Gamma-ray Branching Ratios Research Articles

In-beam study of prompt γ-rays emitted in the 66Zn(p, nγ) 66Ga reaction

The level structure of the nucleus 66Ga has been studied by means of the 66Zn(p, nγ) 66Ga reaction ( Q = −5.957 MeV). Levels in 66Ga up to 730 keV in excitation were selectively populated by varying the proton bombarding energy in the range of 6.00 to 6.82 MeV. The γ-rays associated with these levels were identified both in singles spectra, from a study of their threshold behaviour, and inγγ-coincidence measurements. Altogether 24 levels in 66Ga were identified, of which 10 are known from previous studies of the β + decay of 66Ge to 66Ga, and the remaining 14 are reported here for the first time. Gamma-ray branching ratios for these new levels have been determined and a decay scheme comprising 68 γ-transitions is presented. Angular distributions of de-excitation γ-rays have been measured at proton bombarding energies close to threshold for the levels studied. Comparison of these distributions with the theoretical predictions of the compound nucleus statistical model has led to spin and parity assignments for the levels studied.

New gamma-ray branching ratios in16N and their implications on the muon partial capture rates in16O

Gamma-ray branching ratios have been carefully measured in16N, bombarding NH4NO3 targets enriched in15N with deuterons, using high-resolution gamma-spectrometers. The following results were obtained:I276keV/I396keV=2.76±0.06,I100keV/I276keV≤2·10−3 andI176keV/I296keV≤1·10−2. In the light of these branching ratios the muon partial capture rates to the16N excited bound states are reconsidered and briefly discussed.

Polarisation linéaire de rayonnements γ émis dans la réaction 46Ti(p, p′γ)

Abstract The 46 Ti(p, p′γ) reaction has been studied at proton energies of 5.489 and 5.508 MeV. The linear polarization of γ-rays emitted by 46 Ti levels below 3.25 MeV has been measured using the technique involving a single planar Ge(Li) detector. The spin-parity values 2 + , 3 − , 1 − and 2 + have been assigned to the levels at 2.962, 3.059, 3.168 and 3.236 MeV respectively. Gamma-ray branching and mixing ratios have also been obtained.

Study of the Decay of the 3.696 MeV Level in 25Al

The decay of the 3.696 MeV level in 25Al has been studied by means of the 24Mg(p,γ)25Al reaction at the 1.49 MeV resonance. Gamma-ray branching ratios, direct angular distributions, and lifetimes determined by the Doppler shift attenuation method are reported.

The spins and lifetimes of some low-lying states of 58Ni

Particle-gamma-ray angular correlation studies of the 58Ni(p, p'γ) reaction have been used to determine the spins of the following states of 58Ni: 2.775 MeV (2), 2.943 MeV (0), 3.038 MeV (1, 2), 3.263 MeV (2), 3.420 MeV (3, 4), 3.531 MeV (0), 3.593 MeV (1), 3.620 MeV (2, 3, 4), 3.774 MeV (2, 3, 4), and 4.108 MeV (2). Gamma-ray branching ratios and mixing ratios were also measured. The Doppler-shift attenuation method has been used to measure the lifetimes of the states of 2.902 MeV (100−19+22 fs) and 3.774 MeV (400−100+200 fs) while the mean life of the 2.943 MeV level was found to be 2.9 ± 0.1 ns by direct timing. The internal conversion coefficient of the 2.943 (0+) MeV to 2.902 (1+) MeV has been measured to be 0.48 ± 0.05 and an upper limit of 2 % has been placed on the 2.943 MeV to ground state EO transition. The experimental energy level spectrum of 58Ni and electromagnetic transition rates are compared to shell-model predictions calculated using the two-body interaction matrix elements of Kuo.

