Giannatiempo, A

Nannini, A

Perego, A

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mtsztduration. OCR Outputbe investigated first. We ask for a total of nine shifts to be divided im three runs of equalof Rb and Rb, respectively. The case of Kr appears to be the easier one and would7876 78reduced transitions probabilities for the 0; states in 76 Kr and 78 Kr populated in the decay`°We propose to measure the ratio B(E0;0;]—> OT)/B(E2;0; —> of the E0 to E2SUMMARYComtactmanz O. TengbladSpokesman: P. SomaInstitute of Physics, University, AarhusK. RiisagerCERNM.G.J. Borge, O. TemgbladDipartimento di Fisica, Universita di Firenze — INFN sez. di FirenzeA. Giannatiempo, A. Nannini, A. Perego, P. Soma32 $56 g Study of electric monopole transitions in 76·78Kr.Qc P{/owProposal to the ISOLDE Committeelgg, ZClm lf;QKIXI300004782J_Q]_émrwmc ISC/P28CERN /1sc 92-54*.. J’*· N90 A CERN uBRAR*E$» GENE`]Additional information on the structure of the 0+ states can be obtained by the study OCR Output0;,* —> 2,+ transitions in 8°Kr and 82Kr.particular, we remark that for our calculation the agreement is reasonable also for theavailable experimental data is of the same quality for both sets of calculated data. Inby other authors [4,5] are also reported. It is seen that the general agreement with theof E2 transition rates. This is shown in Table I where the theoretical values obtainsmore stringent test is provided by the comparison of theoretical and experimental valuesdoes not allow us to draw any definite conclusion about the goodness of the description. ADue to the flexibility of the IBA—2 model, the simple comparison of the excitation patternsreasonably reproduce the excitation energy of the low-lying states including the O; states.the isotopes 78*8°·82Kr. By using a different set for the hamiltonian parameters we couldthe problem of a satisfactory description, in terms of the IBA-2 model, of the 0+ states inAs a consequence of our recent experimental work on 8°Kr [7] we were led to reconsiderE2 transition rates obtaining a reasonable agreement with the experiment.parameters determined by Kaup and Gelberg and extended their calculations to incluocspace used. Subsequently, several authors [3 -6] have made use of the same hamiltonianof the 0; states which then were interpreted as "intruder” states lying outside the modelsatisfactorily reproduced the excitation pattern of the low-lying levels with the exceptiona systematic investigation has been performed by Kaup and Gelberg They havecarried out in the framework of the IBA-2 model. In particular, for even krypton isotopes,investigation of the properties of the low-lying levels of this mass region has mainly beenA=70-80 region is still a matter of some debate (see, e.g., ref. The theoreticalThe problem of the nature of low-lying 0+ excited states in even-even nuclei of theN,, are good quantum numbers. The so called "effective monopole charge" 50,,. and ,60,, OCR OutputOnly the last two terms in this expression contribute to the transition rates as N ,, andparameters of the model.the number of neutron and proton cl—bosons, respectively, and 70,,, 70,,, 50,, and BD, arewhere N., and NW are the total number of neutron and proton bosons, Tttdy and fidn are: .6U7\’f7‘d7\' `l' B0u7c’·dv "l' 70uNu `l" 70wNw·order) by the relation:In the standard IBA—2 model the electric monopole operator is given (to the iirstradius which, for the ground state, has been extensively investigated at ISOLDEelement of the same operator whose diagonal matrix element gives the mean square chargeEssentially then, by measuring B(EO), one determines the square of an off diagonal matrix.. P (E0) ·B(E0) 2B(EO) : 2|{0;|T(E0)|0;_ 