Unambiguous Spin Research Articles

Precise excitation energy and γ-ray decay of the lowest T = 2 state in 40K

The excitation energy of the lowest T = 2 state in 40K has been determined as E x = 4384.0 ± 0.3 keV from n-γ and γ-γ coincidence experiments. The state was populated with the 4Ar(p,n) 40K reaction at E p = 8.30 MeV. Gamma-gamma angular correlation measurements yield unambiguous spin assignments J = 0 and 1 for the 1.64 and 2.290 MeV states, respectively. The excitation energy of the T = 2, J π = 0 + state leads to a calculated mass excess of −9120 ± 150 keV for 40Ti.

Spectroscopy of states in 33S by means of neutron-gamma angular correlation measurements

Levels of 33S for E x < 5 MeV have been studied with the 30Si(α, nγ) 33S reaction at bombarding energies of E α = 7.5 and 10.2 MeV. Neutron-gamma angular correlation experiments lead to three unambiguous spin and parity assignments: J π(3.83) = 5 2 +, J π(4.048) = 9 2 + and J π(4.09) = 7 2 + . The measured branching and mixing ratios yield transition strengths for dipole and quadrupole transitions.

The reaction 35Cl(n,γ) 36Cl studied with non-polarized and polarized thermal neutrons

The γ-radiation following capture of non-polarized and polarized thermal neutrons in 35Cl has been investigated. Of the 420 γ-rays ascribed to the 35Cl(n,γ) 36Cl reaction, 236 have been placed in a 36Cl decay scheme. The branching ratios and the excitation energies (with 0.04–0.9 keV errors) of 72 bound states have been determined. Unambiguous spin assignments are given for 11 levels. The multipole mixing ratios for some primary γ-ray transitions have been determined. There exists a significant correlation between (d, p) stripping strengths and (n, γ) reduced primary transition probabilities for transitions to l n(d, p) = 0 levels.

Spectroscopy of 32P (II)

Spins, parities and transition probabilities of levels in 32P at E x > 3.5 MeV have been determined with the 29Si(α, pγ) 32P reaction at bombarding energies of E α = 12.80, 12.93 and 16.30 MeV. Proton-gamma angular correlation experiments and DSA lifetime measurements lead to six unambiguous spin assignments and to many spin limitations. The measured mixing and branching ratios yield many transition strengths for dipole and electric quadrupole transitions. Five, sofar unknown, energy levels are reported. A doublet at 4.03 MeV excitation energy and a high-spin state ( E x = 4.27 MeV; J π = 5 −) were observed. Shell-model predictions have been compared to the present experimental results.

Vector analyzing power and cross section for the reactions [formula omitted

Angular distributions of vector analyzing power and cross section for the reactions 40Ar(d, p)41Ar and40Ar(d, t)39Ar have been measured at an incident deuteron energy of 14.83 MeV. The bound-state data in the (d, p) reaction and the (d, t) data are compared to DWBA calculations. The data for the neutron-unbound states are analyzed in the framework of the DWBA using (i) a form factor for weakly bound neutron and (ii) a resonance form factor, following the approach of Vincent and Fortune. The j-dependence of the (d, p) vector analyzing power permits definitive spin-parity assignments to be made for 19 neutron-bound and 4 neutron-unbound states in 41Ar with excitation energy up to 6.57 MeV. Tentative Jπ assignments have been made for 3 states. The l-value for the 5.62 MeV state has been determined. Data for the observed unbound states are found to be equally well reproduced by the type (i) calculations as by the type (ii) calculations. The (d, t) vector analyzing power data show definite j-dependence although not as strongly as in the (d, p) reaction. For relatively weakly excited states a pre-knowledge of the l-value of the transition is desirable for an unambiguous spin assignment. In general, the j-dependence in the (d, t) vector analyzing power can be utilized for definitive Jπ assignments. On this basis, Jπ values have been assigned for seven states in 39Ar with excitation energies up to 4.47 MeV excitation. Possible spin values for three other states are suggested. Spectroscopic factors for the states in 41Ar and 39Ar have been extracted and are in fair agreement with those obtained by other workers.

High spin states in39K

The reaction 36Ar( alpha , p gamma )39K has been used to measure angular distributions, linear polarizations, mixing ratios, branching ratios and mean lifetimes for a number of high spin states in 39K. The results give the following unambiguous spin and parity assignments: ExJpi ; 2814 keV 7/2-; 3597 keV 9/2-; 3944 keV 11/2-; 5718 keV 9/2- and 6475 keV 11/2+. Using a solid 36Ar target and the Doppler shift attenuation method a mean lifetime of 250+or-65 fs has been measured for the 5718 keV level. There are several discrepancies between the present results and the results of previous work, particularly the heavy ion data published by the Brookhaven group.

