Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 48 (2015)

Long-lived isomer in 126 Pd†
H. Watanabe∗1,∗2 for the RIBF60&62R1 Collaboration†∗1∗2Condensed from the article in Phys. Rev. Lett. 113, 042502(2014)RIKEN Nishina Center
IRCNPC, School of Physics and Nuclear Energy Engineering, Beihang University

are populated through the β decay of the long-lived
isomer in 126 Pd. Therefore, the half-life is determined
to be 23.0(8) ms by taking a weighted average of therespective values. Based on the observed mutual coincidence [see Fig. 2(d)] and γ-ray intensities, we propose
the decay scheme from the long-lived isomer in 126 Pd
to the high-spin states in 126 Ag as shown in Fig. 1.
(10+ )

296.7
86.2

(7− )
(5− )
(4+ )

2406 23.0(8) ms

β2110 0.44(3) µs
2023 0.33(4) µs(2121+x)

542.4
1481
1330.2787.7(2+ )

359.5
227.9

0+(1762+x)(1534+x)741.8693(792+x)

693.3

598.1

0 48.6(8) ms

193.7

126
46 Pd 80

194+xx126
47 Ag 79

20542.4
1008(c)428(d)193.7
227.9

6300
1502.0Eγ [keV]1330.2914.7

1132.8250

400 I II
300
200× 10
10000 400 800 1200 1600
Eelectron [keV]

693.3
787.7

1330.210297keV:
1 693keV:
T1/2=21(2)ms
T1/2=20(3)ms
0.10 20 40 60 80 100 120 0 20 40 60 80 100 120
Time [ms]542.4
1330.2
787.7

296.7

600Counts /8 keV

296.7(b)Counts /
1 keV

40

741.8

359.5

4

193keV:T1/2=25(2)ms
100101742keV:T1/2=23(2)ms
0.1
0 20 40 60 80 100 120
Time [ms]Counts /16 ms

Counts / 1 keV

30

287.0
254.3
296.7
263.2

80

542.4
583.5
598.1
661.9
693.3
741.8
787.7
842.6

500

Counts / 2 keV(a)Counts /16 msCounts / 1 keV

100

193.7
227.9 203.7
263.2
287.0
296.7
359.5
365.0Fig. 1. Decay schemes of the J π = (10+ ) isomer in 126 Pd.

Counts / 2 keVSpectroscopic studies of 126 Pd have been performedat the RIBF facility. Neutron-rich nuclei below 132 Sn
were produced using in-flight fission of a 238 U86+ beamat 345 MeV/nucleon with the intensity ranging from
7 to 12 pnA, impinging on a beryllium target with athickness of 3 mm. The nuclei of interest were separated and identified through the BigRIPS separator
and the following ZeroDegree spectrometer. A totalof 5.3 × 104 126 Pd fragments were implanted into ahighly segmented active stopper, named WAS3ABi,
which consisted of eight double-sided silicon-strip detectors (DSSSD) stacked compactly. The DSSSDs also
served as detectors for electrons following β-decay andinternal conversion (IC) processes. Gamma rays weredetected by the EURICA array that consisted of twelve
Cluster-type detectors.
The decay schemes of the isomeric states in 126 Pd
are exhibited in Fig. 1. For 126 Pd, the J π = (5− ) and(7− ) isomers at 2023 and 2110 keV, respectively, werereported in Ref.1) . In the present work, the γ rays
below these isomers, except for the 86-keV line, havebeen also observed in coincidence with electrons thatwere associated with the prior implantation of 126 Pd,
as demonstrated in Fig. 2(a). With gates on these γrays, a prominent peak can be found in an electron
spectrum [marked with ”I” in the inset of Fig. 2(b)];this corresponds to the conversion electrons for the 86keV, E2 transition (αT = 2.374). In Fig. 2(b), a γray at 297 keV is clearly visible in addition to the γrays below the (5− ) isomer by gating on the 86-keV
IC peak. The appearance of the 297-keV peak is emphasized by taking a γ-ray time condition earlier thanelectron events, as is evident from the inset of Fig. 2(a),suggesting that this new γ ray precedes the highly converted 86-keV transition. Furthermore, the 297-keV γray is observed in coincidence with the other γ rays in126
Pd [see Fig. 2(c) as an example]. Thus, the longlived isomer can be identified at an excitation energyof 2406 keV. A peak marked with ”II” in the inset ofFig. 2(b) is expected to arise from the conversion electrons for the 297-keV transition, being most likely ofan E3 character (αT = 0.1197).
The half-life (T1/2 ) derived from the time distribution of the 297-keV γ ray is in agreement with that ofthe 693-keV one within experimental errors, as illustrated in the insets of Fig. 2(c). Similar half-lives havebeen observed for six other γ rays; these transitions areexpected to belong to high-spin states in 126 Ag which

20200

400600800
Eγ [keV]

1000

1200

1400Fig. 2. Gamma-ray spectra measured with various gateconditions within 50 ms after the 126 Pd implantation.

References
1) H. Watanabe et al.: Phys. Rev. Lett. 111, 152501(2013).

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