Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

Improvements in the performance of the KISS MRTOF
P. Schury,∗1 T. Niwase,∗1,∗2,∗3 M. Wada,∗1 Y. Hirayama,∗1 H. Miyatake,∗1 M. Mukai,∗2 M. Rosenbusch,∗1 andY. X. Watanabe∗1
The KISS facility uses mutinucleon transfer reactions to produce nuclides which are diﬃcult to produce
by fusion or by in-ﬂight ﬁssion and fragmentation reactions. Many of these nuclides are close to stability, andtypically the more stable isobars are produced with orders of magnitude greater rates. This has made it difﬁcult to access some desirable nuclides, such as 188 W,
198, 199
Ir, and 238, 239 Pa, as resolving such nuclides fromthe next stabler isobar requires a high mass resolving
power not only in terms of full-width at half-maximum
but in terms of full-width at 1%—i.e. minimal tails.
Until recently, the MRTOF at KISS has achieved amaximum mass resolving power of ∆m/m ∼ 200,000
and the peak shape had a strong asymmetry, with therelative amplitude at ∆m ≈ +20 ppm being ≈1% ofmaximum. This was not suﬃcient to the task of resolving interesting nuclides nearer stability. However,in the past year the performance of the MRTOF installed at the KISS facility has improved. The mass
resolving power has increased to ∆m/m ∼ 400,000
while the peak shape has been made signiﬁcantly more
Gaussian. The improvement is shown in the top panelof Fig. 1. The lower panel of Fig. 1 demonstrates how
the new peak shape will allow for discernment of 199 Ir
which was previously not possible.
By carefully adjusting the biasing of the MRTOF optical elements, it was possible to both improve the peak
shape and the resolving power. This eﬀort was madereasonable by the use of purpose-built high-voltage
power supplies1) which achieve a high-stability without requiring long time-constant capacitive ﬁltering.
As these power supplies settle in under one minute,it was possible to eﬃciently perform multi-parameter
optimizations. With further tuning we anticipate that∆m/m > 500,000 with a Gaussian proﬁle can beachieved, which will greatly improve our ability to resolve isobars near stability
In future experiments, we plan to use the MRTOF
as a very high-resolution isobar puriﬁer to deliver isobarically (and possibly isomerically) pure beam of radioactive ions for e.g. decay studies. This will require a high stability in the peak position. We havefound that the power supplies contribute a temperature dependent drift of ∆m/∆T = 2.36(4) ppm/K
while thermal expansion of the MRTOF itself resultsin ∆m/∆T = 20.4(6) ppm/K. In the past we observed
very large shifts in the MRTOF peak position as theroom warmed due to the presence of numerous experimenters during online measurements. To try to re∗1
∗2
∗3

Wako Nuclear Science Center (WNSC), IPNS, KEKRIKEN Nishina Center
Department of Physics, Kyushu UniversityFig. 1. (top) Comparison of MRTOF peak shape from 2021
with the improved peak shape achieved in 2022. (bottom) Simulated spectrum for A = 199 isobars based on
measured MRTOF peak shape and calculated production yields. Prior to improving the peak shape it wasvery diﬃcult to observe 199 Ir ions as they produced onlya small ﬂuctuation in the tail of the 199 Pt ion peak.

duce this eﬀect, we gently heated the MRTOF chamber using a PID regulated baking system. The resultis shown in Fig. 2. In the future we will try improving
the thermal regulation.

Fig. 2. Drift of the peak position over 16 days of measurement while roughly regulating the MRTOF chamber at38◦ C. The maximum ﬂuctuation is consistent with athermal ﬂuctuation of ∆Tpk−pk ≈ 0.75 K.

Reference1) P. Schury, et al., Rev. Sci. Instrum. 91, 014702 (2020).

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