iglis-net newsletter no. 6 may 2018research.kek.jp/group/wnsc/iglis-net/img/news-06-2018.pdf ·...

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IGLIS-NET Newsletter No. 6 May 2018

Introduction

This is the sixth issue of the IGLIS-NET (In-Gas Laser Ionization and Spectroscopy

NETwork) newsletter. The IGLIS-NET launched on Dec. 2012 is now constituted by 16

participating research groups and institutes. One of the main activities through the network

is frequent exchange of the communications among these participants. The issue of the

newsletter periodically summarizing the status of the research activities of the participating

groups is another important activity. The present issue includes six status reports from the

IGLIS laboratory at KU Leuven, IGISOL facility at JYFL, GALS at Dubna, RISP at IBS,

SLOWRI at RIKEN and KISS at KEK.

IGLIS-NET News

� Since the previous newsletter the IGLIS laboratory at KU Leuven has been taken into full

use for supersonic gas jet research. A number of studies with different nozzle designs

has been carried out in the last year resulting in collimated gas jets with homogeneous

temperature and density with M ~ 7, the highest Mach number obtained so far in the

IGLIS laboratory. In parallel, work has proceeded into studying the transmission

efficiency of the radiofrequency quadrupole (RFQ) ion guides as well as of the dipole

magnet in combination with its mass resolution.

� At the IGISOL facility in JYFL, a 1 GHz Fabry-Pérot Interferometer has been temperature

stabilized in the CW laser cabin, resulting in reduced systematic uncertainty on the Free

Spectral Range. The long-term frequency stabilization of lasers was also investigated by

locking to wavemeters. Several upgrades are being made to the collinear laser

spectroscopy beamline. The old LabVIEW-based control system has already been

phased out in favor of EPICS and python-base software at FURIOS. The MARA

Low-Energy Branch is under development, focusing on the investigation of proton-rich

nuclei with N ~ Z. A new atom trap chamber connected to the IGISOL mass separator

was installed for laser cooling and trapping of radioactive isotopes and isomers of Cs with

the long-term goal to demonstrate coherent gamma-ray emission in a Bose-Einstein

condensate of 135mCs isomers. A series of successful implantation, release, laser cooling

and trapping tests were done using a stable beam of 133Cs+ ions. The MORA project

which searches for a possible CP violation via the observation of the beta decay from

polarized radioisotopes was awarded funding to develop the infrastructure.

� For the GALS project at Dubna, a software for controlling EdgeWave lasers via CAN bus

was developed using the NI LabVIEW development environment. Additional laser

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equipment have been delivered and the extension of the first laser part of setup will be

completed. The prototype of tape station was manufactured. In order to estimate possible

losses of the ions of interest coming out of the gas cell, simulations of ions’ trajectories

were performed with SIMION. 3D simulation of the beam dynamics in the

mass-separator was carried out. Main spectroscopic data of atomic osmium have been

studied and an appropriate multi-steps transition for laser ionization has been found.

� The Resonant Ionization Laser Ion Source (RILIS) based on solid-state tunable

Ti:Sapphire lasers has been studied at an off-line test bench to develop the future on-line

laser ion source for the Rare Isotope Science Project (RISP). As a milestone of extraction

of rare isotopes produced through uranium fission, double magic nucleus of 132Sn is the

first target. Three-step resonant ionization schemes with four laser lights have been

tested for Sn and the relative ionization efficiencies for the RILIS have been investigated.

In particular, a method to improve the ionization efficiency with four-color laser ionization

scheme assisted by multiphoton Raman transition is introduced. As a preliminary result,

ionization efficiencies of 45% have been measured for Sn with four-color three-step laser

ionization scheme, and RISP target ion source system is currently under development for

further improvement of the RISP laser ion source.

� A novel mass spectrograph, MRTOF (multi-reflection time-of-flight) mass spectrograph,

has been developed at RIKEN RIBF for comprehensive mass measurements of

short-lived nuclei. It has a great advantage in measuring multiple ion species at once

without scanning. It was installed in the GARIS for the SHE-Mass project. The mass of

219Ra++ was determined with a relative precision of 4.1×10−7 from ≈100 events. The

highest precision was demonstrated for 65Ga+ using an isobaric reference of stable 65Cu+

with a relative precision of 3.5×10−8 from more than 10,000 events. During the first phase

of the SHE-Mass project, masses of ≈80 nuclides were measured. Several MRTOF

setups will be placed at three different RI-beam facilities, GARIS-II, KISS and

BigRIPS+SLOWRI, in order to cover all available nuclides at RIBF and to measure

>1000 masses within coming five years.

� Nuclear spectroscopic works were performed at KISS to study the nuclear properties

experimentally for establishing the reliable theoretical model in order to predict the

half-lives and masses of waiting-point nuclei with N = 126. Hyperfine structure (HFS)

measurements of platinum and iridium isotopes were performed to evaluate magnetic

dipole moments and the change of the charge radii. β-γ spectroscopy of tantalum and

osmium isotopes was performed, and a new long-lived isomeric state which was

suggested from the systematics and other experiments was probably found. In order to

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promote the spectroscopy in this region, a new laser system for in-gas-jet laser ionization

spectroscopy was installed, and three-dimensional tracking gas counters for beta-ray

detection and MR-TOF system for the mass measurements is under development.

Recent Publications

Please look at IGLIS-NET website (http://research.kek.jp/group/wnsc/iglis-net/), where the

publications are grouped according to the topics defined in the IGLIS-NET framework.

Any requests or comments about the IGLIS-NET newsletter are welcome. Please send

them via [email protected].

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Status Report (1)

Offline studies at the IGLIS laboratory in KU Leuven

K. Dockx, R. Ferrer*, M. Huyse, S. Kraemer, Yu. Kudryavtsev, M. Laatiaoui, S. Sels,

M. Verlinde, E. Verstraelen, P. Van den Bergh, P. Van Duppen, A. Zadvornaya

KU Leuven

I. Planar Laser-Induced Fluorescence for the characterization of supersonic gas jet

In order to achieve the best spectral resolution in IGLIS experiments it is essential to reduce

both the flow density and the temperature in the region at which atoms interact with the laser

beams. This can be accomplished by applying resonance ionization in the gas jet rather

than within the gas cell. Pressure and temperature in the supersonic gas jet are significantly

reduced compared to those in the gas cell. The gas thermal energy is converted to kinetic

energy during the gas flow acceleration in a de Laval nozzle. In former issues of the

Newsletter we presented an extensive summary of studies with stable copper isotopes

using a nozzle with Mach ~ 5, via a visualization technique referred to as Planar

Laser-Induced Fluorescence (PLIF). We note that such a nozzle was successfully used in

online experiments to study the nuclear and atomic properties of short-lived 214Ac and 215Ac,

reported in Refs. [1, 2].

In a new series of offline tests, copper atoms seeded in argon were extracted through the

M ~ 5 nozzle and excited by a laser-sheet beam. The emitted fluorescence upon

de-excitation was recorded by an ICCD camera, making it possible to measure density,

Figure 1. PLIF images of a 100-mm long jet obtained under optimal and non-optimal

conditions. The spectroscopic results obtained from the fluorescence emitted by the

copper atoms corresponding to the local jet areas at x = 18 and 28 mm are shown in the

insets.

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velocity and temperature profiles of the gas jet. Figure 1 illustrates the formation of a

100-mm long and collimated jet under optimal and non-optimal experimental conditions.

By means of PLIF spectroscopy we obtained information on the local jet temperature (width

of the spectral lines) and jet velocity (Doppler shift) along the jet central line. A total width

(FWHM) of 650 (60) MHz was obtained in agreement with the expected performance of the

nozzle at a working stagnation temperature of about 525 K (see Fig. 2). It is worth noting

here that non-optimal pressure background conditions not only result in larger temperature

and velocity fluctuations but also in poorly collimated gas jets [3].

