - Xenon-
dc.title[Beta]-delayed neutron emission measurement of neutron-rich Sn to Cs isotopes-
dc.typePG_Thesis-
dc.description.thesisnameDoctor of Philosophy-
dc.description.thesislevelDoctoral-
dc.description.thesisdisciplinePhysics-
dc.description.naturepublished_or_final_version-
dc.date.hkucongregation2019-
dc.identifier.mmsid991044146570903414-

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