Strong-coupling Model Research Articles

Study of proposedAl27models by an analysis of inelastic scattering data of 60 to 90 MeV deuterons

Angular distributions for elastic and inelastic deuteron scattering on $^{27}\mathrm{Al}$ were measured at ${E}_{d}=60, 77, \mathrm{and} 90$ MeV. The data are analyzed by coupled channels calculations and discussed in terms of the weak coupling, strong coupling, and rotational-vibrational models for $^{27}\mathrm{Al}$. The analysis supports the concepts of rotational-vibrational interaction in $^{27}\mathrm{Al}$ and suggests the level observed at ${E}_{x}=5.5$ MeV to be the third ${9/2}^{+}$ member of the $K=\frac{5}{2}$ ground state band.NUCLEAR REACTIONS $^{27}\mathrm{Al}(d,d)$, ($d,{d}^{\ensuremath{'}}$), $E=60, 77, \mathrm{and} 90$ MeV; measured $\ensuremath{\sigma}(E,\ensuremath{\Theta})$, $^{27}\mathrm{Al}$ deduced levels; optical model and coupled channels analysis; deduced $L$, ${\ensuremath{\beta}}_{l}$; weak coupling model, rotational model, rotational-vibrational model.

Deformation systematics for the positive parity states in the [formula omitted] shell

The strong coupling model was used to study possible regions of stable deformation for the positive parity states of the odd nuclei in the 1f 7 2 shell. In strongly deformed nuclei, two regions of stable deformation are obtained. In each nucleus where sufficient experimental data is available, a potential having a positive deformation of β ≈ 0.20 can reproduce the observed variation of E x as a function of J( J+1).

The (3He, n) reaction in the lower 2s1d shell

The two-proton transfer reaction (3He, n) has been measured on four gas targets, leO, 1sO, 2°Ne, and 22Ne, with an incident SHe energy of 18.3 MeV. The data were taken with a neutron time-of-flight spectrometer in the angular range 0 ° to 40 ° c.m. The results for selected transitions are compared to DWBA predictions using shell-model spectroscopic amplitudes. In addition, the data for the lsO(3He, n)2°Ne reaction are compared to predictions of the SU(3) strong coupling model.

Lifetime measurements and deformed states inCa41

The Doppler-shift attenuation method has been applied to measure the mean lives of levels in $^{41}\mathrm{Ca}$. States were populated using the $^{40}\mathrm{Ca}(d, p)^{41}\mathrm{Ca}$ reaction at ${E}_{d}=3$ MeV and protons emerging from the reaction were detected near 180\ifmmode^\circ\else\textdegree\fi{} relative to the beam. $\ensuremath{\gamma}$ rays were detected in coincidence with the protons using a 65 ${\mathrm{cm}}^{3}$ Ge(Li) detector placed successively at angles of 53\ifmmode^\circ\else\textdegree\fi{}, 90\ifmmode^\circ\else\textdegree\fi{}, and 140\ifmmode^\circ\else\textdegree\fi{}. Values or limits were obtained for the lifetimes of 39 levels in $^{41}\mathrm{Ca}$. There is a serious disagreement between some of the lifetime values measured in the present experiment and those reported in a previous work. Accurate excitation energies and the decay scheme were also determined. Information from the lifetimes and decay scheme has been used to make spin assignments or restrictions to a number of levels in $^{41}\mathrm{Ca}$. The electromagnetic transition strengths determined from the present lifetime measurements and a previous measurement of $\ensuremath{\gamma}$-ray angular correlations have been compared to the predictions of two models of the negative parity spectrum of $^{41}\mathrm{Ca}$. In addition, an interpretation of part of the positive parity spectrum has been developed using the strong-coupling model. This calculation includes the effects of the Coriolis term in the Hamiltonian which mixes rotational bands, and the calculated excitation energies, transition rates, and pickup spectroscopic factors have been compared with experiment.

Negative parity states of the cross-conjugate nuclei 47V- 49Cr, 47Ti- 49V in the strong coupling model

Band mixing calculations treating more correctly the j 2 term and hole excitations, have been undertaken on the cross-conjugate nuclei 47V- 49Cr and 47Ti- 49V. There is an overall good agreement between the experimental data and the theoretical predictions. In particular, the states whose configurations arise mainly from the ground state orbit are, in general, quite well reproduced. These include the known high spin states up to I π = 17 2 − .

