Gamma-ray Branching Ratios Research Articles

Branching ratios for the three most intense gamma rays in the decay of 47Ca

A sample of 47Ca produced through isotope harvesting at the National Superconducting Cyclotron Laboratory was used to measure branching ratios of 7.17(5)%, 7.11(5)%, and 75.0(5)% for the 489.2, 807.9, and 1297.1 keV characteristic gamma rays, respectively. Based on these updated branching ratios, the ground state to ground state 47Ca to 47Sc beta decay branching ratio has been indirectly measured as 17.7(5)% and the ground state to 1297.1 keV excited state as 82.2(5)%. These values represent a greatly increased precision for all five branching ratios compared to the currently accepted values (Burrows, 2007). The measurements presented here were made relative to the ingrown 47Sc daughter in a47Ca sample and the well-established 159.4 keV gamma-ray branching ratio and the half-life for the decay of 47Sc (Reher et al., 1986; Meadows and Mode, 1968; Mommsen et al., 1980). These measurements were supported by verifying that the half-lives measured from characteristic gamma-ray peaks over multiple spectra for both 47Ca and 47Sc were consistent with previously reported values. Additionally, the half-lives of both 47Ca and 47Sc were independently measured with Liquid Scintillation Counting to reverify the previously reported values used in this study to find updated gamma-ray branching ratio values.

Gamma-ray branching ratios in the decay of 49Cr

The $\gamma$ -decay branching ratios of 49V have been studied in the $\beta$ /EC decay of 49Cr. The $\gamma$ -ray spectrum has been measured with a 70% relative efficiency co-axial germanium detector calibrated in efficiency with a precision of about 0.5%. The primary result is the measurement of the relative branching ratios of the three main $\gamma$ rays in the decay of 49Cr. Large discrepancies were found with a previous experimental work. The 49Cr sample was produced by proton impact on a ZrO2 target and collected at the ISOLDE facility of CERN and enabled us to re-evaluate the decay scheme of 49Cr. The new data allow the use of this nucleus for future high-precision calibration work.

Structure of16C: Testing shell model andab initioapproaches

Excited states in C-16 were populated via the Be-9(N-17,C-16+gamma)X one-proton knockout reaction. The lifetime of the 2(1)(+) state in C-16 was measured using the recoil distance method. The extracted lifetime of tau(+)(21) = 11.4(-0.9)(+0.8)(stat) +/- 0.7(syst(B rho))(-1.5)(+0.0)(syst(feeding)) ps yields a deduced B(E2;2(1)(+) -> 0(1)(+)) = 4.21(-0.26)(+0.34)(stat)(-0.24)(+0.28)(syst(B rho))(-0.00)(+0.64)(syst(feeding)) e(2)fm(4) value in good agreement with a previous measurement. The one-proton knockout cross section is used to extract the proton amplitude of the C-16 2(1)(+) state, which confirms the neutron dominant character of this state. Gamma-ray branching ratios between the 2(2)(+) state and the 2(1)(+) and ground states were also determined. The results are compared with p-sd shell model and no-core shell model (with NN and NN + NNN) calculations. The inclusion of three-body forces are essential in order for the no-core shell model calculations to reproduce the experimental findings on the gamma-ray branching ratios.

Measurements of branching ratios from the 7.12-MeV state inO16and theC12(α,γ)O16reaction cross section

Gamma-ray branching ratios of the 7.12-MeV state in {sup 16}O have been measured using the {gamma}-{gamma} coincidence technique. The extrapolations of several components of the important {sup 12}C({alpha},{gamma}){sup 16}O cross section to helium-burning energies are dependent upon the 7.12{yields}6.92 MeV branching ratio. An experimental upper limit has been placed on this transition; the 7.12{yields}6.13 MeV branching ratio has also been measured. Relative cross sections and {gamma}-ray angular distributions have been measured for the {sup 19}F(p,{alpha}{gamma}) reaction at several energies near E{sub p}=2 MeV, leading to the 6.13-, 6.92-, and 7.12-MeV states of {sup 16}O. Monte Carlo simulations of the various detectors have been developed and the simulated detector efficiencies have been compared and adjusted to experimental measurements. The available experimental data relating to the {sup 12}C({alpha},{gamma}){sup 16}O cross section have been fitted with the R-matrix formalism. The new upper limit on the 7.12{yields}6.92 MeV branching ratio impacts the extrapolation of both the E2 ground-state cross section and the cascade cross section through the 6.92-MeV state.

