Isomeric Beam Research Articles

In-flight production of an isomeric beam of 16N

An in-flight beam of 16N was produced via the single-neutron adding (d,p) reaction in inverse kinematics at the recently upgraded Argonne Tandem Linear Accelerator System (ATLAS) in-flight system. The amount of the 16N beam which resided in its excited 0.120 MeV Jπ=0− isomeric state (T1/2≈5 μs) was determined to be 40(5)% at a reaction energy of 7.9(3) MeV/u, and 24(2)% at a reaction energy of 13.2(2) MeV/u. The isomer measurements took place at an experimental station ≈30 m downstream of the production target and utilized an Al beam-stopping foil and a HPGe Clover detector. Composite 16N beam rate determinations were made at the experimental station and the focal plane of the Argonne in-flight radioactive ion-beam separator (RAISOR) with Si ΔE-E telescopes. A Distorted Wave Born Approximation (DWBA) approach was coupled with the known spectroscopic information on 16N in order to estimate the relative 16N isomer yields and composite 16N beam rates. In addition to the observed reaction-energy dependence of the isomer fraction, a large sensitivity to the angular acceptance of the recoils was also observed.

The science case of the FRS Ion Catcher for FAIR Phase-0

The FRS Ion Catcher at GSI enables precision experiments with thermalized projectile and fission fragments. At the same time it serves as a test facility for the Low-Energy Branch of the Super-FRS at FAIR. The FRS Ion Catcher has been commissioned and its performance has been characterized in five experiments with 238U and 124Xe projectile and fission fragments produced at energies in the range from 300 to 1000 MeV/u. High and almost element-independent efficiencies for the thermalization of short-lived nuclides produced at relativistic energies have been obtained. High-accuracy mass measurements of more than 30 projectile and fission fragments have been performed with a multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) at mass resolving powers of up to 410,000, with production cross sections down to the microbarn-level, and at rates down to a few ions per hour. The versatility of the MR-TOF-MS for isomer research has been demonstrated by the measurement of various isomers, determination of excitation energies and the production of a pure isomeric beam. Recently, several instrumental upgrades have been implemented at the FRS Ion Catcher. New experiments will be carried out during FAIR Phase-0 at GSI, including direct mass measurements of neutron-deficient nuclides below 100Sn and neutron-rich nuclides below 208Pb, measurement of β-delayed neutron emission probabilities and reaction studies with multi-nucleon transfer.

K38 isomer production via fast fragmentation

In radioactive ion beam experiments, beams containing isomers can be of interest in probing nuclear structure and informing astrophysical reaction rates. While the production of mixed in-flight ground state and isomer beams using nucleon transfer can be generally understood through distorted wave Born approximation methodology, low-spin isomer production via fast fragmentation is relatively unstudied. To attain a practical understanding of low-spin isomer production using fast fragmentation beams, a test case of $^{38}\mathrm{K}/^{38m}\mathrm{K}$ was studied at the National Superconducting Cyclotron Laboratory's ReAccelerated Beam facility. Starting from lise++ predictions, the fragmentation momentum distribution was sampled to determine isomer production. In addition, the effects of the gas stopper gradient and charge breeding times were examined. In the case of $^{38}\mathrm{K}$, isomer production peaks at $\ensuremath{\sim}57%$. This maximum is observed just off the lise++ predicted optimum magnetic rigidity, with only small losses in beam intensity within a few percent of this optimum rigidity setting. Control of the isomer fraction was also achieved through the modification of charge breeding times. Fast fragmentation appears to be a feasible method for production of low-spin isomeric beams, but additional study is necessary to better describe the mechanism involved.

Development of an Isomeric beam of 26Al for nuclear reaction studies

This paper describes the production and characterization of a26Al beam comprised of both, its 5+ ground state, and its 0+ isomeric state. The26Al beam was produced in-flight via the p (26Mg, 26Al)n reaction. The isomer fraction of the26Al beam was maximized by choosing a bombarding energy of 158.5 MeV for the26Mg primary beam. The resulting beam had an energy of 120 MeV, a total intensity of 2 × 105 particles/sec, a purity of 98% and an isomer content of 70%. This high-quality 26Al isomeric beam was used to study the26Alm(d, p)27Al reaction relevant for understanding the nucleosynthesis of26Al in the Galaxy.

