Isobaric Analog State Research Articles

Theoretical models for exotic nuclei

We review various theoretical models which have been used to study the properties of the ground state and excited states of nuclei close to and beyond the neutron and proton drip lines. The validity and limitations of these models are discussed with applications to recent experimental findings such as di-neutron correlations in Borromian nuclei, the soft dipole excitations, direct two-neutron and two-proton decays, and odd-even staggerings of reaction cross sections. The role of isoscalar spin-triplet pairing interaction is also pointed out in the low-lying energy spectra as well as the spin- and isospin-dependent decay rates for N = Z and N = Z + 2 nuclei with mass A < 60. A characteristic feature of the Coulomb energy displacement of the Borromian nucleus 11Li is discussed in connection to the energies of isobaric analogue states (IAS) of T = 5/2 multiples in the A = 11 systems.

Nuclear Data Sheets for A = 43

The experimental data are evaluated for known nuclides of mass number A = 43 (Al,Si,P,S,Cl,Ar,K,Ca,Sc,Ti,V,Cr). Detailed evaluated level properties and related information are presented, including adopted values of level and γ–ray energies, decay data (energies, intensities and placement of radiations), and other spectroscopic data. This work supersedes earlier full evaluations of A = 43 published by 2001Ca24 and 1990En08 (also 1978En04, and 1998En04 update).No excited states are known in 43Al, 43Si and 43Cr. Only one excited state is known in 43V which is the probable the Isobaric Analog State (IAS) of 43Cr ground state. Information for 43P, 43S, 43Cl, 43Ar and 43Ti is limited; there is either no decay data available or the decay schemes are incomplete in view of large Q values and known excitations much lower than allowed by Q values. The 43K, 43Ca and 43Sc nuclides remain the most extensively studied from many different reactions and decays.

In Memoriam: George C. Morrison (1930–2015)

Born 14 May 1930, George C. Morrison graduated from the University of Glasgow with his first degree and then studied at the University of Chicago before moving to the Argonne National Laboratory in Chicago. His scientific reputation was built in the field of nuclear structure physics, in particular heavy-ion research and isobaric analogue states. In 1973 George moved back to the United Kingdom and took up a chair of Nuclear Structure Physics at the University of Birmingham, appointed by Professor Bill Burcham.

β-delayed proton emission of 69Kr and the 68Se rp-process waiting point

The slow β-decay of the 68Se waiting point in the astrophysical rp-process can in principle be bypassed by a sequential two proton capture. The rate of this reaction sequence depends exponentially on the 69Br proton separation energy. We studied β-delayed proton emission of 69Kr and extracted a proton separation energy of −641(42) keV. In addition, we determined a 69Kr β-decay half-life of T1/2=28(1) ms and an excitation energy of 3153(55) keV of the 69Kr isobaric analog state in 69Br. X-ray burst model calculations show that regardless of the values of other uncertain masses in the region, the new Sp(Br69) allows for a reaction flow via Se68(2p,γ) of at most 20%. Uncertainties are sufficiently reduced to conclude that Se68(2p,γ) has at best a very small effect on burst light curve and composition, and that 68Se is a strong rp-process waiting point. Our results also exclude the possibility of a suggested longer lived, so far unobserved, 69Br ground state.

Isospin corrections to super-allowed beta decays in nuclei

Isospin corrections to the super-allowed beta decay matrix elements are evaluated in perturbation theory using the notion of the giant isovector monopole state. The calculation avoids the separation into different contributions and therefore presents a consistent, systematic and more transparent approach. Explicit expressions for δc as a function of the mass number A are derived. These corrections affect the values of the Vud matrix element in the Cabbibo-Maskawa-Kobayashi matrix. Also, it is pointed out that in some nuclei with a low number of excess neutrons (protons) Coulomb mixing with the anti-analog state can introduce significant isospin impurities in the isobaric analog state.