Branching ratio measurements of the 7.12-MeV state in 16O

Knowledge of the gamma-ray branching ratios of the 7.12-MeV state of 16O is important for the extrapolation of the 12C(a,g)16O cross section to astrophysical energies. Ground state transitions provide most of the 12C(a,g)16O total cross section while cascade transitions have contributions of the order of 10-20%. Determining the 7.12-MeV branching ratio will result in a better extrapolation of the cascade and E2 ground state cross section to low energies. We report here on measurements on the branching ratio of the 7.12-MeV level in 16O.

Spectroscopy ofPb10682188: Evidence for shape coexistence

In-beam $\ensuremath{\gamma}$-ray spectroscopy of $^{188}\mathrm{Pb}$ has been carried out using Gammasphere. Time-correlated $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence methods have allowed the identification of new structures above and below the two-particle isomeric states. The detailed decay of the proposed ${K}^{\ensuremath{\pi}}={8}^{\ensuremath{-}}$, $1\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{s}$ isomer has been established, together with a rotational band based on the isomer. Both decay and band properties confirm the association with a prolate deformation and the two-quasineutron $9∕{2}^{+}[624]\ensuremath{\bigotimes}7∕{2}^{\ensuremath{-}}[514]$ configuration. The band structure identified above the ${11}^{\ensuremath{-}}$ isomer from the two-proton configuration $9∕{2}^{\ensuremath{-}}[505]\ensuremath{\bigotimes}13∕{2}^{+}[606]$ has a moment of inertia similar to those of the bands known in heavier isotopes and to the one-quasiproton components, but the perturbations and in-band properties are not as expected for a simple, symmetric oblate deformation. This structure is fed by a $({19}^{\ensuremath{-}})$ isomer. Possible configurations for this and other multiquasiparticle states are discussed in the context of multi-quasiparticle calculations for coexisting deformations. Low-spin structures populated partly from the decay of the ${8}^{\ensuremath{-}}$ isomer have also been identified. Several of these may be associated with proposed excited ${0}^{+}$ states. Their properties, including yrare-yrast $E0$ decays and gamma-ray branching ratios, are analyzed using band-mixing models. These and other analyses support a shape coexistence scenario, with some qualifications.

Electromagnetic properties of pseudo-Nilsson bands in 185Os

New data have been obtained for 185Os following the 176Yb(13C,4n)185Os reaction, extendingthe pseudo-Nilsson \(\frac{1}{2}^{-},\frac{3}{2}^{-}[\mathaccent126{4}\mathaccent126{1}\mathaccent126{1}]\) doublet structure and the \(\frac{7}{2}^{-}[\mathaccent126{4}\mathaccent126{0}\mathaccent126{4}]\) band to significantly higher spins. Gamma-ray branching ratio data have been analysed to obtain extensive B(M1) and B(E2) ratios for intraband and interband transitions. The data are compared with particle-rotor calculations based on the pseudo-Nilsson potential and the Woods-Saxon potential. The results indicate that the pseudo-Nilsson approximation provides a good description of the \(\frac{1}{2}^{-}\), \(\frac{3}{2}^{-}[\mathaccent126{4}\mathaccent126{1}\mathaccent126{1}]\) bands up to the first band crossing;the difference in magnitude between the model predictions and data for the \(\frac{7}{2}^{-}[\mathaccent126{4}\mathaccent126{0}\mathaccent126{4}]\) band may be attributed to a lower deformation for the higher-K structure.

New determinations of gamma-ray line intensities of the Ep=550 and 1747 keV resonances of the 13C(p,γ) 14N reaction

Gamma-ray angular distributions for the resonances at E p=550 and 1747 keV of the radiative capture reaction 13C(p,γ) 14N have been measured, using intense proton beams on isotopically pure 13C targets. Experimental gamma-ray spectra were obtained with three HP–Germanium detectors at four angles for E p=550 keV and six angles for E p=1747 keV in the range of 0–90° with respect to the proton beam. From the data, relative intensities for the strongest transitions were extracted with an accuracy of typically 5%, making these resonances new useful gamma-ray standards for efficiency calibration in the energy range from E γ=1.6–9 MeV. Gamma-ray branching ratios were obtained for several levels of 14N and are compared with literature values.

