Decay Hindrance Factors Research Articles

Systematics of alpha decay hindrance factors in doubly-even nuclei

In present work, we have calculated the hindrance factors of 182 even-even alpha emitters using Preston’s formulation of alpha decay probabilities and presented HFs systematics of 1 - and 3 - states in reflection asymmetric even-even quadruple-octupole deformed nuclides (A~216-230). The calculated HFs of both 1 - and 3 - states decrease with reduction in neutron number and this decrease is attributed to onset of intrinsic reflection asymmetry. There is a trend reversal for 1 - states at N=132 ( 218 Ra) and N=134 ( 220 Rn), which might be a possible indication of departure from static octupole deformation. Similarly, HFs systematics is discussed for 224-230 Th and 232-236 U isotopic chains along with 2 + states observed in daughter nuclei in N=132-146 isotonic chains.

High-resolution (p,t) study of low-spin states in Pu240 : Octupole excitations, α clustering, and other structure features

A high-resolution $(p,t)$ experiment at $E_{p}$= 24 MeV was performed to populate low-spin states in the actinide nucleus ${}^{240}$Pu. The Q3D magnetic spectrograph of the Maier-Leibnitz Laboratory (MLL) in Munich (Germany) was used to identify the ejected tritons via $dE/E$ particle identification with its focal-plane detection system. Angular distributions were measured at nine different Q3D angles to assign spin and parity to the excited states based on a comparison with coupled-channels DWBA calculations. In total, 209 states have been excited in $^{240}$Pu up to an excitation energy of 3 MeV. Many previously known states have also been observed and their spin-parity assignments were confirmed. However, many of the populated states have been seen for the first time. The low-spin one-octupole phonon excitations, i.e. $K^{\pi} = 0^-,1^-,2^-,3^-$, could be observed and a new candidate for the $K = 3$ projection is proposed. Furthermore, the double-octupole or $\alpha$-cluster structure of the $0^+_2$ state in $^{240}$Pu has been studied in more detail. It is shown that the $0^+_2$ state in $^{230}$Th has a distinctly different structure. In addition, strongly excited $1^-$ states have been observed at 1.5\,MeV and 1.8\,MeV in $^{240}$Pu. The present study suggests that similar states might be observed in $^{230}$Th. At least two different and distinct structures for $J^{\pi} = 0^+$ states are present in the actinides. These are pairing states and states with enhanced octupole correlations. We have shown that it is crucial to consider negative-parity single-particle states being admixed to some $K^{\pi} = 0^+_2$ rotational bands to understand the $\alpha$-decay hindrance factors and enhanced $E1$-decay rates. Based on our analysis, we have identified the double-octupole or $\alpha$-cluster $K^{\pi} = 0^+$ candidates from $^{224}$Ra to $^{240}$Pu.

α decay properties of 296Og within the two-potential approach**Supported by National Natural Science Foundation of China (11205083, 11505100), the Construct Program of the Key Discipline in Hunan Province, the Research Foundation of Education Bureau of Hunan Province, China (15A159), the Natural Science Foundation of Hunan Province, China (2015JJ3103, 2015JJ2121), the Innovation Group of Nuclear and Particle Physics in USC, the

The present work is a continuation of our previous paper [J.-G. Deng, et al., Chin. Phys. C, 41: 124109 (2017)]. In the present work, the α decay half-life of the unknown nucleus 296Og is predicted within the two-potential approach and the hindrance factors of all 20 even-even nuclei in the same region as 296Og, i.e. proton number 82<Z<126 and neutron number 152<N<184, from 250Cm to 294Og, are extracted. The prediction is 1.09 ms within a factor of 5.12. In addition, based on the latest experimental data, a new set of parameters of α decay hindrance factors for the even-even nuclei in this region, considering the shell effect and proton-neutron interaction, are obtained.

Nuclear Data Evaluation for Mass Chain A=217:Odd-Proton Nuclei.

