The l-forbidden magnetic dipole transition in A = 39

doi:10.1016/0375-9474(88)90351-X

Nuclear Physics A

Volume 477, Issue 3, 15 February 1988, Pages 453-471

https://doi.org/10.1016/0375-9474(88)90351-X Get rights and content

Abstract

The lifetime, τ = 233 ± 25 fs, of the first excited state of ³⁹Ca has been measured by the Doppler-shift attenuation method by detecting γ-rays from the ³He(⁴⁰Ca, α)³⁹Ca reaction. The value of $B(M 1; 32^{+} → 12^{+})$ has been extracted and combined with published values for the mirror transition in ³⁹K to deduce the isovector and isoscalar matrix elements for these l-forbidden transitions. They are compared with the results of a new theoretical calculation of the core-polarisation and meson-exchange-current corrections expressed in terms of an equivalent effective M1 operator. The data and calculations are also compared to recent empirical values of the effective operator from global-shell-model fits to sd-shell data of Brown and Wildenthai and to previous theoretical calculations of Towner and Khanna for both the $l- forbidden 0 d_{32} → 1 s_{12} M 1$ and Gamow-Teller transitions in mass 39 nuclei.

References (38)

O. Häusser et al.
Nucl. Phys.
(1972)
W. Andrejtscheff et al.
Nucl. Phys.
(1981)
E.G. Adelberger et al.
Nucl. Phys.
(1984)
I.S. Towner et al.
J. de Phys.
(1984)
B.A. Brown et al.
Phys. Rev.
(1982)
C.W. de Jager et al.
Phys. Lett.
(1985)
T.K. Alexander et al.
J. Nucl. Mat.
(1981)
P. Taras et al.
Proposal for a national facility
The 8π Spectrometer
(1983)
L.C. Northcliffe et al.
Nucl. Data Tables
(1970)
J.S. Forster et al.
Nucl. Instr. Meth.
(1976)

W.N. Lennard et al.

Nucl. Instr. Meth.

(1985)

P.M. Endt et al.

Nucl. Phys.

(1978)

R.C. Greenwood et al.

Nucl. Instr. Meth.

(1979)

R.M. Tapphorn et al.

Phys. Rev.

(1971)

J.A. Stander et al.

Z. Phys.

(1986)

B.C. Robertson et al.

Nucl. Phys.

(1969)

A. Anttila et al.

Phys. Scripta

(1970)

I.S. Towner et al.

Nucl. Phys.

(1983)

A. Arima et al.

Nuclear magnetic moments and Gamow-Teller transitions

(1986)

H. Hyuga et al.

Nucl. Phys.

(1980)

A. Arima et al.

Cited by (12)

Nuclear data sheets for A = 39
2006, Nuclear Data Sheets
Nuclear spectroscopic information for the known nuclides of mass 39 (Mg,Al,Si,P,S,Cl,Ar,K,Ca,Sc,Ti) has been evaluated. The principal sources of the ‘adopted levels’ presented are Endt's evaluations (1990En08, 1978En02). The data sets for reactions and decays, including all available gamma–ray data, are based mostly on the original literature. There are no data available for the excited states in ³⁹Mg, ³⁹Al, ³⁹Si and ³⁹Ti.
Subtle nuclear structure effects in electron scattering
2001, Nuclear Physics A
I-Forbidden transitions: A sensitive test of the effective magnetic dipole operator
2000, Progress in Particle and Nuclear Physics
The extremely weak l-forbidden $2s_{12} → 1d_{32}$ M1 transition from the ground state of ³²S to the J^π = 1⁺ state at E_x = 7.003 MeV was investigated by 165° and 180° electron scattering. The extracted strength of 0.0040(5) μ_N² represents the smallest B(M1)↑ value ever measured in electron scattering. A combined analysis with the isospin-analogous Gamow-Teller (GT) decays of the J^π = 1⁺ ground states of ³²Cl and ³²P is performed. Empirical corrections of Brown and Wildenthal to the magnetic operators reasonably account for the data. Corrections derived from microscopic approaches are less successful pointing towards a fundamental, not yet understood problem in the description of the effective M1 and GT operators. Some theoretical ideas to explain this discrepancy are discussed.
Confirmation of the l-forbidden Gamow-Teller decay branch of <sup>39</sup>Ca
1994, Nuclear Physics, Section A
A search for Gamow-Teller decay branches of ³⁹Ca to excited states in ³⁹K was conducted with a large HPGe detector which observed the decays of ³⁹Ca samples delivered by a helium-jet transport system. A pair of plastic scintillators in front of the HPGe detector were used to reject events due to bremsstrahlung from the ³⁹Ca positrons. With this setup, weak γ-rays could be observed with a degree of sensitivity not previously achieved. The $l- forbidden 1 d_{32} → 2 s_{12}$ transition to the first excited state in ³⁹K, was observed with a branching ratio of (2.50 ± 0.27) × 10⁻⁵. This result agrees with but is more accurate than the only previous measurement. Thus, the ratio of the l-forbidden Gamow-Teller and isovector M1 matrix elements in mass-39 nuclei continues to disagree with theoretical values obtained by Towner and Khanna from calculations involving core-polarization and meson-exchange currents. This leaves very few possibilities to explain the discrepancy between theory and experiment.
The l-forbidden m1 decay of the 2522 keV level in <sup>39</sup>K
1991, Nuclear Physics, Section A
The mean lifetime of the first excited $12^{+}$ level in ³⁹K has been measured to be τ = 93 ± 13 fs by high recoil velocity DSAM. The level was excited by bombarding a ⁴He-implanted Ta target with a 100 MeV ³⁹K beam. The lifetime was determined by fitting the Doppler-broadened lineshape of the 2522 keV gamma-ray transition to the $32^{+}$ ground state. Together with the measured B(E2), the $B (M 1; d_{32} → S_{12})$ for this l-forbidden M1 transition was determined to be 0.0100 ±0.0027 μ²_N. A theoretical calculation, taking into account core polarization, delta excitation and mesonexchange current contributions, underestimates the B(M)1) by more than a factor of six. The experiment also measured the lifetimes of the 3019 keV and 3883 keV levels to be 20 ±4 fs and 11 ± 6 fs, respectively.
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.

View all citing articles on Scopus

View full text

The l-forbidden magnetic dipole transition in A = 39

Abstract

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

J. de Phys.

Phys. Rev.

Phys. Lett.

J. Nucl. Mat.

The 8π Spectrometer

Nucl. Data Tables

Nucl. Instr. Meth.

Nucl. Instr. Meth.

Nucl. Phys.

Nucl. Instr. Meth.

Phys. Rev.

Z. Phys.

Nucl. Phys.

Phys. Scripta

Nucl. Phys.

Nucl. Phys.