Analogue E2 transitions in the A = 26 nuclei

doi:10.1016/0375-9474(82)90097-5

Nuclear Physics A

Volume 385, Issue 3, 13 September 1982, Pages 461-473

https://doi.org/10.1016/0375-9474(82)90097-5 Get rights and content

Abstract

The mean lifetimes τ = 23 ± 3 and 9 ± 2 fs of the 2.070(J^π = 2₁⁺, T = 1) and 3.16(2₂⁺, 1) MeV states in ²⁶Al (T_z = 0), respectively, have been measured using the Doppler-shift attenuation method and the reaction ²⁵Mg(p, γ)²⁶Al. The relative intensities of the isoscalar E2 transitions 2.070(2₁⁺, 1) → 0.23(0⁺, 1) and 3.16(2₂⁺, 1) → 0.23(0⁺, 1) MeV have been determined to be (3.6 ± 0.7)% and (0.44 ± 0.17)%, respectively. The transition strengths are compared with the analogue transitions in ²⁶Mg( $T_{z} = +1) and^{26} Si (T_{z} = −1$ ) as well as with shell-model calculations.

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Nuclear Data Sheets for A = 26
2016, Nuclear Data Sheets
Evaluated spectroscopic data and level schemes from radioactive decay and nuclear reaction studies are presented for ²⁶O, ²⁶F, ²⁶Ne, ²⁶Na, ²⁶Mg, ²⁶Al, ²⁶Si, ²⁶P, and ²⁶S. This evaluation for A = 26 supersedes the earlier one by P. M. Endt (1998En04) and updates for some nuclides in ENSDF.
Highlights of this evaluation are the following:
This evaluation includes search results for ²⁶S nuclide and its proton–decay mode (2011Fo08).
An isomeric state (2.2 ms) in ²⁶F has been discovered by 2013Le03. The state is proposed at 643.4 keV 1 from γ–ray measurements. Internal-transition and beta-decay branches for the state are also determined. New excited levels in ²⁶Ne have been identified from ²⁶F β⁻ decay (2.2 ms).
For some ²⁶Si resonance states conflicting spin-parity assignments exist in the literature. These are identified by footnotes. 2015Do07 (³He,nγ) propose the first 0+ state above proton separation energy at an excitation energy of 5890 keV and suggested for additional independent measurements to confirm or refute the existence of 5946 keV 4. 2016Ch09 consider 5946 keV level as a distinct excited state in their reanalysis of the literature data with possible spin-parity assignment of 0+ or 4+
This evaluation also includes discovery of an isomeric state, at 164.1 keV 1, in ²⁶P by 2014NiZZ.
Energy levels of A = 21-44 nuclei (VII)
1990, Nuclear Physics, Section A
The experimentally determined properties of A = 21–44 nuclides are complied and evaluated with special emphasis on nuclear spectroscopy.
Separate tables for each of the nuclides reviewed present the available information about the following properties (in this order):
- •
  - excitation energies E_x,
- •
  - γ-ray branching ratios b(γ),
- •
  - γ-ray mixing ratios σ,
- •
  - lifetimes γ_m or widths Λ,
- •
  - neutron, proton, or α-particle resonances,
- •
  - partial widths,
- •
  - single-nucleon transfer reactions,
- •
  - beta-decay,
- •
  - arguments for spin and parity (J^π) and isospin (T) assignments.
For each nuclide a master table summarizing the “best” or adopted values for E_x, J^π; T and τ_m or Λ precedes the auxiliary tables listed above.
The review of each A-chain concludes with a discussion of isospin multiplets.
Figures are presented of the level schemes of all nuclei and, for each A-chain, an overview of the relative energies of the ground states and lowest analogue states of all nuclei in the chain.
The 25Mg(p, γ)26Al reaction; branchings, energies and lifetimes
1988, Nuclear Physics, Section A
The γ-decay has been measured of 75 ²⁵Mg(p, γ)²⁶Al resonances in the E_p = 0.31–1.84 MeV region with Ge detectors at 90° and 55°, the latter in a Compton suppression shield. Several of these resonances had not been observed previously and of about half the decay had not been measured. The spectra have been corrected for summing effects, for the instrumental tails of lower-energy resonances, for the Breit-Wigner tails of neighbouring broad resonances, and for direct capture.