Probing the Single-Particle Character of Rotational States in ^{19}F Using a Short-Lived Isomeric Beam.

A beam containing a substantial component of both the J^{π}=5^{+}, T_{1/2}=162 ns isomeric state of ^{18}F and its 1^{+}, 109.77-min ground state is utilized to study members of the ground-state rotational band in ^{19}F through the neutron transfer reaction (d,p) in inverse kinematics. The resulting spectroscopic strengths confirm the single-particle nature of the 13/2^{+} band-terminating state. The agreement between shell-model calculations using an interaction constructed within the sd shell, and our experimental results reinforces the idea of a single-particle-collective duality in the descriptions of the structure of atomic nuclei.

Probing the Single-Particle Character of Rotational States in F 19 Using a Short-Lived Isomeric Beam

Probing the Single-Particle Character of Rotational States in F 19 Using a Short-Lived Isomeric Beam

“Other” indirect methods for nuclear astrophysics

In the house of Trojan Horse Method (THM), I will say a few words about “other” indirect methods we use in Nuclear Physics for Astrophysics. In particular those using Rare Ion Beams that can be used to evaluate radiative proton capture reactions. I add words about work done with the Professore we celebrate today. With a proposal, and some results with TECSA, for a simple method to produce and use isomeric beam of 26m Al.

Isomer beam elastic scattering: 26mAl(p, p) for astrophysics

The advent of radioactive ground-state beams some three decades ago ultimately sparked a revolution in our understanding of nuclear physics. However, studies with radioactive isomer beams are sparse and have often required sophisticated apparatuses coupled with the technologies of ground-state beams due to typical mass differences on the order of hundreds of keV and vastly different lifetimes for isomers. We present an application of a isomeric beam of 26m Al to one of the most famous observables in nuclear astrophysics: galactic 26 Al. The characteristic decay of 26 Al in the Galaxy was the first such specific radioactivity to be observed originating from outside the Earth some four decades ago. We present a newly-developed, novel technique to probe the structure of low-spin states in 27 Si. Using the Center for Nuclear Study low-energy radioisotope beam separator (CRIB), we report on the measurement of 26m Al proton resonant elastic scattering conducted with a thick target in inverse kinematics. The preliminary results of this on-going study are presented.

TSR: A storage and cooling ring for HIE-ISOLDE

It is planned to install the heavy-ion, low-energy ring TSR, currently at the Max-Planck-Institute for Nuclear Physics in Heidelberg, at the HIE-ISOLDE facility in CERN, Geneva. Such a facility will provide a capability for experiments with stored, cooled secondary beams that is rich and varied, spanning from studies of nuclear ground-state properties and reaction studies of astrophysical relevance, to investigations with highly-charged ions and pure isomeric beams. In addition to experiments performed using beams recirculating within the ring, the cooled beams can be extracted and exploited by external spectrometers for high-precision measurements. The capabilities of the ring facility as well as some physics cases will be presented, together with a brief report on the status of the project.

First spatial separation of a heavy ion isomeric beam with a multiple-reflection time-of-flight mass spectrometer

211Po ions in the ground and isomeric states were produced via 238U projectile fragmentation at 1000 MeV/u. The 211Po ions were spatially separated in flight from the primary beam and other reaction products by the fragment separator FRS. The ions were energy-bunched, slowed-down and thermalized in a gas-filled cryogenic stopping cell (CSC). They were then extracted from the CSC and injected into a high-resolution multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). The excitation energy of the isomer and, for the first time, the isomeric-to-ground state ratio were determined from the measured mass spectrum. In the subsequent experimental step, the isomers were spatially separated from the ions in the ground state by an ion deflector and finally collected with a silicon detector for decay spectroscopy. This pioneering experimental result opens up unique perspectives for isomer-resolved studies. With this versatile experimental method new isomers with half-lives longer than a few milliseconds can be discovered and their decay properties can be measured with highest sensitivity and selectivity. These experiments can be extended to studies with isomeric beams in nuclear reactions.

