Γ-ray Branching Research Articles

Analogue resonances in 49V and 51V

The E p = 1007, 1013 and 1362 keV resonances in the 48Ti(p, p) 48Ti and 48Ti(p, γ) 49V reactions have been studied. The J π values have been determined as 3 2 −, 3 2 − and 1 2 − , respectively. The first two resonances are believed to form the split analogue of the E x = 1384 keV state in 49Ti. The third is probably the analogue of the E x = 1724 keV state. In the 50Ti(p, p) 50Ti and 50Ti(p, γ) 51V reactions the E p = 1366, 1371 and 1377 keV resonances have been investigated. The J π values are determined as 3 2 − for all three resonances. These resonances form the split analogue of the 51Ti ground state. The strengths and γ-ray branching ratios of all above mentioned resonances have been studied. Excitation energies of some low-lying levels are also given. The results are compared with those of other similar investigations and with theoretical predictions.

Study of the 207Pb(d, p) 208Pb reaction

Excitation energies and γ-ray branching ratios are obtained for 208Pb levels below 7.5 MeV. These data combined with known spectroscopic factors and radiation widths give information on level assignments and correlations of E1 radiation and neutron strengths.

Gamma-ray transitions in 29P

A study was made at the 1.381 MeV resonance of the 28Si(p, γ) 29 P reaction. Lifetimes of the resonance level and of the first and second excited states in 29P were determined with the Doppler shift attenuation method, to be 0.013 +0.006 −0.003, 0.24 +0.11 −0.06 and 0.39 +0.19 −0.10ps, respectively. Accurate energies were determined for the four γ-rays seen at this resonance and for the three energy levels involved. Angular distribution measurements yielded an unambiguous spin assignment of 7 2 for the resonance level, and the γ-ray branching ratio of this level was obtained.

Properties of low-lying 53Mn levels from the 52Cr(p, γ) 53Mn reaction; decay of the [formula omitted] analogue state

The 52Cr(p, γ) 53Mn reaction has been used to obtain excitation energies, γ-ray branching ratios, amplitude mixing ratios, spins, parities and mean lives of 53Mn levels up to 3.5 MeV. The E p = 1006 keV resonance is probably the analogue of the E x = 0.56 MeV, J π = 1 2 − level in 53Cr. Its strength, spin and γ-ray branching have been determined.

A study of the excited states of 28Si by means of the 27Al(p, γ) 28Si reaction in the energy range Ep = 1.01–2.00 MeV

The γ-decay of 35 resonances of the reaction 27Al(p, γ) 28Si was studied in the energy range E p = 1.01–2.00 MeV by means of a 10cm 3 Ge(Li) detector. The proton energies of 20 resonances as well as the energies of 11 bound levels were determined to an accuracy varying between 0.8 and 3 keV. Gamma-ray branching ratios of resonant and bound states were determined. The spins of a number of resonant and bound levels were derived from the γ-ray branching ratios. Mean lifetimes of 5 bound levels were determined from γ-ray Doppler shift measurements.

Angular correlation analysis of the 58Ni(p, p′γ) reaction

Energy averaged angular distributions have been measured for 58Ni(p, p'γ) radiations at E p = 6.52 and 6.92 MeV for states up to 4.1 MeV excitation, using a Ge(Li)-NaI(Tl) coincidence-anticoincidence spectrometer. In order to obtain spin assignments and γ-ray multipolarities, the data were analysed in terms of χ 2 fits to predictions of statistical reaction theory. The present results, together with other recent measurements, lead to best energies and J π values for 58Ni levels: namely 1454.0±0.1 keV 2 1 +, 2459.1 ±0.34 1 +, 2775.2±0.22 2 +, 2901.8 ±0.2 1 1, 2942.4±0.20 2 +, 3037.6±0.32 3 +, 3263.4±0.22 4 +, 3420.3±0.33 1 (+), 3530.9±0.3, 3593.4±0.3 1 2 (+), 3620.0±0.44 2 +, 3774.4±0.43 2 (+), 3898.3±0.32 5 +, and 4107.7±0.3 2 6 (+). The previously accepted 4 + assignment for the 3530.9 keV level has been ruled out. Available information concerning the γ-ray branches, multipolarities and transition rates is discussed. Outstanding discrepancies with shell-model predictions for energy spectra and transition rates are pointed out, particularly with regard to the energies of the 1 1 and 1 2 levels and the puzzling γ-ray decay properties of the 0 + 2 state.