Effects of instantons on the YN interaction

Neutron inelastic scattering from thulium-169 has been studied for states above 100 keV via the (n,n′γ) reaction at incident energies in the 0.2- to 1.0-MeV range. A high-resolution Ge spectrometer in conjunction with the time-of-flight technique was utilized. Thirty-six gamma-ray transitions from 16 levels were observed. Gamma-ray angular distributions were measured at En=750 keV and excitation functions at 125 degrees were measured in 50 keV steps over the range of incident energies. Differential gamma-ray production cross sections and gamma-ray branching ratios were obtained. Inferred neutron inelastic level cross sections of the four lowest ground-state rotational band (Kπ=1/2+) members are compared to the sum of calculated compound nucleus and direct interaction cross sections. For the remaining levels, measurements are compared to compound nucleus calculations only. The comparison shows generally good agreement particularly near threshold.

First decay study of the very neutron-rich isotope93Br

The decay of the mass-separated, very neutron-rich isotope Br-93 has been studied by gamma-spectroscopy. A level scheme of its daughter Kr-93 has been constructed. Level energies, gamma-ray branching ratios and multipolarities suggest spins and parities which are in accord with a smooth systematics of the N=57 isotones for Z less-equal 40, suggesting the N=56 shell closure still to be effective in Kr isotopes. So far, there is no indication of a progressive onset of deformation in neutron-rich Kr isotopes.

Thulium-169 neutron inelastic scattering cross section measurements via the [formula omitted]Tm [formula omitted] reaction

Neutron inelastic scattering from thulium-169 has been studied for states above 100 keV via the (n,n′γ) reaction at incident energies in the 0.2- to 1.0-MeV range. A high-resolution Ge spectrometer in conjunction with the time-of-flight technique was utilized. Thirty-six gamma-ray transitions from 16 levels were observed. Gamma-ray angular distributions were measured at E n=750 keV and excitation functions at 125 degrees were measured in 50 keV steps over the range of incident energies. Differential gamma-ray production cross sections and gamma-ray branching ratios were obtained. Inferred neutron inelastic level cross sections of the four lowest ground-state rotational band (K π=1/2 +) members are compared to the sum of calculated compound nucleus and direct interaction cross sections. For the remaining levels, measurements are compared to compound nucleus calculations only. The comparison shows generally good agreement particularly near threshold.

Collective γ-vibrational bands in 165Ho and 167Er

The nuclear structures of 165Ho and 167Er have been investigated by means of Coulomb excitation. These nuclei excited at moderate spins exhibit γ-vibrational bands with K π = 11 2 −, 3 2 − in 165Ho and K π = 11 2 + in 167Er. The γ-vibrational bands in 165Ho are found to be isospectral; heaving very nearly identical in-band γ-ray energies. Gamma-ray branching ratios are analysed to extract information on collectivity and Coriolis mixing. Experimental results are compared with calculations performed with the Cranked Shell Moedl + RPA + particle-vibration coupling and by invoking the generalized intensity relations (GIR) in the unified model scheme. Although this model explains many features of the data, puzzling aspects such as identical transition energies for the bands in 165Ho remain unexplained. The role of the K quantum number in identical bands is discussed.

53Cr(n,n' gamma ) reactions and the level structure of 53Cr.

Gamma-ray decay of levels in the stable isotope $^{53}\mathrm{Cr}$ has been studied using $^{53}\mathrm{Cr}$(n,n'\ensuremath{\gamma}) reactions for incident neutron energies between threshold and 10 MeV. Measured gamma-ray production cross sections have been compared with earlier measurements and with cross sections calculated using precompound-compound-nucleus theory. Some of the present results are at variance with earlier experimental or evaluated results. For example, for the decay of the ${E}_{x}$=1537-keV level we are unable to explain variations in the measured branching ratios of the transition gamma rays as a function of incident neutron energy. The experimental data were analyzed within the framework of several theoretical model calculations of the level structure of $^{53}\mathrm{Cr}$. Quantitative discrepancies are discussed.