On the average about 29 primaries are observed per resonance (with a maximum of 48); 74 primaries are of the resonance → resonance type. Altogether 109 secondary states are excited in the decay, of which 50 had been seen in previous (p, γ) work. The total number of observed decay γ-rays from non-resonance levels amounts to 548, with a maximum number of branches per level of 20.
Accurate energies have been measured for all states. The errors amount to ΔE_x = 0.03–0.26 keV for the non-resonance levels and to 0.04–0.4 keV for the resonances (with ΔE_x = 2 keV for four very broad resonances).
As a byproduct lifetimes (or lifetime limits) have been measured from the observed Doppler shifts for 32 levels for which no previous measurements existed.
Transition strengths in the mirror nuclei 27Si-27Al
1986, Nuclear Physics, Section A
Mean lifetimes of levels in the mirror nuclei ²⁷Si and ²⁷Al have been measured using the Doppler-shift-attenuation (DSA) method and the reactions ¹²C(¹⁶O, n)²⁷Si and ¹²C(¹⁶O, p)²⁷Al. The lifetime values or limits were determined for 14 levels in ²⁷Si and 7 levels in ²⁷Al. For the effective stopping of recoils, the targets were prepared by implanting ¹²C into Ta backings. The Monte Carlo method and the experimental stopping power were used in the DSA analysis. The strengths of the analogue transitions are discussed.
Lifetime measurements of levels in 34Ar: Isoscalar and isovector matrix elements for E2 analogue transitions
1985, Nuclear Physics, Section A
Mean lifetimes have been measured for the low-lying levels in ³⁴Ar(T_z = − 1) excited by the bombardment of ³He-implanted Au targets with a beam of 80 MeV ³²S. The lifetimes determined by fitting Doppler-broadened γ-ray lineshapes are as follows (E_x in keV, τ in fs): 2091, 460 ± 60; 3288, 280 ± 50; 3871, > 270 and 4128, 1301⁺¹⁷⁰₋₁₃₀. The resulting transition matrix elements for the 2⁺₁ → 0⁺₁ and 2⁺₂ → 0⁺₁ transitions are compared with those for the analogue transitions in ³⁴S (T_z = + 1) and ³⁴Cl(T_z = 0) to determine the isoscalar and isovector components. The component values are compared with theoretical calculations and with values of the ratio of neutron to proton matrix elements determined by inelastic scattering with strongly interacting probes.
Isoscalar E2 strengths in the A = 34 mass triplet
1984, Nuclear Physics, Section A
The mean lifetimes τ = 47 ± 5 and 7.5 ± 1.7 fs of the 2.16(J^π = 2₁⁺ T = 1) and 3.38(2₂⁺, 1) MeV states in ³⁴Cl(T_z = 0), respectively, have been measured using the Doppler-shift attenuation method and the reaction ³³S(p, γ)³⁴Cl The relative intensities of the isoscalar E2 transitions 2.16(2₁⁺, 1) → 0(0⁺, 1) and 3.38(2₂⁺ 1) → 0(0⁺, 1) MeV have been determined to be (16.3 ± 0.5)% and (2.1 ± 0.7)%, respectively. The transition strengths are compared with the analogue transitions in ³⁴S( T_z = +1) and ³⁴Ar(T_z = −1) as well as with theoretical calculations.

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Nuclear Physics A

Abstract

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Cited by (9)

Nuclear Data Sheets for A = 26

Energy levels of A = 21-44 nuclei (VII)

The <sup>25</sup>Mg(p, γ)<sup>26</sup>Al reaction; branchings, energies and lifetimes

Transition strengths in the mirror nuclei <sup>27</sup>Si-<sup>27</sup>Al

Lifetime measurements of levels in <sup>34</sup>Ar: Isoscalar and isovector matrix elements for E2 analogue transitions

Isoscalar E2 strengths in the A = 34 mass triplet