TOFT ORNLP *1927 2. 11.25 1 . MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS -1963 . . ORNVP-1927 Cont_651118-5 MASTERS NUCLEAR SPIN.PARITY ASSIGNMENTS HEB 9203 99 RITIMASED FOR ANNOUNCEMENT IN MUCIBAR SCIENCE ABSTRACTS EXCITATION AND DISINTEGRATION OF NUCLEI SY LOW-ENERGY ELECTRONS AND X-RAYS , Ei Guth Oak Ridge National Laboratory Oak Ridge, Tennessee and 2. D. Edge University of South Carolina, Columbia, South Caroliria , In his summary talk at the Padua Conference, i. S. Blair? tering: "It is hard to underestimate the utility of the elec- tron scattering experimeats. A rather small number of groups bave made a fantastic impact on the world of nuclear physics... The advantages of the method are obvious: one understands the interaction which is electromagnetic... Now we have a much . poorer understanding of what goes on when an alpha particle or a proton goes into a nucleus." All this refers to the high energy electron studies at Stanford and Orsay. white 1. The purpose of this paper is to present a few new and to recall a few examples of old low energy election studies, which foreshadow a quite important role of such experiments for nu- '. clear spin parity assignments. In fact, for the excitation of leveis of a few MeV, the use of high energy electrons seems likt shooting at squirrels with a big cannon. Moreover, with better resolution obtainable by low energy electrons, levels can be identified whose location remains uncertain using high energy electrons. Low energy means here: less than 30 MeV; . : the range above this limit has been discussed in another paper at this Conference.* T." : . Since one of these authors (E. G.) has a sort of father- ly interest in all electron scattering experiments (according Ito Hofstadter, an early paper of this author 'foreshadows the use of electron scattering in the investigation of nuclear i size), we wish to emphasize that the high energy electrons are; of course, needed to obtain not only elastic form factors but also correlation functions and inelastic form factor ,imallerian... . . . L Example I: Figure i shows electron excitation of various leve 18 of Into. The curve represents work at Jak Ridge The points are measurements at Boston...In Starford work with A at home,19- Wii * US . 16, NUCLEAR SPIN.PARITY ASSIGNMENTS electrons from 183 MeV to 600 MeV on Int16. the energy of the presumably 1.07 MaV level oan be "best" ustimated a 1.1 MOV; "but different runs gave results which varied by as much as 150 keV!" The best resolution for LINACS was obtained at Düsseldorf by P. Brix, viz. 100 keV at 60 MeV.. From Fig. 1, levels at 1..07 and 1.47 can be deduced. HOW ever, above 1.5 MeV the experimental curve reeds a more preciso determination in order to be able to deduce more levels in that .. range. It will be an important task for future experimental work to show just how many levels can be obtained by this method. It will be interesting to compare electron or X-ray excita- tion with coulomb excitation by heavy particles. Actually, ; Ino has been studied at Oak Ridge using heavy particles but ; these data have got been evaluated yet.. At any rate, there is a practical limitation on the use of coulomh excitation. The highest level which was obtained reliably by that method lies at 2.4 MeV. No such limitation exists for electrons, particu- larly if their energy exceeds 10 MeV. - - Example II: Fig. 2 shows inelastic scattering of 3- electrons on Liv obtained at Boston.? The 0.478 level is clearly seen in spite of the large background of elastic scat- i tering, while in Stanford work at 41.5 MeV this level did not show up. Only recently has this level been obtained in Orsay by a somewhat involved procedure.. - - . - - Unfortunately, this method cannot be used for 2 > 5 be- cause the radiation tail swamps the inelastic peak. LEGAL NOTICE loved in this roport may not intre to his employment or contract This report we prepared us an account of Government sponsored work. Helthor the United States, por the Commission, nor any person acting on behall of the Commission: A. Makos any warranty or representation, expressed or implied, with respect to the acca- racy, completeness, or watalpeus of the information contained in this report, or that the use of may information, appunto, method, or proce B, Asrumos apy Habilities with respect to the use of, or for damage resulting from the use of any information, appartas, betbod, or proches declosed to the report. As wed in the above, "person acthy on behalf of the Commission" includes may on- 'ployo. or contractor of the Commission, or anployée of sucha contractor, to the acteat that mach omploys or contructor of the Comsaistoa, or employee of much contractor prepares, dienomino.cos, or provides accous to, way Information pure with the Commission, or h1z employment with such contractor. privately owned righta; or - . . Example II: In the first successful attempts of photo- excitation, 10 the x-rays from electrons have been used; and the excitation was detected by the activity of the isomeric state of In.. The analysis of such experiments by the preseut author showed that estimates of the widths of levels could be obtained. As a matter of fact, the spin of the activation level (1.07 MeV) through which the isomeric state was produced was correctly guessed, as later work has shown. The same er contains the first discussion of self-absorption and . Lamb's theory in this context and thus is related to the theo- retical basis for the Mössbauer effect. . . . 