Decay Spectroscopy Experiments Research Articles

Response of the FAst TIMing Array (FATIMA) for DESPEC at FAIR Phase-0

The Monte-Carlo simulated response for γ-ray detection of the FAst TIMing Array (FATIMA) for exploitation within the DEcay SPECtroscopy (DESPEC) experimental system at the FAIR Phase-0 facility at Darmstadt, Germany is presented. In this configuration, FATIMA consisted of 36 LaBr3(Ce) detectors surrounding the AIDA, position-sensitive charged-particle active stopper. The decay of the Iπ=8+ isomer-fed decay cascade in 96Pd, measured in the first DESPEC experiment at the FAIR-0 facility was used to validate the simulations. The experimental data yielded in-situ full-energy peak efficiency values for FATIMA of 11.2(11)%, 6.8(7)%, 3.8(4)% and 2.1(4)% at 106, 325, 684 and 1415 keV respectively, consistent with the values derived from the simulated response.

RAPTOR: A new collinear laser ionization spectroscopy and laser-radiofrequency double-resonance experiment at the IGISOL facility

RAPTOR, Resonance ionization spectroscopy And Purification Traps for Optimized spectRoscopy, is a new collinear resonance ionization spectroscopy device constructed at the Ion Guide Isotope Separator On-Line (IGISOL) facility at the University of Jyväskylä, Finland. By operating at beam energies of under 10keV, the footprint of the experiment is reduced compared to more traditional collinear laser spectroscopy beamlines. In addition, RAPTOR is coupled to the JYFLTRAP Penning trap mass spectrometer, opening a window to laser-assisted nuclear-state selective purification, serving not only the mass measurement program, but also supporting post-trap decay spectroscopy experiments. Finally, the low-energy ion beams used for RAPTOR will enable high-precision laser-radiofrequency double-resonance experiments, resulting in spectroscopy with linewidths below 1 MHz. In this contribution, the technical layout of RAPTOR and a selection of ion-beam optical simulations for the device are presented, along with a discussion of the current status of the commissioning experiments.

Performance test of a position sensitive planar germanium detector for phase-III DESPEC experiments

The position sensitivity of a planar segmented double-sided germanium strip detector, with 10 × 10 electrical segmentation in orthogonal directions, has been studied using the coincidence method. The coincidences were set up between an imaging scanner and the PSPGe (Position Sensitive Planar Germanium) detector using a positron source, 22Na, and analyzed by employing the Positron Annihilation Correlation principle. A collimated 241Am source scan was also performed to find position resolution along X and Y axes using low energy gamma-ray source. The primary objective of this work is to study the charge carrier transportation for gamma-ray interactions inside the PSPGe detector. In order to select the electrodes of interest and to obtain the pulse shapes for each event, two-dimensional images have been processed. The net charge induced on the surface of the electrode, calculated using the pulse shape analysis procedure, has been used to profile the position resolution and gamma interaction depth. The present study is an input for the deployment of PSPGe detector in the future decay spectroscopy experiments to be performed at the Facility for Antiproton and Ion Research (FAIR) in Germany. This work investigates the gamma interaction depth by calculating the rise-time of traces stored for each gamma interaction inside the detector volume, providing ≈1 mm resolution along the depth. The position resolution of the detector in lateral directions, determined using the amplitude difference of the transient charges, has also been found to be ≈1 mm.

On the [formula omitted]-detection efficiency of a combined Si and plastic stack detector for DESPEC

A Geant4 simulation has been carried out in order to determine the β-detection efficiency of a rare isotope beam implantation setup, for decay spectroscopy experiments, comprising a number of Double Sided Silicon Strip Detectors (DSSSDs) and two plastic scintillation detectors placed upstream and downstream. The absolute efficiency for the emitted β-particle detection from radioactive fragments implanted in the DSSSDs using fast-timing plastic-scintillator detector, is calculated. The detection efficiency of the setup has been studied with two different distances between the Si layers and plastics. The requirement for the thickness of the Si detector layers and its implication on the β-detection efficiency has been investigated for 1 mm and 300μm thickness of Si layers. The combined efficiency of DSSSD and plastic detectors were also simulated for two different thicknesses of the DSSSD.

