Z. Phys. A 350, 7-8 (1994) ZEITSCHRIFT FURPHYSIKA �9 Springer-Verlag 1994

Short note

The decay of 9~ Zhou Shuhua, Li Jingwen, Zeng Xiantang, Wen Shuxian, Dong Zhiqiang, Zheng Hua, Hu Aidong China Institute of Atomic Energy, P.O. Box 275(49), Beijing 102413, PR China

Received: 4 July 1994

Abstract

By means of X-~f and 7-~f coincidence measurements of the SSCi + 5SNi reaction products, 38 7 lines have been iden- tiffed to be in coincidence with KX(Tc)-rays and assigned to the decay of 9~ Its hulf-lis of 11 4- 3 s has been deduced from the 154.6 keV ")'-decay. The result supports ou~ previ- ous identification of 9~ produced in the same reactions.

The nuclei near the N : Z = 5 0 region have resently been the sub-

ject of intensive study[I-6], mostly due to their significance for both

nuclear structure and astrophysics. The stability of these nuclei

against proton emission is important to the astrophysical rapid pro-

ton capture process. In a previous paper[4], we reported the identi-

fication of a new nucleus 9~ the measurement of its half-life, the

observation of KX(Tc)-rays from its/3+ decay through K-electron

capture and its two decaying 7 lines (992 keV and 1002 keV) from

*?-ray singles measurements following the 115 MeV 35C1 + 5SNi re-

action. S. J.Yennelo et al. have reported the identification of~176

in E/A=T0 MeV 92Mo + ~8Ni reactions by using an A1200 frag-

ment analyzer[6]. Their results imply that the 9~ lives longer

than its flight time through the analyzer, which is of the order of

150 ns. No further decay properties ofg~ have been reported so

far. To obtain more information on the decay property of 9~ we

performed X-7 coincidence measurements studying the 35C1 + ~SNi

reaction products, and assigning 38 decaying ~f lines to belong to

9~ as well as confirming our previous identification.

The experiments were carried out at the HI-13 tandem accel-

erator of CIAE. The experimental arrangement was similar to the

previous[4], except that the beam was shut off during the coun

-ting period such that the X-7 coincidence measurements could be

performed with reduced background. The details will be described

elesewhere. Here only a brief description will be given.

An enriched (90%) 5SNi target of~l .O3mg/cm 2 was bombarded

by 120, 130 and 140 MeV 35C1 ions to produce the nuclei of 9~

through the SSNi(35Cl,p2n) reactions. The residual nuclei recoiling

from the target were captured on Ta foils of 8mg/cm 2 and trans-

ported to a well shielded counting position 30.5cm away from the

target within 1.2 s. The singles X-rays and 7-rays~ as well as X-7

coincidences were studied. This was made possible by a wheel sys-

tem and by use of a Si(Li) X-ray detector(~b6mm • 5.27mm) and

a HPGe 7-ray detector (~57.8mm • 81.6mm). Normally, both the

irradiation and the measurement periods lasted for 30 s in each cy-

cle. During the irradiation period, the output of the preamplifiers

of the detectors were grounded by a relay, while in the counting

period, an electro-magnetic shutter was closed to prevent the beam

from hitting the target. The time sequence of the measurements

was controlled by a microprocessor. The beam current was kept in

a range from 80 nA to 180 nA. The FWHM resolution of the HPGe

detector was 3 keV . The energy calibrations were made by means

of an 241Am source for the Si(Li) X-ray spectrometer, and 6~

137Cs, 54Mn sources as well as 11 known 7-rays from the isotopes

produced in the reactions, ranging from 141.174 keV to 1129.195

keV, for the HPGe -y-ray spectrometer. The time resolution of the

coincidence measurements was 80 ns. The ratio of the random to

real coincidences was ~ 1%.

