Beta-decay energies and masses of short-lived isotopes of rubidium,caesium, francium,and radium

Total decay energies have been measured for a number of neutron-deficient Rb and Cs isotopes, as well as for some neutron-rich isotopes of Fr and Ra. Mass separated sources were produced at the ISOLDE on-line separator at CERN. By applying two differentβ-γ coincidence methods,Q values or their lower limits were determined for^76–78Rb,⁸⁰Rb,^121–124Cs,²²²Fr,^224–226Fr,²²⁹Ra-²²⁹Ac. For many of these nuclei, the atomic mass excesses could be derived, allowing the comparison of masses of far unstable nuclei with predictions from mass formulae. The odd-odd nuclei⁷⁶Rb and⁷⁸Rb appear to be 1?1 1/2 MeV more strongly bound than expected from the systematics.     

Delayed neutron emission probabilities and half-lives of Rb,Sr, Y,In, Cs,Ba and La precursors with A = 93–98, A = 127–131 and A = 142–148

Delayed neutron emission probabilities (P_n) for ^93–98Rb,^{97, 98}Sr,^{97, 98}Y,^127–131 In,^142–146Cs, ^{147, 148g}Ba and ¹⁴⁷La were measured at the SOLIS on-line isotope separator. The P_nvalues for ^{97, 98}Sr,^{97, 98}Y, ^{147, 148}Ba and ¹⁴⁷La were measured for the first time. Delayed neutron emission is energetically unfavourable for ¹⁴⁷Ba and ¹⁴⁸Ba precursors, according to predictions of at least four of the most common mass formulas, however, respective P_n values of (5.21 ±0.52) % and (23.9 ± 2.1 )% were determined. The P_n values were determined by counting β and neutron activities simultaneously. The energy dependence of the counting system was ～ 3 % for the relevant delayed neutron spectra range, i.e., 0–1.5 MeV. Half-lives for all precursors were measured from both β and neutron decay curves.     

Observation of charmed baryon production in νp interactions in BEBC

Two examples of charmed baryon production by neutrinos have been observed in BEBC filled with hydrogen. Both events fit uniquely the reaction νp → μ^?pK^?π⁺π⁺ and thus apparently violate the ΔS = ΔQ rule. None of the appropriate mass combinations is consistent with the mass values of the D⁰ and D⁺ mesons. However, for the mass combinations of the pK^?π⁺ systems, values of (2.285 ± 0.005) GeV and (2.280 ± 0.003) GeV are found for event 1 and 2, respectively. These values agree with the mass of (2.285 ± 0.006) GeV for the Λ_c⁺ charmed baryon determined recently in e⁺e^? collisions at SLAC.     

Heat capacity of isotopically enriched Si, Si and Si in the temperature range 4 K<T<100 K

The heat capacity of isotopically enriched ²⁸Si, ²⁹Si, ³⁰Si samples has been measured in the temperature range between 4 and 100 K. The heat capacity of Si increases with isotopic mass. The values of the initial Debye temperature Θ_D(0) for the three isotopic varieties of silicon have been determined. Good agreement with the theoretical dependence of the heat capacity on isotopic mass has been found.     

Experimental beta-decay energies of several neutron-rich nuclides with mass number 131≦A≦146

With sources obtained from the on-line mass separator LOHENGRIN the beta-decay energies of¹³¹Sn,¹³⁴Sb,^135,136Te,^143,146Ba and¹⁴⁶La have been determined from measuredβ-endpoint energies. The experimental values are compared with the predictions of several mass formulae.     

Differential cross sections for the charge exchange process π+p → π0 (π+p) at 8, 16 and 23 GeV/c

The differential cross section $\text{d}\text{σ}\text{d}\text{t′}$ for the charge-exchange process π⁺p → π⁰ (π⁺p) at 8, 16 and 23 GeV/c is presented for several regions of the π⁺p effective mass. It is found that the dip at t′ ≈ 0.6 (GeV/c)² which is observed in the Δ(1236) mass band becomes a less pronounced structure in the higher mass regions. However, while the slope of the $\text{d}\text{σ}\text{d}\text{t′}$ distributions in the near-forward direction decreases strongly with increasing π⁺p mass, there is no evidence that the observed structure moves to higher values of t′ as the π⁺p mass increases. These results are consistent with a Regge-exchange picture where the position of the dip is determined by the exchanged trajectory, but are inconsistent with a simple geometrical picture.     

