Chanda, Richard N.

Sheline, Raymond K.

Sikkeland, Torbjorn

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Lawrence Berkeley National LaboratoryRecent WorkTitleEXPERIMENTAL OBSERVATION OF A NEW REGION OF NUCLEAR DEFORMATIONPermalinkhttps://escholarship.org/uc/item/9z33j56zAuthorsSheline, Raymond K.Sikkeland, TorbjornChanda, Richard N.Publication Date1961-10-24eScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaDISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain conect information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the • United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. Ls1.m,1;I;1.0I UNIVERSITY OF CALIFORNIA Lawrence Radiation Laboratbry Berkeley, California Contract No. W-7405-eng- 148 EXPERIMENTAL OBSERVATION OF A NFM REGION OF 3IJCLEAR DEFORMATION Raymond K. Sheline, Torbjrn Sikkeland, and Richard N. Chanda October. 24, 1961 11 / 	.1 	 UCRL-9888 EXPERIMENTAL OBSERVATION OF .A NW REGION * OF NUCLEAR DEFORMA.TION Raymond K. Sheline Torbjorn Sikkeland, and Richard N. Chanda Lawrence Radiation Laboratory University of California Berkeley, California October 24, 1961 The nuclear periodic table has three or possibly four regions where nuclei have been experimentally shown to be deformed, namely A ' 19 to 28 and 150 to 190, A2~ 222, and possibly A.-" .8. The work presented in this paper gives experimental evidence for an additional region of deformation. Figure 1 is .a schematic representation of the nuclear periodic table in which previously observed regions of nuclear deformation are là.beled.2, 4, 5, and 6. Up to A=. 11-O,the line of beta stability of the nuclear periodic table involves nuclei whose neutron and proton numbers are about the same. Therefore, the first limited regions of deformation, labeled 5 and 6 in.Fig. 1, have N= Z. AbovecA 40, howerer, the line of beta.stability shifts toward a highe.r neutron ratio. Consequently the neutron and proton shells are some-what out of phase until one reaches the rare earths and actinides, where extended regions of deformation are observed because the 50 to 82-proton region is approximately in phase with the .82 to 126-neutron region and the 82 to 126-proton region with the 126 to 184-neutron region. On the other hand, though highly neutron-deficient and correspondingly unstable the regions labeled 1 and.3 in Fig. 1, where N Z,,shouldcontain deformed nuclei. We, have concentrated our effort in region .1. 2 	 rsIwi,L In order to study the energy levels of nuclei in region 1, it was necessary to discover a number of new La and Pr nuclides. We will report here only on those new nuclides whose mass number, half life, and first excited state are relatively certain. The simplest available method of proving that nuclei are deformed involves the production of odd-odd nuclei wh.ose decay into daughter even-even nuclei gives a characteristic low energy for the first excited state and, if possible, a rotational band built on the ground state with spins 0+, 2+, 4+, 6+ 	. and ratios of energies to the .first excited state 1 . 0 :3.33:7. 00 126 	128 	130 Accordingly, we have produced the nuclei La , La , and La 	with half lives of 1.0 ± 0,3, 6.5 ± 1.0, and 9.0 ± 1.0 mm, respectively. These La nuclei have been made in a variety of ways (see Table 1)4 Table I. Nuclear reactions showing cross bombardments used to produce the 126 	128 	130 nuclides La , La , and La New nuclide 	Nuclear reactions 	Heavy-ion bombarding energy (Mev) La 126 	 Inhl5(016,5n)La126 	 914 Sbl(C12/In)La126 	 117 La128 	 Infl5(016,3n)I,al28 . 	 