Rj Demeijer

RADIOMETRIC FINGERPRINTING OF SEDIMENTS ON THE DUTCH, GERMAN AND DANISH COASTS

Concentrations of natural radionuclides in the heavy-mineral fraction of coastal sands have been shown, in earlier work, to be distinctly different for two regions along the Dutch coast. Because these two regions have different source areas, it was concluded that concentrations of natural radionuclides in the heavy-mineral fraction of coastal sediments represent a radiometric fingerprint. This fingerprint is considered to be a sensitive tool for identifying sediments of different provenance. To further investigate this assumption, samples were collected along the North Sea and Baltic coasts of the Netherlands, Germany and Denmark, as an extension of the earlier work. In the present investigation, we find that two additional source areas may be identified using the radiometric fingerprint. The four regions correspond with glacial terranes of Saalian and Weichsellian age, and the present-day watersheds of the Elbe and Rhine river systems.

O-16 (ALPHA, P) F-19 REACTION AT EALPHA = 40 MEV

The 16O(α, p)19F reaction has been studied at Eα = 40 MeV. In this reaction high-spin states at high excitation energy are selectively excited. A study of positive parity states ranging from Jπ = 12+ to 132+ shows that the reaction can be described in terms of a direct transfer of a three-nucleon cluster with internal quantum numbers l = 0 and s = 12. An analysis in terms of a zero-range DWBA calculation accounts rather well for the shape of the angular distributions. The relative spectroscopic factors S for the transitions to the Jπ = 12+, 32+, 52+, 72+ and 92+ states have been compared with the intensity of the (λ, μ) = (6, 0) component in the SU(3) wave functions and are found to be in excellent agreement with calculated values. For the assumed Jπ = 112+ state at Ex = 9.90 MeV and the Jπ = 132+ states at Ex = 4.65 and 10.42 MeV the S-values are about three times larger than calculated. This might be due to small (sd)(fp)2 admixtures in the wave functions for these states. The analysis of the transitions to the negative parity states indicates that the shape of their angular distributions is sensitive to whether the transferred three-nucleon cluster originates from a p(sd)2 or a (sd)2(fp) coupling. Two negative parity states at Ex = 8.9 and 12.8 MeV are rather strongly populated. They could be the lower spin members of the weak-coupling doublets arising from the coupling of a p12. hole to the 20Ne Jπ = 6+ and 8+ states, respectively. No evidence is found for the excitation of the high-spin members. This is in agreement with the cluster model of Buck et al. which takes into account the spin-orbit potential of the triton cluster.

Two-nucleon T = 0 transfer reactions in the 0p shell

Abstract The 16 O(d, α) 14 N, 14 N(d, α) 12 C and 12 C(d, α) 10 B reactions at E d = 40MeV and the 12 C(α d)1 14 N at E α = 55 MeV were investigated. A total of seventeen transitions are analysed in terms of one-step, zero-range DWBA calculations, using the two-particle coefficients of fractional parentage obtained from the Cohen-Kurath Op shell wave functions. For most transitions, fair agreement is obtained between experiment and calculation, possible exceptions being the transition to the E x = 4.43 MeV, J π = 2 + state in 12 C and to the E x = 2.15 MeV, J π = 1 + state in 10 B, for which the calculations predict too much L = 0 strength. Where possible, a comparison with previous (p, 3 He) results is made. In 14 N a state at E x = 11.04 MeV was observed for which the values ( J π ; T ) = (3 + ; 0) are suggested. In 12 C we found, in addition to the well known T = 0 states, two relatively sharp T = 0 states at E x = 19.50 ± 0.10 and 20.55 ± 0.10 MeV. The shape and strength of the angular distribution for the transitions to these states can be approximately accounted for by the calculations, although no one-to-one correspondence between observed and predicted levels could be established.

PERFORMANCE OF SNAKE, A DEVICE TO ADJUST SHAPE OF A MAGNET FIELD BOUNDARY

Abstract The effect of a SNAKE, a flexible equipotential bar, on the shape of the fringe field of a charged-particle spectrograph magnet has been measured and compared with model calculations. Extensive field measurements have been made at several magnet excitations and for different shapes of the snake. The results verify that the “Effective Field Boundaries” (EFBs) of a magnet can be easily adjusted with the device described, after manufacture.