Nuclear orientation and angular correlation studies of gamma transitions in151Sm from the decay of151Pm

The levels and gamma ray transitions in 151Sm have been investigated using the two complementary techniques of directional correlation, and the directional distribution of radiation emitted by an oriented source. The orientation was produced using the hyperfine field in ferromagnetic gadolinium to polarize an ensemble of 151Pm nuclei at a temperature of 11 mK. The resultant directional distribution of the gamma rays was measured using high resolution Ge detectors. The correlation measurements used an intrinsic Ge detector in combination with a Ge(Li) detector. These two types of result enabled multipole mixing ratios to be determined for 34 gamma transitions in the decay, and unambiguous spin assignments to be made for the levels connected by these transitions. This latter information in particular should make it easier to decide whether this nucleus can be described in terms of Nilsson single particle states.

Nuclear orientation and angular correlation studies of gamma ray cascades in155Gd populated by the decay of155Tb

The low-lying positive-parity levels in 155Gd have been investigated using the two complementary techniques of directional correlation and directional distribution of radiation emitted by an oriented source. The orientation was produced using the hyperfine field in ferromagnetic gadolinium to polarize an ensemble of 155Tb nuclei at temperatures below 10 mK. The resultant directional distribution of gamma rays depopulating levels below 488 keV was measured using higher resolution Ge detectors. The correlation measurements used a NaI(Tl) or an intrinsic Ge detector in combination with a Ge(Li) detector. Most of the cascades investigated contained either the 86 or 105 keV E1 transition to the ground state. Thus the gamma ray of interest was the first member of the cascade in the coincidence measurement. In the case of the nuclear orientation measurements, the gamma ray was the second member of the cascade. This effective reversal of temporal order produces two unique values for the coefficient describing the transition, which in this case, is almost always an E2/M1 admixture. Comparison of the two coefficients for a given gamma ray often enables unambiguous spin assignments to be made. In addition, the mixing ratios involved can be deduced. The decay scheme is discussed and experimental results are compared with the band mixing calculations of Lovhoiden et al. (1970).

Identification and lifetime determination of the6+member of the ground-state rotational band inNe22

The $^{19}\mathrm{F}(\ensuremath{\alpha},p\ensuremath{\gamma})^{22}\mathrm{Ne}$ reaction was used to measure $p\ensuremath{-}\ensuremath{\gamma}$ angular correlations for the 6.31 and 6.34 MeV states in $^{22}\mathrm{Ne}$. The mean lifetimes of the two levels were determined to be 78 \ifmmode\pm\else\textpm\fi{} 15 fs (6.31 MeV) and ${24}_{\ensuremath{-}17}^{+15}$ fs (6.34 MeV) using the same reaction and the Doppler-shift attenuation method. Unambiguous spin and parity assignments of ${6}^{+}$ and ${4}^{+}$ were obtained for the 6.31 and 6.34 MeV states, respectively. An earlier identification of the 6.34 MeV state as the ${6}^{+}$ member of the ground state rotational band is therefore incorrect. The $B(E2)$ value of the 6.31 MeV (${6}^{+}$) \ensuremath{\rightarrow} 3.36 MeV (${4}^{+}$) transition is in good agreement with recent large-basis shell model calculations, and the 6.31 MeV state may be identified as the ${6}^{+}$ member of the ground state rotational band of $^{22}\mathrm{Ne}$.NUCLEAR REACTIONS $^{19}\mathrm{F}(\ensuremath{\alpha},p\ensuremath{\gamma})$, ${E}_{\ensuremath{\alpha}}=12.0, 15.15$ MeV; measured $p\ensuremath{-}\ensuremath{\gamma}$ angular correlations, Doppler-shift attenuation. $^{22}\mathrm{Ne}$ deduced levels, $\ensuremath{\tau}$, $J$, $\ensuremath{\pi}$, $B (\ensuremath{\Lambda})$.

Spin assignments in 63Ni through [formula omitted

Angular distributions of vector analyzing power have been measured for the reaction 62 Ni( d, p ) 63 Ni at a beam energy of 10 MeV. The observed j-dependence of vector analyzing power allows unambiguous spin assignments to be made for the following states in 63Ni (excitation energies in MeV): 0, 1 2 − ; 0.087, 5 2 − ; 0.155, 3 2 − ; 0.515, 3 2 − ; 1.003, 1 2 − ; 2.297, 5 2 + ; 2.700, 1 2 − ; 2.953, 1 2 + ; 3.292, 5 2 + ; 3.932, 5 2 + ; 3.951, 5 2 + ; 4.387, 5 2 + . An assignment of 9 2 + is suggested for the state at 2.519 MeV. The data for the unresolved l n = 4, 1 doublet (1.294, 1.327) MeV indicate the 3 2 − spin assignment for the 1.327 MeV state. The main features for all the data are in agreement with DWBA calculations.

