Electromagnetic transition strengths in 14C and 14N

1968 ◽  
Vol 46 (14) ◽  
pp. 1575-1584 ◽  
Author(s):  
K. W. Allen ◽  
T. K. Alexander ◽  
D. C. Healey
Keyword(s):  
Ground State ◽  
Selection Rule ◽  
State Transition ◽  
Gamma Ray ◽  
The Self ◽  
Isotopic Spin ◽  
Distance Method ◽  
Electromagnetic Transition ◽  
Mixing Ratios ◽  
Recoil Distance

The lifetimes of the 5.10-MeV and 5.83-MeV levels in 14N and the 6.72-MeV level in 14C have been measured using a recoil distance method and the T(12C, nγ)14N and T(12C, pγ)14C reactions respectively. The lifetimes are 12.4 ± 1.4 and 18 ± 2 ps for the 5.10-MeV and 5.83-MeV levels in 14N respectively and 97 ± 15 ps for the 6.72-MeV level in 14C. These measurements are combined with previous determinations of gamma-ray branching and multipole mixing ratios to obtain the strengths of the transitions involved. Comparison of the strengths with recent calculations shows agreement in general. The ground-state E3 transitions from the 5.10-MeV level in 14N and the 6.72-MeV level in 14C are enhanced by 2.2 ± 0.7 and 3.3 ± 0.8 Weisskopf units respectively. The isotopic spin selection rule for E1 and M2 transitions in the self-conjugate nucleus 14N is observed and discussed for some transitions. For example, the allowed M2 transition from the 5.10-MeV to the 2.31-MeV level has [Formula: see text] whereas the isotopic spin forbidden M2 part of the 5.10-MeV to ground-state transition has [Formula: see text]

The Lifetimes of the 3/2+, 975 keV Level in 25Mg and the 3/2+, 945 keV Level in 25Al

1972 ◽  
Vol 50 (18) ◽  
pp. 2198-2205 ◽  
Author(s):  
T. K. Alexander ◽  
O. Häusser ◽  
A. B. McDonald ◽  
G. T. Ewan
Keyword(s):  
Gamma Ray ◽  
Transition Probabilities ◽  
Unified Model ◽  
Distance Method ◽  
Mixing Ratios ◽  
Mean Lifetime ◽  
Recoil Distance ◽  
The Mean ◽  
The Absolute ◽  
Mean Lifetimes

The 3/2+, 975 keV level in 25Mg and the 945 keV level in 25Al were populated in the 2H(24Mg,pγ)25Mg and 2H(24Mg,nγ)25Al reactions respectively and their mean lifetimes for gamma-ray decay were measured by the recoil-distance method. The mean lifetime of the 975 keV level in 25Mg is 14.6 ± 1.5 ps and that of the 945 keV level in 25Al is 6.2 ± 1.6 ps. Using previously measured branching and mixing ratios, the absolute M1 and E2 transition probabilities have been obtained and are compared with predictions of the unified model.

Lifetime measurements of the six lowest lying levels in 35Cl

1969 ◽  
Vol 47 (12) ◽  
pp. 1295-1306 ◽  
Author(s):  
F. Ingebretsen ◽  
T. K. Alexander ◽  
O. Häusser ◽  
D. Pelte
Keyword(s):  
Gamma Rays ◽  
Doppler Shift ◽  
Gamma Ray ◽  
Level Structure ◽  
Branching Ratios ◽  
Distance Method ◽  
Lifetime Measurements ◽  
Mixing Ratios ◽  
Doppler Shift Attenuation ◽  
Recoil Distance

The energies, gamma-ray branching ratios, and mean nuclear lifetimes of the six lowest lying levels in 35Cl have been measured. Gamma rays following the reaction 32S(α,pγ)35Cl were studied using two Ge(Li) detectors with 15-cm3 and 40-cm3 active volumes respectively. The lifetimes of the five lowest lying levels were measured using the Doppler shift attenuation method, with the results: 1219 keV, [Formula: see text]; 1763 keV, 0.55 ± 0.15 ps; 2646 keV, 0.30 ± 0.09 ps; 2695 keV, <0.03 ps; and 3003 keV, <0.05 ps. The lifetime of the 3163-keV level was measured to be 60 ± 7 ps, using a recoil distance method. The level structure is discussed taking into account known lifetimes, spins, parities, and gamma-ray mixing ratios.