Two-proton decay from the isobaric analog state inB8

Two-proton decay from the isobaric analog state in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi mathvariant="normal">B</mml:mi><mml:mprescripts /><mml:none /><mml:mrow><mml:mn>8</mml:mn></mml:mrow></mml:mmultiscripts></mml:math>

Survey of Evaluated Isobaric Analog States

Isobaric analog states (IAS) can be used to estimate the masses of members belonging to the same isospin multiplet. Experimental and estimated IAS have been used frequently within the Atomic Mass Evaluation (AME) in the past, but the associated set of evaluated masses have been published for the first time in AME2012 and NUBASE2012. In this paper the current trends of the isobaric multiplet mass equation (IMME) coefficients are shown. The T = 2 multiplet is used as a detailed illustration.

β Decay in the Region of Neutron-deficient 69,70,71Kr

Decay spectroscopy was performed for neutron-deficient nuclei ranging from zinc to krypton with isospin −32≤Tz≤0. Measurements of correlated β-delayed protons allowed us to determine the isobaric analog states fed from the decay of 65Se and 69Kr, constraining the spin of the 69Kr ground state. Preliminary results regarding the half lives for the Tz=−1 systems, relevant to the rapid proton capture (rp) process, are discussed.

Spatial periphery of lithium and beryllium isotopes

The spatial structure of the periphery of lithium and beryllium isotopes is studied by means of charge-exchange reactions and the (t, p) and (d, p) reactions on their nuclei. It is shown that the 0+ isobaric-analog state of 6Li at 3.56 MeV has a halo structure formed by a proton and a neutron, that there is virtually no manifestation of a neutron halo in the ground state of the 9Li nucleus, and that the 11Li nucleus has a Borromean halo structure that two neutrons form with respect to the 9Li core and which manifests itself in cigar and dineutron configurations. The 10Be nucleus has a substantial two-neutron periphery in either configuration both in the ground and in the 2+ excited state at 3.37MeV.

Corrigendum to “Evaluated experimental isobaric analogue states from T=1/2 to T=3 and associated IMME coefficients” [Nucl. Phys. A 925 (2014) 61–95

Corrigendum to “Evaluated experimental isobaric analogue states from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:mi>T</mml:mi><mml:mo>=</mml:mo><mml:mn>1</mml:mn><mml:mo stretchy="false">/</mml:mo><mml:mn>2</mml:mn></mml:math> to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"><mml:mi>T</mml:mi><mml:mo>=</mml:mo><mml:mn>3</mml:mn></mml:math> and associated IMME coefficients” [Nucl. Phys. A 925 (2014) 61–95

Rotational-vibrational Description of Nucleon Scattering on Actinide Nuclei Using a Dispersive Coupled-channel Optical Model

Tamura's coupling formalism has been extended to consider low-lying rotational bands built on vibrational (single-particle) band heads in well-deformed even-even (odd) actinides. These additional excitations are introduced as a perturbation to the underlying rigid rotor structure that is known to describe well the ground state rotational band of major actinides. Coupling matrix elements needed in extended Tamura's formalism are derived for both even-even and odd actinides. Employed dispersive optical model (DCCOMP) replaces the incident proton energy Ep (for proton induced reactions) by the equivalent Coulomb subtracted energy in all potential terms including both the imaginary and real potentials with the corresponding dispersive corrections. Therefore, the optical potential becomes fully symmetric for protons and neutrons. This potential is used to fit simultaneously all the available optical experimental databases (including neutron strength functions) for nucleon scattering on 238U and 232Th (even even) nuclei. Quasi-elastic (p,n) scattering data to the isobaric analogue states of the target nuclei are also used to constrain the isovector part of the optical potential. Derived Lane-consistent DCCOMP is based on coupling of almost all levels below 1 MeV of excitation energy. The ground state, octupole, beta, gamma and non-axial rotational bands are considered for even nuclei, and rotational bands built on single-particle levels – for odd nuclei. Application of derived potential to odd targets based on a new coupling scheme is foreseen.

