Shape of the Beta-Spectrum of the Forbidden Transition of Yttrium 91

Langer, Lawrence M.; Price, H.C.

doi:10.1103/physrev.75.1109

Cited by 27 publications

(3 citation statements)

References 5 publications

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“…1,2 A beta-transition for which Al= ±2 (yes) yields an electron energy distribution which differs from that for an allowed transition by a factor G~(W 0 -W) 2 + (W 2 -1), if it is assumed that Gamow-Teller rules apply to the beta-process. 3 Such distributions have been observed previously for Y 9 \ Cs 137 , Rb 86 , Sr 90 , Y 90 , and K 42 . 2 -4~10 If the above reasoning is correct, the Sr 89 spectrum should display a similar forbidden "shape.…”

supporting

confidence: 78%

The Forbidden Beta-Decay ofSr89

Slack¹,

Braden²,

Shull³

1949

Phys. Rev.

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LETTERSTO parities as explained below. The arguments are based on two assumptions: (1) Gamow-Teller selection rules govern the beta-decay process, and (2) the nuclear shell model 1 is a reliable guide in the region Z^-40 and N~50.The nucleus 4 oZr 90 contains closed shells of 40 protons and 50 neutrons. Thus, 1 = 0 and the parity is even in the ground state.39Y 90 is an odd-odd nucleus. It is characterized by a (3p)~1(4d) 1 configuration in the notation of Feenberg and Hammack. Thus, the ground state parity is odd. 3 3Sr 90 is an even-even nucleus. It is characterized by a (3p)~2(4:d) 2 configuration. In the ground state the parity is even and, most probably, 7 = 0.Both beta-transitions are associated with change of parity. Thus by G-T rules, both are first-forbidden or both are thirdforbidden. The ft product for the first transition is ~10 9 and for the second ^40 8 . These values are appropriate for firstforbidden transitions with AJ= ±2 (1_2) , but are too small for third-forbidden. Consequently, 1 = 2 in the ground state of Y 90 .Thus the two beta-transitions of Fig. 1 should produce peculiar energy distributions similar to those found in Y 91 , Cs 137 , K 42 , and Rb 86 by various investigators. 2-7 In such cases the energy distribution differs 8 from the allowed form by a factor G~(W Q -W) 2 + (W 2 -l). A carrier-free sample of Sr 90 was obtained from Oak Ridge. This sample had been aged to permit an associated 55-day activity of Sr 89 to die out. Three spectra were measured:(1) Sr 90 and Y 90 in equilibrium together, (2) Sr 90 alone, and (3) Y 90 alone. For the latter two runs, the isotopes were chemically separated by a method due to Kurbatov and Kurbatov. 9 Samples were prepared for the spectrometer by evaporation from solution on thin Zapon films, following the insulin technique of Langer. 10 The spectra were measured in the double-focusing spectrometer described by Kurie, Osoba, and Slack. 11 In the interests of higher counting rates, a wide counter window (0.25 in.) was used, which dropped the resolving power to 1 percent. The window was Zapon film of 3-to 4-kev stopping power, and was supported lengthwise by a single 5-mil wire. A pressure regulator 12 was used to avoid loss of counter pressure caused by window leakage.The results are shown as FK (Fermi-Kurie) plots in Fig. 2 for Sr 90 and in Fig. 3 for Y 90 . As indicated in Fig. 2, the Sr 90 data was obtained by subtracting the Y 90 distribution curve from that for an equilibrium mixture of both Sr 90 and Y 90 . * Assisted by the joint program of the ONR and the AEC.

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supporting

confidence: 78%

The Forbidden Beta-Decay ofSr89

Slack¹,

Braden²,

Shull³

1949

Phys. Rev.

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“…This factor uniquely determines the shape of a once-forbidden transition involving a change of two units of angular momentum and a parity change. 7 The end point of the high energy group determined from this plot is 4.81±0.05 Mev. A similar forbidden Fermi plot for all the data obtained at 6.4 percent resolution is shown in Fig.…”

Section: Experimental Methodsmentioning

confidence: 81%

The Beta-Spectra ofCl38

Langer

1950

Phys. Rev.

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thought to be Fr 212 . 28 It was assigned to At 208 principally on the basis of the appearance of Po 208 at the rate corresponding to the decay of a 1.8 hr. parent. It may be mentioned that by spallation reactions of bismuth another apparent astatine parent of Po 208 is produced which decays with a longer half-life than 1.8 hrs. and has no observable alpha-radiation. 72 It is possible that there are isomers of At 208 which show up in different abundances by the two modes of formation.Through excitation function measurements a 5.76 Mev alphaparticle decaying with 1.8-hr. half-life has been assigned to At 207 . 72 Two other probable astatine isotopes are assigned to At 206 and At 204 somewhat arbitrarily although the mass number range is defined by excitation experiments. The two activities are respectively a 25-min. period of 5.9 Mev alpha-energy and a 10-min. period with a 6.1 Mev alpha-particle. 72 PQ209This new isotope of polonium has a 200-year half-life for alphadecay estimated from yield considerations 71 and the alphaparticle energy has been revised slightly as 4.90 Mev. 73 The electron capture branching is not known accurately but was estimated from the amount of L-x-rays as a maximum of 1 in 10. 24 The electron capture half-life would be accordingly greater than 2000 years. Po 205 and lighter polonium isotopesAs in the case of light astatine isotopes there is little accurate information on the alpha-half-lives of these species and the isotopic assignments are not certain. The energies are sufficiently well known and the isotopic assignments are well enough defined for use in Fig. 1 to show the trend expected in this region. The presently accepted decay properties of Po 206 are a measured half-life of 1.5 hr. with a 5.2 Mev alpha-particle. 24 The 5.35 Mev alphaparticle with 4-hour half-life 3 has been reassigned to Po 204 , 24 while the 40 min., 5.56 Mev alpha-emitter is retained at Po 203 . In each case the degree of alpha-branching is not known.A. Ghiorso, unpublished data.

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“…Thus, the ground state parity is odd. 3 3Sr 90 is an even-even nucleus. It is characterized by a (3p)~2(4:d) 2 configuration.…”

Section: Lettersmentioning

confidence: 99%