New high-precision nuclear mass studies by the
first MRTOF mass spectrometer at theBigRIPS facility
Marco Rosenbusch for the WNSC-IPNS-KEK and SLOWRI/RIKEN
Wako Nuclear Science Center
2-1 Hirosawa, Wako, Saitama 351-0198, Japan• Nuclear mass spectrometry• Multi-reflection time-of-flight technique• The SLOWRI-ZD MRTOF experiment• Technological advances• 2020 online commissioning

Marco Rosenbusch, TCHoU, Tsukuba, Online MeetingPhysics using mass spectrometry
Physics application

δm/m

General physics & chemistry£ 10-5

Nuclear structure and Astrophysics£ 10-6- separation of isobars

Isomer studies and Astrophysics= N·+Z·= N·+Z·+Z·– binding energy- separation of isomers+Z·– binding energy£ 10-7

Weak interaction studies£ 10-8Metrology - fundamental constants£ 10-9CPT tests£ 10-10

QED in highly-charged ions£ 10-11- separation of atomic states

recent CPT tests on 10-12 level: S. Ulmer et al., Nature 524, 196 (2015)
Marco Rosenbusch, TCHoU, Tsukuba, Online MeetingPhysics using mass spectrometry
Physics application

δm/m

General physics & chemistry£ 10-5

Nuclear structure and Astrophysics£ 10-6- separation of isobars= N·+Z·+Z·– binding energy= N·+Z·+Z·– binding energy

Isomer studies and Astrophysics
MRTOF at present£ 10-7

Weak interaction studies
MRTOF future goal

£ 10-8Metrology - fundamental constants£ 10-9CPT tests£ 10-10

QED in highly-charged ions£ 10-11- separation of isomers- separation of atomic states

recent CPT tests on 10-12 level: S. Ulmer et al., Nature 524, 196 (2015)
Marco Rosenbusch, TCHoU, Tsukuba, Online MeetingShell evolution studies
What can we learn from ground-state masses about
the nuclear shell evolution?

S2pSp Sn
Odd-Even Staggering

Estimators for the pairing gaps

S2nTwo-nucleon separation energies

Shell gaps, test of magicity

Input for theory to reveal possible nuclear valence orbit configurations, collectivity
and deformations. New extrapolations into the terra incognita
Marco Rosenbusch, TCHoU, Tsukuba, Online Meeting

Mass measurements of exotic nuclei
Nuclear structure example:
Study of nuclear tensor force
T. Otsuka, Rev. Mod. Phys. 92, 015002 (2020)

N = 32
N = 34F. Wienholtz et al., Nature 498,346 (2013)
D. Steppenbeck et al., Nature 502, 207 (2013)
S. Michimasa et al., PRL 121, 022506 (2018)

Marco Rosenbusch, TCHoU, Tsukuba, Online Meeting

Mass measurements of exotic nuclei
Astrophysical examples

rp-process

R. N. Wolf et al., Phys. Rev. Lett. 110, 041101 (2013)

rp proton capture rate
is mass dependent

r-processH. Schatz, Int J. Mass spectrom. 251, 293 (2006),
Int J. Mass spectrom. 349-350, 181 (2013)
M. R. Mumpower et al., Phys. Rev. C 92, 035807(2015)

High precision and accuracy needed!
Marco Rosenbusch, TCHoU, Tsukuba, Online Meeting

Time-of-flight mass spectrometry
Mass resolving power:• linear TOF-MS: m/Δm > 100• reflector-TOF-MS: m/Δm > 5,000• MRTOF-MS: m/Δm > 100,000
Δm = 2Δt = FWHM of ion TOF distribution

W.R. Plass et al., IJMS 349-350, 134 (2013)
Marco Rosenbusch, TCHoU, Tsukuba, Online Meeting

The multi-reflection time-of-flight (MRTOF) technique
H.Wollnik and M. Przewloka, Int. J. Mass Spectrom. Ion Proc. 96, 267 (1990)

Total time of flight
predominantly determinedby the electrostatic term ofthe system
detector

ion trap

device constant

Ekin ≈ 3keV

injection of ionsmultiple reflections of ionsaveragefrom ion
distribution

precise time of flight measurement

detector
Marco Rosenbusch, TCHoU, Tsukuba, Online Meeting

electrostatic
contribution

Ion focusing• Axial potential shape allows tomodify the phase space of theions via the penetration depth
into the ion mirror• Narrow time-of-flight focus
achieved at the detector
à high resolution by longflight path