The mass of the nucleus148Dy

Usingγγ coincidences theEC(K)/β ⁺ ratio for theβ decay¹⁴⁸Dy→¹⁴⁸Tb has been determined.¹⁴⁸Dy has been produced through the irradiation of⁹³Nb with 249 MeV⁵⁸Ni ions. The mass of¹⁴⁸Dy has been deduced. With the help of knownQα values the masses of¹⁵²Er,¹⁵⁶Yb,¹⁶⁰Hf and¹⁶⁴W have been obtained. The experimental masses are compared with different current mass formulae.     

Double-beta decay Q values of Cd and Te

The Q values of the ¹¹⁶Cd and ¹³⁰Te double-beta decaying nuclei were determined by using a Penning trap mass spectrometer. The new atomic mass difference between ¹¹⁶Cd and ¹¹⁶Sn of 2813.50(13) keV differs by 4.5 keV and is 30 times more precise than the previous value of 2809(4) keV. The new value for ¹³⁰Te, 2526.97(23) keV is close to the Canadian Penning trap value of 2527.01 ± 0.32 keV (Scielzo et al., 2009) [1], but differs from the Florida State University trap value of 2527.518 ± 0.013 keV (Redshaw et al., 2009) [2] by 0.55 keV (2σ). These values are sufficiently precise for ongoing neutrinoless double-beta decay searches in ¹¹⁶Cd and ¹³⁰Te. Hence, our Q values were used to compute accurate phase-space integrals for these double-beta decay nuclei. In addition, experimental two-neutrino double-beta decay nuclear matrix elements were determined and compared with the theoretical values. The neutrinoless double-beta decay half-lives for these nuclei were estimated using our precise phase-space integrals and considering the range of the best available matrix elements values.     

Effective interactions in the Λ-α and Λ-Λ-α systems

The neutron-rich nuclei³³Si,³⁴Si,³⁵Si,³⁵P,³⁶P,³⁷S and³⁸S were investigated by studying¹⁴C and¹⁸O — induced transfer reactions on³⁶S using aQ3D magnetic spectrograph and a position sensitive focal plane gas detector. The previously unknown mass of the isotope³⁵Si was determined. The accuracy of the mass excess values of the isotopes³³Si,³⁴Si,³⁵P and³⁶P has been improved. Excited states of the isotopes³³Si,³⁴Si,³⁵P,³⁶P and³⁸S were identified for the first time. In addition theγ-decay of excited states in³⁷S and³⁸S was studied with a Ge(Li) detector in coincidence with theQ3D focal plane detector. Experimental values for the mass excesses are compared with published mass formulae.     

Isospin-two ππ phase shifts from an experiment π+p→π+n at 12.5 GeV/c

The I = 2 s-wave and d-wave phase shifts σ_s²and σ_d² have been determined in the ππ mass region 0.5–1.5 GeV/c² in four mass bins of width 0.25 GeV/c², using a sample of 17 500 events from a wire chamber experiment. Two different methods were used, leading to consistent results.In the ?-mass region δ_s² ? ?15.5°, which corresponds to an elastic cross section of ? 7.5 mb. The values of δ_d² are about a factor of ten smaller than the corresponding values of δ_s².     