Recent experiments at the JYFLTRAP Penning trap

The JYFLTRAP double Penning trap mass spectrometer at the Ion Guide Isotope Separator On-Line (IGISOL) facility offers excellent possibilities for high-precision mass measurements of radioactive ions. Around 400 atomic masses, including around 50 isomeric states, have been measured since JYFLTRAP became operational. JYFLTRAP has also been used as a high-resolution mass separator for decay spectroscopy experiments as well as an ion counter for fission yield studies. In this contribution, an overview of recent activities at the JYFLTRAP Penning trap is given, with a focus on nuclei discussed in the PLATAN2019 meeting.

New and comprehensive β - and βp -decay spectroscopy results in the vicinity of Sn100

A decay spectroscopy experiment on proton-rich nuclei in the vicinity of the doubly magic Sn100 was carried out at RIKEN Nishina Center. More than 20 nuclei with 43≤Z≤50 and N≤51, produced by fragmentation reactions were investigated via analyses of β-decay, βp-decay, and subsequent γ-ray data. Owing to higher statistics, the precision on the half-lives of many of the ground states and isomers was improved. β-decay endpoint energies of 11 states in 8 nuclei were measured for the first time, and the corresponding QEC and excitation energies were generally consistent with various mass models. Many β-delayed proton emission branching ratios were measured either for the first time or with higher precision compared to literature values, and some of them differed by more than 2σ. Many of the large discrepancies were associated with nuclei with long-lived isomeric states, highlighting large systematic uncertainties involved in these measurements. Twenty-five new γ rays were observed, and ten new states are proposed with unambiguous excitation energies, spins, and parities. Most of the energies of the excited states were consistent within 300 keV or 20%, whichever was greater, compared to shell model predictions in the proton/neutron (p1/2,g9/2) model space assuming a Sr76 core. A signature of a new (1/2-) isomer in Cd97 with T1/2=0.73(7) s was found, in good agreement with shell model predictions.

The GRIFFIN facility for Decay-Spectroscopy studies at TRIUMF-ISAC

Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei, GRIFFIN, is a new high-efficiency γ-ray spectrometer designed for use in decay spectroscopy experiments with low-energy radioactive ion beams provided by TRIUMF’s Isotope Separator and Accelerator (ISAC-I) facility. GRIFFIN is composed of sixteen Compton-suppressed large-volume clover-type high-purity germanium (HPGe) γ-ray detectors combined with a suite of ancillary detection systems and coupled to a custom digital data acquisition system. The infrastructure and detectors of the spectrometer as well as the performance characteristics and the analysis techniques applied to the experimental data are described.

Properties of γ -decaying isomers and isomeric ratios in the Sn100 region

Half-lives and energies of $\ensuremath{\gamma}$ rays emitted in the decay of isomeric states of nuclei in the vicinity of the doubly magic $^{100}\mathrm{Sn}$ were measured in a decay spectroscopy experiment at Rikagaku Kenkyusho (The Institute of Physical and Chemical Research) of Japan Nishina Center. The measured half-lives, some with improved precision, are consistent with literature values. Three new results include a 55-keV $E2\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}$ ray from a new $({4}^{+})$ isomer with ${T}_{1/2}=0.23(6)\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{s}$ in $^{92}\mathrm{Rh}$, a 44-keV $E2\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}$ ray from the $({15}^{+})$ isomer in $^{96}\mathrm{Ag}$, and ${T}_{1/2}({6}^{+})=13(2)$ ns in $^{98}\mathrm{Cd}$. Shell-model calculations of electromagnetic transition strengths in the $({p}_{1/2},{g}_{9/2})$ model space agree with the experimental results. In addition, experimental isomeric ratios were compared to the theoretical predictions derived with an abrasion-ablation model and the sharp cutoff model. The results agreed within a factor of 2 for most isomers. From the nonobservation of time-delayed $\ensuremath{\gamma}$ rays in $^{100}\mathrm{Sn}$, new constraints on the ${T}_{1/2}$, $\ensuremath{\gamma}$-ray energy, and internal conversion coefficients are proposed for the hypothetical isomer in $^{100}\mathrm{Sn}$.

Conception of PIPERADE: A high-capacity Penning-trap mass separator for high isobaric contamination at DESIR

The DESIR (decay, excitation and storage of radioactive ions) facility at GANIL-SPIRAL2 will receive a large variety of exotic nuclei at low energy (up to 60keV) with high intensities. However, the production methods of radioactive beams are non selective, limiting the purity of the beams of interest. Moreover, the high precision needed for nuclear structure and astrophysics studies using beta decay spectroscopy, laser spectroscopy and trap-based experiments at DESIR requires highly pure samples of exotic nuclei. The aim of the double-Pennig-trap mass separator PIPERADE is to deliver large and very pure samples of exotic nuclei to the different experiments in DESIR. New excitation schemes and a large inner diameter of the first trap will mitigate space charge effects to attempt trapping of up to 105 ions per pulse. The purification cycle will be performed in a few milliseconds so that short-lived nuclei can be purified. To extract the nuclides of interest from the large amount of isobaric contaminants, a resolving power of 105 is mandatory. Afterwards the ions of interest will be accumulated in the second trap until they constitute a sufficiently pure sample for the measurements. The status of the project is presented.