Recent work has focused on performing PLIF spectroscopy using nozzles made from

different materials and surface roughness. First results obtained with brass and stainless

steel nozzles following the same contour design do not show significant differences in their

flow parameters ruling out possible effects arising from their distinctly different thermal

expansion coefficients. Figure 3 shows the results obtained using a stainless steel nozzle

with an optimized contour roughness. Further tests with mirror-like nozzle-contour surfaces

resulted in long and homogenous jets with M = 6.7 (2), the highest Mach number obtained

so far in our laboratory [3].

The nozzle temperature was also studied using a mini PT-100 sensor, which was separated

from the inner contour of the nozzle by a layer only 1 mm thick. As shown in Fig. 4, no

significant cooling of the nozzle was observed during working conditions over a time period

of around 3 hours.

[1] R. Ferrer et al., Nat. Commun. 8 (2017) 14520.

[2] C. Granados et al., Phys. Rev. C 96 (2017) 054331.

Figure 2. Local velocity and temperature along the supersonic gas jet for optimal and

non-optimal background pressure values.

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[3] A. Zadvornaya et al., Submitted for publication (2018).

II. Commissioning and characterization of the ion guide system and the mass

separator

Since the previous newsletter the laboratory has been taken into full use for supersonic gas

jet research. In parallel, work has proceeded into studying the transmission efficiency of the

radiofrequency quadrupole (RFQ) ion guides, and comparing the results with different

Figure 4. Temperature of the brass nozzle measured with a mini PT-100 sensor inserted

in the noizzle’s wall and separated by the inner contour by a layer of brass only 1 mm

thick.

Figure 3. PLIF studies on stable copper atoms using two different nozzles (brass and

stainless steel). The hyperfine structure fits for the two isotopes are indicated in the lower

part of the figure.

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models available in the literature. Figure 5 illustrates the schematic of the RFQ ion guides

used to transport the ion from the gas cell to the mass separator. Stable copper ions are

created following laser ionization in the gas cell and by monitoring the ion current on the first

electrodes of the S-RFQ as well as on a downstream Faraday cup, the transmission was

determined to be 90 (5)%. The experimental data were compared with a hard-sphere model,

Stokes model and a combination of these two models as illustrated in Fig. 6 (left). As shown,

the transmission efficiency is rather well reproduced using the hard sphere model. A

completely different situation was found when modelling the transit time of the ions through

the ion guides. In this case simulations with the code IonCool [1], which uses a realistic

atom-ion interaction potential, were necessary to reproduce correctly the time spent by the

ions in the RFQ ion guides (see Fig. 6 (right)).

Figure 5. Schematic of the RFQ ion guides (S-shaped and linear), installed at KU

Leuven. By monitoring the currents I1 and I2, the transmission efficiency of the system

can be measured.

Figure 6. Comparison between the experimental transmission efficiency (left) and the

transit time (right) through the ion guide system and different simulations.

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In addition to the transport efficiency, the beam emittance of the extracted ion beams is

another of the main properties that characterize an RFQ ion guide system. Experiments

have beam performed to determine the longitudinal emittance of the ion beams transported

through the ion guides by gradually applying a blocking voltage on one of the small

apertures through which ions travel in the ion guides. These measurements resulted in a

value for the longitudinal emittance of 1.4 (5) eV. This value is also in agreement with ion

optical simulations (see Fig. 7) considering the hard sphere model. Currently we are

performing experiments to measure the transverse beam emittance to fully characterize the

optical properties of the extracted ion beams.

The transmission efficiency ε of the ion beam through the dipole magnet in combination with

its resolving power R = m /Δm have also been studied resulting in optimal values of R = 300

and ε ~ 80%.

Next steps in the IGLIS laboratory include the production of atomic copper beams by laser

ablation to avoid the heating of the gas cell, and thus the increase of the stagnation

temperature, by the presence of a glowing filament within the gas cell, the characterization

of a new de Laval nozzle with a Mach 8.5 desined at the Von Karman Institute for Fluid

Dynamics, and the test of an ultra-fast gas cell with extraction times down to 20 ms for the

production of 229mTh beams.

[1] S. Schwartz, NIM A 566 (2006) 233.

Figure 7. Measurment (left) and simulation (right) results of the longitudinal emittance of

the ion beams transported through the RFQ ion guides.

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Status Report (2)

Optical science for nuclear and atomic physics at JYFL – status of projects

A. Giatzoglou1,2, S. Geldhof1, R. de Groote1, I.D. Moore1*, P. Papadakis1,3, I. Pohjalainen1,

M. Reponen1

1University of Jyväskylä, 2University College London, 3University of Liverpool

The following report shortly summarizes the various activities of the JYFL team and

collaborators during the period since the fifth IGLIS-NET newsletter. In addition, we have

continued an extensive program of research in connection with the nuClock FET-OPEN

project (www.nuclock.eu). Ongoing work with a variety of 229Th filament samples from TU

Vienna has been continued and we will be submitting a publication in the near future. We

also performed a thorough spectroscopic characterization of 233U sources both from LMU

Munich as well as a local source. This involved direct gamma-ray spectroscopy, alpha

spectroscopy as well as Rutherford Backscattering Spectrometry (using a 1.7 MV Pelletron

accelerator), as well as gamma-ray and alpha decay spectroscopy of foils which were

implanted with recoil ions from the 233U sources. This work is critical to understanding the

intricacies of recoil source preparation. Separately, in connection with collinear laser

spectroscopy, we have an accepted publication in Phys. Rev. A in collaboration with UK

colleagues for the first collinear laser spectroscopy of double-charged fission fragments.

The same work was performed using merged beams from two different sources (online from

proton-induced fission, with a stable calibration source produced from an offline discharge

ion source).

I. Laser frequency determination and stabilization in the CW laser laboratory

In the last newsletter, the major upgrades to the continuous wave (CW) laser cabin housing

the Matisse Ti:sapphire laser, a saturated absorption spectroscopy setup, a new

WaveTrain2 frequency doubler and two Fabry-Pérot Interferometers (FPIs) were presented

(see Fig. 1). One remaining issue at that time was the rather large systematic uncertainty on

the Free Spectral Range (FSR) of both FPIs, which was discovered to be due to

temperature fluctuations within the laser cabin [1]. The commercial 1 GHz Toptica FPI has

since been temperature stabilized using Peltier elements. A thermocouple directly attached

to the FPI is used in a feedback loop to the temperature controller. The FSR has been

re-measured with the resulting systematic uncertainty reduced from 4 GHz to 1.9 GHz. The

remaining systematic uncertainty is thought to be due to non-linearities in the piezo mirror of

the FPI.

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Further work on the long-term frequency stabilization of the Matisse laser for application to

collinear laser spectroscopy has also taken place. Locking of the Matisse to the strongest

hyperfine transition in 85Rb was optimized. A new WS10-U wavemeter has also been

installed, together with a new stabilized HeNe laser (Thorlabs HRS015B) for self-calibration.

Locking of the Matisse to the wavemeter has been achieved, providing stability within about

1 MHz as can be seen in Fig. 2. Several stability and calibration tests were undertaken to

fully understand the new system, e.g. by calibrating the wavemeter to the Matisse while the

laser was locked to the 85Rb transition instead of calibration to the HeNe laser. This resulted

Figure 1. Schematic of the current CW laser cabin layout. Since the last newsletter we

have installed a new WS10-U wavemeter. CLS = collinear laser spectroscopy.

Figure 2. WS10-U readout when the Matisse laser is optimally stabilised to the

wavemeter. The solid red line denotes the average, set to zero, and the dashed red lines

are at three times the standard deviation.