Thallium (, Bismuth (), Astatine (), Francium (), Actinium () and Protactinium () are of odd-proton numbers among the mass chain A = 217. In the present work, the half-lives and gamma transitions for the six nuclei have been studied and adopted based on the recently published interactions or unevaluated nuclear data sets XUNDL. The Q (α) has been updated based on the recent published work of the Atomic Mass Evaluation AME2012 as well. Moreover, the total conversion electrons as well as the K-Shell to L-Shell, L-Shell to M-Shell and L-Shell to N-Shell Conversion Electron Ratios have been calculated using BrIcc code v2.3. An updated skeleton decay scheme for each of the above nuclei has been presented here. The decay hindrance factors (HF) calculated using the ALPHAD program, which is available from Brookhaven National Laboratory’s website, have been calculated for the α- decay data sets for 221Fr-, 221Ac- and 221Pa- α-decays.

Platinum nuclei: Concealed configuration mixing and shape coexistence

The role of configuration mixing in the Pt region is investigated. For this chain of isotopes, the nature of the ground state changes smoothly, being spherical around mass $A~174$ and $A~192$ and deformed around the midshell $N=104$ region. This has a dramatic effect on the systematics of the energy spectra as compared to the systematics in the Pb and Hg nuclei. Interacting boson model with configuration mixing calculations are presented for gyromagnetic factors, $\ensuremath{\alpha}$-decay hindrance factors, and isotope shifts. The necessity of incorporating intruder configurations to obtain an accurate description of the latter properties becomes evident.

Systematics of the α decay to vibrational2+states

We give a systematic analysis of \ensuremath{\alpha} decays to low-lying ${2}^{+}$ states in even-even nuclei. Collective excitations are considered within the spherical quasiparticle random-phase approximation. We use realistic G-matrix elements of the Bonn interaction as a residual two-body force. The only free parameters are the ratio between the isovector and isoscalar strengths and proton-neutron asymmetry. The formalism can reproduce the main experimental trends versus the excitation energy for both the $B(E2)$ values and the \ensuremath{\alpha}-decay hindrance factors. We reproduced most of the available data by using one common parametrization. It turns out that the fine structure of the \ensuremath{\alpha} decay is more sensitive than electromagnetic transitions as a tool for investigating nuclear interaction. With the adopted parametrization, we predict $B(E2)$ values and \ensuremath{\alpha}-decay hindrance factors in even-even nuclei.

Confirmation of triple shape coexistence in179Hg:Focal plane spectroscopy of theαdecay of183Pb

The $\ensuremath{\alpha}$ decay of ${}^{183}\mathrm{Pb}$ has been studied in detail at the focal plane of the RITU gas-filled separator. The four previously known $\ensuremath{\alpha}$ decay branches have been ordered into the decay of two isomers in ${}^{183}\mathrm{Pb}.$ The deduced decay scheme and the interpretation of the inferred $\ensuremath{\alpha}$ decay hindrance factors and $\ensuremath{\gamma}$ rays observed at the focal plane are strongly in favor of the recent suggestion of triple shape coexistence---oblate, prolate, and near-spherical in the daughter nucleus ${}^{179}\mathrm{Hg}.$

Transitional nature of the level structure of217Rn

The level structure and configurations of {sup 217}Rn have been studied following the {alpha} decay of mass separated {sup 221}Ra (30 s). A number of new levels and {gamma}-ray transitions have been observed. A group of low-energy states populated with low {alpha} decay hindrance factors is interpreted as intermediate between the g{sub 9/2} shell model configuration and the 5/2(0.2;0.2) quadrupole-octupole deformed configuration. A second group of states populated with high hindrance factors is interpreted as intermediate between the i{sub 11/2} shell model configuration and the mixed 1/2({minus}0.1;0.5;{minus}2)+3/2({minus}0.1;0.6) quadrupole-octupole configuration. {copyright} {ital 1997} {ital The American Physical Society}