1. The first successful resonance absorption experiments of bremsstrahlung on non-isomers have been done only aw lato a 195723 and 195819... the latterWith a „Vande. Graari at 640.kev.. . :,::;, . . . . - - YIK OS NUCLEAR SPIN. PRITY ASSIGNMENTS For the resolution a lower limit 18: 2-3 keV; this 18 : the accuracy of the photo-thresholde of D2 and Bell. The broad. oning offect of the finite thickness of the target may partly be eliminated, by using targets of different thickness and extrapolating to zero thickness. Example V: Although the first application of electrons to the disintegration of nuclei (Be) used a low energy beam at Notre Dame," very little has been done on the disintegra- tion of deuterons at low energies. There has been only one point obtained in Gottingenalthough the underlying theory has been given and 18 partly plotted in Fig. 3. Recently, the theory has been checked, somewhat indirectly, on a micro- wave confined plasma in the Dak Ridge Fusion Project." Particularly interesting 18 an experiment using polarized electrons and a deuteron target with aligned nuclear spins. Coincidences between polarizations of the outgoing nucleon and of the scattered electron (in double scattering!) could be measured. *** Exemple V:.Another interesting experiment would be electrof'188ion, again observing the scattered electron and the two fission fragments in coincidence. We believe that studies of the types of Examples I and :III which are nuclear analogs of the atomic Franck-Hertz type of experimento, could profitably be carried out in small schools that can afford only small accelerators. ".. ., ilar . . ::.. ... . . . . . . . . . . *operated loy the Union Carbide Corporation for the U. 8. Atomic Energy Commission... ....... .....] :. . . att man ** **** *w.. ,nm ith IM. M . . . N r .. . . Gulte Homil.n.pl NUCLEAR SPIN.PARITY ASSIGNMENTS 1. References J. 8. Blair, Pros. Int. Symp. on Direct Interactions, Padua, .1962 (Gordon and Breach, New York). D. 8. Onley, C3. : : ill. ;:. 2. 3. E. Guth, C. R., Congr. Internat. Physique Mucléaire, 2-8 Juillet 1964, Editions CNSR, Paris (1964). 40. B. T. Chertok and E. C. Booth, lucl. Phys. 66, 230 (1965) 5. H. W. Kendall and J. Deser) Phys. Rev. 130, 245 (1963), albo W. Co Barber, Ann. Rev. Nucl. 'sci. .12, I (1962). . -6. F. K. McGowan, personal communication. 7. B. T. Chertok and E. C. Booth, 1.c. ref. 4. 8. 1.c. ref. 5. M. Bernheim and G. R. Bishop, Phys. Letters 5, Since the energy resolution was 300-540 keV (for incident energies 100-180 MeV), the contribution of the 478 keVlak level could be separated "from the elastic peak of Li by the summed peak with that observed from a metal ... target of enriched wo of the same radiation length." . 8 ..... 1 10. B. Pontecorvo and A. Lazard, c. R. 208, 99 (1939); G. B. . Collins, B. Waldman, E. Stubblefield and M. Goldhaber, . Phys. Rev. 55, 507 (1939);' 11. E. Guth, Phys. Rev. 59, 325 (1941); cf. also v. F. Weisskopf, ibid., p. 318. | 12. E. Hayward and E. G. Fuller, Phys. Rev. 106, 991 (1957). 0. Beckman and R. Sandströn, Nucl. Phys. ', 595 (1958). G. B. Collins, B. Waldman and E. Guth, Phys. Rev. 56, 876 (1939). 15. W. Paul, Naturwissenschaften, 36, 31 (1949). ". 16. E. Quth (unpublished); cf. however, E. Guth and c.'s. Mullin, Phys. Rev. 26, 234 (1949); 1.c. 242 ff. . . . .. . - . . 17. W. B. Ara, et al., Phys. RevLettera 10, 84 (1963). LA •, Phys. Rev. Lettes 7. * . OC . .. :: . . NUCLEAR SPIN.PARITY ASSIGNMENTS :. : ... Figure Captions Fig. 1. Excitation of In215 by 2 MeV electrons. Fig. 2. Excitation of the 0.478-MeV level by 3-Mev1 electrons. Fig. 3. Theoretical croBB section for disintegra- tion of HP by electrons. M=Magnetic dipole. Ewelectric dipole. ... ... . .. :1., ielid Blue Lin.... ... . -. . Centor tine . 7. 4 . vi , . 1 ) .. A n . ! . . o .' PO ' . . 1 . , A : . . . 1 TI . . W :. . . . : .1 . .*.. COUNTS A ...,, .: : :: • . .: . : 1.5 2.0 ELECTRON ENERGY (MeV) · . .. . . . . : * 9000 ::: :: 16,000 8500 14,000 : MOTT PEAK ||* 8000 12,000 500 10,000 COUNTS NUCLEAR EXCITATION COUNTS 8000 7000 6000 6500 4000 6000 IT 2000 « 2.25 3.00 2.50 2.75 SCTRON ENFRGY (MeV). ELECTRON ENERGY (MeV). .... ng m in..in .. .? . .. CROSS SECTION, 01E;) x 1030 cm2 ELECTRON ENERGY (MeV) OM ..9 .. OE We + 38 = 0 : . . . . . 1. I . . ! - . . . .. . ? -- . .. A $ 7. . END 21 1 . "1 DATE FILMED 3/ 9 /66 27 * M . . . . . : • . . .. . O