Decay-Assisted Laser Spectroscopy of Neutron-Deficient Francium

This paper reports on the hyperfine-structure and radioactive-decay studies of the neutron-deficient francium isotopes $^{202-206}$Fr performed with the Collinear Resonance Ionization Spectroscopy (CRIS) experiment at the ISOLDE facility, CERN. The high resolution innate to collinear laser spectroscopy is combined with the high efficiency of ion detection to provide a highly-sensitive technique to probe the hyperfine structure of exotic isotopes. The technique of decay-assisted laser spectroscopy is presented, whereby the isomeric ion beam is deflected to a decay spectroscopy station for alpha-decay tagging of the hyperfine components. Here, we present the first hyperfine-structure measurements of the neutron-deficient francium isotopes $^{202-206}$Fr, in addition to the identification of the low-lying states of $^{202,204}$Fr performed at the CRIS experiment.

Population of high-spin isomeric states following fragmentation of238U

Isomeric ratios have been determined for 23 metastable states identified in A≈200 nuclei from Pt to Rn near the valley of stability following fragmentation of 238U. This includes high-spin states with angular momenta ranging from (39/2)ℏ to 25ℏ. The experimental results are discussed together with those of similar experiments performed in this mass region. Isomeric ratios are compared with theoretical predictions where the angular momentum of the fragment arises purely due to the angular momentum of nucleons removed from the projectile. The theoretical yield of low-spin states is generally overestimated. In these cases the assumption of 100% feeding of the isomer may require modification. However, the yield of high-spin isomeric states [Im ≥ (39/2)ℏ] is significantly underestimated and highlights the requirement for a more complete theoretical framework in relation to the generation of fragment angular momentum. The enhanced population of high-spin states reported here is advantageous to future studies involving isomeric beams at fragmentation facilities such as the Rikagaku Kenkyusho RI Beam Factory (Japan) and next-generation facilities at the Facility for Antiproton and Ion Research (Germany) and Facility for Rare Isotope Beams (USA).

Solving nuclear shape conundrum at HIE-ISOLDE

It is the purpose of this paper to illustrate some of the low-energy nuclear physics that we want to pursue at the new HIE-ISOLDE radioactive-ion-beam facility at CERN. The University of the Western Cape leads an experimental proposal and co-authors two Letters of Intent, in collaboration with European institutions, at HIE-ISOLDE. Timely topics such as the "Exploration of K-isomerism using unique high-K isomeric beams – CERN-INTC-I-101" and "Shape changes and proton-neutron pairing around the N = Z line – CERN-INTC-I-102" are addressed in these Letters of Intent. Our experimental proposal aims at performing a multi-step Coulomb-excitation of radioactive 70Se ion beams using the 208Pb(70Se,70Se*)208Pb* reaction at a bombarding energy of 5.5 MeV/u. The physics goal is a precise measurement of the (2+1 || Ê2 || 2+1) diagonal matrix element, related to the spectroscopic quadrupole moment, in 70Se. Full simulations presented in this work show distinct angular distributions for plausible values of the spectroscopic quadrupole moment; with a predicted uncertainty of approximately ±0.1 eb. Additional diagonal and transitional matrix elements will also be obtained. These results will shed light onto the origin of rarely-found oblate shapes and shape coexistence in this region of rapidly-changing shell structure.

The ILIMA project at FAIR

The Isomeric beams, LIfetimes and MAsses (ILIMA) collaboration will exploit heavy-ion storage rings at the Facility for Antiproton and Ion Research (FAIR) for the study of exotic nuclei. Single-ion sensitivity and exceptional production rates of bare or few-electron radioactive ions, with atomic numbers up to Z=92, promise access to a wide range of short-lived nuclides for the first time. Measuring the masses, lifetimes and decay modes of ground and isomeric states with t1/2>10 μs will reveal key features of nuclear structure and nuclear astrophysics, extending, for example, to r-process waiting-point nuclides in the 208Pb region.

Laser assisted decay spectroscopy at the CRIS beam line at ISOLDE

The new collinear resonant ionization spectroscopy (Cris) experiment at Isolde, Cern uses laser radiation to stepwise excite and ionize an atomic beam for the purpose of ultra-sensitive detection of rare isotopes and hyperfine structure measurements. The technique also offers the ability to purify an ion beam that is contaminated with radioactive isobars, including the ground state of an isotope from its isomer. A new program using the Cris technique to select only nuclear isomeric states for decay spectroscopy commenced last year. The isomeric ion beam is selected using a resonance within its hyperfine structure and subsequently deflected to a decay spectroscopy station. This consists of a rotating wheel implantation system for alpha and beta decay spectroscopy, and up to three high purity germanium detectors for gamma-ray detection. This paper gives an introduction to the Cris technique, the current status of the laser assisted decay spectroscopy set-up and recent results from the experiment in November 2011.