Anomalous [formula omitted] and [formula omitted] states in 99Rh from the decay of 21 min 99Pd

Levels in 99Rh populated in the decay of 21 min 99Pd were investigated. From singles γ-ray energy and intensity measurements employing high-resolution and efficiency Ge(Li) detectors, from coincidence relationships established from γ-γ coincidence experiments employing two Ge(Li) detectors and from β +-γ coincidence experiments employing a plastic scintillator and a Ge(Li) detector, it was found that levels at 64.6, 200.6, 427.3, 464.3, 851.1, 874.4, 1018.3, 1111.2, 1167.4, 1366.5, 1527.4, 1535.9, 1761.2, 1814.8, 1969.2, 2040.3, 2051.9, 2070.6, 2143.7, 2181.3, 2199.2, 2268.0, 2343.3, 2388.8, 2709.3, 2737.4, 2758.9 and 2835.4 keV are populated in the decay of 22 min 99Pd. Possible levels at 2618.1, 2639.4, 2860.3, 2957.4 and 3047.0 keV are suggested on the basis of energy sums. The fraction of decay of 99Pd to the 16 d 99Rh ground state was determined in milking experiments to be 0.02 ± 0.01 and from the proposed decay scheme, which gives 0.029 ± 0.002. From singles positon spectra and from β +-γ coincidence measurements, the Q EC value for 99Pd decay was determined to be 3405 ± 20 keV. The half-life of 99Pd was measured to be 21.4 ± 0.2 min. From log ft values obtained and from γ-ray branching information, limits for the J π values of many levels in 99Rh were placed. The level structure of the “anomalous” 5 2 + and 7 2 + states in 99Rh is compared with similar levels in other odd-mass Rh isotopes and with recent calculations on the pairing-plus-quadrupole model.

A study of levels in 25Mg by the 24Mg(d, pγ) 25Mg and 25Mg(p, p' γ) 25Mg reactions

Angular correlation studies of the 24Mg(d, pγ) 25Mg reaction at E d = 3.95 MeV have been carried out using Method II of Litherland and Ferguson. The deduced spins of the 2.801, 3.970 and 4.353 MeVlevels are 3 2 , 7 2 and 3 2 respectively. The spins and parities of the 4.277, 5.005, 5.108 and 5.742 MeV levels are shown to be ( 1 2 , 3 2 ) −, ( 3 2 , 5 2 7 2 ), ( 1 2 , 3 2 and ( 5 2 , 7 2 ), respectively; the γ-decay suggests j π(5.245) = 9 2 − or 11 2 + . The γ-ray branching ratios have been measured for 15 levels in 25Mg ranging in excitation from 1.61 to 6.43 MeV and the mixing ratios have been determined for some transitions. A study of the decay of the 2.738 MeV level using the 25Mg(p, p' γ) 25Mg reaction yielded probable E2/M1 mixing ratios of −0.47 +0.12 −0.20 and 2.9 ± 0.5 for the 2.738 → 1.960 and 2.738 → 0 MeV transitions respectively.

The 23Na(α,γ)27Al reaction. A survey of the reaction and some properties of the 27Al nucleus

The 23Na(α,γ) reaction has been studied in the region Eα = 2–3 MeV. The γ-ray spectra from a total of 16 resonances have been surveyed using a 40 cm3 Ge(Li) detector. Excitation energies, γ-ray decay modes, branching ratios, and γ-ray yields of these resonances are given. Below Eα = 2.7 MeV, all resonances have [Formula: see text] and the α-particle capture proceeds with [Formula: see text]. The resonances at Eα = 2.696 and 2.797 MeV have strong branches to the Jπ = 11/2+ state in 27Al at 4.509 MeV excitation energy. A measurement of γ-ray angular distributions at these resonances yields Jπ(2.969 res.) = 9/2+, 11/2 and Jπ(2.797 res.) = 9/2+ for the resonances, and Jπ(5.671) = 9/2+, 7/2 and Jπ(4.580) = 9/2+, 7/2 for bound states in 27Al. Investigation of this latter level at the Ep = 2.114 MeV resonance in the 26Mg(p,γ)27Al reaction restricts the spin to 7/2. New excited states in 27Al were found at Ex = 5.504, 5.671, and 7.815 MeV. A state at Ex = 5.499 MeV was confirmed.

