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Il Nuovo Cimento (1943-1954)

, Volume 10, Issue 9, pp 1219–1260 | Cite as

Die lage der ersten anregungsstufe in kernen mit gerader protonen und gerader neutronenzahl

  • P. Stàhelin
  • P. Preiswerk
Article

Summary

The introduction refers to previous short communications [3] on the first excited state of even-even nuclei (Chap. 1). A survey shows that the lowest excitation energy of even-even nuclei is a smooth function of the neutron and proton number. In sequences of neighbouring nuclei the excitation energy increases if the number of protons or of neutrons approaches the next magic number (Chap.2). Several nuclei which seemed to disobey this rule were reinvestigated experimentally, and in every case the new data obtained confirm the rule (Chap.3). The 145 keV radiation which accompanies the transmutation of Cl34 into S34 [29] is an isomeric (M 3) transition between the known33-min state and the ground state of Cl34, the half life of which is 1.45 s. An 0+ → 0+ transition with an ft-value of 2 700 s leads directly to the ground state of S34 (§ 3.2). Two different isotopes of antimony, Sb12 and Sb116, have indistinguishable half lives of (16 ±2) min. The 1.3 MeV level which previously was attributed to Sn120 [42] belongs to Sn116. The 60-min activity, with a γ-ray of 0.70 MeV [41], probably has to be reassigned to mass number115 (instead of 116) (§ 3.10). In Hg196 a reported γ-ray of 175 keV [46] could not be confirmed, and a new line corresponding to a first level at 426 keV was found, which agrees with our rules (§ 3.13). Further experiments deal with Mo96, Zr92 and Mo92. The dependence of the lowest excitation energy on the number of protons and neutrons is interpreted in terms of the shell modell (Chap.4). It is shown that a strong configurational interaction must be assumed (Chap.5), and that in general the first excited state is due to a simultaneous excitation of the neutron and the proton structure (Chap.6).

Riassunto

L’introduzione si richiama a precedenti brevi comunicazioni sul primo stato eccitato dei nuclei pari (Cap. 1). Un breve esame mostra che la più bassa energia di eccitazione dei nuclei pari-pari è una funzione continua del numero dei neutroni e dei protoni. In serie di nuclei vicini l’energia di eccitazione cresce se il numero dei protoni o dei neutroni si avvicina al prossimo numero magico (Cap.2). Sono stati riesaminati sperimentalmente alcuni nuclei ehe sembravano disobbedire a questa regola ed in ogni caso i nuovi risultati ottenuti confermano la regola (Cap. 3). La radiazione di 145 keV che accompagna la trasformazione di Cl34 in S34 [29] è dovuta a una transizione isomerica (M 3) tra lo stato 33-min noto e lo stato fondamentale di Cl34, il cui semiperiodo è 1,45 s. Una transizione 0+→ 0+ con valoreft di 2 700 s porta direttamente allo stato fondamentale dell’S34 (3.2). Due differenti isotopi del’ antimonio, Sb120 e Sb116 hanno semiperiodi indistinguibili di (16 ±2) min. Il livello a 1.3 MeV che precedentemente si attribuisce all’Sb120 [42] appartiene allo Sn116. L’attività di 60 min con emissione γ di 0,70 MeV [41] deve probabilmente essere riassegnata al numéo di massa 115 (invece del 116) (3.10). Nel Hg196 non si è potuto confermare la radiazione γ di 175 keV riportata [46] e si è trovato una nuova riga corrispondente a un primo livello a 426 keV, che si accorda con le nostre regole (3.13). Ulteriori esperimenti sono stati eseguiti con Mo96, Zr92, e Mo92. La dipendenza della piè bassa energia d’eccitazione dal numero dei neutroni e dei protoni è interpretata in termini del modello a strati (Cap.4). Si dimostra che si deve ammettere una forte interazione fra le conflgurazioni (Cap.5) e ehe in generale il primo stato eccitato è dovuto a una eccitazione simultanea della struttura neutronica e protonica (Cap.6).

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Copyright information

© Società Italiana di Fisica 1953

Authors and Affiliations

  • P. Stàhelin
    • 1
  • P. Preiswerk
    • 1
  1. 1.Eidgenössissche Technische HochschuleZürich

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