Parity nonconservation for neutron resonances in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">Th</mml:mi></mml:mrow><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>232</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow></mml:math>

Frankle, C.M.; Bowman, J. D.; Bush, J. E.; Delheij, P. P. J.; Gould, C.R.; Haase, D. G.; Knudson, J. N.; Mitchell, G. E.; Penttilä, S. I.; Postma, H.; Roberson, N. R.; Seestrom, S.J.; Szymański, J.; Yoo, S.H.; Yuan, V. W.; Zhu, X.

doi:10.1103/physrevc.46.778

Cited by 60 publications

(13 citation statements)

References 17 publications

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“…To fit the experimental data we need t m ͞t f ϳ 10 (keeping in mind the kinematic enhancement factor ϳ1͞kR ϳ 5 3 10 2 for the low-energy data [5][6][7]). Note that the above picture is somewhat similar to the "quasielastic mechanism" suggested in Ref.…”

Section: School Of Physics the University Of New South Wales Sydneymentioning

confidence: 99%

“…The residual interaction and even the spin-orbit interaction for the bare nucleon can be very different from those we know from the fit of the low-energy shell-model states. Therefore, in the present work we make a step in the opposite direction and consider the experimental data [5][6][7] as a direct measurement of the memory time: t m ͞t f ϳ 10. In this case we can expect the angle of neutron spin rotation of c ϳ a ϳ 10 24 per mean free pass of a nonmonochromatic beam (DE ϳ 1 MeV).…”

Section: School Of Physics the University Of New South Wales Sydneymentioning

confidence: 99%

“…We have demonstrated that the angle of neutron spin rotation and the longitudinal polarizing power can reach c ϳ a ϳ 10 25 10 24 per mean free path. The upper estimation (ϳ10 24 ) is based on the experimental data [5][6][7] when we treat it as a measurement of the memory time t m .…”

Section: School Of Physics the University Of New South Wales Sydneymentioning

confidence: 99%

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Energy-Averaged Parity Nonconserving Effect in Neutron Scattering from Heavy Nuclei

Sushkov

1996

Phys. Rev. Lett.

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The effect of parity nonconservation (PNC) averaged over compound resonances is considered using a semiclassical approximation. We demonstrate that the result of averaging depends crucially on the properties of the residual strong nucleon-nucleon interaction. The way to elucidate this problem would be to investigate experimentally the PNC spin rotation c or the longitudinal polarization a of a nonmonochromatic neutron beam: E ϳ DE ϳ 1 MeV. The magnitude of the effect can reach c ϳ a ϳ 10 25 10 24 per mean free path. [S0031-9007(96)01884-4] PACS numbers: 24.80.+y, 11.30.Er, 25.40.Ny Enhancement of parity nonconservation (PNC) in neutron scattering near compound resonances was predicted in 1980 [1] and first observed experimentally in Dubna in 1981 [2] for the lowest p-wave resonance in 117 Sn. During the next decade the effect was observed for several other resonances in different nuclei. The magnitudes of the effect were in brilliant agreement with the statistical theory [1] (for review of the theory see [3,4]). A new development arose in 1990-1991 when the Los Alamos data for 238 U [5] and especially for 232 Th [6] were published (also see paper [7]). The effect was observed for a large number of resonances, and it was clear that its average value was not zero, in contrast with the expectations of the statistical theory. There have been a number of theoretical works devoted to this problem (for a review see Ref.[4]), but the situation remains unclear.Let us first consider the possible ways of resolving the problem. (1) The nonzero average is just a statistical fluctuation, because the number of resonances where the effect has been observed is still not very large.(2) There is some gross structure in the effect. The average effect is nonzero when averaged over an interval e much larger than the spacing between the resonances and much smaller than 1 MeV (D ø e ø DE ϳ 1 MeV), but the average over the interval DE ϳ 1 MeV is still zero, or at least very small. (3) There is a nonzero average effect for DE ϳ 1 MeV.The first possibility cannot be ruled out. However, even if the present value is a fluctuation, there is a question about the expected average value. The existence of the gross structure would mean that there are some intermediate states of opposite parity separated by the interval e. These are the so-called doorway states, and several papers have addressed this approach. A critical analysis of these suggestions is given in the review [4]. In short, the argument against the doorway state approach is very simple: The small interval e can work only if it is greater than the widths of the corresponding states. However, the spread width of any known intermediate state is G spr ϳ 1 MeV, and this probably kills the gross structure scenario. In the present Letter we consider the third scenario: a nonzero average over the interval DE ϳ G spr ϳ 1 MeV. It will be important for us that only the elastic channel is open [͑n, g͒ can be neglected anyway]. This is why DE should not be larger than 1 MeV. To avoid any misunder...

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Section: School Of Physics the University Of New South Wales Sydneymentioning

confidence: 99%

Section: School Of Physics the University Of New South Wales Sydneymentioning

confidence: 99%

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Energy-Averaged Parity Nonconserving Effect in Neutron Scattering from Heavy Nuclei

Sushkov

1996

Phys. Rev. Lett.