Isobaric analogue states of 10Be- 10B

A study has been made of the 5.96 and 6.26 MeV levels of 10Be. Electromagnetic transitions following the 9Be(d,p) 10Be reaction were examined. Spectra in coincidence with the proton groups were analysed to determine γ-ray branching ratios. The result of a γ-γ correlation measurement upon the cascade γ-rays from both states was consistent with J = 2 for both states. The correlation observed for the decay of the 5.96 MeV states is not consistent with that of a 1 − state. However, it is suggested that a 1 −−2 + doublet exists at 5.96 MeV in 10Be with the J = 2 member decaying predominately by cascade through the 3.37 MeV state; and the J = 1 member decaying predominately by a direct ground state transition. Experimental confirmation of the doublet structure at 5.96 MeV was obtained and a level separation of 1.6±0.5 keV determined with the 2 + level being lower in excitation. Proton angular distributions at 2.8 MeV deuteron energy were determined for the individual members of the doublet to establish the parities of the states. Spectroscopic factors and reduced widths for the individual members of the doublet were extracted from plane-wave and distorted-wave analyses of the angular distributions.

High-resolution Ge(Li) study of the decay of 129gTe and 128mTe

The decay of 129mTe and 129gTe to levels in 129I has been studied using Ge(Li) detectors for high-resolution γ-ray spectroscopy with some supporting data from NaI(Tl) detectors in coincidence. A total of 46 gamma rays is accounted for by 16 excited states (one tentative) in 129I up to 1401.6 keV. These include ten new gamma rays not previously reported, a new level in 129I at 1282.1 keV ( 5 2 + ) and a probable new level at 1204.2 keV ( 3 2 +, 5 2 + ) (values of J π in parentheses). The decay scheme was arrived at primarily on the basis of precise γ-ray energy determinations (to ±50 eV in many cases and never worse than ±200 eV). Beta-decay log ƒt values were determined from our γ-ray intensity balances coupled with published β-branchings. Most-probable spins and parities were deduced based on the γ-ray branching, the log ƒt value and published angular correlations of other workers. The J π = 1 2 + state predicted by Kisslinger and Sorensen in the region of 200 eV and observed in 125I and 127I is not seen; we find log ƒt ≧10.6 for the allowed β-decay from 129gTe to such a level. We likewise find no evidence for the 11 2 − state at ≈ 930 keV as predicted by Kisslinger and Sorensen; the allowed β-decay to this state would have log ƒt ≧ 11.0.

Shell-model calculations on A = 38 nuclei

The shell model is used to investigate properties of levels in the A = 38 nuclei. An inert 28Si core with a residual two-particle interaction between the outer nucleons is assumed. The negative parity states are described by a closed 2 s 1 2 shell, five nucleons in the 1 d 3 2 shell and one nucleon in the 1 f 7 2 or 2 p 3 2 shell. For the positive parity states, all configurations in the 2 s case1 2 and 1 d 3 2 shell are taken into account. The effective two-particle interaction is chosen to be a modified surface delta interaction. The four parameters of this effective interaction are determined in a least-squares fit to the excitation energies of 15 nuclear levels. The rms deviation of the calculated energies from the experimental energies is 0.28 MeV. From the values of these parameters, the energies and wave functions of about 50 levels are derived. The wave functions are used to determine γ-ray branching ratios, mean lives, ƒt values in allowed β-decay and spectroscopic factors for the 37Cl(d, p) 38Cl reaction. The computed branching ratios, mean lives and ƒt values agree generally within a factor of 2.5 with the experimental values. Good agreement with experiment is obtained for the spectroscopic factors.