M. Rosenbusch et al., Nucl. Instr. Meth B 463, 184 (2020)

MRTOF mass spectrograph

P. Schury et al., Nucl. Instr. Meth B 335, 39 (2014)

Marco Rosenbusch, TCHoU, Tsukuba, Online Meeting

MRTOF-MS Advantages•

Measurement duration is short: < 10-20ms percycle
à short lived isotopes accessible•

Several isotopes can be measured at the sametime
à efficient use of expensive accelerator timeHigh mass resolving power m/Δm > 500,000
à nuclear isomer separation possible

normalized ion count•

Early 2021

Winter 2020

P. Schury et al., Phys. Rev. C 95, 011305(R) (2017)

Marco Rosenbusch, TCHoU, Tsukuba, Online MeetingCurrent MRTOF facilities at RIBF

First SHN recently measured!
P. Schury et al., Phys. Rev. C 104, L021304 (2021)

Marco Rosenbusch, TCHoU, Tsukuba, Online Meeting

The SLOWRI-ZD MRTOF experiment

Reference ions

• Ions stopped in a cryogenic gas cell
• Extraction and transport to a trap
chamber with triple-trap system• Preparation/cooling of ions in central
flat ion trap
• Ions are forwarded to MRTOF-MS andinjected• After multiple reflections à ejection
and time-of-flight detection

Drawing: M. Wada

New gas cell design for perpendicular extraction
A. Takamine, S. Iimura, D. Hou

M. Rosenbusch et al., Nucl. Instr. Meth B 463, 184 (2020)

Marco Rosenbusch, TCHoU, Tsukuba, Online Meeting

The SLOWRI-ZD MRTOF experiment
β-ToF

•

Energy adaption available bypulsed drift tube•

In-trap ion separation available(two methods tested)•Beta-ToF detection available

T. Niwase et al., Nucl. Instrum. Meth. A 953, 163198 (2020).
P. Schury et al., Phys. Rev. C 104, L021304 (2021).
T. Niwase et al., Phys. Rev. C, under review (2021). (arxiv 2108.06245)

Marco Rosenbusch, TCHoU, Tsukuba, Online MeetingTechnological advances: CGITS• Molecular contaminants from gas cellionized by high-energy beam
• In-trap ion separation essential to isolateions of interest• Concentric-Geometry In-Trap Separation(CGITS) was successfully employed

used during commissioning 2020
First MRTOF in-trap cleaning with deflector:
Y. Toker et al., J. Instrum. 4, P09001 (2009).
Usage of mirror endcaps:
J. T. Johnson et al., Anal. Chem. 91, 8789 (2019).
Further application and development of deflector:
T. Dickel et al., Nucl. Instrum. Meth. 777, 172 (2015).
P. Fischer et al., Rev. Sci. Instrum. 89, 015114 (2018).
Marco Rosenbusch, TCHoU, Tsukuba, Online MeetingTechnological advances: In-trap deflector• Selective kick-out now possible• Selective protection of several
masses now possible• Proper design: Kick out of unwanted
ions with weak 30V pulse

First MRTOF in-trap cleaning with deflector:
Y. Toker et al., J. Instrum. 4, P09001 (2009).
Usage of mirror endcaps:
J. T. Johnson et al., Anal. Chem. 91, 8789 (2019).
Development of deflector:T. Dickel et al., Nucl. Instrum. Meth. 777, 172 (2015).
P. Fischer et al., Rev. Sci. Instrum. 89, 015114 (2018).
Marco Rosenbusch, TCHoU, Tsukuba, Online MeetingTechnological advances: Tuning method and high MRP
1 hour measurement (each)

139K+ ionsbad tunegood tunewide energy range

m/Δm > 1,000,000 for A=40m/Δm > 900,000 for A=80
Marco Rosenbusch, TCHoU, Tsukuba, Online Meeting

The multi-reflection time-of-flight (MRTOF) technique
H.Wollnik and M. Przewloka, Int. J. Mass Spectrom. Ion Proc. 96, 267 (1990)

Total time of flight
predominantly determinedby the electrostatic term ofthe system
detector

ion trap

device constant

Ekin ≈ 3keV

injection of ionsmultiple reflections of ionsaveragefrom ion
distribution

electrostatic
contribution
offsettime
non-static
fieldsprecise time of flight measurement

detector
Marco Rosenbusch, TCHoU, Tsukuba, Online Meeting

ion-trap
physics
and ToF detect.

