The γ decay of90Ru

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  • 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=50 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 i10

    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

    I. D.Rudolph et at., Phys. Rev. C 47 2574(1993).

    2. W.Gelletly et al., Phys. Lett. B 253, 287(1991).

    3. M.F.Mohar et at., Phys.Rev.Lett. 66, 1571(1991).

    4. Zhou Shuhua eta]., Chinese Journal of Nuclear Physics, 13

    193(1991)

    5. L.K.Zhang, S.Wen, H.gheng et at., Z. Phys. A346, 183(1993)

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

    7. P.Komninos, E.Nolte, P.Blasi, Z.Phys. A314, 135(1983)