2 2 °*\lR and the atomic number Z as follows:strength p2(EO) between O? and O? states are expressed in terms of the nuclear radiuswhere NP is the proton number. The reduced transition probability B(EO) and transitioni=1T(E0) = e >~~. In a single particle model the electric monopole operator T(E0) is given by:2. Electric monopole transitionsOCR Outputof their decay via electric monopole transitions.76present proposal is the study ofthe 0] —> 0] transition in 38 Kr. OCR Outputas to put to a stringent test the different theoretical interpretations. The subject of thebe provided by the measurement of as many monopole transition strength as possible sothat a real improvement in our understanding of the 0] states in krypton isotopes couldthesis that the 0] state lies indeed within the IBA—2 model space. It appears howevervalues of the monopole strength p2(EO] (see Table II). This gives some support to thecadmium isotopes, we found a reasonable agreement between experimental and calculatedOn the other hand, by adopting for ,30,, and ,30,, the same values determined for the0.007(6) ] 0.0020] —> 0]2] —+ 2] ] $0.05 | 0.00090; A 0;* |0.021(0)] 0.028 | 0.00s(a) | 0.011p2(JfL —> Ref.]7] ] theor. ]Ref.]5,11]] theor.8°Kr 82Kr,80,, = 0.25efm’, 50,, = 0.1efmtheoretical ones evaluated using for the E0 operator the parameters valuesTable II The experimental values of p2(E0) in 8°·82Kr compared to thetransition in 80Krdetermined for the 0] —> 0], 0] —> 0] transitions in 82Kr [5 ,11] and for the 0] ——> 0]riot feasible for even krypton isotopes, since the monopole strength p2(E0) has only beenon E0 transitions between O] —> 0] and 2] —+ 2] states. At present such an analysis is4Cd [9 ,10] we recently determined the value of 50,, and H0., by exploiting the datau°·112·11and B0., has only been extracted for a restricted number of nuclei. In a detailed study ofHowever, the experimental data on E0 transitions are so limited that information on 60,,have to be determined by a comparison of experimental and theoretical values of B(E0).Nazionali di Legnaro (Padua — Italy) [7], wld W6 plan to do the same for 78Kr (an enriched OCR Outputscattering at 6.5 MeV, via the Doppler shift attenuation method in gas at the LaboratoriFor 80Kr we determined the lifetime of the 0; level, populated through inelastic protonB(E2)(efm) :-10 24to the expression:The B (E2) value can be evaluated from the value of the lifetime ·r of the 0; level accordingp(E0) =X - B E2 2ltransition strength via the equation:high precision [12 ,13] so that, if the B(E2; O; —> 2i') value is known, one can deduce thethe gamma deexciting the O; level. The quantities SZK and org can be calculated to acry the K—conversion coefficient for the relevant E2 transition and E, is the energy ofwhere OK is the so called "electronic” factor for the K—conversion of the EO transition,K[s](;j —> T)-—-;B(E0* 0; " OT) = 2.56- 109A§E5[MeV]—aI((E2)q2 BE2O2" f2‘1From the experimental value of q2 it is possible to deduce the ratio B(EO)/B(E2):where IK is the intensity of the K-internal conversion line for the indicated transition.I1<(0S·* Zi)g= ' 'z IK(0E·* OT)Lthe measurement of the branching ratio:The determination of the monopole transition strength p2(E0) requires, as a first step,ISOLDE.8Kr and 76Kr populated in the decay of Rb and 76 Rb, which can be easily produced at78is schematically reported in Fig. 1. We propose to investigate the O; —+ OT transitions inThe systematics of experimental low·lying positive parity states in even krypton nuclei3. The determination of the monopole strength pin *BKrz 767scheme (see in Fig. 3 the comparison between 8°Kr e 78Kr) which could cause some OCR Outputpopulation