Is it possible to observe an isoscalar E1-multipole in reactions?

Burkova, N. А.; Zhaksibekova, K.A.; Zhusupov, M. A.; Eramzhyan, R.A.

doi:10.1016/0370-2693(90)90007-s

Cited by 37 publications

(19 citation statements)

References 23 publications

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“…The last term of Eq. (14) suggests that the transition matrix elements involving a virtual excitation of the α particle described by…”

Section: B Transition Matrix Elementsmentioning

confidence: 99%

Isospin-forbidden electric dipole capture and the α(d, γ)⁶Li reaction

Baye¹,

Tursunov²

2018

J. Phys. G: Nucl. Part. Phys.

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At the long-wavelength approximation, E1 transitions are forbidden between isospin-zero states.Hence E1 radiative capture is strongly hindered in reactions involving N = Z nuclei but the E1 astrophysical S factor may remain comparable to, or larger than, the E2 one. Theoretical expressions of the isoscalar and isovector contributions to E1 capture are analyzed in microscopic and three-body approaches in the context of the α(d, γ) 6 Li reaction. The lowest non-vanishing terms of the operators are derived and the dominant contributions to matrix elements are discussed.The astrophysical S factor computed with some of these contributions in a three-body α + n + p model is in agreement with the recent low-energy experimental data of the LUNA collaboration.This confirms that a correct treatment of the isovector E1 transitions involving small isospin-one admixtures in the wave functions should be able to provide an explanation of the data without adjustable parameter. The exact-masses prescription which is often used to avoid the disappearance of the E1 matrix element in potential models is not founded at the microscopic level and should not be used for such reactions. The importance of capture components from an initial S scattering wave is also discussed. PACS numbers: 25.40.Lw,23.20.-g,21.10.Hw,21.60.Gx * dbaye@ulb.ac.be † tursune@inp.uz In some radiative-capture reactions between light nuclei, electric-dipole transitions are strongly suppressed [1]. This effect is due to an isospin selection rule: E1 transitions are isospin-forbidden in capture reactions involving N = Z nuclei [2].At the long-wavelength approximation, which is a good approximation for this type of reactions, the isoscalar part of the E1 operator vanishes and transitions take place via its isovector part. Matrix elements of isovector operators vanish between isospin-zero states. However, except for the deuteron, realistic wave functions of N = Z nuclei are not pure eigenstates of the isospin operator and E1 transitions are not exactly forbidden. Their strength may keep an order of magnitude similar to the strength of the usually much weaker E2 transitions. This effect is particularly spectacular for the 12 C(α, γ) 16 O reaction where the isospin-forbidden E1 component is enhanced by resonances (see references in Ref. [1]). Disentangling the E1 and E2 strengths is experimentally very difficult and the theoretical calculations of the E1 component are still quite uncertain. The role of E1 transitions is also complicated in other reactions of astrophysical interest such as d(d, γ) 4 He, 4 He(d, γ) 6 Li, and 16 O(α, γ) 20 Ne. It may also play some role in the triple α mechanism generating 12 C. An ab initio description of the two lightest cases is in principle possible at present. The astrophysical S factor of the d(d, γ) 4 He reaction has been computed with an ab initio calculation in Ref. [3]. The E1 component is mainly obtained from T = 1 isospin components in 4 He introduced by coupled p+ 3 H and n+ 3 He configurations. Its largest contribution reache...

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“…The last term of Eq. (14) suggests that the transition matrix elements involving a virtual excitation of the α particle described by…”

Section: B Transition Matrix Elementsmentioning

confidence: 99%

Isospin-forbidden electric dipole capture and the α(d, γ)⁶Li reaction

Baye¹,

Tursunov²

2018

J. Phys. G: Nucl. Part. Phys.

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“…Theoretical calculations (refs. [21,22,23,24,25,26,27,28]) vary over a factor of about ten. Experimental measurements are difficult because of the extremely small cross sections involved; electric dipole radiation is strongly suppressed because the nearly equal charge-to-mass ratios of the deuteron and alpha particle give the d + α system a very small dipole moment in all cases.…”

Section: Hementioning

confidence: 99%

Nuclear reaction rates and primordial6Li

1997

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We examine the possibility that Big Bang Nucleosynthesis (BBN) may produce non-trivial amounts of 6 Li. If a primordial component of this isotope could be observed, it would provide a new fundamental test of Big-Bang cosmology, as well as new constraints on the baryon density of the universe. At present, however, theoretical predictions of the primordial 6 Li abundance are extremely uncertain due to difficulties in both theoretical estimates and experimental determinations of the 2 H(α, γ) 6 Li radiative capture reaction cross-section. We also argue that present observational capabilities do not yet allow the detection of primeval 6 Li in very metal-poor stars of the galactic halo. However, if the critical cross section is towards the upper end of its plausible range, then improvements in 6 Li detection capabilities may allow the establishment of 6 Li as another product of BBN. It is also noted that a primordial 6 Li detection could help resolve current concerns about the extragalactic D/H determination. 26.35.+c,26.44.+h,25.90.+k

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“…The most recent theoretical calculations of the low energy cross section for reaction (1) have been performed within the framework of the microscopic resonating group method (RGM) [4], in the quasimicroscopic potential model [5,6], and in the framework of the multicluster dynamic model [7]. The importance of the E1 capture at astrophysically relevant energies was noted in Refs.…”

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confidence: 99%

“…[2,4 -7]. Despite the fact that the E1 transition is forbidden in the long wavelength approximation, the El multipole can dominate over the E2 [5,7] because of the significant difference between the mass of the free n particle and twice the mass of the free deuteron at low energies.…”

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confidence: 99%

Astrophysical factor for the radiative capture reaction α+d→6Li+γ

et al. 1995

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We consider the radiative capture process u+d-+ Li+ y at energies, E,~3 00 keV, that are relevant for astrophysical processes. Due to the peripheral character of the reaction, the overall normalization of the astrophysical factor S24 is entirely governed by one quantity, the asymptotic normalization coefficient Col for Li-+ u+ d. Using the recently well established value for this constant Co& = 2.3~0.12 fm ", we calculated S24 taking into account both E1 and E2 contributions. Our recommended value for S24 is 2.57 MeV nb at the most effective energy for the capture reaction in astrophysical processes, E, = 70 keV, which gives a reaction rate 0.036 cm mole ' s ' at the temperature 0.8X 10 K. We found a significant energy dependence of S24 at astrophysical energies. At energies of less than 110 keV, the E1 component dominates over the E2 component. At E, =70 keV, the E1 contribution to the total transition is about 58%%uo.

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Is it possible to observe an isoscalar E1-multipole in reactions?

Cited by 37 publications

References 23 publications

Isospin-forbidden electric dipole capture and the α(d, γ)⁶Li reaction

Isospin-forbidden electric dipole capture and the α(d, γ)⁶Li reaction

Nuclear reaction rates and primordial6Li

Astrophysical factor for the radiative capture reaction α+d→6Li+γ

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Is it possible to observe an isoscalar E1-multipole in reactions?

Cited by 37 publications

References 23 publications

Isospin-forbidden electric dipole capture and the α(d, γ)6Li reaction

Isospin-forbidden electric dipole capture and the α(d, γ)6Li reaction

Nuclear reaction rates and primordial6Li

Astrophysical factor for the radiative capture reaction α+d→6Li+γ

Contact Info

Product

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Isospin-forbidden electric dipole capture and the α(d, γ)⁶Li reaction

Isospin-forbidden electric dipole capture and the α(d, γ)⁶Li reaction