Gabrielli, I.

Harvey, B. G.

Hendrie, D.L.

Mahoney, J.

Meriwether, J.R.

Valentin, J.

eScholarship - University of California

Lawrence Berkeley National LaboratoryRecent WorkTitleSCATTERING OF ALPHA PARTICLES BY 55MnPermalinkhttps://escholarship.org/uc/item/45d0q9p6AuthorsGabrielli, I.Harvey, B. G.Hendrie, D.L.et al.Publication Date1968-09-01eScholarship.org Powered by the California Digital LibraryUniversity of California·1 .'. ,t "" RECEIVED LAWRENCE RADIATION LABORATORY OCT 21 1958 UBRARY AND DOCUMENTS SECTION ; i f \ \ \ University of California Ernest O. Radiation \ \. Lawrence Laboratory "-. j. SCA1>~:ERlNG OF ALPHA PARTICLES BY 55Mn ~, \ UCRL-18488 ...... 1.. Gabrielli~H. G. Harvey, D. L. Hendrie, J. Mahoney, J·\R· Meriwether and J. Valentin \ \ F /' Septt;!rnber 1968 ,. / ,.I, Ii ~ .~ TW<?-WEEK lqAN COpy This is 'Q library Circulating Copy which may be borrowed for two weeks. For a personal retention copy, call Tech. Info. Diuision, Ext. 5545 To be submitted to: Nuovo Cimento UNIVERSITY OF CALIFORNIA Lawrence Radiation Laboratory Berkeley, California AEC Contract No. W-7405-eng-48 SCATTERING OF AIPHA PARTICLES BY 55Mn I. Gabrielli, B. G. Harvey, D. L. Hendrie, J. Mahoney, J. R. Meriwether and J. Valentin September 1968 UCRL-18488, . Preprint 1 I .1 -iii- UCRL-18488 Summary SCATTERING OF ALPHA PARTICLES BY 55MI/ I. Gabrielli+, B. G. Harvey, D.L. Hendrie, J. Mahoney, J. R. Meriwether++ andJ. Valentin+++ Lawrence Radiation Laboratory University of California Berkeley, California September 1968 , .. The elastic and inelastic scattering 6f 50 MeV alpha particles by 55Mn has been measured. The angular distributions of the scattered alphas from several excited levels were analyzed by means of the distorted-wave Born approximatiqn. Transition strengths were determined for most of the levels observed. Energy resolution permitted the observation of the first excited state (0.126 MeV) separated from the elastic peak. Two single states previously observed in alpha scattering were each resolyed into two states (2.25 and 3.37 MeV, probable tran-sition, £ = 2; 4.27 and 4.39 MeV, probable transition, £ = 3). * This work was, performed under the auspices of the U. S. Atomic Energy Comission. tNATO fellow. Present address: Istituto di Fisica dell'Universita tt Trieste, Italy. Present address: University of Southwestern Louisiana, Lafayette, Louisiana. ttt . Present address: Universit~ de Grenoble, Grenoble, France. -1- UCRL-1848S· Introduction. A number of studies have recently been performed on levels of 55Mn . This nucleus has an unusual feature in that its ground state has five (f7/ 2) protons coupled to give the spin of 5/2-(1) In addition to investigations of the excited states by inelastic scattering of protons(2,3,4) and neutrons(5), a measurement by means of 43 MeV alpha scattering has been reported (6) •. In the latter experi-ment, with a resolution of2S0 keV, the first excited state (126 keV) could not be resolved from the elastic peak. The angular distribution of alphas elastical-ly scattered from 55Mh has been studied in terms of optical model parameters for ~ beam energy of 43 MeV(7), 22.2 MeV(S), and 24.7 MeV(9). We have measured the scattering of 50 MeV alphas, with the improved resolu~ tion which is now available with cooled silicon counters, in order to obtain the angular distribution 6f alphas from the first excited state, to investigate the levels of a collective nature and to determine transition strengths. In addition, the availability of better alpha scattering data from 55Mn, along with other ex-perimental data, can be the basis for a description of the low-lying excited states of a quadrupole nature as a coupling of a proton to the quadrupole state of a· 54cr core, or a hole to the 56Fe (10,11) • Experimental Procedure The beam of 50 MeV alphas, provided by the 88" cyclotron was focused onto a self~supporting evaporated foil of 55Mn, which was 250 g/cm2 thick. In addition to carbon and oXygen, a small amount of Al and Cl contaminants were present in the Mn target due to the method of target construction. Scattered particles were detected in four lithium-drifted