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in a stability of ~1.5 MHz. The long-term stability of both HeNe lasers has also been

investigated with the wavemeter (and will soon be confirmed using the

temperature-stabilized FPI). The old Melles Griot 05-STP-912 HeNe laser is stable to within

about 3 MHz over 24 hours (specified: 1-8 hours ±1 MHz, 1 month ±2 MHz, 8 hours

±3 MHz). For interest we have also locked the Spectraphysics 380 dye laser to the

wavemeter and compared the long-term stability to locking via an iodine absorption line. The

latter method has been traditionally used at JYFL to lock the dye laser during collinear laser

spectroscopy studies. Locking of the dye laser to the wavemeter resulted in a stability of

1 MHz, an improvement of about a factor of five than with the iodine reference cell.

[1] S. Geldhof et al., Hyperfine Interact. 238 (2017) 7.

II. Status and upgrades of the collinear laser spectroscopy beamline at IGISOL

Several upgrades are being made to the collinear laser spectroscopy beamline, with the aim

of improving the sensitivity of the setup and to expand the applicability of the method.

Improved vacuum conditions will minimize background in optical spectra. A new suite of

diagnostics will be introduced into the beamline, including charged-particle detectors for

improved ion beam tuning and monitoring during experiments, and silicon detectors for

beam identification purposes.

A data acquisition system has been acquired and commissioned, and new control software

was designed and tested. The core of the new system is a 16-bit digital-to-analog (DAC)

card, a new high voltage amplifier, and a time-to-digital converter (TDC) card with a

precision of 500 ps. The new DAC offers better precision and long-term stability of the

scanning voltage that is used to Doppler-shift ions into resonance with the fixed-frequency

laser. The output of the DAC is amplified with the new amplifier, which provides better

linearity and faster setting times than the existing solution. Finally, the TDC card allows for

software-based time gating of the incoming data and furthermore enables suitable time-gate

analysis to be performed offline. Figure 3 shows an example of the time-of-flight of stable

isotopes of palladium, observed during a mass scan.

Up to now, collinear laser spectroscopy at the IGISOL facility has only been performed on

ions. This limits the elements that can be investigated to those that have favourable optical

transitions in the ionic system. To alleviate this, a charge exchange cell, previously used at

the TRIGA facility, Mainz, was brought to IGISOL. Commissioning of this new addition to the

beamline is ongoing. The first fast atom beams have already been produced, and first offline

optical spectroscopy is planned for the near future. The availability of fast atom beams

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opens up a new programme at the facility, since many refractory elements do not have

suitable ionic transitions. The initial focus of the programme at the IGISOL will be on the

refractory elements below Z = 28 and Z = 50.

III. An EPICS-based control system for the FURIOS laser laboratory

Laser systems such as those in operation at the FURIOS laser ion source require regular

monitoring and optimization to ensure the lasers are operating nominally. Typically, this is

achieved using a combination of tools including power- and wavelength meters as well as

control devices such as software-controlled motor-actuated mirror mounts. The first

iterations of laser control and monitoring software at FURIOS were built using National

Instruments LabVIEW. LabVIEW provides a convenient visual coding environment and a

broad device ecosystem. While it is a suitable means to build a control system for a laser

laboratory, the programs can easily become complex and are difficult to maintain without a

deeper utilization of the LabVIEW’s advanced features. In a laboratory with frequent new

users combined with a requirement of optional features which might be needed at short

notice, a shallow learning curve would be highly beneficial. Furthermore, relying on a

commercial software vendor brings additional licensing fees.

EPICS – Experimental Physics and Industrial Control System [1] is being utilized in many

major large-scale accelerator facilities such as GSI, Germany, and at RIBF in RIKEN, Japan.

Figure 3. Time-of-flight spectra obtained on the collinear laser beam line as the IGISOL

mass separator is tuned through the stable isotopes of palladium.

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The system uses Input/Output Controllers (IOCs) to publish data and perform tasks over the

network to Channel Access (CA) clients in real time. The advantage is that the client user

interface can be written with minimal effort using various tools, for example with modern

programming languages such as Python [2]. The device driver interface can be a native

EPICS program or a custom program utilizing e.g. Python EPICS bindings (PCASpy [3]).

The LabVIEW-based control systems are being phased out at IGISOL in favor of EPICS with

the aim of a coherent networked control system where the driver interfaces are decoupled

from the user interfaces.

At FURIOS, the old LabVIEW-based control system has already been phased out in favor of

EPICS and python-based software, though it is still kept available until the new systems

have been thoroughly tested. At the time of writing, remote accessible systems at FURIOS

include oscilloscopes (Tektronics TDS 3034B), wavemeters (HighFinesse WS6 and

WS10-U), power meters (Thorlabs PM100USB interfaces) and a selection of motor-actuated

mirror mounts. In addition, various analog and digital I/O counter devices are utilized to

perform ion pulse counting and laser monitoring over the network. The control system has

matured to a point where it has successfully been used to perform laser resonance

ionization spectroscopy on stable silver isotopes in an atomic beam unit using the

ground-state transition at 328 nm, and to study self-seeded grating-laser characteristics with

minimal manual input. The control systems at FURIOS are still under constant development

to implement more features to the EPICS device driver interfaces and to connect those to

intuitive user interfaces.

[1] https://epics.anl.gov/about.php

[2] http://cars9.uchicago.edu/software/python/pyepics3/

[3] https://github.com/paulscherrerinstitute/pcaspy

IV. Status of the MARA-LEB

The MARA Low-Energy Branch (MARA-LEB), which will be focused on the investigation of

proton-rich nuclei with N ~ Z, is under development at JYFL. The construction of the setup

has been separated into three individual phases. The first phase includes all the necessary

equipment needed to stop and thermalize ions at the focal plane of MARA and to transport

them to a detection station. The second phase concentrates on the coupling of laser

ionization and spectroscopy capabilities to the equipment constructed in phase one. The

final phase will introduce mass measurements to the facility in the form of a Multi-Reflection

Time-of-Flight Mass Spectrometer (MR-TOF-MS). The status of the facility was presented in

the proceedings of the ISIS conference [1] and is updated further here.

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The compact gas cell, in which the recoils exiting the MARA separator are to be stopped,

has been built and will be tested at JYFL in the coming months using a recoil-alpha source.

The design of the radiofrequency ion guides and ion optical focusing elements which will

focus and accelerate the ions exiting the gas cell towards the experimental stations is almost

finalized. A 90°-bent RFQ will transport the ions from the gas cell towards the second

vacuum chamber through a pumping aperture. A long segmented RFQ will further transport

the ions towards the high-vacuum extraction chamber where they will be stepwise

accelerated and focused using a combination of extraction electrode, Einzel lens and

ground electrode.

A 90° magnet dipole, which will provide additional mass-separation capabilities and is used

to divert the ion beam towards the roof of the RITU cave, has been designed and a

quotation has been requested. Power supplies for the dipole magnet and all ion optical

elements have been purchased. The required components for the vacuum system, including

the two-stage differential pumping system necessary for isolating the gas cell volume from

the high-vacuum ion transport line have been purchased and tested.

The different components of MARA-LEB will be controlled through the JYFL Accelerator

Laboratory control system. The MARA-LEB specific control modules have been purchased

and the system is under development.

In addition to the developments taking place for MARA-LEB phase one, components of

MARA-LEB phases two and three are also under construction. Parts of the laser system

have been procured and assembled at JYFL, and some components for the MR-TOF-MS

were also constructed.

[1] P. Papadakis et al., AIP conference proceedings, article in press.

[2] S.I.S Inc., Simion 8.1, 1027 Old York Rd., Ringoes, NJ, USA.

V. Towards gamma-ray coherent emission in ultracold 135mCs

Excellent progress has been made on the new facility at IGISOL for laser cooling and

trapping of radioactive isotopes and isomers of Cs, with the long-term goal to demonstrate

coherent gamma-ray emission in a Bose-Einstein condensate (BEC) of 135mCs isomers.