Gamma decays of isobaric analog states relevant to neutrino detection.

Measurements have been made of the gamma ray branching ratios for the decay of the lowest isobaric analog states of $^{71}\mathrm{Ge}$ and $^{81}\mathrm{Kr}$. These states could be populated by high-energy neutrinos in gallium- and bromine-based detectors. Although these states are unbound to particle decay, all channels with significant penetrabilities are isospin forbidden, so that gamma decay is a possibility. Our results indicate that these states decay mainly by neutron emission and therefore contribute very little to detection sensitivities for $^{71}\mathrm{Ga}$ and $^{81}\mathrm{Br}$.

Spectroscopy of 18O: Radiative capture, 14C( alpha, gamma )18O.

The electromagnetic deexcitation of the six known $^{14}$C+\ensuremath{\alpha} resonances in the range ${E}_{\ensuremath{\alpha}}$=1.7--2.7 MeV was observed with a Ge(Li) detector. Results for the branching ratios of the 7.62-, 8.04-, and 8.13-MeV $^{18}\mathrm{O}$ levels were found to be in agreement with previous measurements. Deexcitation of the 7.86-, 8.21-, and 8.28-MeV levels was observed for the first time. The radiative widths of these three (\ensuremath{\alpha},\ensuremath{\gamma}) resonances were determined. Electromagnetic transition strengths were derived for all the resonances from the gamma-ray branching ratios and the total radiative widths. A selective and enhanced E1 decay (\ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}2}$ W.u.) of the ${3}_{3}^{\mathrm{\ensuremath{-}}}$ state is observed; among the available ${2}^{+}$ states lower in excitation, this ${3}_{3}^{\mathrm{\ensuremath{-}}}$ state is observed to deexcite only to the ${2}_{3}^{+}$ state. The ${2}_{3}^{+}$ state is well understood to involve excitations of the $^{16}\mathrm{O}$ core, whereas the ${2}_{2}^{+}$ and ${2}_{1}^{+}$ states arise mainly from simple two neutron (sd-shell) configurations. The relevance of the \ensuremath{\alpha}${+\mathrm{}}^{14}$C radiative capture reactions for nucleosynthesis of heavier elements, at the hadronization phase of the big bang, is discussed.

Measurement of the short lived cumulative fission yield in u-235

Abstract Three thin metal foils of 93.15% enriched 235U (3mg each) have been irradiated with thermal neutrons at a thermal power of 500 watts, to measure the cumulative fission yield of 148Ce (T½=56s) and some other short lived fission products. Gamma spectra were collected using a 50 cm3 Ge(Li) detector and the yields were calculated using a computer code developed for calculation of cumulative fission yield by first determining the appropriate gamma ray activity as of the end of the irradiation, correcting for detector efficiency and gamma ray branching ratio, and finally, dividing by the number of fission in the sample. Fission rate was determined by fission rack method. The cumulative fission yield of 148Ce, 89Kr, 136mI, 144La, 90Kr, 139Xe, 137Xe, and 140Cs were determined.

Energy levels, decay scheme, gamma-ray branching ratios, and lifetimes in 49V with (p, nγ) reaction

The reaction 49Ti(p, nγ)49V has been studied at an incident energy of Ep = 5.74 MeV using a pulsed beam. Energy levels, a decay scheme, and gamma-ray branching ratios have been obtained from the observed gamm-ray spectra. Lifetimes are obtained by a direct timing technique. Energy levels up to 3667 keV excitation have been observed including some that were seen previously only through other reactions. New gamma-ray transitions have also been observed. The results obtained are compared with those from previous works.

Measurement and application of DDγ, DTγ and D 3Heγ reactions at low energy

The gamma ray branching ratios for the reactions T(d, γ) 5He, D(d, γ) 4He, 3He(d, γ) 5 Li have been measured between center of mass energies of 25 to 100 keV. The branching ratios are observed to be roughly constant over the energy range of the measurements with best values Γ dtγ/ Γ dtα = (5.4±1.3)× 10 −5Γ ddγ/Γ ddp= (1.1 ±0.3) × 10 −7 and Γ d3Heγ/ Γ d3Heα = (5.0±1.2) × 10 −5. These branching ratios are used to calculate the reactivities for the production of the gamma rays by high temperature plasmas. Specific applications to TFTR plasmas will be presented.