silicon detectors, cooled to -25°C, yielding resolutions of 50 to 75 keV depending on the scattering angle. The beam was col-lected in a Faraday cup and checked with a monitor counter placed at a fixed angle .,.2- UCRL-18488 "' of 20 0 with respect to the beam. A sample spectrum is shown in Fig. 1, with an: indication of the analyzed levels and the values of their excitation energies, -; .. computed with reference to the elastic peak and to the 1.884 MeV level. For the final extraction of the cross sections an IBM 7094 computer program(12) has ,. been used, with which several levels not completely resolved in the spectra have been separated. Results Fig. 2 shows the experimental elastic angular distribution and its best fit to the optical model with four free parameters (13) • V t op = The values of the optical p"arameters (V = 198 MeV, W = 27.9 MeV, R = 1.35 FIn, and a = 0.59 FIn) are consistent with those of other alpha scattering experiments •. The experimental inelastic angular di::tributions were compared with theoretical differential cross sections obtained from the collective model distorted-wave Born approximation (DWBA) using these optical parameters (l4) • By comparison of the experimental and theoretical differential cross sections at the first four diffraction maxima, the transition strengths were computed for most of the i observed levels. The strengths are reported in terms of B(E£) t which is indepen-"" dent of the spin of the initial and final states. where RO is the charge radius ( = 1.2A~/3), 2 is the angular momentum transfer, ~ and Z is the charge of the target nucleus. In addition, the strengths are given in single:·partic1e:'.units for the states of known spin (16): . . ,. 2J +1 o G = 2J+1 -3-B(Et) t UCRL-18488 f . where J O is the spin of the ground state and J the spin of the excited state. The estimated precision of the strengths is about 10% • In Fig. 3 are given the experimental differential cross sections of alphas scattered from levels which are well represented by the theoretical distributions for an angular momentum transfer of two (t = 2). The latter are shown as the dashed curves which have been normalized to the data. The transition strengths to these states are listed in Table 1. It· should be noted that the sum of the observed i = 2 strengths in 55Mn (sum of the ~2 c values) is nearly equal that of the 0.847 MeV, 2+ state in 56Fe (15,16) and in the range of values reported for the 0.835 MeV, 2+ state in 54Cr (16). Neverthe-less, it does not look appropriate to invoke the weak coupling model ~ere. The i = 2 strength is spread over nearly 3 MeV and a disproportionate fraction of the strength goes to the 0.126 MeV state. In Fig. 4 are shown the experimental angular distributions which appear to agree with ~ value of i = 3; the theor~tica1predictions of the DWBA analysis are shown as the dashed curves. Our data is not consistent with a negative parity assignment to the state at 1.289 MeV; it appears to be populated by reasonabl(f strong i = 3 transition. Although the possibility Of a double excitation process. forming this state cannot be ruled out, it is interesting to note that an 11/2+ assignment is also consistent with the data of Ref. 5. , ~1 Peterson(4) has recently conjectured about the validity of the weak coupling '\".) model for states with octuple core excitations. In general our results are consistent with this view and with his spin assignments. Although we find the 4.27 MeV state slightly stronger than the 4.39 MeV states our uncertainties ", ~. ," • -4- UCRL-18488 make it undesirable to reverse his assignments here. Although we were unable to reliably extract the 3.60 MeV level that Peterson saw, we were able to get an additional 1 = 3 transition to a level at 3.05 MeV. Comparing the relative strengths of the two states, we decided to assign 3/2+ to the 3.05 MeV stat~ and ' ~, to change Peterson's assignment to the 3.60 MeV state from 3/2+ to 1/2+~ reflects these assignments and their strengths compared with 56Fe • Table II The 1.527 MeV, 3/2- state is present at all angles, but with a loW cross section (less than 1 mb/sr