Shell model level structure of216Fr

Sources of ${}^{220}$Ac in secular equilibrium with ${}^{221}$Pa were produced using the reaction ${}^{209}$Bi${(}^{18}$O,$3n)$${}^{224}$Pa. The alpha decay of ${}^{220}$Ac and coincident gamma and electron spectra were used to study the level structure of ${}^{216}$Fr. The levels in ${}^{216}$Fr can be interpreted in terms of the $\ensuremath{\pi}{(h}_{9/2})$${}_{9/2}^{5}\ensuremath{\nu}{(g}_{9/2})$${}_{9/2}^{3},$ $\ensuremath{\pi}{(h}_{9/2})$${}_{0}^{4}{(f}_{7/2}{)}_{7/2}\ensuremath{\nu}{(g}_{9/2})$${}_{9/2}^{3},$ and $\ensuremath{\pi}{(h}_{9/2}{)}_{9/2}^{5}\ensuremath{\nu}{(g}_{9/2}{)}_{0}^{2}{(i}_{11/2}{)}_{11/2}$ shell model configurations. The alpha decay hindrance factors of the ground state to ground state transitions in the sequence ${}^{224}\mathrm{Pa}{\ensuremath{\rightarrow}}^{220}\mathrm{Ac}{\ensuremath{\rightarrow}}^{216}\mathrm{Fr}{\ensuremath{\rightarrow}}^{212}$At suggest the collapse of quadrupole-octupole Nilsson orbitals into the more degenerate shell model orbitals. The sequence of hindrance factors in this odd chain are mirrored in the corresponding odd proton and odd neutron sequences beginning with ${}^{223}$Pa and ${}^{223}$Th, respectively.

Alpha decay of 186Pb and 184Hg: The influence of mixing of 0(+) states on alpha -decay transition probabilities.

Fine structure in the \ensuremath{\alpha} decay of mass-separated $^{186}\mathrm{Pb}$ and $^{184}\mathrm{Hg}$ has been studied at the GSI on-line mass separator. Alpha singles spectra as well as \ensuremath{\alpha}-x-t and \ensuremath{\alpha}-e-t coincidence events were collected. The \ensuremath{\alpha} decay of $^{186}\mathrm{Pb}$ revealed feeding to a low-lying ${0}^{+}$ state at 328(12) keV in $^{182}\mathrm{Hg}$. This state can be interpreted as being the bandhead of the deformed rotational band observed previously in in-beam studies. In the \ensuremath{\alpha} decay of $^{184}\mathrm{Hg}$, feeding towards the first excited ${2}^{+}$ state at 153 keV and the ${0}_{2}^{+}$ state at 478 keV in $^{180}\mathrm{Pt}$ was observed. The hindrance factor of the \ensuremath{\alpha} decay towards the excited ${0}^{+}$ state gives information about the particle-hole character of the states connected in the \ensuremath{\alpha} decay. A two-level mixing calculation is introduced. From the mixing in Pt and the \ensuremath{\alpha}-decay hindrance factors, small mixing is deduced fro ground stattes of neutron-deficient Hg and Pb nuclei.

Levels of 232U fed in 236Pu alpha decay.

The \ensuremath{\gamma} spectrum following the \ensuremath{\alpha} decay of $^{236}\mathrm{Pu}$ has been reinvestigated with a high-resolution HPGe detector. Accurate energies and intensities are reported for 26 \ensuremath{\gamma} transitions, of which 20 were observed for the first time. A decay scheme is constructed using the Ritz combination principle, \ensuremath{\gamma}\ensuremath{\gamma} coincidence data, and previously known data from nuclear reactions and ${\mathrm{from}}^{232}$Pa ${\mathrm{\ensuremath{\beta}}}^{\mathrm{\ensuremath{-}}}$ decay. We observe feeding of the ground-state rotational band up to spin 8, the \ensuremath{\beta} vibrational band to spin 4, the K=0 octupole vibrational band to spin 5, and the bandhead of the \ensuremath{\gamma} vibrational band. New states of $^{232}\mathrm{U}$ at 927.3 and 967.7 keV, populated with low \ensuremath{\alpha}-decay hindrance factors, are assigned as members of a second-excited ${\mathit{K}}^{\mathrm{\ensuremath{\pi}}}$=${0}^{+}$ band. The ratio of E1/E2 transitions in the decay of these states suggests that the E1 transitions to members of the K=0 octupole band may be rather fast (\ensuremath{\approxeq}${10}^{\mathrm{\ensuremath{-}}3}$ Weisskopf units). Systematics of hindrance factors for \ensuremath{\alpha} decay to vibrational states are presented.