Such an approach allows one to overcome the two fundamental problems which have

hindered the realization of a nuclear gamma-ray laser: the accumulation of a large number

of isomeric nuclei, and the reduction of the gamma-ray emission linewidth. For a full

theoretical discussion of the mechanism of collective nuclear de-excitation of nuclear

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isomers in a BEC we refer to the recently published work by our University of College

London colleagues [1].

In 2017, a new beamline from the electrostatic switchyard of the IGISOL mass separator

was constructed to connect the mass separator to a new atom trap chamber which arrived

after the summer. The new Pyrex chamber (see Fig. 4) was coated with a special organic

film to reduce the loss of Cs atoms when they collide with the walls. The coating also

increases the thermalization rate of atoms, which are released from a heated (up to 1000 K)

yttrium neutralizer foil following implantation of the ion beam delivered from IGISOL. In

December, a series of successful implantation, release, laser cooling and trapping tests

were done using a stable beam of 133Cs+ ions at 30 keV, produced from an off-line surface

ion source located on the second floor of the facility. Analysis of the dynamics of evaporation,

laser cooling and trapping following implantation is underway, highlighted in Fig. 5. A

publication from these off-line studies is under preparation.

Figure 4. Top left: the new Pyrex chamber connected to the beamline at IGISOL. The

small flange on the left will be replaced by the filament holder and feedthroughs. Top

right: building up of the optics and anti-Helmholtz coils around the chamber. Additional

correction coils have been added to compensate for any laboratory fields, and the

banana cables for heating the filament are connected. Bottom: picture of the glowing

yttrium neutralizer foil.

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In a recent on-line experiment at the Penning trap facility, JYFLTRAP, we determined that a

yield of ~9000 135mCs isomers/s at a primary beam intensity of 10 μA in proton-induced

fission of uranium can be expected to be implanted into the neutralizer foil. The first on-line

experiment for trapping 135mCs has been scheduled for May 2018.

[1] L. Marmugi et al., Phys. Lett. B 777 (2018) 281.

VI. MORA – Matter’s Origin from the RadioActivity of trapped and laser-oriented ions

One of the fundamental open questions in physics is connected to the matter-antimatter

asymmetry of the Universe. Precision experiments on nuclear beta decay complement

high-energy physics experiments in searches for signatures of physics beyond the Standard

Model. These signatures may arise through violations of symmetries in nature, for example

a measurement of a specific correlation parameter in beta decay would infer an asymmetry

in time (T), which through the known Charge-Parity-Time (CPT) symmetry must therefore

break Charge-Parity (CP). It is the search for a possible CP violation which might explain the

matter-antimatter asymmetry in the Universe.

The MORA (Matter’s Origin from the RadioActivity of trapped and laser-oriented ions)

project gathers experts of ion manipulation in traps and laser orientation methods for

searches of New Physics (NP) in nuclear beta decay. The searches will be performed in the

coming years at the IGISOL facility (and later at the DESIR facility, SPIRAL-2) via a precise

measurement of the so-called triple D correlation, which is sensitive to time reversal

Figure 5. Evaporation/release profiles following the implantation of a 30 keV beam of

stable 133Cs+ ions into the neutralizer foil. The sudden increases in the fluorescence

signal from the MOT represent increases in filament current. The filament temperature

has been calibrated.

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violation. As such, the measurement of D in nuclear beta decay is a complementary probe to

the electric dipole moment of the neutron.

The measurement of the D correlation parameter requires the polarization of an ensemble of

radioisotopes (in our case we will use 23Mg+ ions) and the subsequent observation of their

beta decay. MORA will use an efficient polarization method, consisting of the confinement of

ions in a Paul trap and exposing the cloud to circularly polarized laser light. In the coming

months a careful yield test using different light-ion fusion-evaporation reactions will proceed

at IGISOL to determine not only the yield, but the isobaric contamination as well as the RF

cooler transmission efficiency for A = 23 ions as a function of primary beam intensity.

Figure 6 illustrates the location of MORA in the IGISOL-4 experimental hall.

In 2017, MORA was awarded 600 kEUR of funding from the Region Normandie to develop

the required infrastructure. The first phase of the experiment will begin at IGISOL in 2019

and in a second phase, after 2022, will move to the DESIR facility, SPIRAL-2, in France.

Figure 6. Location of the MORA experiment at IGISOL. The trap is based on the design

from LPCTrap however will accommodate a higher trapping capacity. The

Multi-Reflection Time-of-Flight Mass Spectrometer (MR-TOF-MS) will be installed in

2018.

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Status Report (3)

GALS – setup for production and study of heavy neutron rich nuclei at Dubna

S.G. Zemlyanoy1*, V.I. Zagrebaev1, K.A. Avvakumov1, N.Yu. Kazarinov1, Yu. Kudryavtsev2,

V. Fedosseev3, R. Bark4, Z. Janas5

1JINR, 2KUL, 3CERN, 4NRF, South Africa, 5University of Warsaw, Poland

The realization of the project GALS, devoted to the production and study of heavy neutron

rich nuclei by multinucleon transfer reactions is in progress. The main results obtained in

2017 are following:

1. A software for controlling EdgeWave lasers via CAN bus was developed using the NI

LabVIEW development environment. Its interface (see Fig. 1) has the same functions as

the EdgeWave Laser Control utility, but allows controlling two lasers from the same

window. Using the CAN bus compared to RS232 interface allows reducing the number

of connections, improves resistance to interference and reliability of data transfer.

2. Additional laser equipment (CW TiSa and Dye lasers, beam stabilization and diagnostic,

Figure 1. The main tab of the software for controlling EdgeWave lasers via CAN bus.

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doubling optics etc.) have been delivered to the lab and it is under stage of installing in

the laser lab. This way the extension of the first laser part of setup will be completed and

test experiments on selective resonance laser ionization will be started in the 2018 using

the reference cell.

3. The prototype of tape station was manufactured and its testing has been started in

iThemba labs.

4. In order to estimate possible losses of the ions of interest, coming out of the gas cell,

their interactions with the gas jet and background gas were modeled (see Fig. 2).

Simulations of ions’ trajectories were performed with the commercial software package

SIMION [1] using the hard sphere collision model and the additional code describing the

gas jet [2, 3]. In the model, the thermal ions propagate in a filled-cone direction

distribution of half angle 30° out of the gas cell orifice, which has a diameter of 0.5 mm.

The SPIG with an inner diameter of 3 mm consists of six rods (with a diameter of

1.5 mm and 630 mm long) cylindrically mounted on a sextupole structure, the distance

from the orifice was set to 2 mm. The radiofrequency (4.7 MHz) voltage with

peak-to-peak amplitude of 300 V is applied to the neighboring rods in the opposite

phase, and the whole SPIG has a voltage of −210 V compared to the gas cell [4]. The

Figure 2. Simulated trajectories of the ions at SPIG entrance. The collisions with the

buffer gas are marked with red.

20


pressure of gas (argon) was set to 500 mbar in the gas cell and the background

pressure was set to 2×10−2 mbar. The simulations predict transport efficiency close to

100% on the first 65 mm of ions’ path within the SPIG. When the ions proceed from the

gas jet to the background, they quickly lose most of the kinetic energy, which lead to

high losses or at least very high time of flight. To improve the expected transport

efficiency and lower ions’ time of flight, a segmented quadrupole ion guide is being

developed.

5. 3D simulation of the beam dynamics in the GALS mass-separator was carried out [5].

This simulation used 3D map of the AM magnetic field calculated using OPERA 3D

code [6]. The number of particles used in this simulation was equal to 2×104. The

computational model of the analyzing magnet is shown in Fig. 3.

Figure 3. Computational model of the analyzing magmet.

Figure 4. Initial particle distribution in

plane {x,y}.

Figure 5. Ion distribution in the magnet

focal plane.