Angular correlation measurements on the excited states of 42Ca

The excited states of 42Ca up to an excitation of 4.2 MeV were studied with a particle -y-ray angular correlation technique in order to measure their spin values and electromagnetic decay properties. Unique spin assignments were obtained for states at 3.25 MeV ( J = 4), 3.88 MeV ( J = 1) and 4.23 MeV ( J = 1). Possible spin values were restricted for the states at 4.00 MeV ( J = 2 or 3) and 4.11 MeV ( J = 1, 2 or 3). Gamma-ray branching and mixing ratios were measured. The mixing ratios for the transitions 2 2 + → 2 1 +, 2 3 + → 2 1 +, 2 4 + → 2 1 +, were found to be +0.09±0.08, −1.7 −0.5 +0.3 and 0.00±0.10, respectively. The results are discussed with reference to two sets of theoretical calculations, firstly those assuming an inert 40Ca core and then those considering core excitation. The core excitation model gives reasonably good agreement with the experimental results.

A study of the reaction 46Ti(p, γ)47V at the 1.363 MeV resonance

Abstract The reaction 46Ti(p, γ)47V has been studied at the 1.363 MeV resonance by means of a 30 cm3 Ge(Li) detector. Gamma-ray branching ratio and angular distribution measurements have been made. From these measurements together with the results of previous stripping reaction studies the spins and parities of a number of levels are deduced.

Étude de transitions γ dans les noyaux 40K et 28Al

Gamma-ray branching ratios in the nuclei 40K and 28Al have been determined from particle-gamma coincidence measurements of the reactions 39K(d, pγ) 40K and 27Al(d, pγ) 28Al. In 40K, results are given for only a few levels below 4 MeV that were excited with sufficient intensity. Some γ-rays from 41K(d, pγ) 42K were also seen. Decay schemes were obtained for most of the levels of 28Al up to nearly 4 MeV excitation energy. The fifth excited state of 28Al is shown to be a doublet separated by 2.9 ± 0.8 keV.

Experimental study of low-lying levels and decay structure in the nucleus 62Cu

Abstract The reaction 62 Ni(p, nγ) 62 Cu has been used to investigate the low-lying levels of 62 Cu and their γ-decay. Gamma-ray angular distributions were carried out using incident proton energies close to threshold for the states under investigation and comparison of these results were made with the predictions of the compound nucleus statistical model. In addition to levels seen in the β + /EC decay of 62 Zn, namely the ground state (1 + ), 40.84 keV (2 + ), 243.43 keV (2 + ), 287.86 keV (2 + ), 548.25 keV (1 + ) and 637.20 (1 + ), other levels were found at 389.9 keV, 426.1 keV, 644.9 keV, 675.1 keV, 698.3 keV, 727.5 keV, 756.3 keV and 915.5 keV. The 426.1 keV, 675.1 keV and 727.5 keV states are assigned to be 3 + , 3 + and 2 (+) respectively, and possible spin values for the remaining levels are advanced. Gamma-ray branching ratios were obtained, and a decay scheme for 62 Cu comprising 30 transitions is presented.

The High Excited Levels of 27Al

The spectrum and angular distribution of alpha particles scattered by 27 Al at 22.2 MeV bombarding energy have been measured. Among the prominent peaks in the spectrum, those corresponding to excited states at 5.434, 6.547, 7.28 and 7.50 MeV were studied by measuring the gamma ray spectrum in coincidence with scattered alpha particle. From the measured gamma ray branching ratios, (5/2, 7/2, 9/2) + was assigned to the former two levels and 7/2 - was assigned to the latter two levels. In addition, from gamma ray transition rate consideration, 3/2 - , 9/2 + and (3/2, 5/2) + were found appropriate for 4.055, 4.508 and 5.491 MeV level respectively.

Étude de 53Mn suivant la réaction (α, pγ)

The 53Mn levels are investigated up to 2.4 MeV excitation following the 50Cr(α, pγ) 53Mn reaction. The (αp, γ) angular correlations are measured in the Litherland-Ferguson geometry II. The measured excitation function between 8 and 11 MeV permitted to choose for each level a suitable incident energy. For the levels at 1.438, 1.617, 2.271 and 2.404 MeV the following J π values are proposed: 11 2 −, 9 2 −, 5 2 and 3 2 − . Gamma-ray branching and mixing ratios were also obtained. In 53Mn, the M1 transitions are inhibited so that they are in the shell-model equivalent nucleus 51V. Also the level ordering is the same for both nuclei. The results are compared with previous experiments and theoretical predictions.