Energy levels in 72Ge from the decays of 72Ga and 72As

The γ-ray decay scheme and nuclear energy levels in 72Ge have been studied from the decays of 72Ga and 72As using a high-resolution 7 cm 3 Ge(Li) detector as the central detector in a Compton suppression spectrometer and using NaI(Tl)-Ge(Li) coincidence data. A discussion of all experimental variables encountered in reducing the Ge(Li) detector data is included. Careful hand and computer analyses determined as accurately as possible the energies and intensities of 122 separate γ-ray transitions; 85 of them observed in 72Ga and 85 in 72As. Of the total number of γ-rays observed, 106 have been placed in a proposed level scheme containing 32 levels. These include 20 new levels, six of which are tentative. The end-point energies of the various β-transitions, their branching ratios and log ft values are deduced from the γ-ray branching ratios.

Decay of 13.5 h 109gPd to levels of 109Ag

The β- and γ-decay of the 13.5 h 109gPd to levels of 109Ag has been studied with the use of Ge(Li) detectors, NaI(Tl) crystals and coincidence equipment. The energies (in keV) and relative intensities of γ-rays observed are: 45(3.6), 88(8900), 104(2.2), 135(3.2), 146(2.7), 311(100), 391(2.5), 413.5(26), 415.2(23), 425(1.8), 448(2.6), 551(1.5), 558(6.2), 602(21.5), 636(27), 647 (65), 702(9.2), 707(4.5), 737(5) and 782(33). Excited states in 109Ag were observed at 88 (41 sec 109Ag), 133, 311, 415.2, 702, 724, 736, 840, 863 and 870 keV. Spin and parity assignments for most of the levels were made on the bases of log ft values and γ-ray branching ratios along with data on Coulomb excitation from previous workers. The levels at 0, 311, 415.2, 702 and 863 keV have negative parity and have previously been observed in Coulomb excitation studies. The positive-parity levels at 133 keV has high spin and is apparently the g 9 2 single-quasi-particle level. The negative-parity levels of the odd-mass silver isotopes are understandable in terms of phonons coupled with the p 1 2 single-quasi-particle. However, properties of the positive-parity levels, particularly the low-lying 7 2 + level are not well explained by current nuclear models.

Decay of 9.6 d 125Sn to levels of 125Sb

The decay scheme of 9.62 d 125gSn has been investigated using NaI(Tl) and Ge(Li) detectors in conjunction with a 4096-channel multi-parameter pulse-height analyser system. Previously unreported γ-rays have been observed at 283, 652.6, 1087.4 and 1164.3 keV. Coincidence evidence indicates the presence of a new level at 2253.1 keV as well as a significant γ-ray branching to the 5 2 + level at 332.0 keV. The β-branching to the ground state has been redetermined to be 82.5±5% and new log ft values calculated. The pattern of levels is found to correspond closely with that predicted by the calculations of Kisslinger and Sorensen.

Weakly excited resonance levels in the 13C(p, γ) 14N reaction

Three midget resonances in the 13C(p, γ) 14N reaction were observed at E p = 1012±2 keV, 1523±2 keV and 1701±1 keV corresponding to 14N excitation energies of 8.489, 8.963 and 9.129 MeV, respectively. The 8.489 MeV state decays by γ-ray emission predominantly to the 5.10 MeV state with an angular distribution, W( θ) = 1 + (0.59 ± 0.06) P 2 (cos θ) − (0.46 ± 0.10) P 4 (cos θ). This angular distribution together with the observed γ-ray width ( ωΓ γ ≊ 0.01 eV ) and branching ratios determine that J π = 4 −, T = 0 for this level. The 8.963 MeV level decays by γ-ray emission at least two-thirds to the 6.44 MeV state. This fact and the small transition rate ( ωΓ γ ≊ 0.003 eV ) identify the level as 5 +. The only observed transition ( ≧80%) from the 9.129 MeV level is to the ground state ( ωΓ γ ≊ 0.03 eV ) with an angular distribution, W( θ) = 1 + (0.22 ± 0.09) P 2 (cos θ). These data establish J π = 2 −, T = 0 for this level. Arguments are given for shell-model assignments to these levels.