After subtracting the background and the contaminations of the

K~(Mo), Kfl(Nb) and Kfl(Zr) to the K~(Tc) peak, 38 ~, lines were

observed in the X-7 coincidence spectrum gated by KaX(Tc) for

the 120 MeV bombarding energy. The energies (in keV) of these 7

lines are 154.6,178.9, 184.6, 192.3, 203.3, 216.0, 228.3, 258.2, 281.8,

295.4, 319.4, 336.5, 345.1,355.2, 366.1,377.4, 398.6, 425.5, 439.6,

452.9, 477.6, 491.8, 518.3, 625.9, 644.8, 720.3, 771.6, 795.8, 821.3,

831.6,849.9, 986.2, 991.0, 1003, 1033, 1178, 1237 and 1551. As an

example, the Kc~X(Tc) gated 7 spectrum for the 7-ray energy range

from 100 to 300 keV is shown in figure 1 a). To assist the assignment

of these 7 lines, data were analysed from a separate experiment, in

which 124 MeV 35C1 beam was used to bombard a 2mg/cm 2 ~SNi

target enriched to 99.8% and evaporated on a 30 mg/cm 2 lead

backing. 7-7 coincidences were measured by five HPGe spectro-

2O

15 0

10

100

400 ,

~ 350 -

(J 30O

250

200

150

150

I ' ' ' '

, - 4 i 10

i i i i

201

] , , , , [ , , , ,

(a) ~ o

i I I I I i i ' '

250 300

Channels

o

~ ~ �9 �9 ~ ,~ ~

*

260 280 300 320

i ' ' ' ' l ' ' ' ' i '

I I

340

Channe~ Fig.1 a) A part of the T-ray spectrum gated by the K~X(Tc) in the T energy range from 100 keV to 300 keV. b) A part of the ?-ray spectrum gated by 511 keV ?-ray showing the 154.6 keV peak preceded by j3 + decay.

meters equipped with BGO Compton-suppression shields. The five

strongest peaks 154.6, 295.4, 319.4, 336.5 and 491.8 keV were iden-

tified by ?-? coincidences gated by 511 keV ?-ray. This indicates

that the five ?-rays were preceded by the ~+ decay of ruthenium

isotopes, Figure 1 b) shows the 154.6 keV peak in the coincidence

spectrum gated by the 511 keV ?-ray. The 154.6 keV ? -ray is a

well isolated peak even in the ? singles spectrum. The hatf-life of

this ?-ray was deduced to be 11 4- 3 s from the wrlations of its

intensity with irradiating and measux~ng time relative to the 397

keV ? of STMo. This is in agreement with out previously reported

hatf-life 13 4- 5 s for 9~ within the experimental error. The ratio

of the peak area of the 154.6 keV ? to that of 397 keV as s function

of the bombarding energy from 115 to 140 MeV follows the be-

haviour of the cross section ratio of 9~ to S~Mo catculated with a

CASCADE code quite well(see fig.2). From the CASCADE catcula-

tions the production cross section at 120 MeV beam energy is about

0.42rob for 9~ while less than 0.Olmb for the other ruthenium

isotopes. Besides, the 204.0, 393.7, 892.8 and 1096.9 keV decay

~f-rays of 91Ru, which were measured in a 54Fe(4~ reaction

by P.Komninos et at. [7], were not observed in our X-? coincidence

spectra. Thus, other isotopes of ruthenium can be eliminated as

O .rl .IJ

1O o - . . . . ~ . . : . . ' ' ' , . . . . I . . . . i . . . . , ' ' ' ' _

\ \ \ \

),

Y 110 115 120 125 130 135 140

Energy (in MeV)

Fig.2 The ratios of the peak nxea of the 154.6 keV T to the 397 keV ? of STMo as a function of beam energy (• compared with the ratios of the cross sec- tions of 9~ to SVMo (1~), normalized at 120 MeV. The lines are to guide the eye.

lO-i

10-2

sources of the observed 38 T lines in the KaX(Tc) gated 7 spec-

trum and we therefore assign these 7 lines to the decay of 9~

The 991 and 1003 keV ? lines listed above correspond to the previ-

ously reported 992keV and 1002keV lines in the ? singles spectrum,

respectively. The small differences in energies between the two sets

of data are due to lack of statistics and to the uncertainty in the

energy calibration of the ?),-ray spectrometer. The present result

supports our previous identification and half-life measurement of 90Ru .

The authors would like to thank to Yan Chunxiang, Xu Jincheng

and Chen Zhonglin for stimulating discussions. We appreciate the

support of the tandem accelerator operators in delivering the 35C1

beam, of Xu Guoji for providing the targets and capture foils and

Huo Hua for improving the performenee of the wheel transportation

device. This work is supported by the China National Nuclear

Corporation. Grant No. Y41201936121.

References

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193(1991)

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6. S.J.Yennelo et at., Phys. Rev. C 48 2620(1992)

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