Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 53

Production of isomers around 52 Fe nucleus via projectile fragmentation
K. Kawata,∗1,∗2 S. Ota,∗2 J. Zenihiro,∗1 C. Iwamoto,∗2 N. Kitamura,∗2 H. Sakai,∗2 S. Masuoka,∗2S. Michimasa,∗2 K. Yako,∗2 T. Harada,∗2 H. Nishibata,∗2 R. Tsunoda,∗2 N. Imai,∗2 J. Hwang,∗2 N. Zhang,∗4 andF. Endo∗5
The nuclear responses of isomeric high-spin states
are attractive topics. A recent theoretical study on
the spin-isospin response of the 12+ isomeric state in52
Fe showed that the widths of the GT strength distributions from the ground and isomeric states may differ from each other due to the diﬀerent collectivities,1)
which may call for the modiﬁcation of a simple Brink
hypothesis. To perform nuclear reactions on such isomers, isomeric nuclear beams should be prepared since
the isomers are still short-lived nuclei.
Projectile fragmentation is a popular method to produce short-lived nuclei. In order to prepare the isomerbeam, it is necessary to understand the production
mechanism of isomers through the projectile fragmentation process. We studied the isomer ratios in thevicinity of 52 Fe as a function of the linear momentum
transfer. Although the ratios are conventionally described by a classical model assuming the contributionof the angular momentum transfers during the projectile fragmentation process,2) it is still not clear how theangular momentum is transferred to the fragmented
particles. To learn the role of the angular momentum
transfer, we studied not only the isomer ratio but also
the momentum distribution of the isomeric state of
the fragmentation process. In this paper, we report anew systematic measurement of production cross sections of the isomers 52 Fe(12+ ),53 Fe(19/2− ), 54 Co(7+ ),and 54 Fe(10+ ) by primary beams of 58 Ni(0+ ) and59
Co(7/2− ).

Fig. 2. Isomer ratio of 52 Fe(12+ ). Red triangles show theresult from the 59 Co(7/2− ) beam, and the blue squares
show the result from the 58 Ni(0+ ) beam.

The experiment was performed at the SB2 course
in HIMAC, a synchrotron facility in Chiba. Figure 1
shows the experimental setup at the SB2 course. The
primary beams of 58 Ni and 59 Co at 350 MeV/nucleon
bombarded a 14-mm-thick 9 Be production target. Thefragments are separated and momentum analyzed bya fragment separator consisting of two dipole magnets
and quadrupole magnets. In order to obtain isomerratios, the number of fragments and γ rays from theisomers were counted. A Xe scintillator was used forcounting the fragment, and four Ge detectors were used
for detecting γ rays. The isomer ratio of a certain
fragment nucleus is the ratio of the number of emitted
gamma rays obtained after correcting for the eﬃciency
to the number of fragments.
Plastic
When the velocity of the fragment is the same asΔpScintillator
thatof the projectile, no momentum is transferred toF2the fragment.
SEM target D1
PlasticEnergy
Figure 2 shows the preliminary result of the isomer
slit
D2degrader
wedge
ratio of 52 Fe(12+ ). The momentum-transfer dependegrader slit
dence of the isomer ratio is clearly observed. The59−Xe
Ge*4 isomer ratio with the Co(7/2 ) beam at each moΔEcounter PPAC
mentum is larger than that with the 58 Ni(0+ ) beam.
It is inferred that the initial angular momentum of theprojectile has a signiﬁcant eﬀect on isomer production.
Fig. 1. Experimental setup in the SB2 course (16H362).
The data analysis is ongoing. The diﬀerence beThe number of primary beams was counted by a secondary emission monitor (SEM), which consists of atween the momentum distributions of isomers and nonthin Cu film. We identified the fragment by using theisomers will be investigated in order to clarify the role
ToF-∆E method. ToF was measured from F2 to F3,of angular momentum transfer from the viewpoint ofand ∆E was measured by a Xe scintillation detector.
the correlation between the linear momentum transfers
The number of isomers was counted by a Ge detector.
and angular momentum transfers.
∗1
∗2
∗3
∗4
∗5RIKEN Nishina Center
Center for Nuclear Study, University of Tokyo
Toho Universicity
Institute of Modern Physics
Tohoku University

References

1) H. Z. Liang et al., Phys. Rev. C 98, 014311 (2018).
2) W. -D. Schmidt et al., Z. Phys. A 350, 215 (1994).

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