65 121(C12 	 84 Sbl23(C12,1n)La28 	 117 130 	 sb 1 (c12,3n)La13° 	 53 Sb123(C12 ,5n)La13° 	 84 using the heavy-ion current of the Berkeley Hilac. A heavy-ion bombarding energy was chosen which would give maximum yield of a. desired isotope This energy (see Table I) was estimated by using Cameron's mass table 1 and by 3 	 UCRL-9888 assuming the average kinetic energy of each emitted neutron to be 1 to 5 Mev. The reaction products recoiling out of 1 mg/cm 2 self-supporting targets of In and Sb were caught in a 1.8-mg/cm Pd foil which was then dis-solved in hot aqua regia. With Ba as holdback carrier the La activites were precipitated in LaF 3 nd the precipitate washed once with dilute HF. The procedure took about 1.7 min from the end of bombardment to the start of counting. When the same targets were bombarded by ions that produce elements below La in atomic number, the chemical procedure separated only a small fraction.of the activity. This suggests that the radiochemical purity of the sample was satisfactory. The purity was also checked by separating some of the La activities carrier-free by elution with amnionium a-hydroxy isobityrate from a column of Dowex-50 cation-exchange resdn. The mass assignments are.also4uite definite. In the first place, there is the evidence on the mass numbers from the cross bombardments shown in Table I. In the second place the La 1.2 6 is shown to decay into a species that has a spectrum identical 2  with that of Ba126, Finally, the La130 emits a very strong 356 ± -kev garma ray. A 359-key ga ray is observed 3 in the Coulomb excitation of Ba130 To verify the above mass. assignments, we are now determining the excitation functions. 126 	128 	130 The energy levels in the daughter nuclei Ba' , Ba , and Ba 	are used to determine whether or not these nuclei are deformed. The first ex- .126 	128 	130 cited state of the even-even Ba nuclides including Ba . , Ba , and Ba are .pl.otte.d in Fig.2. The lowering of the first-excited-State .energy with mass number is -similar to that observed in the normal rare earths. A more detailed analysis of these energies is therefore necessary. -There are at least three ways to use the first-excited-state energy as a criterion for -UCRL-9888 deformation. These are (a) a direct comparison between the energy, of the first excited state and an (E2+) crit.  suggested by Alder et a1.,(b) a determination of an empirical deformation, 	from a relationship between/rig and and (c) a comparison of 	from the relationship -of Migdahl. These three methods are utilized in Table II, where comparisons are made with ohr nuclei with similar deformations but from other regions of deformation. .A compari-. son of Ba126 ,  Ba128, and B'3° 	 126 with other .defoed nuclei inicates that Ba is like 186 0s186, nd Rá22l., . Thus all of these nuclei have a firt--excited-state energy less than (E24).t and.have very similar emp.(0oJ9 to. 0.2l) cr.and 	ig.°'  to o.18). 	 - . 188 	. 	Similar statements apply to a compa.rison of Ba 128 to Os 	and Ra 222  .130.190 On the other hand, both Ba 	and Os 	seem to be in a transition region. Their first-excited-state energies are ach higher than the-(E 2 . ) it  and each has = .0.16 and 	= 0.12. Osmium-190 has a rotational-hand - 	-emp.. 	 .Mig. 	 -- which cannot be fi.tted.well with the simple I(I±i) relatioiihip but is fitted by the nonaxially symmetric rotator model of Davydpv and.FillipovJ it seems very probably that Ba130 would be very similar. in .this regard In addition to gaa-ray singles spectra, ga.ma-gamma,coincienceS were als.o taken, using standard fast-slow, circuitry and; in some .:Cases, a two-dimensional coincidence analyzer. Coincidences were found in each of the La nticlides. The ratio of the supposed second excited state Tvaried. from 2.55 in Ba130 to 3.13 in Ba126.  