-8 -6 -4 -2 0 2 4 6 8

x, mm

-8

-4

0

4

8

y, m

m

269 270 271

21


Figure 5 shows the calculated distribution of the particles in the analyzing magnet focal

plane for the ions with A = 269, 270, and 271. The estimated mass resolution of

mass-separator Rm = 1400.

Manufacturing of separator magnet and vacuum chamber was finished. Joint assembly

of a yoke and coils of a separator and also tests has been carried out at the site of the

producer. Joint assembly with vacuum chamber of separator and testing will be

performed in 2018.

6. Main spectroscopic data of atomic Osmium have been studied and an appropriate

multi-steps transition for laser ionization has been found. Most suitable transitions are

presented in Table 1.

Figure 6. The vacuum chamber of separator and separator magnet.

Table 1. Possible schemes of two λ (λ3 = λ2 or λ3 = λ1) or three λ ionization. In all case the

first step begins from the ground state: E0 = 0 cm−1 with configuration 5d66s2 5D4. The

third step of most two wavelength ionizations is non-resonant. As the first stage of this

project the scheme marked in bold is planned. The transition will be excited with

frequency doubling using high power diode laser TA-Pro.

λ1 (air), Å E1, cm−1 State I J1 λ2 (air), Å E2, cm−1 State II J1 λ3 (air), Å

2909.06 34365.33 6s6p 5F0 5 4752.16 55402.47 6s7s ? ? 6043.15

3018.04 33124.48 6s6p 7P0 3 5580.66 51038.49 6s7s e5D 0 λ1 or λ2

3267.94 30591.45 6s6p 7P0 4 5509.33 48737.34 ? 4 λ1

3301.56 30279.95 6s6p 7F0 5 4815.96 51038.49 6s7s e5D 4 λ1 or λ2

4260.85 23462.90 6s6p 7D0 5 3157.24 55127.00 ? ? λ1 or λ2

4420.47 22615.69 6s6p 7D0 4 4066.69 48737.44 6s7s e7D 4 λ1 or λ2

4420.47 22615.69 6s6p 7D0 4 3827.14 47198.7 6s7s e7D 5 λ1 or λ2

22


[1] D.A. Dahl, Int. J. Mass Spectrom. 200 (2000) 3. Srouce: Scientific Instrument Services,

Inc., Ringoes, NJ – SIMION (www.simion.com).

[2] E. Traykov (GANIL, CEA/DSM-CNRS/IN2P3, Caen, France), private communication.

[3] Yu. Kudryavtsev et al., Nucl. Instrum. Methods B 297 (2013) 7.

[4] S. Zemlyanoy, K. Avvakumov, V. Fedosseev et al., Hyperfine Interact. 238 (2017) 31.

[5] N.Yu. Kazarinov, Physics of Particles and Nuclei Letters 13, No. 7 (2016) 836.

[6] Opera3D 2012 Oxford OX5 1JE, England.

23


Status Report (4)

Status of the development of Resonant Ionization Laser Ion Source at RISP

S.J. Park*, H. Ishiyama, J.Y. Kim, B.-H. Kang, G.D. Kim, S.C. Jeong

Rare Isotope Science Project, Institute for Basic Science

I. Ion source development at the RISP off-line test bench

Ion sources based on the hot-cavity have been set up and successfully operated at the

off-line test facility at RISP (Rare Isotope Science Project) in Korea. In the RISP off-line test

facility two different kinds of ion source have been under development: the surface

ionization source and the laser ion source. Both ion sources are based on the hot-cavity

made from Ta cylinder with 32 mm length, 3 mm inner diameter, and 5 mm outer diameter.

The off-line test bench is comprised of a TIS (Target Ion Source) system, an extraction

electrode, a beam optics system, a mass separator, a beam diagnostic system, and their

control systems. In addition, we have installed the Ti:Sa laser system for the development of

the laser ion source for RISP. This off-line test system allowed us to evaluate the beam

quality for certain selected isotopes extracted from different ion sources. Recently, ionization

efficiencies have been measured to evaluate the performance of our prototype TIS

system [1, 2]. For the surface ionization ion source development, ionization efficiencies of

more than 75% have been measured for the two alkali metals Rb and Cs from the Ta

prototype of the RISP surface ionization source using an oven, called a mass marker [2].

For the laser ion source development, the laser ionization scheme development using a

reference cell and the ionization efficiency measurement from the RISP TIS system are

under progress especially for the consideration of Sn ion beam.

In the test facility, the singly charged ions are typically extracted from the ion source and

accelerated to 20 kV by the extraction electrode. The extracted ion beam is bent through a

90° bending magnet and sent to the diagnostic chamber onto which various measurement

devices can be mounted: a wire scanner, an emittance scanner, and a Faraday cup. The

mass spectrum displayed in Fig. 1(a) shows the Sn ions observed with the laser beams

introduced into the ionizer cavity. The 133Cs ions in Fig. 1(a) were surface ionized in the

hot-cavity, which were not affected laser lights and were used as a reference position in the

mass spectrum. The ten stable Sn isotopes were clearly separated with the mass resolving

power of more than 500 as shown in Fig. 1(b).

[1] S.J. Park et al., Nucl. Instrum. Methods B 414 (2018) 79.

[2] S.J. Park et al., Nucl. Instrum. Methods B 410 (2017) 108.

24


II. Laser system for RILIS

A tunable laser system consisting of four Ti:Sa lasers pumped by a high repetition rate

Q-switched Nd:YAG laser has been installed for application in the laser ion source

development for RISP (Fig. 2). The pump laser is a frequency-doubled Nd:YAG laser from

Lee Laser, which operates at 10 kHz repetition rate with a maximum of 100 W average

output power at 532 nm.

Figure 1. (a) Mass spectra with the Sn isotopes from the laser ion source and Cs ions

from the surface ionization ion source. (b) Detailed view (zoom) of Sn mass spectrum.

Figure 2. Laser system consisting of four Ti:Sa lasers pumped by a Nd:YAG laser,

generating two IR beams (811 nm and 823 nm) from the fundamental light and two UV

beams (286 nm and 301 nm) via third harmonic generation.

25


The Ti:Sa laser system can generate narrow-band (~5 GHz) tunable laser radiation in the

700 – 1000 nm (fundamental) and 350 – 500 nm (frequency doubling) spectral regions. With

third harmonic generation capabilities, the beams near UV region were generated for the

first step excitation transition. With an output power of approximately 3 W in the fundamental,

~30 mW in the third harmonic was available for the laser spectroscopy. A small fraction of

the Ti:Sa laser beam was transported to a fiber coupler to allow simultaneous monitoring of

timing and wavelength. All laser beams were spatially overlapped and transported to the

reference cell or the hot-cavity in the test facility.

Resonance laser ionization of atoms operates as shown in Fig. 3. In a typical three-step

laser ionization scheme, laser radiation at frequencies at ω1, ω3 excites the atom in the

lower ground state (3P0) resonantly via atomic intermediate states, and radiation at

frequency ω4 ionizes it. When the laser light at ω2 is added the ionization efficiency can be

increased by exciting the atoms in the upper ground state (3P1) as shown in Fig. 3(a). In the

same way, one can add one more laser light to ionize the atoms in the third ground state

Figure 3. Laser ionization shcemes for Sn as used during the experiments. (a)

Four-color laser ionization of Sn consisnts of two three-step laser ionization processes

with laser lights at 286.42 nm (ω1) – 811.63 nm (ω3) – 823.68 nm (ω4) and

301.00 nm (ω2) – 811.63 nm (ω3) – 823.68 nm (ω4) which result in the ion signal S1 and

S2, respectively. (b) The atoms in 3P2 can be photo-ionized by multi-photon process by

three laser lights at ω1, ω2 and ω3.

26


(3P2). However, this additional ionization of the atoms in the 3P2 state can be possibly done

via a multiphoton process as shown in Fig. 3(b) in our four-color three-step ionization

scheme, which will be introduced below in more detail.