Charge-exchange scattering to the isobaric analog state at medium energies as a probe of the neutron skin

The charge-exchange $(^{3}\mathrm{He},t)$ scattering to the isobaric analog state (IAS) of the target can be considered as ``elastic'' scattering of $^{3}\mathrm{He}$ by the isovector term of the optical potential (OP) that flips the projectile isospin. Therefore, the accurately measured charge-exchange scattering cross section for the IAS can be a good probe of the isospin dependence of the OP, which is determined exclusively within the folding model by the difference between the neutron and proton densities and isospin dependence of the nucleon-nucleon interaction. Given the neutron skin of the target related directly to the same density difference, it can be well probed in the analysis of the charge-exchange $(^{3}\mathrm{He},t)$ reactions at medium energies when the two-step processes can be neglected and the $t$-matrix interaction can be used in the folding calculation. For this purpose, the data of the $(^{3}\mathrm{He},t)$ scattering to the IAS of $^{90}\mathrm{Zr}$ and $^{208}\mathrm{Pb}$ targets at ${E}_{\mathrm{lab}}=420$ MeV have been analyzed in the distorted wave Born approximation using the double-folded charge-exchange form factor. The neutron skin deduced for these two nuclei turned out to be in a good agreement with the existing database.

Evaluated experimental isobaric analogue states from T=1/2 to T=3 and associated IMME coefficients

Isobaric multiplets can be used to provide reliable mass predictions through the Isobaric Multiplet Mass Equation (IMME). Isobaric analogue states (IAS) for isospin multiplets from $T=1/2$ to $T=3$ have been studied within the 2012 Atomic Mass Evaluation (Ame2012). Each IAS established from published experimental reaction data has been expressed in the form of a primary reaction $Q$-value, and if necessary, has been recalibrated. The evaluated IAS masses are provided here along with the associated IMME coefficients. Quadratic and higher order forms of the IMME have been considered, and global trends have been extracted. Particular nuclides, requiring experimental investigation, have been identified and discussed. This dataset is the most precise and extensive set of evaluated IAS to date.

Folding model study of the charge-exchange scattering to the isobaric analog state and implication for the nuclear symmetry energy

The Fermi transition (\Delta L=\Delta S=0 and \Delta T=1) between the nuclear isobaric analog states (IAS), induced by the charge-exchange (p,n) or (3He,t) reaction, can be considered as "elastic" scattering of proton or 3He by the isovector term of the optical potential (OP) that flips the projectile isospin. The accurately measured (p,n) or (3He,t) scattering cross-section to the IAS can be used, therefore, to probe the isospin dependence of the proton or 3He optical potential. Within the folding model, the isovector part of the OP is determined exclusively by the neutron-proton difference in the nuclear densities and the isospin dependence of the effective nucleon-nucleon (NN) interaction. Because the isovector coupling explicitly links the isovector part of the proton or 3He optical potential to the cross section of the charge-exchange (p,n) or (3He,t) scattering to the IAS, the isospin dependence of the effective (in-medium) NN interaction can be well tested in the folding model analysis of these charge-exchange reactions. On the other hand, the same isospin- and density dependent NN interaction can also be used in a Hartree-Fock calculation of asymmetric nuclear matter, to estimate the nuclear matter energy and its asymmetry part (the nuclear symmetry energy). As a result, the fine-tuning of the isospin dependence of the effective NN interaction against the measured (p,n) or (3He,t) cross sections should allow us to make some realistic prediction of the nuclear symmetry energy and its density dependence.

Trends in the Isobaric Multiplet Mass Equation Coefficients

Isobaric analogue states (IAS) can be used to study the charge independence of the nuclear force via first order perturbation theory. In this case the IAS multiplet masses are expected to follow a quadratic form as described by the Isobaric Multiplet Mass Equation (IMME) with coeffi cients accessible through experimental measurements. Higher order effects are expected to appear through cubic, or higher, polynomial terms. The current IMME coeffi cient trends, as based on the IAS states included in the 2012 Atomic Mass Evaluation and NUBASE2012 are shown.

Chimiothérapie (CT) de maintenance par bevacizumab/pemetrexed chez des patients (pts) avec un cancer bronchique non à petites cellules non épidermoïdes (CBNPCne) avancé : survie globale actualisée de l’essai randomisé de phase III AVAPERL

For a selective excitation of spin-flip strength, (6Li,6He) reactions can be a useful tool, because: a) 6Li and 6He have ground-state spin and parity values Jπ = 1+ and 0+, respectively; b) 6He has no particle-stable excited state, thus effects from ejectile excitation can be avoided. The (6Li,6He) experiments were performed at 100 MeV/nucleon, at which incident energy the reaction is expected to be single-step dominant. Through the analysis of the good-resolution (6Li,6He) data on 13C, 26Mg, 27Al and 58Ni targets, the evidence for a proportional relationship between 0° cross sections and the corresponding Gamow-Teller transition strengths is examined. Suppression of non-spin flip excitations is discussed based on the hindrance of the excitation of the isobaric analog state.