Electromagnetic properties ofTh230studied by Coulomb excitation

The Coulomb excitation of /sup 230/Th by 135 MeV /sup 32/S ions was studied using the particle-gamma coincidence technique. Scattered projectiles were detected within an angular range of 30/sup 0/< or =THETA< or =172/sup 0/, and the impact-parameter dependence of the gamma-ray intensities was measured. Excitation of the ground-state rotational band was observed up to the 10/sup +/ state, while the ..beta..- and ..gamma..-vibrational bands were seen up to the 4/sup +/ and 8/sup +/ states, respectively. Levels belonging to the K/sup ..pi../ = 0/sup -/ and 1/sup -/ octupole vibrational bands were also identified. From the scattering-angle dependent gamma-ray intensities E2 transition matrix elements within the ground band and interband matrix elements connecting levels of the ..gamma.. band with the ground band are deduced. Gamma-ray branching ratios for transitions from the ..gamma..- and octupole-vibrational bands to ground-band levels are also determined. Both transition matrix elements and branching ratios are compared with nuclear-model predictions.

Level structure ofGe67and its implications for the general structure of nuclei in the1f−2pshell

From the results of prompt and $\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$-ray singles and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence measurements, twenty-four excited states and forty-six gamma transitions are identified in the level scheme of $^{67}\mathrm{Ge}$. Angular distributions and directional correlations of prompt $^{67}\mathrm{Ge}$ gamma rays have been measured to obtain the spins of the $^{67}\mathrm{Ge}$ ground state and excited states at 18.2, 122.7, 243.6, 711.3, and 1019.9 keV. Parities are assigned to the first five states on the basis of $\mathrm{fp}$ shell systematics and observed $^{67}\mathrm{Ge}$ gamma-ray branching ratios. The 752-keV excitation energy of the first ${\frac{9}{2}}^{+}$ level in $^{67}\mathrm{Ge}$ is determined from an excitation function for the $^{64}\mathrm{Zn}(\ensuremath{\alpha}, \mathrm{n}\ensuremath{\gamma})^{67}\mathrm{Ge}$ reaction. The angular distribution and correlation measurements also provide $\frac{E2}{M1}$ mixing ratios for the 104.4, 120.8, 122.7, 243.6, 589.0, and 897.5 keV $^{67}\mathrm{Ge}$ gamma rays. The level scheme of $^{67}\mathrm{Ge}$ and the corresponding schemes for $^{63,65}\mathrm{Ni}$, $^{65,67}\mathrm{Zn}$, and $^{69}\mathrm{Ge}$ are observed to have strong similarities at low excitation. Systematic trends in $E2$ transition rates are interpreted in the context of shell and collective features of the nuclei. It is found that models based on a single particle coupled to a vibrational or deformed core do not explain the observed systematics, and are an inaccurate representation of these nuclei. The systematics do agree with a many-nucleon shell model emphasizing the short-range pairing interaction and configuration mixing for the valence neutrons.NUCLEAR REACTIONS $^{64}\mathrm{Zn}(\ensuremath{\alpha}, \mathrm{n}\ensuremath{\gamma})$, $^{63}\mathrm{Cu}(^{6}\mathrm{Li}, 2\mathrm{n}\ensuremath{\gamma})$, $^{58}\mathrm{Ni}(^{14}\mathrm{N}, \ensuremath{\alpha}\mathrm{n})$; $^{67}\mathrm{Ge}$ level scheme, $E\ensuremath{\gamma}$, $\ensuremath{\gamma}(\ensuremath{\theta})$, $\ensuremath{\gamma}\ensuremath{\gamma}(\ensuremath{\theta})$, $\ensuremath{\delta}(\frac{E2}{M1})$, ${J}^{\ensuremath{\pi}}$. Directional correlations with an oriented source. Ge(Li) detectors, enriched targets. Nuclear systematics, nuclear deformation.