This agrees very well with the -ratiQs -of energies for the first to second and third excited. .states of the rotational bandbuilt on the ground state, which are given in Table II for similarly deformed nuclei. For an axially symmetric rotator,, these :ratios should be 1.00 	3.33 : 7.00 : 12.00. However, it must be -pointed out - clearly that none of the second-excited--state spins have been measurçd, 'and the decay.- 5 	 UCRL-9888 Table II. Comparisons between the nuclei ,Ba126,Ba 128 and Ba 130  and nuclei from other regions of deformation. a 	 f2/2 Jucleus E (E ) 	b 	c 	d 	e 	-.. 2+ 2+ crit. rig. Ratios of energies in (key) 	(key) emp. 	Mig. exp. 	the rotational band Ba126 256 279 0.251 0.20 0.16 Ba128 279 .2 72 0.225 0.18 0.15 l30 :265 0 .172 o16• 0.12 Gd15 123 200 0.62 0.29 0.25 0.30 1 . 0 :3. 02 :5.8 Dy 156 138 196 0.333 0.23 0.19 1 . 0 : 2 .93:5.59 186. 12 17 0.273 0.20 0.17 0.24 1.0:3.28 186 157 0.27 0.19 0.15 0.20 1 . 0 :3. 19: 6 .33 o188 155 144 0.215 0.18 0.1 0.18 1.0:3. 09 0s190 188 12 0.174 0.16 0.12 1 . 0 : 2 .93:5. 60 : 8 . 89 Ra222 111 110 0.228 0.19 0.15 1 . 0 : 2 .79:5.78 R 22 a 8.5 108 0.295 0.21 0.18 1.0:2.98 Th226 .72.1 106 0.1 0.23 0.20 1.0:3.1:6.33 Throughout the Table, energy values are taken from.R K. Sheline, Revs. Modern Phys. 32, 1 1960) except the values for B a126, Ba12 ,.. and 	(reported here- in) and Dy'S [see ,E. P. Gregorev and B. S. Dzhelepov, DokladyAkad, Nauk. SSSR 135, 56 (1960)]. Values of (E2+)ôrit. Z 13/.rg are given (see Ref. 3). This (E + ) crit is the criterion by which nuclei maybe. assumed to be spherical. [for E2 > (E2+)crit I or deformed [for E2+~ (E2+)crjt. 1 Often the transition is not as abrupt as indicated by the single value.. 	 . 	 .. 	 . .. Ratio of 2 = 3 2/E2 to = 2MAR2/5(l+O.3Th+..) where R0=1.2Ah/3>O_13cm  and = 1.08/A'/3. 	g See Ref. 5. See Ref. 6. Experimental deformations calculated from the available values of the transi-tion probabilities for Coulomb excitation. 6 	 UCRL- 9888 scheme work is incomplete. The coincidence data thus far available strongly favor a 'otational-band interpretation and seem inconisteiit with -a vibrational interpretation. Nonetheless, a more complete proof of the existence of a rotational band. must await complete :coincidence analysis... .A trend similar to Pig. 2.f or the first excited states of even-even Ce nuclei has also been observed. However, in this case mass assignments and half-lives of the Pr nuclides are not .nearly as certain. This evidence does tend to confirm the existence -of an -extended region of deformation, however. The existence of the region of deformation labeled 1 in Fig. 1 suggests that (a) it should be possible to observe deformed even-even Nd nuclei and possibly also Sm nuclei with presently available heavy-ion beams, and (b) it is certainly feasible to observe a large number of deformed odd-A-Ba, La,-Ce, Pr, Nd, and Pm nuclidesb The -observation of odd-A nuclei in this region would be particularly interesting because it would allow assignments of Nilsson orbits in this new region of deformation- 	 - Recent calculations on the equilibrium deformations for nuclei in regions 1 and 3 on Fig-..l indic.te a considerable -deformation in each region. These -calculations and this experiment should -provide - impetus to the -observa-tion of deformations in-the neutron--deficient actinides, region 3 in Fig.. 1. Such experiments might be undertaken by the observation of the a fine structure resulting from decayof even-even nuclei produced from the following typed of - 	2O1 . 16 	212 	196 	20 - - 	- 208 nuclear reactions-: Pb - :( o ,8n)Th and-Hg (He ,8n)Th ACKNOWLEDGMENTS - We are grateful particularly to Mr. Albert Ghiorso for his encourage-inent and help in all phases of this research, to Mr. Daniel O'Connell for the targets, to Mines. -Roberta Garrett, Suzanne Hargis, and Beverly Isaacs for -help with the chemistry and plotting, to the -Hilac crew for their help during bombardments, to Mr.. Charles A, - Comm for the design of the target assembly, and to Almon -E. Larsh, Alfred Wydler and William GoJdsworthy for help with the electronics. 