Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 49 (2016)

Magnetic moment measurement of isomeric state in 99 Zr andcharacterization of the abrasion-fission mechanism
F. Boulay,∗1,∗2,∗3 J. M. Daugas,∗2,∗3 G. S. Simpson,∗4 Y. Ichikawa,∗3 A. Takamine,∗3 D. S. Ahn,∗3 K. Asahi,∗5H. Baba,∗3 L. Balabanski,∗3,∗6 T. Egami,∗7 T. Fujita,∗3,∗8 N. Fukuda,∗3 C. Funayama,∗5 T. Furukawa,∗9G. Georgiev,∗10 A. Gladkov,∗3,∗11 M. Hass,∗12 K. Imamura,∗3,∗13 N. Inabe,∗3 Y. Ishibashi,∗3,∗14T. Kawaguchi,∗7 T. Kawamura,∗8 W. Kim,∗11 Y. Kobayashi,∗15 S. Kojima,∗5 A. Kusoglu,∗10,∗16
S. Momiyama,∗17 I. Mukul,∗12 G. Neyens,∗18 M. Niikura,∗17 H. Nishibata,∗8 T. Nishizaka,∗7 A. Odahara,∗8Y. Ohtomo,∗3,∗5 D. Ralet,∗10 T. Sato,∗5 Y. Shimizu,∗3 T. Shimoda,∗8 T. Sumikama,∗3 H. Suzuki,∗3 H. Takeda,∗3L. C. Tao,∗3,∗19 Y. Togano,∗5 D. Tominaga,∗7 H. Ueno,∗3 H. Yamazaki,∗3 and X. F. Yang,∗18

Number of Entries

Counts (11ns/bin)

3000
2500
2000

Counts (11ns/bin)(TDPAD)3) method was used to perform such measurements. The 99 Zr nuclei were selected and identified through BigRIPS and were implanted in a nondisturbing copper crystal at F8. An external magnetic
field of 0.250 T was applied to induce a Larmor precession of the nuclei. This perturbation modified thenumber of photons emitted at a given angle dependingon the time. To detect this variation, 4 germanium detectors were placed around the crystal at 90◦ relativeto each other.

The region of neutron-rich isotones N=59 is on theborder of a sudden change of the ground state shapeof nuclei1,2) . A direct consequence is the existence ofmany nuclei with isomeric states in this region. Thesenuclei are well produced by fission. Measuring themagnetic moment of these states often allows a clear
determination of their single-particle structure and allows us to determine the spin parity of the isomericstate.
The production of spin-aligned nuclei is primordial
for these types of studies; however, the explanations of
the production mechanisms of such nuclei are not wellknown. An alignment of 18(8)% was previously measured for isomers produced in the abrasion-fission reaction4,5) . The purpose of the experiment described here
is to probe different momentum regions and determine
the one with the highest alignment rate. Owing tothe high beam intensity delivered by RIBF, three different momentum selections of 99 Zr were probed with
sufficient statistics accumulated.
Thus, the NP1306-RIBF99 experiment performed atRIKEN with the BigRIPS spectrometer has two aims.
The first is to measure the magnetic moment of the99
Zr isomeric state. The second is to measure the alignment ratio of the 99 Zr produced by the abrasion-fission
reaction of a 238 U beam sent at 345 MeV/A on a 100µm-thick target of 9 Be.
The time-dependent perturbed angular distribution102

10T=306(15) ns
T=306(15) ns

102

101

1500

11000200200

400

400600800600

800

1000

1000

1200
Time (ns)1200

Time (ns)

500
050

100

150

200

250300Eγ (keV)Fig. 1. Preliminary gamma energy spectra measured for99
Zr with the decay curve associated to the 130.2 keVline.

The online analysis did not allow us to extract a preliminary magnetic moment measurement. The analysis is in progress. However, some basic observables
could be preliminarily extracted to confirm the expected properties. In Fig. 1, the gamma energy spectra associated with 99 Zr is shown. We can see the twocharacteristic lines from the decay of the isomeric state
at 251.96 keV. The fit on the decay curve for the line
at 130.2 keV gives a lifetime of 306(15) ns, which iscompatible with the adopted value of 293(10) ns.

GANIL CEA/DSM CNRS/IN2P3
CEA DAM∗3 RIKEN Nishina Center∗4 LPSC∗5 Department of Physics, Tokyo Institute of Technology∗6 IFIN/HH/ELI-NP∗7 Department of Physics, Hosei University∗8 Department of Physics, Osaka University∗9 Department of Physics, Tokyo Metropolitan University∗10 CSNSM∗11 Department of Physics, Kyungpook National University∗12 Weizmann Institute∗13 Department of Physics, Meiji University∗14 Department of Physics, University of Tsukuba∗15 Department of Informatics and Engineering, University ofElectro Communications∗16 Physics Department, Istanbul University∗17 Department of Physics, University of Tokyo∗18 K. U. Leuven∗19 School of Physics, Peking University∗1∗2References
1) S. Hilaire, M. Girod Eur. Phys. J. A 33, 237 (2007).
2) A.G. Smith et al., Phys. Lett. B 591, 55 (2004).
3) G. Neyens, Rep. Prog. Phys. 66, 633 (2003).
4) G. Ilie et al., Phys. Lett. B 687, 305 (2010).
5) G. Neyens et al., Acta Phys. Pol. B 38, 1237 (2007).

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