III. Reference cell experiment for ionization scheme development

A compact atomic beam reference cell (RC) [1] designed by Kron at Mainz University was

used for ionization scheme development. Measurements were performed in a

crossed-beam geometry as illustrated in Fig. 4. A graphite oven placed in the RC was filled

with metallic tin powder and heated electro-thermally to produce a Sn atomic beam. The

atoms were photo-ionized shortly after by the resonant laser radiation in a transversal

geometry and the resonantly atoms were then guided by ion-optical elements into the

secondary electron multiplier (SEM).

Figure 5 shows the typical ion signal obtained from the RC. The dashed curves S1 show the

ion signal when three laser beams at ω1, ω3, and ω4 are used, while the dot-dashed curves

S2 are obtained when ω2 is chosen instead of ω1 in the first excitation step (see Fig. 3(a)).

The solid curves S12 are the ion signal when using all four laser beams at ω1, ω2, ω3 and ω4

(see Fig. 3(a)). We define the ionization efficiency εi as the integral of the ion signal Si over

time.

In the case of the interaction between thermal atoms and laser radiation, as in a hot-cavity

type laser ion source, the collisional effect between the three ground states 3P0, 3P1 and 3P2

should be taken into account, resulting in ε1 + ε2 > ε12. In the atomic beam experiment as in

the one using an RC, however, one can expect ε1 + ε2 ≈ ε12. At the temperature of about

Figure 4. Reference cell (RC) for laser ionization spectroscopy. (a) Picture of the RC

setup. (b) Schematic drawing of the RC.

27


2200 K the populations in the 3P0 and 3P1 states are almost same, but the ionization

efficiency ε12 cannot be increased by a factor of two compared to a typical three-step laser

ionization scheme (ε1 or ε2). However, in our RC experiment, we observed the case ε1 + ε2 <

ε12 under certain conditions. This implies that there is an additional channel to improve the

ionization efficiency. Figure 3(b) shows a possible excitation scheme to explain this

improvement in the laser ionization efficiency. This excitation scheme includes the strong IR

light at ω3 rather than ω4. For I(ω3) << I(ω4), as shown Fig. 5(a) the ionization efficiencies

were measured to be ε12/(ε1 + ε2) ≈ 1 which is the result expected in the atomic beam

experiment. For I(ω3) >> I(ω4), as shown Fig. 5(b) the ionization efficiencies were measured

to be ε12/(ε1 + ε2) ≈ 1.2. This result shows that the strong laser light at ω3 plays an important

role to increase the ionization efficiency supporting the nonlinear process as shown in

Fig. 3(b).

[1] T. Kron et al., Hyperfine Interact. 216 (2013) 53.

IV. Laser ionization efficiency of Sn

As a preliminary investigation of the laser ionization efficiency using the four-color three-step

laser ionization scheme, the laser ionized ion current produced from the mass marker was

measured using a Faraday cup after the mass separator. As shown in Fig. 6, the ion current

was normally kept at a certain value about 35 nA for about 7 h until the sample introduced

into the oven completely petered out. The ionization efficiency for Sn was measured to be

about 45% which is the improvement by a factor of about two compared to the recent results

of 22% with a similar setup [1]. This efficiency measurement requires good reproducibility for

different conditions and the optimized ionization scheme should be adopted.

Figure 5. Sn ionization signal from the RC for (a) I(ω3) << I(ω4) and (b) I(ω3) >> I(ω4).

28


In order to minimize the isobaric contamination from the surface ionization at the hot-cavity,

the relative ionization efficiencies were investigated depending on the temperature of the

hot-cavity. The temperature of the Ta heater was fixed at about 1800°C and the temperature

of the hot-cavity was varied. In Fig. 7 diamond and triangle curves show the signal S1 and S2

respectively. The disk curve shows the signal S12 while the empty circles are the sum of the

ion signals S1 and S2. On the right region at the temperature around 2000°C we can see

S12 < S1 + S2 due to the higher population exchange between the ground states. However,

on the left region at the temperature below 1700°C, we can see S12 ≈ S1 + S2 and even

S12 > S1 + S2. Furthermore, the ionization efficiency increases back as the temperature of

the hot-cavity decreases. From this result, we demonstrate that the four-color ionization

scheme can efficiently enhance the ionization efficiency of Sn particularly due to a

Figure 6. Ioniozation efficiency measurement data for Sn.

Figure 7. Measured ion current depending on the temperature of the hot-cavity.

29


multi-phonon Raman transition in the laser ion source as in the reference cell experiment. It

should be noted that the operation of the laser ion source with the hot-cavity at a relatively

low temperature has the advantage of reducing the contamination of the ions generated by

the surface ionization. Further investigation will be made to characterize the RISP laser ion

source as well as to evaluate the RISP TIS system.

[1] Y. Liu et al., Nucl. Instrum. Methods B 243 (2006) 442.

30


Status Report (5)

SLOWRI Development

M. Wada* for the SLOWRI collaboration

RIKEN Nishina Center (RNC) & KEK Wako Nuclear Science Center (WNSC)

I. Introduction

The atomic mass is a fundamental quantity in nuclear physics. The mass defect, the

difference between the atomic mass and the sum of the masses of the individual

constituents, is representative of the total binding energy of the atom that determines the

existence of the atom, where it is stable and the decay mode and decay energy if it is

unstable. Systematic comparisons of the atomic masses can indicate nuclear deformation,

nuclear shell effects, the particle drip lines, and key information for the origin of heavy

elements, such as gold or uranium, in the universe. Up to now, the masses of ≈2300

nuclides have been determined experimentally with a relative precision of better than

1 ppm [1, 2]. However, more than 600 of them were determined indirectly by reaction

Q-values or decay energies which are known to have sizeable ambiguities. Approximately

1000 nuclides were experimentally identified but their masses are still not known as

indicated in Fig. 1. The half-lives of these nuclides are distributed in a few orders of

Figure 1. Chart of nuclides showing mass known nuclides (gray boxes) and unknown

nuclides (colored boxes). The color codes indicate the nuclear half-lives. The light gray

boxes indicate their masses were detemined by indirect methods. The insert shows

distribution of half-life for mass unknown nuclides.

31


magnitude, however, dominantly in a range of 10 – 100 ms. Typical mass spectrometers for

short-lived nuclei are summarized in Fig. 2. The Penning trap mass spectrometer (PTMS) is

a state-of-the-art device for the most precise and accurate mass measurements, however, it

requires an ion cyclotron resonance time of one second or longer if a mass resolving power

of one million is needed. Furthermore, PTMS does not make allowance for any impurities.

Consequently, only one species can be measured at a time. Large storage rings at GSI and

Lanzhou and in-flight mass spectrometers such as TOFI and SPEG have also played

important roles in mass measurements of unstable nuclei. The most urgently needed

nuclear data at present requires relative mass precisions of 10−7 for nuclei with half-lives of

10 – 100 ms. This represents a “blank zone” because no appropriate devices exist to

measure such nuclei with the desired precision (Fig. 3).

[1] W. Huang, G. Audi, M. Wang, F. Kondev, S. Naimi, X. Xu, Chi. Phys. C 41 (2017)

030002.

[2] N. Wang, G. Audi, F. Kondev, W. Huang, S. Naimi, X. Xu, Chi. Phys. C 41 (2017)

030003.

[3] Y. Ito et al., to be submitted.

[4] P. Schury et al., Phys. Rev. C 95 (2017) 001305(R).

[5] S. Kimura et al., arXive: 1706.00186.

[6] Y. Ito et al., arXive: 1709.06468.

Figure 2. Typical methods for mass measurement of unstable nuclei.