The 57Fe(n, γ)58Fe reaction

The circular polarization of γ-rays from the capture of polarized thermal neutrons in an isotopically enriched target of 57Fe has been measured. The analysis of 19 primary transitions resulted in unambiguous spin assignments for 14 bound states of 58Fe. For five of these, at Ex = 4.02, 4.14, 4.32, 4.36 and 4.44 MeV, all with Jπ = 1+, no spin assignments have been reported previously. The γ-ray energies and intensities of these transitions have been measured. The 57Fe(n, γ) reaction Q-value was determined to be 10044.6 ± 1.0 keV. A significant correlation between the (d, p) strength and the (n, γ) reduced transition strength has been found for p-bound states with Ex = 0–5 MeV.

Spin assignments in 61Ni from the 60Ni( [formula omitted], p) 61Ni reaction

Angular distributions of vector analyzing power and differential cross sections were measured for the 60Ni(d, p) 61Ni reaction at a deuteron energy of 10 MeV. The observed j- dependence of the vector analyzing power allowed unambiguous spin assignments for the fol- lowing states in 61Ni (excitation energies in MeV): 0.0, 3 2 − ; 0.068, 5 2 − ; 0.284, 1 2 − ; 1.186, 3 2 − ; 2.701, 5 2 + . A definitive assignment of 1 2 − is made to that member of an unresolved doublet at 2.123 MeV which proceeds by l n = 1 transfer. An assignment of 9 2 + is indicated for the member of the doublet which proceeds by l n = 4 transfer. Most of the data are well reproduced by DWBA calculations employing available deuteron and proton optical model parameters. The behavior of the vector analyzing power for the two low lying 61Ni states formed by l n = 1 transfer was measured for angles from 2.5° to 15° using a magnetic spectrograph and found to be in agreement with DWBA predictions.

Spectroscopy of 32P

Particle-gamma angular correlations have been measured with the 29Si(α,pγ) 32P reaction at bombarding energies E α = 10.65, 10.69 and 11.00 MeV. Together with DSA lifetime measurements these experiments lead to seven unambiguous spin assignments to levels below 3.5 MeV excitation energy in 32P. In addition, the measured mixing ratios and branching ratios yield many dipole and quadrupole transition strengths. The previously known 3.44 MeV level is a doublet with components at 3 443.0±0.6 and 3 444.0±0.9 keV.

Spin assignments in 59Ni from the [formula omitted] reaction

Angular distributions of the vector analyzing power and the absolute cross section were measured for the 58Ni(d, p) 59Ni reaction at a deuteron energy of 10 MeV. The observed j-dependence of the vector analyzing power allowed unambiguous spin assignments for the following states in 59Ni with excitation energies in MeV: 0.0, 3 2 −; 0.341, 5 2 − ; 0.465, 1 2 −; 0.879, 3 2 − ; 1.303, 1 2 −; 1.686, 5 2 −; 3.454, 3 2 −; 3.858, 3 2 −; 4.495, 5 2 + . The data are well reproduced by DWBA calculations employing deuteron and proton optical model parameters obtained from analyses of elastic scattering cross sections and polarizations. A tentative spin assignment of 9 2 + is made for the level at 3.061 MeV. A 5 2 + assignment to the level at 3.538 MeV is suggested on the basis of the empirical behavior of the j-dependence of the vector analyzing power for l = 2 transitions. Measurements of the vector analyzing power for the four low-lying 59Ni states formed by l = 1 transfer were made for angles from 2.5° to 15° using a magnetic spectrograph. A very strong j-dependence was observed for these far-forward-angle measurements in agreement with DWBA predictions.

Concerning high-spin negative parity states in 20Ne

Unambiguous spin and parity assignment have been made from angular correlation measurements to states in 20Ne at 15.18 MeV (6 +) and 17.40 MeV (9 −). Our results are in disagreement with an earlier 9 − assignment to the 15.18 MeV state. The 17.40 MeV state is assigned to the K = 2 − rotational band based on the 2 − state at 4.97 meV.