Electroexcitation of rotational bands in 25Mg

The electric quadrupole and hexadecapole excitations of 25Mg have been investigated by inelastic electron scattering. The measured C2 and C4 form factors are compared with the strong-coupling model; good agreement is obtained.

The level scheme of 137Pr; evidence for prolate nuclear shape

The level scheme of 137Pr was investigated by means of the γ-rays following the β-decay of 137Nd as well as by prompt γ-rays accompanying ( α, xn) reactions. We measured γ-ray single spectra, γγ coincidences (both in-beam and off-beam), angular distributions of prompt γ-rays and conversion electrons. About 100 γ-rays were assigned to the 38 min decay of 137Nd most of which fit into a scheme of 26 deduced levels. From in-beam experiments we tentatively assigned an 11 2 − level which is the basis of a strong cascade of stretched E2 transitions with a probable level sequence of 23 2 − − 19 2 − − 15 2 − − 11 2 −. The interpretation of this cascade in the framework of a strong coupling model indicates a prolate deformation of 137Pr. Another indication for such a deformation was obtained from the very low energy (75 keV) of the first 3 2 + level which could not be interpreted in an intermediate coupling model, but is suggested by a Nilsson scheme.

Gamma-ray spectroscopy in31P: levels below 7.5 MeV (populated in28Si(α,pγ) reaction)

Gamma-ray angular distributions have been measured following the 28Si( alpha ,p gamma )31P reaction using both NaI(Tl) crystals, in coincidence with an annular particle telescope, and GeLi detectors. Lifetimes have been determined using the DSAM and gamma -ray polarizations measured using a 3 GeLi Compton polarimeter. Several new definite spin assignments are given. Many multipole mixing ratios, lifetimes and new branching ratios are reported. An interpretation of the positive parity states is proposed based on the strong coupling and rotation-vibration models. A striking feature in the spectrum of the negative parity states is pointed out which suggests particle-phonon coupling is important. Shell-model calculations based on the MSDI interaction have been extended to include the transition strengths from higher spin positive parity states.

Lifetime measurements and collective behavior inV49

Lifetimes of levels in $^{49}\mathrm{V}$ have been measured using the Doppler-shift attenuation method. States were populated with the $^{46}\mathrm{Ti}(\ensuremath{\alpha},p)^{49}\mathrm{V}$ reaction at a beam energy of 10 MeV. Protons were detected near 180\ifmmode^\circ\else\textdegree\fi{} relative to the beam and most Doppler shifts were measured between $\ensuremath{\gamma}$ spectra accumulated at ${\ensuremath{\theta}}_{\ensuremath{\gamma}}=53 \mathrm{and} 140\ifmmode^\circ\else\textdegree\fi{}$. Values or limits were obtained for the mean lifetimes of 25 levels in $^{49}\mathrm{V}$ from 748 to 2812 keV in excitation energy. The positive parity levels appear to form two rotational bands with ${K}^{\ensuremath{\pi}}={\frac{3}{2}}^{+} \mathrm{and} {\frac{1}{2}}^{+}$. The first 2 MeV of the negative parity level scheme is reproduced rather well with calculations using the strong coupling model. This model also predicts the transition strengths reasonably well. These results suggest strong collective behavior in the states of both parities.NUCLEAR REACTIONS $^{46}\mathrm{Ti}(\ensuremath{\alpha},p\ensuremath{\gamma})$, ${E}_{\ensuremath{\gamma}}=10$ MeV; measured Doppler-shift attenuation. $^{49}\mathrm{V}$ deduced levels, $\ensuremath{\tau}$, $J$, $\ensuremath{\pi}$, $B(\ensuremath{\Lambda})$, branching ratios. Enriched target.