Relative transition strengths for levels of C 11

A measurement of the γ-ray branching of the levels at 6.35, 6.90 and 7.50 MeV in C 11 is described. The states of C 11 were populated by the reaction Be 9(He 3,n)C 11∗ and the resulting de-excitation γ-rays studied. Time-of-flight techniques were used to select neutron groups leading to the states in question, and γ-ray spectra were recorded in coincidence with each individual group. The spectra were analysed to determine the dominant branches present and the following results were obtained: 6.35 → 0 (65±5%), 6.35 → 2.00(35±5%), 6.90 → 0(89±3%), 6.90 → 4.32 (11±3%), 7.50 → 0 (25±5%) and 7.5 → 2.00 (75±5%). Based upon the similarity of branching, it appears likely that these states in C 11 correspond to analogue states in B 11 at energies of 6.81, 7.30 and 7.99 MeV, respectively, for which similar branching ratios have been observed. The observed γ-ray branching is consistent with J π(6.35 MeV= 1 2 ±, 3 2 ± or 5 2 −, J π(6.90 MeV) = 3 2 ±, or 5 2 ± or 7 2 − and J π(7.50 MeV) = 1 2 ± or 3 2 ± . A comparison with the analogue states in B 11 lends support for J π(6.35 MeV)= 3 2 +, J π(6.90 MeV) = 5 2 + and J π (7.50 MeV) = 1 2 + or 3 2 + . The decay of the 7.50 MeV state is shown to indicate a nucleon configuration of (1 p 1 2 ) 5(1 p 1 2 )(1 d 5 2 ) and is also discussed in terms of a possible Be 7+α cluster configuration.

Some recent research with the liverpool tandem van de graaff

Abstract Two experiments recently completed with the Liverpool EN tandem will be described. 1. 1. Measurements have been made on the d, p reactions on the chromium isotopes over a range of energies using surface barrier counters. Scattering experiments have been made on the same targets and the results analyzed by optical model and D.W.B.A. 2. 2. Triple γ-ray correlations and γ-ray branching ratios have been measured for nuclei in the f 7 2 shell to extend the nuclear data in this region for comparison with shell model calculations.

Gamma radiations from excited states of N 16

A magnetic-lens type beta-ray spectrometer has been used to study the radiations from the reaction N 15(d, p) N 16. Targets of CrN 15 were made by induction-heating chromium foils to 1300°C in a N 15-enriched gas atmosphere. Photoelectron spectra of γ-rays K-converted in Cd and Au radiators yielded γ-ray energies of 397.3±1.0, 296.2±1.0, 275.9±1.0, 120.1±0.5, and 100±3 keV. Excited levels of N 16 at 397.3±1.0, 296.2±1.0 and 120.1±0.5 keV are inferred from the γ-ray energies. The K internal conversion coefficient of the 120 keV first-excited to ground state transition of N 16 has been measured by the “external-internal” conversion method to be 7.23(1±0.20)×10 −3. This value shows the 120 keV transition to be E2 which is consistent with the previously indicated spin and parity assignments of 2 − and 0 − for the ground level and first-excited level, respectively. The relative γ-ray branching of individual levels was also measured.

E2 transitions from the second 2+ level of even-even nuclei

A survey has been made of available data for the γ-ray branching of the second 2+ level of over 50 even nuclei with A > 30, together with data for the E2-M1 mixing of the (2′ → 2) cascade transition. In addition, presently available data for the Coulomb excitation cross sections for the second 2+ level of some 24 even nuclei have been collected. From these data, three ratios of reduced E2 transition probabilities have been calculated, and compared with the predictions of various theories. The comparisons indicate that by far the most successful theory to date for predicting such ratios is the recent asymmetric rotor model of Davydov and Filippov, Perhaps the most striking success of this theory is the prediction for the ratio B(E2; 2′ → 0)/ B(E2; 2 → 0) as a function of the energy ratio E 2(2+)/ E 1(2+). However, there are some experimental results which remain unexplained, particularly for the ratio B(E2; 2′ → 2)/ B(E2; 2′ → 0).