Vector analysing power and cross section for 90Zr( [formula omitted], p) 91Zr at 11 and 12 MeV

Angular distributions of the vector analysing power and the cross section were measured for 90Zr( d , p) 91Zr. Measurements were made on two transitions at a deuteron energy of 11 MeV and on 20 transitions at 12 MeV. The observed j-dependence of the vector analysing power provided unambiguous spin assignments for most final states. Measurements of the cross section and vector analysing power were also made for deuteron elastic scattering at 11 MeV in order to determine the potential parameters for DWBA calculations. The DWBA predictions are in good agreement with the measured (d, p) cross sections and in qualitative agreement with the analysing powers. Enriched targets.

Vector analysing power and cross section for (d, p) reactions on 40Ca, 46Ti, 48Ti, 50Ti, 52Cr and 54Fe

Angular distributions of the vector analysing power and the absolute cross section were measured for (d, p) reactions on 40Ca, 46Ti, 48Ti, 50Ti, 52Cr and 54Fe at deuteron energies of 10 or 11 MeV. The observed j-dependence of the vector analysing power allowed unambiguous spin assignments for about 15 states in each residual nucleus. Distorted-wave Born approximation calculations employing deuteron and proton optical-model parameters obtained from analyses of elastic cross sections and polarizations qualitatively reproduce the measured angular distributions. The energies of the 2p 3 2 , 2p 1 2 , if 7 2 and If 5 2 neutron si in the residual nuclei were determined. The strength of the nuclear spin-orbit interaction calculated from the splitting of the p-states is in good agreement with the strength obtained from analyses of nucleon-nucleus elastic scattering.

Lifetime and angular-correlation measurements in 47Ti

Mean lifetimes of levels below 2.42 MeV in 47Ti were determined with the 47Ti(p, p′γ) 47Ti reaction using the Doppler-shift attenuation method. The results are: 1253 keV, 210±20 fs; 1445 keV, 1.5 −0.3 +0.5 ps; 1550 keV, 2.25 −0.50 +0.50 ps;1795 keV, > 2 ps; 1825 keV, > 2 ps; 2164 keV, 31±8 fs; 2168 keV, 25±6 fs; 2260 keV, 1.2 −0.3 +0.5 ps; 2297 keV, 11±7 fs; 2365 keV, > 1.5 ps; 2408 keV, 31 −10 +13 fs; 2416 keV; > 2 ps. The 48Ti(τ, αγ) 47Ti reaction was used to measure α-γ angular correlations. Decay modes, branching ratios and multipole mixing ratios were determined. Unambiguous spin assignments were obtained for the 1253 keV level ( 9 2 − ) and the 1445 keV level ( 11 2 − )and the number of possible spin values was restricted for some of the higher levels. The energies and spins of the four lowest levels as well as the B( M1) and B( E2) values of their γ-decay are generally in good agreement with calculations based on the rotational model and suggest that these levels are strongly collective.

The spectroscopy of 54Fe via the reaction 54Fe(p, p'γ) 54Fe at 10 MeV

In the 54Fe(p, p'γ) 54Fe reaction at 10 MeV, angular correlations of gamma rays coincident with protons detected near 180°, have been measured. From an analysis of the angular correlations, unambiguous spin assignments have been made for the 3.345(3), 4.074(3), 4.579(2), 4.781(3), and 4.949(4) MeV states. Model-dependent spin assignments have been made for several other states. The angular correlation analysis also yielded multipole mixing ratios for many transitions and branching ratios for the decay of all states of 54Fe below 5 MeV. From the same data, an analysis of the Doppler shifts of the coincident gamma rays allowed determination of the lifetimes of the 1.409, 2.959, 3.164, 3.836, 4.048, 4.074, 4.265, 4.287, 4.781 and 4.949 MeV states. Utilizing all the measured quantities, estimates have been of the strengths of 20 E2, 9 M1, and 4 E1 transitions. To aid in understanding the nature of the observed levels, the po- sitions of various np- mh states have been estimated using a monopole residual interaction. It is found that 2p-4h states as well as lp-3h states may occur at low excitation energies. The 2.540 MeV (O 2 +) state is probably of the configuration 2p-4h. The decay properties of all states below 3.5 MeV are compared to the predictions of theoretical calculations in which lp-3h proton ( 2 p 3 2 and 1 f 5 2 ) excitations were considered.

The 57Fe(t, p) 59Fe and 58Fe(d, p) 59Fe reactions

The level structure of 59Fe has been investigated using the (d, p) and (t, p) reactions at incident energies of 10 MeV and 12 MeV respectively. Unambiguous spin assignments are made for many levels from a comparison of the angular-momentum transfer of the two reactions. It is shown that the experimental data provide strong support for the existence in 59Fe of a rotational band structure.