R. Sielemann

Quadrupole moments of high-spin isomers in astatine isotopes

Abstract The quadrupole moments of the isomeric π( h 9 2 ) 2 i 13 2 and π( h 9 2 ) 3 states in 209,210,211 At show a large increase with the removal of neutrons from the closed N=126 shell. The increase is discussed in terms of an enhanced polarization of the broken core by the aligned valence protons in high-spin orbitals.

Strong Probe Atom Dependence of the Electric Field Gradient in Bismuth

The nuclear quadrupole interaction of the 8+ isomers in206, 208Po was measured in the semimetallic host Bi. The comparison of the extracted electric field gradient eq for PoBi with the values for the neighboring elements Bi and Pb as probe atoms in Bi reveals a very drastic increase from Pb to Bi and to Po by an order of magnitude: eqPbBi∶eqBiBi∶eqPoBi=1.64(10)∶4.8(3)∶16(2)(all values at room temperature in units of 1017 V/cm2). This behavior is discussed in terms of the changing number of outerp-electrons of the probe atoms.

Quadrupole moment of the 19/2− isomer in115Sb

The quadrupole moment of the 19/2− isomeric state in115Sb has been measured using the time differential perturbed angular distribution method. From the quadrupole coupling constante2Qq/h=66(3) MHz atT=370 K in a Bi host the moment ratio is obtained relative to the stable ground state of121Sb as ¦Q(115Sb, 19/2−)/Q(121Sb, 5/2+)¦ =1.45(7) resulting in a moment of ¦Q(115Sb, 19/2−)¦=52(6) fm2.

Temperature dependence of the quadrupole interaction of67Ge and67Zn in s-p metals

The temperature dependence of the electric quadrupole interaction was measured on the 9/2+ isomeric state of67Ge in metallic Zn, Cd, In, and Sn and on the 9/2+ isomeric state of67Zn in Cd metal. For all investigated systems, the temperature dependence reproduces very well aT1.5-relation. The analysis shows that the strength of the temperature dependence in the pure metals is correlated to 1/(M θD2) (θD=Debye-temperature). This favours lattice vibrations as the main component of the temperature dependence of the electric field gradient. The strength of the temperature dependence measured on an impurity atom generally differs from the value of the pure host. Possible explanations for this effect are discussed.

The half-lives of the first and second excited states in 66Ga

Abstract The half-lives of the first and second excited states at 43.9 and 66.3 keV in 66 Ga were determined by measuring the time dependence of the 43.9 and 22.4 keV γ-transition intensities. The levels in 66 Ga were populated by the 66 Za(p, n) 66 Ga and 63 Cu(α, n) 66 Ga reactions. The results are T 1 2 (43.9 keV) = 16(4) ns and T 1 2 (66.3 keV) = 23(2) ns. A g -factor measurement reported in the literature is reanalysed.

Intrinsic point defects in niobium: Trapping at100Pd and111In impurities observed by PAC

Radiation-induced lattice defects in high-purity niobium have been investigated in the temperature range of 30K to 540 K by means of γ-γ perturbed angular correlation (PAC) measurements using the radioactive probes100Pd/100Rh and111In/111Cd. Both probes were produced within the niobium samples by means of heavy-ion nuclear reactions. At the Pd impurities trapping of defects occurred during heavy-ion irradiation at about 30 K in two defined configurations: defect 1(Pd) withvQ1=e2qQ/h=42(±2) MHz, η1=0 and defect 2 (Pd) withvQ2=(±2) MHz, η2=1. Two defects were observed at the In impurities in annealing stage III (around 250 K) after heavy-ion as well as electron irradiations: defect 1(In) withvQ1=87(±1) MHz, η1=0 and defect 2(In) withvQ2=105(±2) MHz, η2=0.65(±0.02). A third defect (defect 3(In):vQ3=177(±2) MHz, η3≲0.2) appeared above 260 K after heavy-ion irradiation only. The data are interpreted in terms of interstitial trapping at the Pd impurities and vacancy trapping at the In impurities. Information on the microscopic structure of defect 1(In) and 2(In) is obtained from a PAC-single-crystal experiment. For defect 1(In) axial 〈111〉-symmetry is found, which leads us to identify this defect with a monovacancy as nearest neighbor with respect to the In probe. Defect 2(In) is the trapped divacancy for which an orientation is found that is consistent with both vacancies being nearest neighbor to the probe but second nearest neighbors to each other.

Probe specific temperature dependence of the quadrupole interaction of 67Ge in zinc metal

Abstract The quadrupole interaction of the isomeric 9 2 + state of 67Ge was studied in zinc metal as a function of temperature by the DPAD method following the reaction 64Zn(α,n)67Ge. The temperature dependence differs from that of a Zn probe in zinc metal.

Quadrupole moments of neutron isomers in Sm isotopes

The quadrupole moments of the neutron isomers in140,142Sm were determined by measuring the quadrupole interaction of Sm in Gd using single crystals. The moment for the 10+ isomer in140Sm was determined to be ¦Q¦=167(48) fm2 and for the 7− isomer in142Sm ¦Q¦=112(27) fm2. The quadrupole moments are a measure for a deformation which turned out to be very similar to the deformation found for corresponding proton isomers in Gd isotones.

Antimony in cadmium — An extreme case of probe atom dependent EFG

The electric field gradient of Sb in Cd was determined by a PAD measurement on112Sb recoil-implanted into a Cd single crystal. We observe an extremely small value compared with known values on the probes Cd, In, and Sn in a Cd matrix. Strong local electronic effects may be responsible for this result.

Neutrino recoil experiments in metals

Using nuclear recoil due to neutrino emission during the electron-capture decay of111Sn to111 In in combination with111In/111Cd PAC we were able to obtain microscopic information about isolated low energy recoil processes in otherwise undamaged copper, silver, gold, aluminium, and lead.