C. Friedli

RAPID TRACE DETERMINATION OF RADIOSTRONTIUM IN MILK AND DRINKING WATER

A rapid method for determining traces of radiostrontium in milk and drinking water is described. The technique involves a batch treatment of the milk sample with a cation exchanger (DOWEX 50W X8) followed by a solvent extraction with a crown ether (DC18C6) and a precipitation of SrCO3. In the case of water, the strontium is extracted directly with the crown ether. The average separation yield is 74% for milk and 91% for water. The overall separation procedure takes about 8 hours. Activities as low as 0.03 Bq/1 can be determined with a low background GM-counter.

Lithium and beryllium trace determination using heavy-ion activation analysis

A novel procedure for measuring the concentrations of lithium and beryllium in different inorganic and biological samples has been studied using18O heavy-ion activation analysis. The specific reactions,7Li(18O,αn)2cF and9Be(180,2α)19O, are sensitive and selective if the bombardment energy is 25-MeV18O4+. The detection limits for non-destructive analyses are 10 ng Li and 2 ng Be for a 100-second cyclic irradiation. The technique has been tested by analyzing NBS reference materials. It can be applied to a large range of solid samples.

Trace determination of beryllium by heavy ion activation analysis

A novel procedure for measuring the concentration of trace beryllium in different samples has been studied using11B heavy ion activation analysis. The specific reaction,9Be/11B, 2n/18F, is sensitive and selective when using a 10 MeV11Be3+ bombardment energy. The detection limit for a nondestructive analysis is 0.1 ng for a 2 h irradiation in a μA cm−2 beam current. A precision of 12% was achieved at the 50 μg g−1 level. Beryllium has been determined in a standard beryllium-copper alloy NBS-SRM C1123. Glass samples containing up to 61 trace elements were also analyzed nondestructively. When using a clean vacuum irradiation chamber, the technique might allow ultra-trace determinations, dealing with solid samples of a few milligrams.

Trace determination of boron, silicon and sulfur with oxygen-18 ion bombardment

In order to determine traces of boron, silicon and sulfur, B(18O, x)27Mg, Si(18O, x)43Sc and S(18O, x)47V reactions have been investigated between 15 and 44MeV. At 34 MeV, only a few of the systematically identified nuclear interferences produce27Mg and the detection limit is 30ng boron for a 10 minute irradiation with a 0.3μA·cm−2 oxygen-18 beam. Silicon analysis has shown nuclear interferences from Al, P and K; interference-free detection limit is 80 ng silicon for an hour irradiation with a 0.4 μA·cm−2 beam at 39 MeV. There is no nuclear interference for the sulfur determination and the detection limit is 5 ng sulfur for a 30 minutes irradiation with a 0.5 μA·cm−2 beam at 39 MeV. Thus a selective and sensitive sulfur determination can be achieved.

Trace determination of silicon by heavy ion activation analysis

The Si(11B, x)34mCl and Si(19F, x)44mSc reactions have been studied in order to work out their capabilities in determining traces of silicon. The first one has been tested with beam energies ranging from 19 to 27 MeV11B; only Mg and Al have shown nuclear interferences and a 30-min 27 MeV11B irradiation yields a 14 ng detection limit. The second reaction, investigated in between 35 and 46 MeV19F, yields a 16 ng detection limit with a 2 hrs 46 MeV19F irradiation; at that energy only Al and P present nuclear interferences.

Some Aspects of the Behaviour of 90Sr in the Environment

By determining Sr apparent half-lives in soil, grass and milk over several years, it was shown that the concentration of Chernobyl Sr has rapidly decreased in these samples. Migration in the soil sublayers is certainly the major cause of this disappearance, as shown by profiles. But grass is also involved in this soil decontamination; indeed, the 9 Sr/Ca ratio is about 4 times higher in grass than in the corresponding soil. An estimation of the Sr migration rate is given and an explanation of the phenomenon is discussed.

Studies in heavy ion activation analysis. X: Trace determination possibilities with 11B ion bombardment

Abstract11B induced radioactivation was used to study the trace determination of light elements with 1≤Z≤17. 49 nuclear reactions were investigated with ion beam energies ranging from Elab=10 MeV to Elab=27 MeV. Five elements were found to be determinable nondestructively, selectively and sensitively: Li, Be, B, Mg and Si. Nuclear interferences have also been defined and quantified. The technique has been applied to simultaneous Li-B trace determinations in glass samples and to Mg determination in Al2O3 ceramic material.

Studies in heavy ion activation analysis trace determination possibilities with9Be bombardment

Abstract9Be induced radioactivation was used to study the trace determination of 19 elements at 3 different ion beam energies (Elab=14, 32 and 63 MeV9Be2+). Nine nuclear reactions, yielding radionuclides with half-lives longer than 2.5 m, present potential analytical features. Beside the very sensitive detection of B and N, the multielemental determination of Na, Si, Ca, Sc, and Zn is possible with a9Be ion beam of appropriate incident energy. Nuclear interferences have also been investigated and quantified.

Heavy ions activation analysis: Theoretical approach for optimizing cyclic analyses

Abstract A computer program using mathematical relations developed for cyclic irradiations has been written on an APPLE IIe computer. It allows a fast study of how parameters such as the number of cycles and the ratio of the half-life of the radionuclide of interest to the irradiation, counting and delay times influence the number of counts detected. The variation of the background due to the production of other radionuclides from the matrix has also been taken into account. Thus, for the analysis of a given material the best value of each of the adjustable parameters can be estimated so that a determination as sensitive and precise as possible can be obtained in the minimum of time. The case of the determination of traces of beryllium in an AsGa matrix, using the 9Be(18O, 2α)19O reaction is presented as an example of application.

Studies in heavy ion activation analysis. VI: trace determination possibilkities with 7Li ion bombardment

Abstract7Li induced radioactivation was used for the trace determination of hydrogen via the1H(7Li, n)7 Be reaction. At 21 MeV7Li, only boron and magnesium present small nuclear interferences. An activation curve has been established by bombarding a stack of thin mylar foils. The comparison of this curve with the excitation function for the forward reaction, namely7Li(p, n)7 Be, shows that the recoil range from the superficial hydrogen atoms is only 1.7 mg·cm−2, allowing post-irradiation etching. Hydrogen has been determined in titanium and lead bronze at the 100 ppm level with a relative precision of 6 to 10%. Studies of 32 potential interfering elements suggest the extension of Li activation to the trace determination of Na[23Na(7Li,6Li)24Na] and K[39K(7Li, d)44m,44Sc].