Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 51 (2018)

Improved wide bandwidth mass analysis with MRTOF-MS
P. Schury,∗1 M. Wada,∗1,∗2 M. Rosenbusch,∗2 Y. Ito,∗2 H. Haba,∗2 Y. Hirayama∗1 D. Kaji,∗2 S. Kimura,∗1,∗2,∗3
H. Koura,∗4 H. Miyatake,∗1 J. Y. Moon,∗7,∗1 K. Morimoto,∗2 K. Morita,∗2,∗5 A. Ozawa,∗2,∗3 M. Rosenbusch,∗2M. Reponen,∗2 A. Takamine,∗2 T. Tanaka,∗2,∗5 Y. X. Watanabe,∗1 and H. Wollnik∗6
In recent studies of fusion-evaporation reactions
using GARIS-II,1) higher order evaporation channel (pxn, αxn, etc.) products were observed withthe multi-reﬂection time-of-ﬂight mass spectrograph2)(MRTOF-MS). As exempliﬁed in Fig. 1, in many cases,
such products had A/q suﬃciently diﬀerent from theneutron evaporation products of primary interest as tomake a diﬀerent number of laps within the MRTOF.
As a result, they have a diﬀerent ﬂight path than thereference ions, which complicates the mass analysis.
We have previously3) developed an analytic framework for making use of such wide mass bandwidthspectra. However, the technique was only accurate
on the few-ppm level—suﬃcient for identiﬁcation, but
insuﬃcient for the precision mass analysis we desire.
While the earlier technique was useful at identiﬁcationof ions within a large mass bandwidth, it was also complicated and required at least two measurements beperformed in series under substantially similar conditions, making it prone to errors from e.g. slight voltage
drifts. Utilizing our presently unique ion preparation
trap geometry, we have been able to modify the operation of the MRTOF to allow two measurements to bemade nearly in parallel, a scheme we call “concomitantreferencing.” This in turn has allowed for developmentof an improved method to determine the masses of ions
within a large mass bandwidth.
In the present implementation of concomitant referencing, the measurement cycle is split into two subcycles. Reference ions making diﬀerent number of laps
in each of the sub-cycles are utilized to precisely determine the circulation period, Tref , of the reference ions
during the measurement. We then use the original
wide mass bandwidth analysis method to determine
the number of laps analyte ions made in the MRTOF,
and to determine their m/q with suﬃcient accuracy for
identiﬁcation . Once the number of laps are known, themeasured Tref is used to adjust the reference ion ToF,
tref , to match the ﬂight path of the analyte ion:t′ref = tref − ∆n · Tref ,(1)

where ∆n is the diﬀerence in laps between reference
and analyte. Finally, t′ref is used in the single-reference
analysis methodology5) to determine the analyte ion’s
∗1
∗2
∗3
∗4
∗5
∗6
∗7KEK Wako Nuclear Science Center (WNSC)
RIKEN Nishina Center
Institute of Physics, University of Tsukuba
Advanced Science Research Center, JAEA
Dept. Physics, Kyushu University
Dept. Chem. and BioChem., New Mexico State University
Institute for Basic Science- 170 -Fig. 1. Portion of online time-of-flight spectrum observedin the study of 169 Tm(48 Ca, X) reaction. The A=213
isotopes performed 145 laps in the MRTOF, as did thereference ions. The A=210 isotopes performed 146 lapsin the MRTOF, complicating the mass analysis.

mass-to-charge ratio:()2tanalyte − t0manalyte = mref,t′ref − t0(2)where t0 is an inherent delay between the ions leaving
the ﬂat ion trap and the start of the TDC, previously4)
determined to be t0 =45(5) ns.
Oﬄine tests with 85,87 Rb have demonstrated an−7up toaccurate relative mass accuracy of δmm ∼10∆n=4.
This makes MRTOF mass spectrometry
highly-competitive with storage rings6–8) in terms ofmass accuracy and bandwidth.
References
1) D. Kaji et al., Nucl. Instrum. Methods Phys. Res. B
317, 311 (2013).
2) P. Schury et al., Nucl. Instrum. Methods Phys. Res B
335, 39 (2014).
3) P. Schury et al., Int. J. Mass Spectrom. 359, 19 (2013).
4) P. Schury et al., Phys. Rev. C 95, 251 (2017).
5) Y. Ito et al., Phys. Rev. C 88, 011306(R) (2013).
6) F. Bosch, Yu. A. Litvinov, Int. J. Mass Spectrom. 349,151 (2013).
7) J. W. Xia et al., Nucl. Instrum. Methods Phys. Res. A
488, 11 (2002).
8) M. Wakasugi, Rare RI Ring Collaborations, JPS Conf.
Proc. 6 010020 (2015).