Decay Chains of Fast Alpha Emitters in the Actinide Region

Abstract

With the advent of increasingly advanced spectroscopic instruments after the turn of the century, it has become accessible to unravel the structure of instantly ‘vanishing’ nuclei, with lifetimes as short as 1 μs, and responsible for pile-up events in analog electronics. Experimental data has been recorded by the Nuclear Structure Group at Lund University for 48Ca/50Ti + nat.Hf reactions during the preparation stages of the ‘Spectroscopy along Decay Chains of Element 114, Flerovium’ which was carried out in two subexperiments in 2019 and 2020 at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany. These reactions have yielded hints of spectroscopic information for fast α-decaying nuclei in anticipated long α-decay chains in the actinide region. Many of these nuclei have not been studied in detail since their discovery decades earlier.

This work adds new indications which contribute to the nuclear structure information for some of these fast α emitters. The investigated region of the nuclidic chart is in the vicinity of heavy-, neutron-deficient isotopes normally considered a stepping stone for answering open questions of how approaching the N = 126 shell closure affects the nuclear structure of isotopes in this region. The recorded data was prepared to implement a decay-chain-hunting procedure. Comprehensive data analysis has been carried out to deduce the decay chains of the several, fast α emitters lying in the region of the neutron-deficient uranium isotopes. The most prevalent decay chain seen is that of the 225U isotope of which all four α decays are observed and a decay scheme including α-decay fine structure has been produced. This acted as a proof-of-concept technique for further searches. More importantly, there are strong indications of possibly two new states as well as an improved half-life of 217Ra. Some of the very fast α decays have been observed successfully. Lastly, indications of a handful of new excited levels have been found. Building on the work done in this project is expected to lead to exciting findings that would increase our knowledge and understanding of the nuclear structure of these fast α-decaying isotopes.

Popular Abstract

An exciting area in the field of physics is the study of the structure of the nucleus – the positively charged central part of the atom that forms the building blocks of matter – and unravelling its mysteries to better understand how and why they have the properties that we observe. Unstable nuclei undergo radioactive decay to relatively more stable nuclei in a lower energy state and release energy in the process. Heavy and superheavy elements predominantly decay by emitting an α particle, which is a helium nucleus, consisting of two positively charged protons and two electrically neutral neutrons. Emission of γ-ray photons that are electromagnetic radiation might follow after an α decay. These decays allow us to probe the nucleus and get information on its states and configuration. Alpha-decay spectroscopy is a valuable technique used for nuclear structure studies where one investigates the α decay or a chain of α decays of a radioisotope.

This work focuses on an alpha-decay spectroscopy experiment performed at the GSI HelmholtzCentre for Heavy Ion Research in Darmstadt, Germany. 48Ca and 50Ti ions were accelerated and bombarded on a nat.Hf target for investigating the α-decay chains of the resulting nuclei. Energies of the α particles and γ rays emerging from the nuclei along the decay chains were measured. The decay chains are expected to contain many fast α-decaying nuclei with lifetimes ranging in milliseconds to fractions of a microsecond. The study of these α decays has become accessible only in recent decades with the advent of highly advanced spectroscopic electronics that allow high-resolution α-decay spectroscopy capable of picking out the fast α decays. Through this study, it is desired to achieve validation of existing decay schemes, devise a proof-of-concept technique to extract α decay chains with fast α emissions and add further nuclear structure information for some of these fast α emitters.

The analysis of the recorded experimental data led to findings of a handful of the α decays from fast α emitters lying in the region of the neutron-deficient uranium isotopes. The decay chain of the 225U nuclei of which all four successive α decays has been observed and contained hints of new fine structure – alternate α decay modes – of α decay into 217Ra nuclei. The tentative fine structure of alpha decay implies the possible discovery of new nuclear states. An improved half-life of the 217Ra nuclei could also be determined. Building on the work done in this project is expected to lead to exciting findings that would increase our knowledge and understanding of nuclear structure.

• author: Sayed, Tanvir
• supervisor: Luis Sarmiento
• organization: Department of Physics; Particle and nuclear physics
• course: FYSM63 20232
• year: 2024
• type: H1 - Master's Degree (One Year)
• subject: Physics and Astronomy
• keywords: alpha decay, alpha emissions, fine structure, decay chain, decay scheme, alpha spectrometry, actinide, nucleus, nuclear structure, nuclear states, energy levels, uranium isotopes, U310 experiment, parasitic runs, decay station, TASISpec+, moving window deconvolution, digitisers, alpha-gamma coincidence, 221-Th decay, fine structure of alpha decay to 217-Ra, GSI, Gamow's theory, Geiger-Nuttall, chain search, short half-lives
• language: English
• id: 9147935
• date added to LUP: 2024-02-12 11:24:33
• date last changed: 2024-02-12 11:24:33