7 	 UCRL-9888 FOOTNOTES AND REFERENCES * Work supported by the U. S. Atomic Ene.rgy Commission. visitor, on leave from Florida State Univerity, Tallahassee, Florida. C 1. A. G. W. Cameron, A Revised. Semi-Empirical .Mass Formula, with Appended Table ofMass Excesses and Nuclear Reaction Energies, Atomic Energy of Canada, Ltd. Report AECL-433, March 1957 (Chalk River Report CRP-690). 2;, M. I.Kalkstein and J. M. HoiLlander, Phys. Rev. 96, 730 (1954). 	3. 	L.W.:Fagg, Phys..Rev. 109, 100 (1958). . 	K;Alder, A. phr, T. Huus, B. Mottelson, and A. Winther, Revs. Modern Phys. 28, 1132 (19.56). B.: Elbek.) in Pr.oceedings of the International Conference on Nuclear Structure, Kingston, Canada, 1960, D. A. Bromley and E. W. Vogt, Eds. (University of Toronto Press, Toronto, 1960), p. 601; N. K. Glendenning and J. Sawicki, Lawrence Radiation Laboratory Report UCRL-9178, May 1960, The.parameter Penip.  is an empirical relationship between 'rig.  and P. A. B. Migdahl, Nuclear Phys. 13,655 (1959). Migdahl suggests = 2 MR 2/5 (2.33 A.. S. Davydov and G. F. Fillipov, Nuclear Phys. 8, 237 (1959). E. Marshalek, L. Person, and R. K. Sheline, Lawrence Radiation Laboratory, unpublished. work. am FIGURE LEGENDS Fig. 1, Schematic representation of the nuclear periodic table showing the neutron (vertical solid lines) and proton (horizontal solid lines) closed shells. The dotted vertical and horizontal lines represent semiclosed shells, which have an effect on regions of deformation. The thin banana-shaped curve approxim3tely encloses nuclei that have been experimentally studied. Regions where nucle,i have been experimentally observed to be deformed are indicated with cross hatching. Additional regions where it is reasonable to expect to find deformed nuclei are labeled 1 and 3. This research is con-cerned with region. 1. This figure is patterned after one suggested byE. K. Hyde. Fig, 2. First excited states of even-even Ba nuclides. The levels in 126128 	 130 Ba 	, Ba 	, and Ba 	are the results of this research. The dotted lines shows (E+)crit , the dividing point between spherical and deformed nuclei. E 1 0 82 	 126 	 184 126 / 	 \ 	/ )0. 	3 ( 4 ) 50 	 - 	 - -, 30- 	'i'17IJ-i 14 202840  50 • 	I 40 - - -L - -y 	- - -40 28  28 2Ô W 14  0 20 40 60 80 100 120 140 160 180 2( 10 Neutron number MU —24533 Fig. 2 1430.' 1200 800 > a, C w 400 823,' 605./ 470_ 25616 279M•._-- 124 	126 	128 	130 	132 	134 	136 	138 Mass number MU —24532 Fig. 1 -10- This report was prepared as an account of Government sponsored work. Neither the United States, nor the Con-mission, nor any person acting on behalf of the Commission: Makes any warranty or representation, expressed or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, appa-ratus, method, or process disclosed in this report may not infringe privately owned rights; or Assumes any liabilities with respect to the use of, or for damages resulting from the use of any infor-mation, apparatus, method, or process disclosed in this report. As used in the above, "person acting on behalf of the includes any employee or contractor of the Com-mission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, disseminates, or provides access to, any information pursuant to his employment or contract with the Commission, or his employment with such contractor. 

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EXPERIMENTAL OBSERVATION OF A NEW REGION OF NUCLEAR DEFORMATION

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EXPERIMENTAL OBSERVATION OF A NEW REGION OF NUCLEAR DEFORMATION

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