Shape coexistence and evolution inSr98

Shape coexistence between the strongly deformed ground state and the weakly deformed ${0}_{2}^{+}$ state in $^{98}\mathrm{Sr}$ has been a major topic of interest due to the energy difference of 215 keV, which is the smallest in all even-even nuclei. The electric monopole transition strength ${\ensuremath{\rho}}^{2}(E0)$ is an important quantity that can relate the deformation difference and the shape mixing between the two ${0}^{+}$ states, which are admixtures of the vibrational (S) and the rotational (D) states in a simple mixing model. In a $\ensuremath{\beta}$-decay spectroscopy experiment, the experimental ${\ensuremath{\rho}}^{2}(E0)$ was measured. A value of 0.053(5) is consistent with the previous measurement and was combined with known electric quadrupole transition strengths $B(E2)$ in calculations of a two-state mixing model. Based on a systematic study on neighboring Kr, Zr, and Mo isotopes, the mixing of the ${0}^{+}$ and ${2}^{+}$ states in $^{98}\mathrm{Sr}$ was determined to be 8.6% and 1.3%, respectively, corresponding to deformation parameters ${\ensuremath{\beta}}_{\text{D}}=0.38(1)$ and ${\ensuremath{\beta}}_{\text{S}}=\ensuremath{-}0.23(2)$. These parameters reproduce experimental transition strengths well except for the ${4}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+}$ transition, which suggests a smaller D-band deformation for $J\ensuremath{\ge}4$.

Study of ground and excited state decays inN≈ZAg nuclei

A decay spectroscopy experiment was performed within the EURICA campaign at RIKEN in 2012. It aimed at the isomer and particle spectroscopy of excited states and ground states in the mass region be ...

DESCANT andβ-delayed neutron measurements at TRIUMF

The DESCANT array (D euterated S cintillator A rray for N eutron T agging) consists of up to 70 detectors, each filled with approximately 2 liters of deuterated benzene. This scintillator material o_ers pulse-shape discrimination (PSD) capabilities to distinguish between neutrons and γ -rays interacting with the scintillator material. In addition, the anisotropic nature of n – d scattering allows for the determination of the neutron energy spectrum directly from the pulse height spectrum, complementing the traditional time-of-flight (ToF) information. DESCANT can be coupled either to the TIGRESS (T RIUMF-I SAC G amma-R ay E scape S uppressed S pectrometer) γ -ray spectrometer [1] located in the ISAC-II [2] hall of TRIUMF for in-beam experiments, or to the GRIFFIN (G amma-R ay I nfrastructure F or F undamental I nvestigations of N uclei) γ -ray spectrometer [3] located in the ISAC-I hall of TRIUMF for decay spectroscopy experiments.

Exotic nuclei studied with the 8pi spectrometer at TRIUMF

The 8pi gamma-ray spectrometer has performed decay spectroscopy experiments at TRIUMF-ISAC between 2000 and 2013. A series of ancillary detector subsystems have been developed to enable or enhance particular aspects of decay spectroscopy. This facility allows a broad range of research in the fields of nuclear structure, nuclear astrophysics and fundamental symmetries. In this contribution, an overview is given of the detector systems and the research performed with the device during its operation at ISAC.

Status of the MLLTRAP setup and future plans

The MLLTRAP Penning trap system serves as a development environment, both for mass spectrometry as well as for novel in-trap decay-spectroscopy experiments at the MATS facility at FAIR. This contribution gives an outline on the development work done at MLLTRAP and presents the current status.

First results from the CRIS experiment

The ability to study rare isotopes with techniques such as mass spectrometry and laser spectroscopy is often prevented by low production rates and large isobaric contamination. This has necessitated the development of novel beam cleaning techniques that can efficiently isolate the isotope of interest. The Collinear Resonance Ionization Spectroscopy (CRIS) experiment at ISOLDE, achieves this by resonantly ionizing a bunched atom beam in a region of ultra high vacuum. This method is motivated by the need to measure the hyperfine structure and isotope shift at the extremes of isospin where typical production rates drop to 1 atom/s. The technique also offers the ability to purify an ion beam and even select long-lived isomeric states (> 1 ms) from the ground state, which can be subsequently studied by decay spectroscopy or mass spectrometry experiments. This paper will report on the successful commissioning of the CRIS beam line and the recent laser spectroscopy results and laser assisted nuclear decay spectroscopy on the neutron deficient francium isotopes.