Q-value (decay or reaction)

In-flight spectrometer

Storage RingPenning Trap

MRTOF (multi-reflection TOF)

Ultra FastLow Precision

FastLow Precision

Isochronous

Electron Cooling

Very SlowHigh Precision

SlowUltra H igh Precision

FastH igh Precision

N ew method

UniversalAmbiguity from levels

TOFI, SPEG ..

GSI ESR

IM P CSReRIKEN RI- Ring

ISOLDE, JYFL...

RIKEN , Giessen, ISOLDE ..

indirect direct

32


[7] M. Rosenbusch et al., arXive: 1801.02823.

[8] Y. Bai et al., AIP conf. Proc. 455 (1998) 90.

[9] F. Sarazin et al., Phys. Rev. Lett. 84 (2000) 5062.

[10] R. Knöbel et al., EP. J. A. 52 (2016) 138.

[11] Chen et al., Nucl. Phys. A 882 (2012) 271

[12] Yu. A. Litovinov et al., Nucl. Phys. A 756 (2005) 3.

[13] http://research.jyu.fi/igisol/JYFLTRAP_masses/

[14] https://isoltrap.web.cern.ch/isoltrap/database/isodb.asp

[15] H.S. Xu et al., Int. J. Mass Spectrom. 349 (2013) 162.

II. Multi-reflection time-of-flight mass spectrograph

We developed a novel mass spectrograph, MRTOF (multi-reflection time-of-flight) mass

spectrograph to cover the “blank zone”. It is a time-of-flight mass spectrograph build to

extend the flight path. Bunched ions between a pair of electronic ion mirrors. A small kinetic

energy spread among the ions can be compensated for in the mirrors; higher energy ions go

deeper and are reflected later than lower energy ones that go shallower and are reflected

earlier, resulting in the desired energy isochronous condition. A typical flight time is 10 ms

with a width of 25 ns, corresponding to a mass resolving power of 200,000. This is

compatible with short-lived nuclei with half-lives of ≈10 ms. We determined the mass of

Figure 3. Plots of relative mass precision vs. half-life with typical mass

spectrometers [3 – 15].

33


219Ra++ (half-life of 10 ms) with a relative precision of 4.1×10−7 from ≈100 events [1].

A great advantage of the MRTOF is that it can measure multiple ion species at once without

scanning. Figure 4 shows a TOF spectrum for A = 204 and 205 isobars that includes nine

nuclides [2]. Occasionally, contaminant ions having a different number of laps may appear in

a spectrum. To discriminate such intruder peaks, we always take two or more spectra with

different number of laps. The highest precision MRTOF mass measurement was

demonstrated for 65Ga+ using an isobaric reference of stable 65Cu+ [3]. The mass was

determined with a relative precision of 3.5×10−8 using more than 10,000 events. The result

agrees with the data measured by a PTMS. Such high accuracy was achieved because the

isobaric reference ions, 65Cu+, were simultaneously measured with high statistics. Using the

TOF of the reference ions, the temporal drifts in the measured TOF, which arise from voltage

or thermal fluctuations, were compensated. However, suitable reference ions are not always

available. To remedy this, we developed a universal referencing method, named the

“concomitant” method, which takes advantages of our novel trap geometry that can accept

ions from two directions. Reference ions from any sources can be supplied to one side of

the ion trap, while radioactive ions are supplied to the other side, alternating one shot after

the other in each (typically 15 ms) flight cycle.

This new mass spectrograph has performed well and have demonstrated that it is ideal for

the mass measurement of very rare, short-lived, heavy nuclides. At first, we installed it in the

GARIS at RIKEN RIBF for the SHE-Mass project, to perform high precision mass

measurements of trans-uranium elements. During the first phase of the project, masses of

≈80 nuclides were measured, six of which (246, 247, 248Es, 249, 250, 252Md) were measured for

the first time [4], and more than 30 masses were directly measured for the first time [5]. Our

measurements agree significantly with PTMS data for known nuclides. However, a few

Figure 4. ToF spectrum for A = 204, 205 isobars.

34


measured masses, including the stable 81Br, disagreed with the values given in the literature.

This showed possible inaccuracy of the indirectly measured masses and suggests that it is

worth re-measuring the nuclides whose masses were determined by indirect methods.

[1] Y. Ito et al., to be submitted.


[3] S. Kimura et al., arXive: 1706.00186.

[4] Y. Ito et al., arXive: 1709.06468.

[5] M. Rosenbusch et al., arXive: 1801.02823.

III. The ongoing mass measurement project with multiple MRTOF

In the next phase of the SHE-Mass project, we will place several MRTOF setups at three

different RI-beam facilities of RIKEN RIBF in order to cover all available nuclides at RIBF

and to measure >1000 masses within coming five years. Figure 5 shows the regions of

nuclides that will be measured at GARIS-II, KISS, and BigRIPS+SLOWRI. The GARIS-II will

be continuously used for superheavy elements but the device has moved to the new

location in the Ring Cyclotron facility. An advantage of the new location is that we can place

the MRTOF to the first triplet ion trap of the gas cell in the focal plane chamber of the

GARIS-II. This improvement will allow us to measure the hot-fusion superheavy elements

such as Mc and Nh. The KISS facility provides some particular neutron rich nuclides

synthesized by multi-nucleon transfer reactions which are difficult to be obtained with other

facilities. The BigRIPS provides universal radioactive ion beams by in-flight fission and

projectile fragmentation reactions. The beams from the BigRIPS are not only high energy

Figure 5. Expected regions of nuclides to be measured at different facilities of RIBF.

35


(≈100 MeV/u) but contain ≈30 nuclides in the vicinity of the anticipated nuclide. Combining

the RF-carpet gas catcher and the MRTOF, very efficient mass measurements of nuclides

far from the stability can be performed. Thanks to the “spectrographic” feature of MRTOF,

multiple nuclides can be measured simultaneously. When we aim at very exotic nuclide,

such as 80Ni, it takes long measurement time, however, many neighborhood nuclides can be

seen in the same spectrum with very high statistics. One symbolic MRTOR setup, z-MRTOF,

will be placed at the end of the ZeroDegree Spectrometer, where we can obtain many exotic

nuclei with parasitic mode.

IV. Conclusion

The MRTOF mass spectrograph is a powerful device for comprehensive mass

measurements of short-lived nuclei. Multiple MRTOF devices at RIKEN RIBF will provide

hundreds of important mass data for various scientific studies.

Figure 6. Previous and new MRTOF setup for superheavy elements.

36


Status Report (6)

Status of KISS project

Y. Hirayama1*, Y.X. Watanabe1, M. Miyatake1, M. Wada1, P. Schury1, Y. Kakiguchi1,

M. Oyaizu1, M. Mukai2, M. Ahmed2, S. Kimura2, J.H. Park3, J.Y. Moon3, H. Ishiyama3,

S.C. Jeong3, A. Taniguchi4, H. Watanabe5, S. Kanaya6, H. Muhammad6, A. Odahara6,

T. Shimoda6

1KEK, 2U. Tsukuba, 3IBS RISP, 4KUR, 5RIKEN, 6Osaka U.

I. In-gas-cell laser ionization spectroscopy of platinum and iridium isotopes

We performed the nuclear spectroscopy using the 136Xe beam with the energy of

10.75 MeV/nucleon and a maximum intensity of 100 pnA. We introduced a

doughnut-shaped gas cell [1] with the 198Pt rotating target system in order to increase the

extraction yield not only by increasing the 136Xe primary beam intensity but also by reducing

the argon-gas plasma density in the gas cell. The 136Xe beam was directed onto the 198Pt

rotating target placed at the front of the gas cell, and was stopped at a tungsten beam dump

Figure 1. HFS measurements of 199g, 199mPt. (a) level scheme. (b) Measured HFS

spectra of 198g, 199g, 199mPt. (c) Evaluated magnetic dipole moments, the change of the

charge radii, and the evaluated deformation parameters by using liquid drop model.