Atomic masses of147m, 148m, 149m Tb,148Dy,150m, 152m Ho derived from decay properties

Using nuclear fusion reactions of⁴⁰Ar ions with¹¹²Cd,¹¹⁴Sn and¹¹⁶Sn and subsequentγ-ray spectroscopy, the probability ratios of positron emission and electron capture,β ⁺/EC _k andβ ⁺/(EC+β ⁺), are determined for individualβ-transitions in the decay of^147m ,^148m ,^149m Tb,¹⁴⁸Dy and^150m ,^152m Ho. From comparison with theoretical ratios the followingQ _EC values, given in keV, are derived:^147m Tb, 4.620(60);^148m Tb, 5.730(30);^149m Tb, 3.610(50);¹⁴⁸Dy, 2.680(30);^150m Ho, 6.625(120) and^152m Ho, 6.470(80). The present decay-energy data are compared with earlier measurements and the new information obtained for the mass surface around¹⁴⁶Gd is discussed.     

Hydrogen burning of 24, 25, 26Mg in explosive carbon burning

The absolute resonance strengths of the ^24–26Mg(p, γ)^25–27Al reactions have been studied. The absolute values S_c.m.=1.03 ± 0.11, 2.3 ± 0.2 and 2.2 ± 0.2 eV for the frequently used standard resonances at E_p=823, 434 and 454 keV in the reactions ^24–26Mg(p, γ)^25–27Al, respectively, have been determined. In addition, absolute values for use as standards were determined for the 684 keV ²⁵Mg(p, γ)²⁶Al and 840 and 1966 keV ²⁶Mg(p, γ)²⁷Al resonances. New relative values were determined for the strengths of the if²⁵Mg(p, γ)²⁶Al resonances at ifE_{p = 0.3–1.7 MeV} and the ²⁶Mg(p, γ)²⁷Al resonances at E_p = 0.3–2.1 MeV. The resonance energies and total widths obtained in the present work are also given. The branching ratios and angular distributions of the γ-rays used in the absolute strength determinations were obtained in the same set-up as the absolute strength measurement. Using the revised resonance strengths, the astrophysical reaction rates of hydrogen burning of ^24–26Mg in explosive carbon burning in the stellar temperature region of T = (0.1–5.0) × 10⁹ K are compared with Hauser-Feshbach calculations. The present reaction rates are also discussed in the frame of the MgAl cycle.     

Optical isotope shifts in neodymium

Isotope shifts have been measured in Nd II from which the shifts between pure configurations 4f ⁴ 6s and 4f ⁴ 5d can be determined. The specific mass shift for such a “transition” was estimated to be + 3 mK for a change of two neutrons. By comparison with electronic X-ray isotope shifts the following values were obtained for the change in the nuclear charge distributionδ〈r ²〉 [fm²]: (142, 144) 0.277; (144, 146) 0.257; (146, 148) 0.286; (148, 150) 0.381; (142, 143) 0.130; (144, 145) 0.111. Field shifts in several optical transitions have been compared with values of ¦ψ(0)¦² obtained from Hartree-Fock wave functions; agreement is good. Other specific mass shifts have been estimated 4f ⁴ 6s? 4f ⁴ 6p, ?1 mK; 4f ⁴ 6s? 4f ³ 5d ², ?30 mK. These values are in good agreement with calculated values of ?1.1 and ?30.6 mK.     

Alpha decay studies of tellurium,iodine, xenon and cesium isotopes

Very neutron-deficient isotopes in the trans-tin region were produced by reactions of 290 MeV ⁵⁸Ni ions on ⁵⁸Ni targets, and studied by on-line mass separation at GSI. Twelve α-emitters — ^107–110Te, ^110–113I, ^111–113Xe, ¹¹⁴Cs — were identified. Systematics of Q_α values and reduced α-widths for this new island of α-emission are discussed.     

Precise atomic masses of147Eu,147Gd,and151Tb derived from their decay properties

Theβ-decay energies of¹⁴⁷Eu,¹⁴⁷Gd, and¹⁵¹Tb were determined by usingγ-spectroscopical methods. The comparison of experimental with calculatedK-capture probabilities yielded theQ _EC values 1.690( _?16 ⁺²¹ )MeV and 2.203( _?13 ⁺¹⁹ )MeV for¹⁴⁷Eu and¹⁴⁷Gd, respectively. By measuring the ratio of positron decay to electron capture for two branches in¹⁴⁷Eu decay, the decay energiesQ _EC=1.702(13) MeV andQ _EC=1.709(18)MeV were derived. Also fromEC/β ⁺ ratios the valuesQ _EC=2.225(75) MeV for¹⁴⁷Gd, andQ _EC=2.566(12)MeV for¹⁵¹Tb were obtained. Earlier discrepancies in the mass adjustment of these isotopes were removed. In course of the present studiesγ-decay properties of¹⁴⁷Eu and¹⁴⁷Gd were reinvestigated.     

