N. Rud

CHANGE OF DIET OF THE GREENLAND VIKINGS DETERMINED FROM STABLE CARBON ISOTOPE ANALYSIS AND 14 C DATING OF THEIR BONES

Bone samples from the Greenland Viking colony provide us with a unique opportunity to test and use (super 14) C dating of remains of humans who depended upon food of mixed marine and terrestrial origin. We investigated the skeletons of 27 Greenland Norse people excavated from churchyard burials from the late 10th to the middle 15th century. The stable carbon isotopic composition (delta (super 13) C) of the bone collagen reveals that the diet of the Greenland Norse changed dramatically from predominantly terrestrial food at the time of Eric the Red around AD 1000 to predominantly marine food toward the end of the settlement period around AD 1450. We find that it is possible to (super 14) C-date these bones of mixed marine and terrestrial origin precisely when proper correction for the marine reservoir effect (the (super 14) C age difference between terrestrial and marine organisms) is taken into account. From the dietary information obtained via the delta (super 13) C values of the bones we have calculated individual reservoir age corrections for the measured (super 14) C ages of each skeleton. The reservoir age corrections were calibrated by comparing the (super 14) C dates of 3 highly marine skeletons with the (super 14) C dates of their terrestrial grave clothes. The calibrated ages of all 27 skeletons from different parts of the Norse settlement obtained by this method are found to be consistent with available historical and archaeological chronology. The evidence for a change in subsistence from terrestrial to marine food is an important clue to the old puzzle of the disappearance of the Greenland Norse, obtained here for the first time by measurements on the remains of the people themselves instead of by more indirect methods like kitchen-midden analysis.

Recent reservoir ages for Danish fjords and marine waters.

AMS (super 14) C dates were measured for 28 mollusk shells collected live in Danish waters over the period AD 1885 to 1945. Fourteen samples were from fjords and 14 were marine samples from the Danish Skagerrak-Kattegat coastal area and from the Belts. Reservoir ages were calculated for all samples on the basis of the tree-ring calibration curve. For the marine samples, which cover the period AD 1885-1916, we found a weighted-average reservoir age of 377+ or -16 yr. The marine Delta R values (the difference between the measured (super 14) C age and the age deduced from marine, mixed-layer model calculation of Stuiver, Pearson and Braziunas (1986)) were found to be uniform within the experimental uncertainty with a weighted average of Delta R = 13+ or -16yr. Based on the observed scatter, the standard deviation is 21 yr. This result shows that it is justified to use the marine calibration curve with standard parameters (Delta R = 0) when (super 14) C-dating marine samples from the Danish area. Our value is consistent with the result Delta R = -33+ or -27 yr previously found for the Norwegian and Swedish Skagerrak-Kattegat coasts. In contrast, reservoir ages for Danish fjords were found to vary from 400 to >900 yr, far beyond experimental uncertainty. We ascribe this to varying content of dissolved, old soil carbonate (hard-water effect). Therefore, dating of samples from such fjord environments is expected to be uncertain by several hundred years.

AMS 14C DATING OF LIME MORTAR

Abstract A method for refining lime mortar samples for 14 C dating has been developed. It includes mechanical and chemical separation of mortar carbonate with optical control of the purity of the samples. The method has been applied to a large series of AMS datings on lime mortar from three medieval churches on the Aland Islands, Finland. The datings show convincing internal consistency and confine the construction time of the churches to AD 1280–1380 with a most probable date just before AD 1300. We have also applied the method to the controversial Newport Tower, Rhode Island, USA. Our mortar datings confine the building to colonial time in the 17th century and thus refute claims of Viking origin of the tower. For the churches, a parallel series of datings of organic (charcoal) inclusions in the mortar show less reliable results than the mortar samples, which is ascribed to poor association with the construction time.

Large transient magnetic fields for rare-earth ions recoiling in gadolinium and g-factors of high-spin states in 156, 158, 160Gd

Abstract We have determined the transient magnetic field for Coulomb-excited rare-earth nuclei recoiling with velocities in the range between 0.7ν0 and 6ν0 into ferromagnetic gadolinium cooled to a temperature T = 80 K. Measured and calculated g-factors in 169Tm have been used as calibration standards. The transient field is found at first to increase with increasing recoil velocity, and then to level off, approaching a nearly constant value of 5.5 kT at ν = 6ν0. At the higher velocities (3ν0 The transient field calibration has been corroborated making use of known g-factors of low-spin states in 156, 158, 160Gd populated by Coulomb excitation of thick Gd single crystals. For the high-spin states in these nuclei, the g-factors are found to decrease slightly, with the ratio g(10 + ) g(2 + ) reduced to 0.89±0.12, 0.83±0.11, and 0.93±0.13, respectively. Similar decreases have been observed previously for other N = 90−96 nuclei.

