The conserved-vector-current (CVC) theory predicts a deviation from the allowed shape of the B 12 and N 12 beta spectra. The ratio of the shape factors of the two spectra is expected to have an energy dependence of (1.10rb0.l7)% per MeV. If the CVC hypothesis is not invoked, this ratio is estimated to be an order of magnitude smaller. The two spectra have been measured with a magnetic spectrometer and found to give for this ratio the value (1.30±0.31)% per MeV. The branching fraction of the N 12 decay to the 7.6-MeV state of C 12 has been determined to be (3.0±0.5)%.
Der Zerfall von Ti51 wird mit Absorption derβ-Strahlen,β-Spektrometer, Szintillationsmessung derγ-Strahlung und mit Koinzidenzmessungen untersucht. Eineγ-Strahlung von 0,32 MeV wird gefunden. Es wird im Mittel 1γ-Quant proβ-Zerfall ausgesandt. Dieγ-Energie pro Zerfall ist 0,35 MeV. Dasβ-Spektrum ist komplex. Das härteste Teilspektrum ist nicht mitγ-Strahlung gekoppelt und hat eine Maximalenergie von 2,2 MeV mit einem möglichen Fehler von ±0,1 MeV. Diese Zerfallsenergie paßt zu dem vonJensen undSuess angegebenen Diagramm der Zerfallsenergien und ist eine Bestätigung der magischen Zahl 28
An arrangement for the measurement of angular correlations between fi-particles and circular polarized 7-radiation is described and a result on Na 2~ is given. A correlation coefficient A =(+0,12+0,03) was obtained, which indicates a ratio of Gamow-Teller to Fermi matrix element MG/M F > t O.
The observed near equality of the vector beta coupling constant given by the decay of O 14 and the muon decay coupling constant led Feynman and Gell-Mann 1 to postulate the conservation of the vector part of the beta-decay current. Gell-Mann 2 pointed out that a consequence of this conserved vector current (CVC) theory is an additional coupling in the beta interaction analogous to the anomalous magnetic moment of the nucleon ("weak magnetism"). The interference between this term and the Gamow-Teller transition amplitude for a l + -*0 + , AT = 1 beta transition then results in a deviation from the allowed shape of the B 12 and N 12 spectra. The magnitude of the effect can be calculated 2 ' 3 from the rate of the analogous Ml gamma transition in C 12 . If S(E) is the spectrum of each transition, divided by the corresponding allowed Fermi spectrum, then the CVC theory predicts S(E, B 12 )/S(E, N 12 ) = const[l + (A + 6A)E]f(E),where the constants arises from this interference term. The quantity/(£) is the inner bremsstrahlung correction. The expected value for A is (1.33 ± 0.15)% per Mev with an electromagnetic correction 4 6A of (-0.25± 0.15)% per Mev. The uncertainty in A comes from the uncertainty in the C 12 gamma-decay rate and the uncertainty in 6A is an estimate of the error from using the shell model. Without the CVC theory hypothesis, A is estimated to be roughly 5 times smaller. 4 ' 5The beta spectra of B 12 (# max = 13.369 Mev) and N 12 (£ max = 16.43 Mev) were analyzed with the iron-free single-lens magnetic spectrometer described by Hornyak et al. 6 The baffle system was modified for the high electron energies involved. B 12 (20.3 msec) was produced by bombarding targets of natural boron with 1.65-Mev deuterons, and N 12 (12.5 msec) was produced by bombarding targets of enriched (96%) B 10 with 2.75-Mev He 3 ions. Both beams were pulsed at 60 cps at the ion source of the electrostatic ac-.celerator. The targets consisted of approximately 0.3 mg/cm 2 of boron deposited by cracking diborane on foils of thickness 0.5 mg/cm 2 and 3 mg/ cm 2 for B 12 and N 12 , respectively. The beta rays were detected in a 10-mm thick anthracene scintillator. This is sufficiently thin (approximately 2.3-Mev range for electrons) to give nearly identical pulse-height spectra for all energies in the range studied (5-13 Mev). The use of a thin scintillator allows amplifier gain and discriminator settings to be left constant, reduces background as a result of its small volume, and produces a negligible small pulse tail extending into the noise background. 7 The activity produced on the target was monitored by the reaction protons from B 1C V, p)B n for B 12 and B 10 (He 3 ,£)C 12 for N 12 . A silicon p-n junction counter mounted in the spectrometer near the target served as a proton detector.The spectra were sampled at 0.5-Mev intervals in the range 5 to 10.5 Mev for B 12 and 5 to 13 Mev for N 12 , the data being collected at alternating high-and low-energy points to minimize effects of target deterioration and instrumental drif...
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