at the smallest measured angles). The hypothesis, that this is a single pa~ic1e level, is consistent with our data. The angular distribution'of the state at 5.04 MeV agrees fairly well with the DWBA curve for an 1 = 4 transition, but the oscillations are quite small and not well-defined. -5- , UCRL-18488 References (1) E. H. Schwarcz: Phys. Rev. 129, 7~7 (1963) with reported references. (2) S. S. Vasil'ev, E. A. Romanovskii and G. F. Timushev: Zh. Eksperim. i Teor. Fiz,' 42, 395 (1962) JETP 15, 274 (1962) and Vestnik Moscow Univers. Ser. III, no. 6, 90, (1961). (3) M. Mazari, A. Sperduto and W. W. Buechner: Phys. Rev. 108; 103 (1957); J. H. Bjerregaard, P. F. Dahl, O. Hansen and G. Sidenius: Nuc1. Phys. ~ 641 (1964). (4) R. J. Peterson: Phys. Letters 27B, 446 (1968). (5) R. C. Iamb and M. T. McEllistrem,: Phys. Letters 4, 211 (1%3); Nucl. PhYs. AlO?, 153 (1968). (6) H. W. Broek,: Phys. Rev. ~ Bl160 (1965). (7) K. T. R. Davies, G. R. Satch1er,R. M. Drisko·and R. H. Basse1: Nucl. Phys. ~ 607 (1963). (8) N. Takahashi, S. Kato,M. Takeda, T. Yamazaki and S. Yasukawa: J. Phys. Soc. Japan gQ, 1544. (1965). (9) L. McFadden and G. R. Satch1er: Nucl. Phys. §.!, 177 (1966). (10) V. K. Thankappan an.d W. W. True: Phys. Rev. 137:; B793 (1965). (11) J. R. Meriwether, I. Gabrielli, D. L. Hendrie, J. Mahoney andB. G. Harvey: Phys. Rev. 146, 804 (1966). (12) A. Springer. (Ph';D., Thesis): University of California, Lawrence Radiation Laborato~y Report UCRL-11681 (1965), unpublished. (13) Code MERCY altered from SEEK written by Melkanoff, Rayna1 and Sawada: University of California at Los Angeles Report UCLA-66-10. (14) Code JULIE by R. Drisko: Oak Ridge National Laboratory Report ORNL-3240. • -6- UCRL-18488 (15) D. L. Hendrie,J. Valentin, I. Gabrielli,J. Mahoney, and J. R. Meriwether: to be published. (16) R. H. Stelson and L. Grodzins: Nuclear Data b 42 (1%5) • ~. -7- UCRL-18488 -8- UCRL-18488 Table II. Transition strengths for the octupole levels of 55Mn and 56Fe ,I Q B(E3)t (fm6'} Jlr G i: 55Mn -1.289 586 (11/2+)a 1.6 -3·05 ± .02 647 {3/2+)b '5.4 -3·60 ± .02c 422c (1/2+) 7.6c -4.09 ± .02 765 (5/2+)b 4.3 -4.20 ± .02 3170 (11/2+)b 8.8 -4.27 ± .02 1537 (7/2+) b 6.4 -4.39 ± .02 1467 (9/2+)b 4.9 total 8008 56Fe -4.52 82l6d 3- 7.ld a Ref. 5 b Ref. 4 c ' Taken from Ref. If-and calculated from his strengths. dRef • 15 • 1 \,,1 -9- UCRL-18488 Figure Captions Fig. 1. A sample energy spectrum at a laboratory angle of 36°. Fig. 2. The elastic angular distribution in terms of the ratio of the experi-mental to the Rutherford cross section. The dashed curve is the optical model fit to the data. Fig. 3. The angular distributions from the levels which agree with an 2 = 2 distribution according t~o,:the DWBA analysis (dashed curve). "Fig. 4;. The angular distributions from the levels which agree with an 2 = 3 distribution according to the DWBA analysis (dashed curve). -10- UCRL-18488 ji 0 L G A ~j A g.s., 5/2 8 0.126 MeV, 7/2-C 0.983 (912-) 0 1.298 (11/2-) E 27AI F 1.527 (3/2-) N B G 1.884 (5/2-,7/2-) H 2.25 . - .... ~' ... 1 2.37 (/) J 2.82 -c K 3.05 Q) • > L ISO W M 4.09 p J c N 4.19 0 0 4.27 R H E P 4.39 0 12C R 5.04 X 1/2 Channel number XBLSBB-3555 Figure 1 ,. ~ . ~:~ . • .c -:3 a:: -q . I "'0 "-b 0.1 "'0 Q. )( Q) -q "'0 "-b -0 0.01 0.001 o 10 20 30 e I I, Figure 2 ---Optical model fit Vo = 198.1 MeV . W = 27.87 MeV a = 0.588 fm R = 1.35 fm 40 50 60 70 c.m. XBL688-3556 • 10 .... "-en· ...... .0 E q 't:I ...... 'b 't:I 10 0.1 0.01 . _ ........ '''''-'''''''--'-'''''-'' ..... ...----.-.-- . __ ._------32 - UCRL-18488 '" o 30 40 50 60 70 Sc.m. XBL6BB- 3553 Figure 3 -.... en , .0 E -q ""0 , b ""0 UCRL-1848g 0.6 \. 0.1 -o 10 20 30 40 50 60 70 8 c.m. XBL6SS-3554 Figure h , This report was prepared as an account of Government sponsored work. Neither the United States, nor the Com-mISSIon, nor any person acting on behalf of the Commission: A. 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 8. 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 Commission" 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. 

SCATTERING OF ALPHA PARTICLES BY 55Mn

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