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“…Parity nonconservation (PNC) in the nucleon-nucleon interaction has been observed in the left-right asymmetry in p − p scattering [1], in nucleon-nucleus scattering induced by polarized projectiles (such as p [2] or n [3]) in spontaneous α-decay [4], [5] and in the circular polarization [6] [7], [8] or asymmetry [9], [10], [11], [12] (from polarized nuclei) of the radiation emitted in nuclear γ-decay. There are also theoretical predictions for new PNC experiments in induced α-decay [13], [14] and asymmetry of the radiation emitted in nuclear γ-decay [15], [16].…”

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confidence: 99%

Parity mixed doublets inA=36 nuclei

Horoi

1994

Phys. Rev. C

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The γ-circular polarizations (P γ ) and asymmetries (A γ ) of the parity forbidden M1 + E2 γ-decays: 36 Cl * (J π = 2 − ; T = 1; E x = 1.95 MeV) → 36 Cl(J π = 2 + ; T = 1; g.s.) and 36 Ar * (J π = 2 − ; T = 0; E x = 4.97 MeV) → 36 Ar * (J π = 2 + ; T = 0; E x = 1.97 MeV) are investigated theoretically. We use the recently proposed Warburton-Becker-Brown shell-model interaction.For the weak forces we discuss comparatively different weak interaction models based on different assumptions for evaluating the weak meson-hadron coupling constants. The results determine a range of P γ values from which we find the most probable values: P γ = 1.1 · 10 −4 for 36 Cl and P γ = 3.5 · 10 −4 for 36 Ar.

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“…However, few years ago it was discovered [2,3] that all seven asymmetries for 232 Th have the same, positive sign. This tendency was observed also in other nuclei.…”

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confidence: 99%

Is large weak mixing in heavy nuclei consistent with atomic experiments?

1995

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The hypothesis of a large weak matrix element between single-particle states in heavy nuclei (∼ 100 eV) contradicts the results of atomic PNC experiments.PACS numbers: 11.30. Er, 24.80.Dc, 27.80.+w, 35.10.Wb The scattering cross-sections of longitudinally polarized epithermal (1 -1000 eV) neutrons from heavy nuclei at p 1/2 resonances have large longitudinal asymmetry. This parity nonconserving (PNC) correlation is the fractional difference of the resonance cross-sections for positive and negative neutron helicities. For a long time the most natural explanation of the effect was based on the statistical model of the compound nuclei. In fact, not only the explanation, but the very prediction of the huge magnitude of this asymmetry (together with the nuclei most suitable for the experiments) was made theoretically [1] on the basis of this model.An obvious prediction of the statistical model is that after averaging over resonances, the asymmetry should vanish. However, few years ago it was discovered [2,3] that all seven asymmetries for 232 Th have the same, positive sign. This tendency was observed also in other nuclei.All the attempts [4][5][6][7] to explain a common sign require the magnitude of the weak interaction matrix element, mixing opposite-parity nuclear levels, to be extremely large, ∼ 100 eV. The same assumption seems to be necessary to explain unexpectedly large P-odd correlations observed in Mössbauer transitions in 119 Sn and 57 Fe [9,10]. In a recent paper [8] it was pointed out that such a large magnitude of the weak mixing can be checked in an independent experiment. The proposal is to measure PNC asymmetry in the M4 γ-transition between the (predominantly) single-particle states 1i 13/2 + and 2f 5/2 − in 207 Pb. The experiment sensitivity to the weak matrix element value is expected to reach 5 − 13 eV.In the present Comment we wish to note that close upper limit on the weak mixing in 207 Pb can be extracted now from the measurements of the PNC optical activity of atomic lead vapour [11]. The experiment was performed at the atomic M1 transition from the ground state 6p 2 3 P 0 to the excited one 6p 2 3 P 1 . The nuclear spin of 207 Pb being i = 1/2, the total atomic angular momentum of the ground level is F = 1/2, and the upper level is split into two: F ′ = 1/2, 3/2. The following upper limit was established at the 95% confidence level for the relative magnitude of the nuclear-spin-dependent (NSD) part of the optical activity:Hereand P is the main, nuclear-spin-independent, part of the PNC optical activity. In heavy atoms the NSD P-odd effects were shown to be induced mainly by contact electromagnetic interaction of electrons with the anapole moment of a nucleus which is its P-odd electromagnetic characteristic induced by PNC nuclear forces [12,13].The electromagnetic PNC interaction of electrons with nuclear AM is of a contact type. It is conveniently characterized in the units of the Fermi weak interaction constant G = 1.027 × 10 −5 m −2 (m is the proton mass) by a dimensionless constant κ....

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Parity nonconservation for neutron resonances inTh232

Cited by 60 publications

References 17 publications

Energy-Averaged Parity Nonconserving Effect in Neutron Scattering from Heavy Nuclei

Energy-Averaged Parity Nonconserving Effect in Neutron Scattering from Heavy Nuclei

Parity mixed doublets inA=36 nuclei

Is large weak mixing in heavy nuclei consistent with atomic experiments?

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