RADIONUCLIDE CONCENTRATIONS IN THE NORTHERN PART OF THE NETHERLANDS AFTER THE CHERNOBYL REACTOR ACCIDENT

Concentrations of radionuclides originating from the Chernobyl reactor accident were measured as a function of time in air, rainwater, grass, cows milk, vegetables and dust by means of high-resolution gamma-ray spectroscopy. Special attention was paid to grass and milk originating from the same meadows. Also, milk of cows temporarily kept inside after the accident was monitored until a few days after their release from the stables. Activity ratios in various types of samples and the implication of the sheltering measures for cows are discussed.

Measurements of radon-daughter concentrations in and around dwellings in the northern part of the Netherlands: a search for the influences of building materials, construction and ventilation

The concentration of radon daughters has been determined in and around 80 dwellings located in the northern part of the Netherlands by using a one-filter method. Median values of 2.0 and 0.4 mWL were measured for the indoor and outdoor concentrations, respectively. The average outdoor concentration was about an order of magnitude higher for wind directions between SE and SW than for SW-NW. On the average, dwellings with double-pane windows and/or concrete floors were found to have significantly higher radon concentrations than those with single-pane windows and/or wooden floors. For the living room of a particular dwelling 18 measurements were carried out. The data for this dwelling indicate a linear relation between the concentration indoors and outdoors with a slope of 3.8 +/- 2.0. This unexpected behaviour is thought to be related to ventilation via the crawl space. Measurements of ventilation patterns and measurements of radon concentrations in the living room and the crawl space are consistent with this picture.

INVESTIGATION OF STATES IN P-30 VIA THE SI-30(HE-3,T) P-30 REACTION T 30 MEV

The 30Si(30He, t)30P reaction has been measured for about 100 levels in 30P with Ex < 8.8 MeV. Little selectivity in the population of states has been observed. For 75 levels angular distributions have been analysed using a “fingerprint method” by determining the L-value from a comparison in shape with transitions to states with known Jπ. For possible mixed L-transitions a dominance of the higher L-value is observed for almost all cases. Coulomb displacement energy calculations utilizing shell-model wave functions have been used to identify T = 1 states.

MODELLING THE MIGRATION OF CONTAMINANTS IN SOIL

Abstract A new and general model entirely based on physical principles describing the migration of radioactive contaminants in soil is developed. This model is applied to the particular problem of transport of 137Cs in sandy soil over the last three decades, and the results are as far as possible compared with the (so far very scant) experimental data. The sensitivity of the calculated concentration profiles to variations in the model parameters is discussed; Fickian diffusion in the solid phase is in this application found to be the dominant parameter.

STRUCTURE STUDIES OF NA-23 FROM THE NE-20(ALPHA,P)NA-23 REACTION AT E-ALPHA = 39.5 MEV

Abstract The nuclear structure of 23 Na has been studied by means of the 20 Ne (α, p ) reaction at E α = 39.5 MeV. Differential cross sections were measured over an angular range from ≈ 7° to ≈ 70° for ≈ 50 states. The angular distributions are compared with distorted-wave Born approximation (DWBA) calculations assuming a transfer of a “triton-like” cluster of nucleons with relative orbital angular momentum 0 and spin 1 2 . The spectroscopic amplitudes for the J π = 1 2 + − 13 2 + states are compared with the leading term of an SU(3) projection from wave functions recently calculated for 20 Ne and 23 Na by treating sd shell orbitals outside a closed 16 O core. Satisfactory agreement is achieved for the lower-spin states at low excitation energies. For high-spin states at higher excitation energies the importance of configurations with particles outside the sd shell is apparent.

Measurements of time-averaged radon-daughter concentrations with passive dosemeters

With standard dosemeters of the Karlsruhe type it is possible to measure simultaneously time-integrated radon and radon-daughter concentrations. For this purpose the dosemeters were equipped with a lid and a bottom foil. Pre-etching conditions for either type of foil were optimized; under these conditions no effects of plate-out were observed. The method seems to be sensitive to neutral radon daughters only. Possible improvements of the dosemeter geometry are indicated.