of the 0; state but also the disadvantage of a far more complicated decayCompared to the case of 8°Kr we have for the *Kr the advantage of a stronger76785. Conclusions and beam requestanalysis is performed.multiplexed mode, remote-controlled by a Macintosh II computer, on which a first on—lineThe data acquisition is performed by means of a multi—channel analyzer operating instandard germanium detector.conveniently done by simultaneously recording e.g. the 0; ———> 21gamma—ray, using a+field settings) it is necessary to normalize the corresponding energy spectra. This is most0; —+ 2]transitions are necessarily measured at different times (for different magneticl"Since the intensities of the K—conversion electron lines corresponding to 0; —> 0]* and2.6 keV for 1 MeV electrons.1% in the 150-1500 keV energy range. Typical energ resolution of the silicon detector isthe maximum transmitted energy about 3 MeV. The overall full peak efficiency is aboutcooled down to liquid nitrogen temperature. The momentum acceptance is Ap/p:0.18 andThe electrons are deflected by a magnetic Held onto a 5cm2 >< 6mm silicon detectorsystem shown schematically in Fig. 2.Our experimental set—up to measure the ratio q2 is based on an electron transport4. Experimental set—uppopulating the 0; level via the (p,t) reaction on 78Kr [14].sample of this gas has been bought). For 76Kr one could possibly use the same methodto measure at short notice. OCR Outputthe apparatus makes it simple in use and easily transportable, so that we could be readyruns, each of 3 shifts} will be sufficient to perform the measurements. The compactness ofBasing on our experience on Kr, we estimate that a total of 9 shifts (divided in 38°detector.moment modifying the experimental set—up to provide a more effective shielding of thedifficulties due to gamma induced background on the silicon detector. We are at theS. Matsuki ct al.: Nucl. Phys. A370, 1 (1981). OCR Output[14]F. Résel et al.: Nucl. Data Tables 21, 110 (1978).[13]D.A. Bell ei al.: Can. J. Phys. 48, 2542 (1970).[12]A. Zemel et al.: Phys. Rev. C 31, 1483 (1985).[11]A. Giannatiempo ct al.: Phys. Rev. C 44, 1844 (1991).[10]A. Giannatiempo ct al.: Phys. Rev. C 44, 1508 (1991).ISOLDE STATUS REPORTS 1990 IS—80 S.R. 1989.submitted for publication.A. Giarmatiempo et al. ISOLDE STATUS REPORT ISO1-037 S.R. 1990 and to beA. F. Baxfield and K.P. Lieb: Phys. Rev. C 41, 1762, (1990).S. Brussermann et al.: Phys. Rev. C 32, 1521 (1985).H.P. Hellmeister: Nucl. Phys. A332, 241 (1979).B. Wérmaim et al.: Nucl. Phys. A431, 170 (1984)—L_3]U. Kaup, A. Gelberg: Z. Phys. A293, 311 (1979).[ 2]J.H. Hamilton: Nucl. Phys. A520, 377C (1990)[ 1]FERENCEStransitions we propose to investigate. OCR Outputtinuous arrows mark the E0 transitions already studied. Dashed arrows mark the E0Pig.1 — Schematic excitation pattern of low energy states in even krypton isotopes. ConKrKr Kr Kr Kr Kr8474 7G788O82YY0+;L+JL_ , O 0+ ?L0*2+ +2+ +21000 4 "’°+2+ /i+5+ —_6if] 2000BOOOJvalve, (10) Si(Li) detector, (ll) lead screen.window, (5) entrance baH‘le, (6) pole pieces, (7) Hall probe, (8) thermostat, (9) vacuumconversion electrons: (1) iron channel, (2) target, (3) beam catcher, (4) plexiglassFig.2 — Schematic view of the electron transport system for the measurement of internals cmxy x4¤:W r Zé?’\§<§, 111’€ ;’\f @ @ 1;-el ; I epi;} I 1u `\E*.;;—‘x {1 1 \_ \bear? OCR OutputSJ K2 L ,

Study of electric monopole transitions in $^{76,\,78}$ Kr

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Study of electric monopole transitions in 76, 78^{76,\,78}76,78Kr

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Study of electric monopole transitions in $^{76,\,78}$ Kr