37


without entering the gas cell. As a result, we successfully extracted the laser ionized 199gPt+,

199mPt+, 196, 197, 198gIr+ with one order of magnitude higher yield than that with the primary

beam intensity of 20 pnA.

Figure 1(a) and (b) show the level scheme of 199Pt, and the measured HFS of 199g+mPt by

detecting β-rays and γ-rays with the energy of 392 keV emitted from the 199gPt and 199mPt,

respectively. Due to the in-gas-cell laser ionization spectroscopy, the measured response

function of 198Pt (Iπ = 0+) has broad width. However, we can evaluate the magnetic dipole

moment and the change of the charge radius by analyzing the resonance peak by using the

measured response function. This is because the resonance width of HFS is mainly

governed by the magnetic dipole moment. Figure 1(c) shows the evaluated values which

are consistent with the systematics of magnetic dipole moments and the deformation

parameters. The details were discussed in Ref. [2]. The analysis of HFS of iridium isotopes

were finished, and we are summarizing them as a paper [3].

[1] Y. Hirayama et al., Nucl. Instrum. Methods B 412 (2017) 11.

[2] Y. Hirayama et al., Phys. Rev. C 96 (2017) 014307.

[3] M. Mukai et al., in preparation.

II. β-γ spectroscopy

β-γ spectroscopy was performed by using newly installed high-efficiency and

low-background multi-segmented gas counter (MSPGC) [1] for β-ray detection and four

super clover Ge (SCGe) detectors for γ-ray detection. The radioactive isotopes extracted

from KISS were implanted into the Mylar tape surrounded by MSPGC, which consists of 32

counters (16 pairs of telescope). This counter is sensitive to not only β-rays but also

characteristic X-rays and internal conversion electrons. These events are identified by

analyzing the multiplicity (M) of the gas-counter. Therefore, it is feasible to identify γ-rays of

internal transitions emitted from an isomeric state by detecting the following characteristic

X-rays and/or internal conversion electrons, which were mainly M = 1 (only one counter is

fired) and also M = 2 events (only one telescope is fired). The absolute detection efficiency

of 16 telescope pairs in the MSPGC is as high as about 50% for β-rays (M = 2 events)

emitted from the tantalum and osmium isotopes due to a lower energy threshold of around

100 keV than typical plastic-scintillator β-telescopes. Four SCGe detectors were installed in

order to detect β-delayed γ-rays from the internal transition of isomeric states. The absolute

detection efficiency was measured to be about 14% at energy of 400 keV.

38


185, 186, 187Ta isotopes were produced by the MNT reactions between 136Xe beam

(72 MeV/nucleon) and nat.W target (9.65 mg/cm2) at the yield-measurement and

extraction-test experiment (Spokesperson: P. Walker). Measured β-delayed γ-rays of

185, 186, 187Ta were consistent with the reported ones [2]. Moreover, we probably measured

the γ-rays emitted from an isomeric state of 187Ta which was found at GSI-ESR. According to

the result, P. Walker submitted physics proposal of “The Structure and Decay of High-K

Isomers in 187Ta” to the last RIKEN NP-PAC, and it was successfully approved.

The extraction of laser ionized 196Os (t1/2 = 34.9 (2) min.) isotope by using newly developed

ionization scheme [3] was successfully confirmed from the consistency of the measured

half-life and β-delayed γ-ray spectrum with the reported ones [2]. Then, we performed β-γ

spectroscopy of 195, 197, 198Os isotopes. We revised the accuracy of half-life of 195, 197Os, and

measure the half-life of 198Os for the first time successfully. From the measured γ-ray energy

spectrum in coincidence with MSPGC as shown in Fig. 2, we found new intense γ-ray

transitions for 195Os. These γ-rays were measured in coincidence with the characteristic

X-rays of osmium, and the half-lives gated on these γ-rays were much shorter than that of

the ground state of 195Os. These results suggested that these γ-rays would be emitted by

internal transitions from the predicted long-lived isomeric state with Iπ = 13/2+. Now, the

further analysis is in progress.

[1] M. Mukai et al., Nucl. Instrum. Methods A 884 (2018) 1.

[2] NNDC, https://www.nndc.bnl.gov/

[3] Y. Hirayama et al., J. Phys. B 50 (2017) 215203.

Figure 2. Measured γ-ray energy spectra in coincidence with MSPGC of 195Os. The

γ-ray transitions in red were observed for the first time and would be eimitted from the

long-lived isomeric state with Iπ = 13/2+.

39


III. In-gas-jet laser ionization spectroscopy

In order to determine electromagnetic moments and isotope shifts with higher precision by

in-gas-jet laser ionization spectroscopy technique, we have developed Laval nozzle and

S-shaped RFQ, and installed new laser system as shown in Fig. 3(a), (b), and (c),

respectively. We can successfully extract and transport laser ionized stable-platinum atoms,

which were evaporated from a filament in the gas cell, through the S-shaped RFQ.

Figure 3(c) shows the employed laser ionization scheme for the elements of atomic number

Z = 72 – 78, schematic configuration of laser system, and the photo of installed laser system

on 20th March 2018. The laser system consists of pumping laser of Nd:YAG (EdgeWave,

355 nm, 60 W), narrow-band seed laser (TOPTICA, DLC DL PRO HP), and dye-amplifier

(Sirah). We will start the R&D work, such as optimizations of laser transport and gas-jet

formation, with the new laser system from April 2018.

IV. Three-dimensional tracking proportional gas counter

We successfully developed the high-efficiency and low-background gas counter [1] for β-ray

detection. The background event rate is 0.1 counter-per-second (cps). In order to perform

the half-life measurements of more neutron-rich nuclei around N = 126, it is essential to

reduce the background event rate down to 0.01 cps. We have started the development of

Figure 3. Equipment for in-gas-jet laser ionization spectroscopy. (a) Laval nozzle, (b)

S-shaped RFQ, and (c) new narrow-band laser system.

40


three-dimensional tracking proportional gas counter to suppress the background rate from

tracking and identification of background events. For the three-dimensional tracking, we

replaced the anode wire from BeCu wire to high-resistive carbon wire (1 kΩ/cm), and

performed the position measurement by using one proto-type gas counter.

Figure 4 shows the calibrated position and position resolution. The position linearity was

good, and position resolution was also enough high to identify β-ray events emitted from the

implantation position. We can reduce the background event rate down to 0.01 cps based on

GEANT4 simulation.

For 32 counters (64 channels), we have started to optimize the compact and low-noise

pre-amplifier, shaping-amplifier, and discriminator circuits. We plan to start the performance

test from May 2018 by using the full setup.

[1] M. Mukai et al., Nucl. Instrum. Methods A 884 (2018) 1.

V. MR-TOF system

Figure 5 shows the newly installed beam line for MR-TOF [1] system. The KISS beam can

be deflected by using the switching deflector, implanted into He gas cooler for the

thermalization, and extracted toward trap and bunching system in order to inject the

extracted beam to MR-TOF. We tested the beam switching deflector and electric quadrupole

lens by using iridium stable isotopes, and optimized the parameters to transport the beam

Figure 4. Measured position linearity and position resolution by using proto-type gas

counter with high-resistive carbon wire.

41


with 2 mm in full-width-at-tenth-maximum to implant it into the He gas cooler, whose gas

pressure would be around 2 mbar and entrance window diameter is 2 mm. Now the

pumping test of He gas cooler is in progress, and the pressure reached down to ~1×10−6 Pa.

We will install the trap and buncher system, and MR-TOF on April 2018. Then, we plan to

perform offline commissioning of whole system including MR-TOF for mass measurements

of the nuclei around N = 126.


Figure 5. Photo of MR-TOF system at KISS.

iglis-net newsletter no. 6 may 2018research.kek.jp/group/wnsc/iglis-net/img/news-06-2018.pdf ·...

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