Continuous gamma radiation feeding high-spin isomers in 148, 149, 151, 152Dy and 147Gd

Abstract The energy, multipolarity and multiplicity spectra of the continuum gamma radiation feeding high-spin isomers in 148, 149, 151, 152Dy and 147Gd have been measured at several bombarding energies. The final nuclei were selected via a delayed coincidence technique while the use of a NaI(Tl) Compton shielded crystal allowed the primary gamma-ray spectra to be generated reliably from the observed spectra. It was found that: (i) the energy of both the gamma-ray statistical cascade and the neutron cascade increases with increasing excitation energy, the latter much more rapidly than expected; (ii) the multiplicity of gamma-ray cascades, in which a statistical transition was detected, is generally lower than that of the average cascade; (iii) stretched E2 spin-correlated transitions occur above J≅ 39 h in 152 Dy and above ∼ 50.5 h in 147 Gd , indicating the onset of collectivity at these spins — in addition, a region of predominantly dipole emitting states is located below T≲ 44 h in 147 Gd ; (iv) effective moments of inertia derived from the bump edge are 50–100% larger than those deduced from the density of stretched E2 transitions in the bump; (v) in 149,151Dy the bump edge is very sharp but no multiplicity features are observed; (vi) although the four Dy isotopes were populated at approximately the same excitation energy, they display considerable differences in their continuum properties. Probable interpretations of these observations are discussed, in particular we have suggested that several of the observed effects are consistent with the possible presence of high-K collective bands above the yrast line.

Radiocarbon Anomalies Observed for Plants Growing in Icelandic Geothermal Waters

Distribution profiles of radiocarbon in dissolved inorganic carbonate have been measured along two transects in the southern Pacific, east of New Zealand. Use of accelerator mass spectrometry, with its small-sample-size capability, made it possible to sample near-surface waters with a depth resolution of a few tens of meters. Sampling of deeper water was guided by salinity and temperature data transmitted by a conductivity-temperature-depth probe. The measurements, taken over the Chatham Rise, show highly structured profiles that can be correlated with known circulation patterns in this region.

The K-Shell Population of Ions Penetrating Ferromagnetic Solids

K-vacancy fractions as well as cross sections for creation and quenching of K-vacancies have been measured for O, F, Mg, Si, and S projectiles moving through solid Fe, Co, Ni and Gd at velocities ranging from 1.5v0 to 10.5v0. Two different techniques were used, i.e., the beam-X-ray and the probe-layer method, respectively. Based on comparisons with semiempirical estimates a number of different K-shell processes were identified. Direct Coulomb ionization and excitation and electron capture dominate at high velocities, whereas collision-perturbed deexcitation and quasi-molecular effects are important at low velocities. Distinct level-swapping effects are observed for O and F in Fe. The present data provide the basis for an investigation of the origin of the transient magnetic field in a recent paper.

M1 admixtures in transitions from γ-vibrational states in 152Sm, 154Gd and 156Gd

Abstract Measurements of M1 admixtures in a number of transitions depopulating 2, 3 + and 2, 2 + γ-vibrational states in 152 Sm, 154 Gd and 156 Gd are presented. In the case of 152 Sm, it is verified that the intrinsic static quadrupole moments of the γ band and the ground state band are equal to within 10%. It is concluded that the small M1 admixtures present in transitions between the two bands can be accounted for in first-order perturbation theory as a result of K = 1 impurities. The M1 admixture in the intraband transition 2, 3 + −2, 2 + of 152 Sm and 154 Gd is estimated and attributed to | g K − g R | ≈ 0.15 in both cases.

Measurement of g-factors in 170Yb, 172Yb and 174Yb by transient field interaction at high recoil velocities

Abstract A beam of 40 Ca ions at 168 MeV has been used to Coulomb excite high-spin states in 169 Tm and 170, 172, 174 Yb which recoiled through thin polarized iron at ν / c ≈ 3.5%. An enhanced transient field ≈ 6 times larger than the Lindhard-Winther prediction was observed and calibrated against the known g -factors in 169 Tm. Individual g -factors could not be extracted because of strong feeding; nevertheless, deviations from rotational behaviour (constant g -factors) would be detectable. Empirical fits to microscopic calculations of the rotational g -factors below spin 12 + suggest that if deviations from the simple rotational formula occur, they should be of the form g ( J ) = g 0 (1 + αJ 2 ). We find the following values in 170, 172, 174 Yb: α × 10 3 = −0.5±1.5, +1.0±1.5. The uncertainties are the level at which deviations from rotational behaviour are expected to occur. The results are discussed in terms of Coriolis anti-pairing effects.

The GT matrix elements in the decay of the mirror nuclei 47Cr, 51Fe and 55Ni

Abstract Three new mirror nuclei, 47 Cr, 51 Fe and 55 Ni, have been identified in ( 3 He, 2n) reactions. The measured half-lives were as follows: 47 Cr , 452 ± 18 ms ; 55 Fe , 245 ± 7 ms ; 55 Ni , 189 ± 5 ms . Known mass data were utilized to deduce log ƒt values and Gamow-Teller matrix elements for the three mirror β-decays. The experimental GT matrix elements are compared to the results of shell-model calculations.