The γ-decay of a [formula omitted] analogue state in 51Mn

A high-accuracy investigation of the γ-decay of the E p = 1059 and 1071 keV resonances in the reaction 50Cr(p, γ) 51Mn has been performed. The E p = 1059 keV resonance is shown to be the analogue state corresponding to the E ∗ = 1899 keV, J π = 3 2 − parent state in 51Cr. From (p, γ) angular distributions, mixing ratios of the primary γ-transitions depopulating this resonance and J π values of many states populated in the γ-decay have been determined. The total γ-width of this 1059 keV resonance is found to be Γ γ = 0.055 eV. The analogue-anti-analogue transition strength is 0.009 W.u. and fits well into our systematics of IAS → AIAS transitions in f-p shell nuclei. The main part of the M1 strength in the γ-decay of the IAS is absorbed in 1 2 − and 3 2 − core polarized states. A comparison of the level scheme of 51Mn obtained from the decay schemes of the (p, γ) resonances with calculations in the Coriolis strong coupling model shows evidence for a g.s. deformation of 51Mn.

New aspects of the rotational model in25Mg

Spin assignments have been made to the25Mg levels in theEx=5–6 MeV region fromγ-ray angular distributions measured in the22Ne(α, n y) reaction atEα=8.0 and 8.8 MeV and fromp-γ angular correlations measured in the24Mg(d, p γ) reaction atEd=6 MeV. Unique spin assignments ofJ=7/2, 5/2, 5/2, and 9/2 could be made to the levels atEx=5005, 5511, 5851, and 5967 keV, respectively. Ambigious assignments have been made to the levels atEx=5245, 5524, 5785, 6032 keV (J=11/2, 7/2), 5455 keVJ=13/2, 9/2), and 5738 keV (J=3/2, 5/2). The present data confirm previous assignments ofJ=1/2 to the levels atEx=5108 and 5466 keV, respectively. Lifetime estimates have been obtained, using the Doppler-shift attenuation method, for the levels atEx=5245 keV (τ=30–60 fs), 5785 keV (τ=50–100 fs), 5967 keV (τ=50–100 fs), and 5455 keV (τ>1ps). All other levels in theEx=5–6 MeV region haveτ<60 fs. A breakdown of theK-selection rule has been observed in theγ-decay of some high spin states, indicating a deviation from the strong coupling model.

Time resolved emission from intermediate strong coupling states in quinoxaline vapor

A frequency doubled, pulsed dye laser is used to excite electronic emission in quinoxaline vapor. The S 1 1 (Π*-n) vibrationless state (excited in the region of 3693 A) has a collision free lifetime of ≤ 50 nsec; statistical limit intersystem crossing occurs. A distinct two component “fluorescence”, with collision free lifetimes as long as ≈ 40 μsec, follows excitation in the S 2 1(Π*-Π) region (2800-3200 A). An intermediate strong coupling model, with extensive S 2-S 1 mixing and weaker singlet - triplet coupling, is proposed to explain experimental observations. The fast “fluorescence” component is interpreted in terms of a sequential decay theory of Tramer et al.

The level structure of 184Os from 184Ir decay and 185Re(p, 2nγ) in-beam spectroscopy

Levels of 184Os populated in the decay of 3.1 h 184Ir and in the 185Re(p, 2nγ) reaction have been investigated. The measurements included γ-ray singles, β + ray endpoint, conversion coefficient, β +- γ coincidence and detailed γ-γ coincidence determinations. The results have established an extensive 184Os level scheme, which includes well developed ground state, γ-vibrational and K = 3 octupole bands and which accommodates all the intense transitions observed in both the radioactivity and in-beam γ-ray measurements. Deviations of the level energies in the K π = 0 +and K π = 2 + bands and of the interband reduced transition probabilities from the predictions of the strong-coupling model are discussed in terms of the rotationvibration interaction, and the systematics of the octupole vibrational excitations in even-mass W and Os nuclei are reviewed. It is concluded that the 184Ir ground state configuration has a spin of 5, and that it contains large admixtures of K = 0 or K = 1 character.

The parity of the 3134 keV,J=1 State in18F

The16O(3He,ϱγ)18F reaction atE(3He)=2.95 MeV was used to study the low-lying states in18F belowE x =3.2 MeV. A combination of γ-ray angular distribution and linear polarization measurements using a single planar Ge(Li) polarimeter resulted in aJ π =1− assignment to the 3134 keV state. In addition, the positive parity assignments to the 937(3+) and 1702(1+) keV states have been verified. Information on branching and mixing ratios as well as on lifetimes are reported. The results are discussed in terms of the weak-coupling and strong-coupling models.