Angular correlation studies of the low-lying levels of 57Co

Proton-gamma angular correlations and gamma-ray branching ratios were measured for the first nine excited states of 57Co using the 54Fe(α, pγ) reaction. In contradiction to earlier reports, the 1.754 and 2.127 MeV states were found to be single, well isolated states, and the 1.687 MeV state was observed to have a large gamma-ray branch (44 %) to the ground state. From the data obtained here and in previous experiments, J π values were deduced for the following levels whose energies are shown in MeV: 1.222, 9 2 −( 5 2 −) ; 1.375, 3 2 −; 1.502, 1 2 −; 1.687 ( 11 2 −, ( 7 2 − 5 2 −); 1.754, 3 2 −; 1.894, 7 2 −; 1.917, 5 2 −; 2.127, 5 2 − and 2307, 7 2 −( 5 2 −) . Possible, but less probable, assignments have been enclosed in parentheses.

Étude de transitions γ dans le noyau 19O

The 18O(d, pγ)19O reaction has been investigated at Ed = 5 MeV. A Ge(Li) detector and a NaI(Tl) crystal were used to detect γ-rays in coincidence with reaction particles detected near 180°. Excitation energies have been obtained for the 19 levels at 1470±3, 2369±4, 2777±3, 3157±3 and 3944±3 keV and gamma-ray branching ratios have been determined for these levels.

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.

Polarization and angular correlation measurements following the 40Ar(p, nγ) 40K reaction

Gamma-ray angular distributions and polarization correlations have been measured using the reaction 40Ar(p, nγ) 40K. All the experiments were carried out with bombarding energies close to threshold for the states under investigation. Comparison with compound nuclear predictions has yielded the following spin assignments to states in 40K; 1.959(2 +), 2.047(2 −), 2.070(3 −), 2.103(1 −), 2.261(3 +), 2.290(1 +), 2.291(4, (3)), 2.419(2,3), 2.575(2,4) and 2.625(0 −). Multiple mixing ratios together with the gamma-ray branching ratios have been determined for all these levels. A short theoretical treatment of the polarization of gamma rays from aligned nuclei using the phase-consistent formalism of Brink and Rose is included.

Shell-model calculations on negative-parity levels in A = 35, 37 and 39 nuclei

Shell-model calculations of negative-parity states in 35Cl, 35S, 37Cl, 39Ar and 39K have been performed by assuming an inert 32S core with the residual interaction taking place within 1 d n 3 2 1 f 7 2 and 1d n case3 2 2 p 3 2 configurations (with n = 2, 4 or 6). For the effective two-body interaction the modified surface delta interaction (MSDI) has been used. The MSDI interaction parameters as well as the single-particle binding energies have been deduced from a least-squares fit to experimentally known levels in A = 35, 37 and 39 nuclei. Excitation energies. M1 and E2 transition strengths, gamma-ray branching ratios, magnetic dipole moments, spectroscopic factors and log ft values for allowed β-decay have been calculated. Where comparison with experimental values is possible, the agreement is reasonable. The calculated strengths of the strong analogue to anti-analogue M1 transitions are in excellent agreement with recent experimental results for 35Cl and 37Cl, whereas a discrepancy exists for 39K.

Lifetime measurements of the six lowest lying levels in 35Cl

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.

Gamma-ray branching ratios of the low-lying levels of 29Al

A 12.7 cm × 10.2 cm NaI(T1) gamma-ray spectrometer has been used in conjunction with a 61 cm magnetic particle spectrometer to measure gamma-ray branching ratios for levels in 29Al at excitation energies of 1.76, 2.23, 2.87, 3.07, 3.19, 3.44 and 3.58 MeV.

Electromagnetic transition strengths in 14C and 14N

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]

Branching ratios of 27Al bound states

A 12.7 cm × 10.2 cm NaI(Tl) gamma-ray spectrometer has been used in conjunction with a 61 cm magnetic particle spectrometer to measure gamma-ray branching ratios for bound states of 27Al at excitation energies of 2.21, 2.73, 2.98, 3.00, 3.68, 3.96, 4.05, 4.41, 4.51 and 4.58 MeV.