Implications on the chiral quark bag from the deuteron asymptoticD-state

Fission yields of^124–132In in the thermal neutron fission of²³⁵U were determined for the first time. Charge displacementsΔZ=Z _p?Z _UCD were calculated for the corresponding mass chains. Both fission yields and charge displacement values were compared with those obtained by systematics by Wahl et al. and Wolfsberg. It was found that the fission yields of the In isotopes obey the gaussian distribution. The displacement function of Wolfsberg seems to give the better representation of the experimental results. Half-lives of^124–131In were determined from beta decay curves.     

Energy levels in As from the As(p,d) As reaction

The ⁷⁵As(p, d) ⁷⁴As reaction has been used to identify 23 excited states in ⁷⁴As. The l_n values, or mixture of l_n values, to 19 levels have been determined from DWBA fits. The spectroscopic sum rules show a neutron shell filling which is consistent with other N = 42 isotones.     

Does proton decay follow the exponential law?

Tetrads cause the breakdown of symmetry in gravitational theories. Their vacuum expected values reduce the symmetry of the vacuum from that of the action to what is global Poincaré invariance at ordinary distances. Gravitational theories can be written in terms of rescaled fields in such a way that the Planck mass never appears. The rescaled fields are dimensionless, except for gauge fields and tetrads, both of which acquire the dimension of mass. The empirical distribution of energy throughout spacetime causes the tetrads to assume vacuum expected values of the order of the Planck mass,m _p . Thus the gravitational constant,G=hc/m _p ² , may be viewed not as a fundamental constant, but as a mass scale that is dynamically determined by the large-scale structure of the universe. Generalized tetrads may also break internal symmetries.     

Aspects of chiral pion-nucleon physics

The next-to-leading order chiral pion-nucleon Lagrangian contains seven finite low-energy constants. Two can be fixed from the nucleon anomalous magnetic moments and another one from the quark mass contribution to the neutron-proton mass splitting. We find a set of nine observables, which to one-loop order only depend on the remaining four dimension-two couplings. These are then determined from a best fit. We also show that their values can be understood in terms of resonance exchange related to Δ excitation as well as vector and scalar meson exchange. In particular, we discuss the role of the fictitious scalar-isoscalar meson. We also investigate the chiral expansion of the two P-wave scattering volumes P₁⁻ and P₂⁺ as well as the isovector S-wave effective range parameter b⁻. The one-loop calculation is in good agreement with the data. The difference P₁⁻ − P₂⁺ signals chiral loop effects in the πN P-waves. The calculated D- and F-wave threshold parameters compare well with the empirical values.     

Properties of the 2' and 2” states in 106, 112, 114Cd

Angular correlations have been measured between γ-rays from the 2 → 2 → 0 cascades in ^106,112,114Cd and the beam of 11.0 MeV α particles effecting Coulomb excitation. Multipole admixtures for the 2 → 2 transitions, as deduced from these correlations, when combined with earlier results establish their B(E2) and B(M1) values. For the transitions from the 1312 and 1208 keV states in ^112,114Cd the B(E2) values in single-particle units are 18±4 and 24±7. These values are typical for transitions from “two-quadrupole-phonon” states in this mass region whereas that of the 1718 keV transition in ¹⁰⁶Cd has the smaller value of 7.0±2.3. The B(E2) values of the 2 → 2 transitions in ^112,114Cd from the 1468 and 1363 keV states are < 0.3 single-particle units. The B(M1) values of all five transitions are ≈ 10^?2$\text{(}\text{e}\text{h}\text{?}\text{2Mc}\text{)}{}^2$.