The multi-reflection time-of-flight (MRTOF) techniqueIons of well known mass andexotic ionsà comparison of times-of-flightfor the same number of laps

H.Wollnik and M. Przewloka, Int. J. Mass Spectrom. Ion Proc. 96, 267 (1990)

electrostatic
contribution

detector

ion trap

Ekin ≈ 3keV

offsettime

injection of ionsmultiple reflections of ionsY. Itoisobaric
reference

precise time of flight measurement

detector

relative precision below 10-7 achieved

Marco Rosenbusch, TCHoU, Tsukuba, Online MeetingTechnological advances: Wideband accuracy
reference ions / online ions

MRTOF voltage fluctuations/drifts(solved)MRTOF Mass Spectrographaveragefrom ion
distribution

Time-dependent ejection fieldof ion trap
Radiofrequency trapping fieldof ion trapMicro-ramping of MRTOF mirrors
Marco Rosenbusch, TCHoU, Tsukuba, Online Meeting

non-staticfields

Technological advances: Time-dependent ejection
non-staticfields

single reflection
example 100 ns transition time

M. Rosenbusch et al., Int. J. Mass Spectrom. 456, 116346 (2020)

Marco Rosenbusch, TCHoU, Tsukuba, Online MeetingTechnological advances: Time-dependent ejection
non-static
fieldsP. Schury
5 ns switch

Marco Rosenbusch, TCHoU, Tsukuba, Online MeetingTechnological advances: RF shunting

strongtime-dependent
field3 MHz≈ 500 Vppsilence

stored energywikipedia

FET switch to ground
disturbs resonanceswitchsolution not so easy

Marco Rosenbusch, TCHoU, Tsukuba, Online MeetingTechnological advances: Ion trap RF adaption
RF amplitude switch for GC/reference ionsaveragefrom ion
distribution

referencegas cellgas cell

20 ms

5 ms

ion-trap
physics

20 ms

5 ms

Marco Rosenbusch, TCHoU, Tsukuba, Online Meeting2020 online commissioning• Gas cell with MRTOF MS to use BigRIPS beams

MRTOF experiment
BRIKEN (2021) • Installed behind Zero Degree spectrometer• Symbiotic operation with in-beam gamma runs

HiCARI experiment (2020)
In-beam gamma spectroscopy(non-destructive measurement)

Marco Rosenbusch, TCHoU, Tsukuba, Online Meeting2020 online commissioning• Transport to the BigRIPS F11 position in October2020• Test of apparatus in online condition beginningof November, identification of chemicalcompounds obtained from the gas cell
• Taking part in different experiments of theHiCARI group by receiving parasitic beam during
November and December 2020

Marco Rosenbusch, TCHoU, Tsukuba, Online Meeting2020 online commissioning
Challenges:• Molecular contamination in general• Discharges in Gas Cell
• Chemical reactions in the Gas Cell
(unstable efficiency)• Quite strong pulses from CGITS cleaning• Decision: we trust only isobars

Marco Rosenbusch, TCHoU, Tsukuba, Online MeetingZD MRTOF system: 2020 online commissioning••••

Mass measurements in four different regions of the nuclide chartThree nuclear masses measured for the first time
Eleven nuclear masses improved in precision
Total system efficiency measured (0.3% - 1.5%)

ToF – 15043169 ns [ns]Marco Rosenbusch, TCHoU, Tsukuba, Online Meeting2020 online commissioning
88,89As measured for the first time!

S. Brett et al., Eur. Phys. J. A (2012) 48: 184

slide by W. Xian
Marco Rosenbusch, TCHoU, Tsukuba, Online Meeting2020 online commissioning

average deviation from true massaccuracy benchmark using isobars

Marco Rosenbusch, TCHoU, Tsukuba, Online Meeting

mass number A

WNSC
RIKEN
JAEA
IMPHKU

M. Rosenbusch, M. Wada, P. Schury, Y. Hirayama, H. Miyatake, Y.X. Watanabe
S. Iimura, H. Ishiyama, T. Kojima, T. Sonoda, S. Kimura, M. Mukai, S. Nishimura, S. Naimi, T. Niwase, A. Takamine
Y. ItoD.S. Hou, J. Liu
Collaborators
S. Chen, J. Lee, W. Xian