Coulomb excitation of 24Mg with 35Cl ions

1969 ◽  
Vol 47 (18) ◽  
pp. 1929-1940 ◽  
Author(s):  
D. Pelte ◽  
O. Häusser ◽  
T. K. Alexander ◽  
H. C. Evans
Keyword(s):  
Quadrupole Moment ◽  
Cross Section ◽  
Ground State ◽  
State Transition ◽  
Gamma Ray ◽  
Coulomb Excitation ◽  
Absolute Cross Section ◽  
Ground State Transition ◽  
Section Measurement ◽  
Anisotropy Measurement

The Coulomb excitation of a thick 24Mg target was studied with 35Cl ions of 61, 57, and 52 MeV. The absolute cross section and the anisotropy of the angular distribution of the ground state transition from the 1.369-MeV state in 24Mg was measured, and their dependence on B(E2) and the quadrupole moment, Q, of the 1.369-MeV state was calculated. A B(E2) of 24.5 ± 2.2 Weisskopf units (W.u.) was deduced from the line shape of the 1.369-MeV gamma ray observed with a 40 cm3 Ge(Li) detector. The quadrupole moment determined from the anisotropy measurement was Q = −0.38 ± 0.16 b. From the cross-section measurement, Q = −0.47 ± 0.19 b was obtained using B(E2) = 24.5 ± 2.2 W.u. The dependence of this value of Q on B(E2) is discussed.

PROPERTIES OF LEVELS AT 6.69 AND 6.88–6.89 MeV IN 28Si

1966 ◽  
Vol 44 (5) ◽  
pp. 1087-1097 ◽  
Author(s):  
R. J. A. Levesque ◽  
R. W. Ollerhead ◽  
E. W. Blackmore ◽  
J. A. Kuehner
Keyword(s):  
Excited State ◽  
Alpha Particle ◽  
Ground State ◽  
State Transition ◽  
Gamma Ray ◽  
The Other ◽  
Ground State Transition ◽  
Angular Correlations ◽  
First Excited State ◽  
Strong Ground

Levels at 6.69, 6.88, and 6.89 MeV were observed in the 16O(16O, α)28Si reaction, and angular correlations were measured for the resulting gamma-ray transitions, using the geometry in which the alpha particle is detected at 0°. The level at 6.69 MeV had not been reported previously and was assigned spin and parity 0+. The doublet of levels at 6.88–6.89 MeV was not resolved in these measurements, but angular correlations of the gamma-ray transitions were possible, using spectrum subtraction techniques. One member of the doublet, previously assigned spin 3, has a strong ground-state transition; the angular correlation for this transition confirms a 3− assignment to this level. The other member of the doublet, which decays almost entirely to the first excited state, could not be assigned a spin on the basis of these measurements. However, taken in conjunction with other measurements, an assignment of 4+ is favored.

Positive-Parity Bands in 29Si

1971 ◽  
Vol 49 (10) ◽  
pp. 1263-1274 ◽  
Author(s):  
A. A. Pilt ◽  
R. H. Spear ◽  
R. V. Elliott ◽  
J. A. Kuehner
Keyword(s):  
Angular Distribution ◽  
Excited State ◽  
Linear Polarization ◽  
Ground State ◽  
Gamma Ray ◽  
Positive Parity ◽  
Rotational Bands ◽  
Mixing Ratios ◽  
First Excited State ◽  
Nilsson Model

A study has been made of several high spin members of the ground state (Kπ = 1/2+) and first-excited state (Kπ = 3/2+) rotational bands in the presumed oblate nucleus 29Si. Gamma-ray angular distribution and linear polarization measurements have confirmed the spin and parity of the 4081 keV level to be 7/2+, and levels at 4742 and 5283 keV have been shown to have Jπ = 9/2+ and (7/2+, 3/2+) respectively. Branching and mixing ratios for the transitions from these states have also been determined; in conjunction with previously measured lifetimes, transition strengths are calculated. The results are compared with the predictions of a Nilsson-model calculation including the effects of coriolis mixing of the low-lying positive parity bands.