Energy-density-functional calculations including proton-neutron mixing

We present results of calculations based on the Skyrme energy density functional including the arbitrary mixing between protons and neutrons. In this framework, single-particle states are superpositions of proton and neutron components and the energy density functional is fully invariant with respect to three-dimensional rotations in the isospin space. The isospin of the system is controlled by means of the isocranking method, which carries over the standard cranking approach to the isospin space. We show numerical results of the isocranking calculations performed for isobaric analogue states in the A=14 and $A=40-56$ nuclei. We also present such results obtained for high-isospin states in $^{48}$Cr, with constraints on the isospin implemented by using the augmented Lagrange method.

Spatial periphery of lithium isotopes

The spatial structure of lithium isotopes is studied with the aid of the charge-exchange and (t, p) reactions on lithium nuclei. It is shown that an excited isobaric-analog state of 6Li (0+, 3.56MeV) has a halo structure formed by a proton and a neutron, that, in the 9Li nucleus, there is virtually no neutron halo, and that 11Li is a Borromean nucleus formed by a 9Li core and a two-neutron halo manifesting itself in cigar-like and dineutron configurations.

Isospin mixing of the isobaric analog state studied in a high-resolution56Fe(3He,t)56Co reaction

High-energy-resolution ${}^{56}$Fe(${}^{3}\mathrm{He},t$)${}^{56}$Co reaction measurements were performed at forward angles including ${0}^{\ensuremath{\circ}}$. From the spectra obtained, the splitting of the Fermi transition strength and thus the isospin mixing between the ${J}^{\ensuremath{\pi}}={0}^{+}$ isobaric analog state (IAS) at 3.60 MeV and a neighboring ${0}^{+}$ state at 3.53 MeV have been investigated. In order to distinguish between states excited in Fermi and Gamow-Teller (GT) transitions, the measurements were performed at two ${}^{3}$He beam energies of 140 and 100 MeV/nucleon. Owing to the different incident energy dependencies of the $\ensuremath{\sigma}\ensuremath{\tau}$- and $\ensuremath{\tau}$-type effective interaction strengths, it is expected that the Fermi transitions are stronger relative to GT transitions at lower beam energies. Therefore the excitation of a state by the Fermi transition could be identified by the $\ensuremath{\Delta}L=0$ angular distribution and the ratio of transition strengths at these two incident energies. In the energy region around the IAS at 3.60 MeV, it was found that the state at 3.53 MeV is also excited by the Fermi transition and thus it has ${J}^{\ensuremath{\pi}}$ values of ${0}^{+}$. A value of 32.3(5) keV could be deduced for the off-diagonal matrix element of the Hamiltonian that causes the isospin mixing. A corresponding isospin impurity of $28\ifmmode\pm\else\textpm\fi{}1$% was obtained.

Neutrino-nuclear response and photonuclear reactions

Photo nuclear reactions are shown to be used for studying neutrino/weak nuclear responses involved in astro-neutrino nuclear interactions and double beta decays. Charged current weak responses for ground and excited states are studied by using photo nuclear reactions through isobaric analog states of those states, while neutral current weak responses for excited states are studied by using photo nuclear reactions through the excited states. The weak interaction strengths are studied by measuring the cross sections of the photo nuclear reactions, and the spin and parity of the state are studied by measuring angular correlations of particles emitted from the photo nuclear reactions. Medium-energy polarized photons obtained from laser photons scattered off GeV electrons are very useful. Nuclear responses studied by photo nuclear reactions are used to evaluate neutrino/weak nuclear responses, i.e. nuclear beta and double beta matrix elements and neutrino nuclear interactions, and to verify theoretical calculations for them.