A Study of Levels in 21Ne

A versatile facility for studying nuclear reaction has been built. The 20Ne-(d,pγ)21Ne reaction has been studied using particle-gamma and gamma-gamma coincidence technique. Surface barrier solid state detectors and Ge(Li)-detectors were used together with a multi-dimensional storage of data in a PDP-15 on-line computer. Energies and gamma radiation branching ratios of levels in 21Ne up to 4.7 MeV have been measured. Levels in 21Ne are discussed in terms of modern shell model calculations and the Nilsson strong-coupling model.

A Search for a Missing Jπ=3/2+ level in 21Na

The 20Ne(3He,d)21Na reaction has been studied at 16 MeV bombarding energy. The emitted deuterons have been analysed in a double focusing magnet. Levels in 21Na were deduced. Furthermore the 20Ne(p,γ)21Na reaction has been investigated using a 44 cm3 Ge(Li) detector. Gamma ray branching ratios and life times have been measured at the 1 169, 1 311 and 1 504 keV resonances. The experimental information is discussed in terms of the Nilsson strong-coupling model and recent shell model calculations.

Collective properties of 49Cr

The mean lifetimes of levels below 3 MeV excitation in 49Cr were measured using the reaction 49Ti(α, nγ) 49Cr. The Doppler-shift attenuation method was used in a neutron-gamma coincidence measurement. The lifetime of the first excited state was determined with the recoil distance method. The results are : 272 keV, 19±5 ps; 1085 keV, 260±90 fs; 1563 keV, 590 −120 +300 fs; 1704 keV, > 5.5 ps; 1742 keV, > 4 ps; 1982 keV, > 6.5 ps; 2169 keV, > 4.5 ps; 2433 keV, > 6 ps; 2504 keV, < 12 fs; 2614 keV, 65 ±20 fs. The lifetimes of the second and third excited states in combination with known multipole mixing ratios gave evidence for spin assignments of 9 2 − for the 1085 keV level and 11 2 − for the 1563 keV level. The energies and spins of the four lowest levels as well as the B(M1) and B(E2) values of their γ-decays are in good agreement with calculations based on the strong coupling model and suggest that these levels are strongly collective. Dipole transitions of the higher levels to the ground and first excited states are highly retarded.

Collective States in 151Sm

Inelastic deuteron scattering experiments with a target of 151Sm have been carried out with bombarding energies of 5 MeV and 12 MeV. The scattered deuterons were analyzed with a magnetic spectrograph and B(E2) values for the states populated were extracted from the ratios of inelastic to elastic cross sections. The gamma rays following Coulomb excitation of 151Sm by 50 MeV 35Cl ions were also studied with Ge(Li) detectors. Levels at 65.8 keV, 168.4 keV, and 295.1 keV were populated with B(E2) values of 0.80 e2(barn)2, 0.15 e2(barn)2, and 0.46 e2(barn)2 respectively. If it is assumed that the strong-coupling model is appropriate and that the level at 65.8 keV is the first excited member of a rotational band based on the I = 5/2 ground state, the measured B(E2) value corresponds to a deformation of β = 0.21. It must be noted, however, that the observed states do not satisfy the properties expected for a well-ordered ground-state rotational band.

Rotational structure in 29Si

Abstract Properties of excited states below 5.3 MeV in 29Si have been deduced, from proton-γ angular correlations in inelastic proton scattering, and from γ-ray angular distributions in the 26Mg(α, nγ) reaction. Spins 7 2 , 9 2 , 3 2 , 5 2 , and 7 2 have been assigned to the levels at 4.08 MeV, 4.74 MeV, 4.84 MeV, 4.89 MeV and 5.28 MeV respectively, and previous spin assignments have been confirmed for all other levels below 5.3 MeV. Branching ratios have been measured for all these levels. A number of multipole mixing ratios have been deduced, and have been supplemented by angular correlation data from inelastic α-particle scattering. The results are shown to be consistent with some predictions of the strong-coupling rotational model.

Self-Consistent Strong-Coupling Model of the Nucleon. II

Self-Consistent Strong-Coupling Model of the Nucleon. II