CRIS: A new method in isomeric beam production

The Collinear Resonance Ionization Spectroscopy (CRIS) experiment at ISOLDE, CERN, uses laser radiation to stepwise excite and ionize an atomic beam for the purpose of ultra-sensitive detection of rare isotopes, and hyperfine-structure measurements. The technique also offers the ability to purify an ion beam that is heavily contaminated with radioactive isobars, including the ground state of an isotope from its isomer, allowing decay spectroscopy on nuclear isomeric states to be performed. The isomeric ion beam is selected by resonantly exciting one of its hyperfine structure levels, and subsequently ionizing it. This selectively ionized beam is deflected to a decay spectroscopy station (DSS). This consists of a rotating wheel implantation system for alpha- and beta-decay spectroscopy, and up to three germanium detectors around the implantation site for gamma-ray detection. Resonance ionization spectroscopy and the new technique of laser assisted nuclear decay spectroscopy have recently been performed at the CRIS beam line on the neutron-deficient francium isotopes. Here an overview of the two techniques will be presented, alongside a description of the CRIS beam line and DSS. © Owned by the authors, published by EDP Sciences, 2013.

Storage ring at HIE-ISOLDE

We propose to install a storage ring at an ISOL-type radioactive beam facility for the first time. Specifically, we intend to setup the heavy-ion, low-energy ring TSR at the HIE-ISOLDE facility in CERN, Geneva. Such a facility will provide a capability for experiments with stored secondary beams that is unique in the world. The envisaged physics programme is rich and varied, spanning from investigations of nuclear ground-state properties and reaction studies of astrophysical relevance, to investigations with highly-charged ions and pure isomeric beams. The TSR might also be employed for removal of isobaric contaminants from stored ion beams and for systematic studies within the neutrino beam programme. In addition to experiments performed using beams recirculating within the ring, cooled beams can also be extracted and exploited by external spectrometers for high-precision measurements. The existing TSR, which is presently in operation at the Max-Planck Institute for Nuclear Physics in Heidelberg, is well-suited and can be employed for this purpose. The physics cases as well as technical details of the existing ring facility and of the beam and infrastructure requirements at HIE-ISOLDE are discussed in the present technical design report.

Determination of the isomeric fraction in a postaccelerated radioactive ion beam using the coupled decay-chain equations

A method based on the coupled decay-chain equations for extracting the isotopic and the isomeric composition of a postaccelerated radioactive ion beam is presented and demonstrated on a data set from a Coulomb excitation experiment. This is the first attempt of analyzing the content of a postaccelerated radioactive ion beam using this technique. The beam composition is required for an absolute normalization of the measurement. The strength of the method, as compared to present online-based methods, lies in the determination of the isomeric fraction of a partially isomeric beam using all data accumulated during the experiment. We discuss the limitations and sensitivity of the method with respect to the γ -ray detection efficiency and the accumulated flux.

Isobar separation at FRS-ESR – a development towards pure isomeric stored beams

One important goal of the ILIMA project at FAIR is the study of masses and decay properties of relativistic isomeric beams stored and cooled in the planned storage-ring complex. A new scheme is described, where a storage-cooler ring is used for high-resolution mass separation. Experimental results on the separation of the isobaric pair 140Pr-140Ce are presented.

FIRST USE OF POST-ACCELERATED ISOMERIC BEAMS FOR COULOMB EXCITATION STUDIES OF ODD-ODD NUCLEI AROUND N=40

We report on the first use of post-accelerated radioactive isomeric beams. Long-lived isomeric states in 68 Cu and 70 Cu have been produced and separated at ISOLDE, CERN. Subsequently they were post-accelerated to 2.86 MeV/u and sent to a target in the center of the MINIBALL spectrometer, used for the detection of the γ-rays of interest. The preliminary results from the Coulomb excitation of the Iπ=6-, 1+ states in 68 Cu and the Iπ=6- one in 70 Cu , compared to a large-scale shell model calculations, hint the importance of the excitations across the Z=28 gap for the understanding of the nuclear structure in the neutron-rich N=40 region.