Comment on the question of reflection asymmetry in 229Pa.

The alpha decay hindrance factors from the $^{229}\mathrm{Pa}$ 5/${2}^{+}$ ground state to the 5/${2}^{\ifmmode\pm\else\textpm\fi{}}$ parity doublet bands in $^{225}\mathrm{Ac}$ suggest strong reflection asymmetry in $^{229}\mathrm{Pa}$ and the expectation that a 5/${2}^{\ifmmode\pm\else\textpm\fi{}}$ parity doublet will be found in this nucleus.

Alpha decay hindrance factors and reflection asymmetry in nuclei.

All available hindrance factors of alpha transitions to low-lying negative-parity states in doubly even nuclei, to odd-{ital A} parity doublets and to doubly odd parity doublet bands, are used to study the systematics of reflection asymmetry in the {ital A}{similar to}218--230 region. Special attention is given to the polarization effect of the odd particle in increasing reflection asymmetry and therefore decreasing hindrance factors to the opposite parity states of octupole bands.

Octupole deformation in 221Fr

The level structure of 221Fr has been reinterpreted in terms of the 1 2 ± , 3 2 ± and very tentative higher-lying 3 2 ± parity doublet bands predicted for the 87th proton in an axially symmetric, reflection asymmetric field with ϵ 3=0.08. Decoupling parameters of the K= 1 2 ± parity doublet bands are large and of opposite sign and approaching an absolute value of ∼3.8. The alpha decay hindrance factors of states in 221Fr imply anomalously large mixing between the parity mixed Nilsson orbitals with the approach of shell model spectroscopy.

U233levels populated in theαdecay ofPu237

The 45.3-day nuclide $^{237}\mathrm{Pu}$ decays primarily via electron capture. The only information available up to now concerning the nuclide's $\ensuremath{\alpha}$-decay properties has been the observation of two $\ensuremath{\alpha}$ groups with energies of 5.65 and 5.36 MeV. In the present study, the photon spectrum of $^{237}\mathrm{Pu}$ was investigated with x- and $\ensuremath{\gamma}$-ray Ge(Li) detectors. A total of 21 transitions was found to belong to $^{237}\mathrm{Pu}$ decay; of these, 16 were assigned to its $\ensuremath{\alpha}$-decay branch. An $\ensuremath{\alpha}$-decay scheme was constructed on the bases of transition energy fits and known $^{233}\mathrm{U}$ levels (including some observed only in reaction studies). The amounts of direct $\ensuremath{\alpha}$-decay feedings were then calculated from intensity balances, and a total $\ensuremath{\alpha}$-branching of (4.2 \ifmmode\pm\else\textpm\fi{} 0.4) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$% was deduced. $\ensuremath{\alpha}$-decay hindrance factors identify the band heads of the $(\frac{5}{2})[752]$ and $(\frac{7}{2})[743]$ orbitals in $^{233}\mathrm{U}$ at 298.9 and 503.5 keV, respectively. Contrastingly, the $^{233}\mathrm{Pa}$ and $^{233}\mathrm{Np}$ decay studies had assigned the $(\frac{7}{2})[743]$ state to the level at 298.9 keV.RADIOACTIVITY $^{237}\mathrm{Pu}$, measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$; deduced $\ensuremath{\alpha}/\mathrm{electron}$-capture ratio. $^{233}\mathrm{U}$, deduced levels, ${J}^{\ensuremath{\pi}}$.