Capture Gamma-Ray Spectra for the 59Co(n, γ)60Co Reaction Using Resonance Energy Neutrons

1975 ◽  
Vol 53 (4) ◽  
pp. 351-359 ◽  
Author(s):  
W. V. Prestwich ◽  
A. M. Lopez
Keyword(s):  
Neutron Energy ◽  
Ground State ◽  
State Transition ◽  
Gamma Ray ◽  
Resonance Energy ◽  
High Energy ◽  
Final States ◽  
Ground State Transition ◽  
Energy Distributions ◽  
Direct Capture

Capture gamma-ray spectra for the reaction 59Co(n, γ)60Co were obtained for different neutron energy distributions. Significant contributions from the high energy resonances were observed. Analysis of the data for the ground state transition indicates that the contribution to the process from potential direct capture is substantially smaller than previous estimates. No retardation of transitions to final states exhibiting an ln = 3 (d,p) stripping pattern, such as that observed for 132 eV capture, is evident for the higher energy resonances.

Lifetimes in 32S

1970 ◽  
Vol 48 (1) ◽  
pp. 47-55 ◽  
Author(s):  
R. W. Ollerhead ◽  
T. K. Alexander ◽  
O. Häusser
Keyword(s):  
Gamma Rays ◽  
Ground State ◽  
Doppler Shift ◽  
State Transition ◽  
Gamma Ray ◽  
Branching Ratio ◽  
Dipole Transition ◽  
Average Lifetime ◽  
Line Shapes ◽  
Doppler Shift Attenuation

Lifetimes have been measured for five levels in 32S. The levels were populated by inelastic scattering of protons, and the gamma rays were detected at angles between 0° and 127° using a 40 cm3 Ge(Li) detector mounted inside a split annular NaI(Tl) crystal. The spectrometer was used simultaneously as both an escape-suppressed and a three-crystal pair spectrometer. Decay schemes and lifetimes have been determined using thick targets of PbS, MoS2, and sulfur cooled to 77 °K. Lifetime information was obtained both from analysis of the observed gamma-ray line shapes and from analysis of the Doppler shift attenuation in the different target materials. The two methods of analysis agree within the errors. A weak ground-state transition was observed from the J = 3 level at 5.012 MeV, establishing its parity as negative. Analysis of the line shape observed at 0° and the Doppler shift attenuation gave an average lifetime of 7.5 ± 0.5 × 10−13 s. The observed branching ratio (4 ± 0.4% to the ground state) implies an E3 enhancement of 20 ± 2.4 Weisskopf units (W.u.). A similar analysis gave a lifetime of 4.9 ± 0.9 × 10−13 s for the J = 1 level at 4.699 MeV, which implies that the dipole transition to the ground state is highly retarded. Lifetimes have also been measured for levels at 3.780 MeV [Formula: see text], 4.288 MeV (7.4 ± 0.6 × 10−14 s), and 5410 MeV (1.9 ± 0.2 × 10−13 s); the transition strengths are tabulated and discussed.

scholarly journals On a Possible Origin of the Gamma-ray Excess around the Galactic Center

Symmetry ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1432
Author(s):  
Dmitry O. Chernyshov ◽  
Andrei E. Egorov ◽  
Vladimir A. Dogiel ◽  
Alexei V. Ivlev
Keyword(s):  
Dark Matter ◽  
Gamma Rays ◽  
Molecular Clouds ◽  
Alternative Explanation ◽  
Gamma Ray ◽  
Galactic Center ◽  
The Self ◽  
Large Area ◽  
Mhd Turbulence ◽  
The Standard Model

Recent observations of gamma rays with the Fermi Large Area Telescope (LAT) in the direction of the inner galaxy revealed a mysterious excess of GeV. Its intensity is significantly above predictions of the standard model of cosmic rays (CRs) generation and propagation with a peak in the spectrum around a few GeV. Popular interpretations of this excess are that it is due to either spherically distributed annihilating dark matter (DM) or an abnormal population of millisecond pulsars. We suggest an alternative explanation of the excess through the CR interactions with molecular clouds in the Galactic Center (GC) region. We assumed that the excess could be imitated by the emission of molecular clouds with depleted density of CRs with energies below ∼10 GeV inside. A novelty of our work is in detailed elaboration of the depletion mechanism of CRs with the mentioned energies through the “barrier” near the cloud edge formed by the self-excited MHD turbulence. This depletion of CRs inside the clouds may be a reason for the deficit of gamma rays from the Central Molecular Zone (CMZ) at energies below a few GeV. This in turn changes the ratio between various emission components at those energies and may potentially absorb the GeV excess by a simple renormalization of key components.

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