The GRIFFIN spectrometer

Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei (GRIFFIN) is an advanced new high-efficiency γ -ray spectrometer being developed for use in decay spectroscopy experiments with low-energy radioactive ion beams provided by TRIUMF’s Isotope Separator and Accelerator (ISAC-I) radioactive ion beam facility. GRIFFIN will be comprised of sixteen large-volume clover-type high-purity germanium (HPGe) γ -ray detectors coupled to custom digital signal processing electronics and used in conjunction with a suite of auxiliary detection systems. This article provides an overview of the GRIFFIN spectrometer and its expected performance characteristics.

Recent developments at MLLTRAP: Improving the system for mass measurements and in-trap observation of nuclear decays

The MLLTRAP double Penning-trap setup, installed at the Maier-Leibnitz Laboratory in Garching, presently serves as an environment for development work for mass spectrometry and decay-spectroscopy experiments at future radioactive ion beam (RIB) facilities. Here, an m/q separator is presently being set up as an element for beam transport of charge-bred ions, which are required for mass measurements of highly-charged ions. Moreover, a novel type of experimental setup, dedicated to in-trap decay spectroscopy, is under development to be implemented in the future MATS facility at FAIR. It combines the high-resolution mass-purification capabilities of a Penning trap with a customized “detector-trap” setup, consisting of an arrangement of position-sensitive Si-strip detectors that replaces the conventional ring electrode of the trap, providing both, ion storage and detection of decay products. In this way, decay-spectroscopy experiments of mass-selected nuclides, trapped as a carrier-free source, thus avoiding any background or scattering effects, will become feasible via direct in situ spectroscopy of stored ions.

Developments in Penning trap (mass) spectrometry at MLLTRAP: Towards in-trap decay spectroscopy

A novel type of experimental setup, dedicated to in-trap decay spectroscopy in a Penning trap, is presently being developed at the double Penning-trap facility MLLTRAP, installed at the Maier-Leibnitz Laboratory in Garching. This new tool for α and electron decay spectroscopy is envisaged to be implemented in the future MATS facility at FAIR. It combines the high-resolution mass-purification capabilities of a first Penning trap with a customized ‘detector-trap’ setup, consisting of an arrangement of position-sensitive silicon (Si)-strip detectors that replaces the conventional ring electrode of the trap, providing both, ion storage and detection of decay products. In this way, decay-spectroscopy experiments of mass-selected nuclides, trapped as a carrier-free source, thus avoiding any background or scattering effects, will become feasible via direct in situ spectroscopy of stored ions.

Conversion electron spectroscopy at IGISOL

Conversion elecron spectroscopy has been an important part of the nuclear spectrocopy research at the Department of Physics of the University of Jyväskylä since the commissioning of the first cyclotron in the mid 1970s. At the IGISOL facility a specialiced conversion electron spectrometer ELLI was developed in the late 1980s. The first results with ELLI were obtained using the beams from the old MC-20 cyclotron to study newly discovered isotopes of refractory fission products. In the present K130 cyclotron laboratory ELLI has been utilized in many decay-spectroscopy experiments both neutron-deficient and neutron-rich side of the valley of stability. In the early 2000s the new JYFLTRAP ion trap system overthrew ELLI from its permanent place in the IGISOL beamline. Conversion electron spectroscopy has continued with the new Penning trap that has been used in in-trap electron spectroscopy tests and post-trap electron spectroscopy is foreseen.

JYFLTRAP: a Penning trap for precision mass spectroscopy and isobaric purification

In this article a comprehensive description and performance of the double Penning-trap setup JYFLTRAP will be detailed. The setup is designed for atomic mass measurements of both radioactive and stable ions and additionally serves as a very high-resolution mass separator. The setup is coupled to the IGISOL facility at the accelerator laboratory of the University of Jyvaskyla. The trap has been online since 2003 and it was shut down in the summer of 2010 for relocation to the upgraded IGISOL facility. Numerous atomic mass and decay energy measurements have been performed using the time-of-flight ion-cyclotron resonance technique. The trap has also been used in several decay spectroscopy experiments as a high-resolution mass filter.