Studies of Mendelevium Isotopes with Mass Numbers 248 Through 252

Five isotopes of mendelevium, with mass numbers 248 through 252, were studied by means of $\ensuremath{\alpha}$-particle spectroscopy. The isotopes were produced by bombarding $^{241}\mathrm{Am}$ and $^{243}\mathrm{Am}$ targets with $^{12}\mathrm{C}$ and $^{13}\mathrm{C}$ ions accelerated by the Berkeley heavy-ion linear accelerator. The half-lives of the nuclides and the energies of the main $\ensuremath{\alpha}$-particle groups, respectively, were observed to be: $^{248}\mathrm{Md}$: 7 \ifmmode\pm\else\textpm\fi{} 3 sec, 8.32 \ifmmode\pm\else\textpm\fi{} 0.02 MeV; $^{249}\mathrm{Md}$: 24 \ifmmode\pm\else\textpm\fi{} 4 sec, 8.03 \ifmmode\pm\else\textpm\fi{} 0.02 MeV; $^{250}\mathrm{Md}$: 52 \ifmmode\pm\else\textpm\fi{} 6 sec, 7.75 \ifmmode\pm\else\textpm\fi{} 0.02 MeV; $^{251}\mathrm{Md}$: 4.0 \ifmmode\pm\else\textpm\fi{} 0.5 min, 7.55 \ifmmode\pm\else\textpm\fi{} 0.02 MeV; $^{252}\mathrm{Md}$: 2.3 \ifmmode\pm\else\textpm\fi{} 0.8 min, no $\ensuremath{\alpha}$ decay. The $\ensuremath{\alpha}$-particle energies of $^{245}\mathrm{Es}$, $^{246}\mathrm{Es}$, and $^{247}\mathrm{Es}$, produced mainly by ($\mathrm{HI},\ensuremath{\alpha}\mathrm{xn}$) reactions, were measured to be 7.73 \ifmmode\pm\else\textpm\fi{} 0.02, 7.36 \ifmmode\pm\else\textpm\fi{} 0.03, and 7.31 \ifmmode\pm\else\textpm\fi{} 0.03 MeV, respectively, and the half-life of $^{247}\mathrm{Es}$ was found to be 4.7\ifmmode\pm\else\textpm\fi{}0.3 min. Excitation curves for producing the Md isotopes and some other activities are presented. Estimates for the electron-capture branching of the Md isotopes are given. $\ensuremath{\alpha}$-decay hindrance factors were calculated using the spin-independent equations of Preston. The $\ensuremath{\alpha}$-decay energy systematics of the mendelevium isotopes is discussed.

Population of0+States in Actinide andA≈190Nuclides by the (p,t) Reaction

The ($p,t$) reaction has been studied for targets of $^{230,232}\mathrm{Th}$, $^{234,236,238}\mathrm{U}$, $^{242,244}\mathrm{Pu}$, $^{248}\mathrm{Cm}$, $^{182,184,186}\mathrm{W}$, and $^{196}\mathrm{Pt}$. Uniformly strong (\ensuremath{\sim}15% of ground-state cross section) transitions were found to populate excited ${0}^{+}$ states in all of the actinide nuclides. The observed ${0}^{+}$ states were previously known for five of the actinide nuclei, and in these cases the states were characterized by small $\ensuremath{\alpha}$-decay hindrance factors and large $E0$ matrix elements. They have been previously classified as $\ensuremath{\beta}$ vibrations. The strong excitation of the ${0}^{+}$ states in the ($p,t$) reactions, combined with all other available evidence, suggests that throughout the actinide mass range these ${0}^{+}$ states represent a stable collective excitation different in character from both the $\ensuremath{\beta}$ vibration and the most common formulation of the pair vibration. No such excitations were seen in the W-Pt region.

Studies of Lawrencium Isotopes with Mass Numbers 255 Through 260

Six isotopes of element 103, with mass numbers 255 through 260, have been studied by means of $\ensuremath{\alpha}$-particle spectroscopy. The half-lives of the nuclides, and the energies and the intensities of their main $\ensuremath{\alpha}$-particle groups were observed to be: A large number of target-projectile combinations were used in synthesizing the lawrencium isotopes. Representative excitation curves for producing the nuclides are displayed. Upper limits for decay by electron capture have been determined. $\ensuremath{\alpha}$-decay hindrance factors have been calculated using the spin-independent equations of Preston. The $\ensuremath{\alpha}$-decay energy systematics of the heaviest elements is discussed.