Technetium measurements by accelerator mass spectrometry at LLNL

Abstract

Technetium-99 is a long-lived, high-abundance fission product which has been widely distributed in the environment through atmospheric testing, the nuclear fuel cycle, and nuclear medicine. It has a high potential for migration in the environment as the pertechnetate anion. At the Center for Accelerator Mass Spectrometry, methods are being developed for the detection of this radionuclide by accelerator mass spectrometry (AMS), including extraction from environmental samples, concentration and purification of the 99 Tc, conversion to a form appropriate for AMS analysis, and quantification by AMS. Besides interference from the stable (though relatively rare) atomic isobar 99 Ru, the detection of 99 Tc by AMS presents some technical challenges which are not present for the other radionuclides typically measured by AMS. These challenges are related to the lack of a stable Tc isotope. Here we present the status of our 99 Tc methods including discussion of interferences and sensitivity, and recent results for environmental samples and the IAEA reference material IAEA-381, Irish Sea water. Sensitivity is presently ~10 µBq (~1×10 8 atoms) per sample, limited primarily by 99 Ru introduced from process chemicals, and precision/reproducibility is ~15-25%.

Critical comparison of radiometric and mass spectrometric methods for the determination of radionuclides in environmental, biological and nuclear waste samples

“…The long half-life of 99 Tc (0.211 My) and low specific activity (6.3 × 10 8 Bq/g) makes mass spectrometry a sensitive method for the determination of 99 Tc, AMS [192][193][194], TIMS [195][196] and ICP-MS [46][47][48][49][50][51][52][53]197] have been used for the determination of 99 Tc. In AMS, the separated TcO 4 -is mixed with Al or Nb to prepare a target, the sputtered TcO -ions is then stripped to TcO 14+ , separated in mass spectrometry, and measured by a gas ionization chamber.…”

“…The sensitivity of this method depends very much on the amounts of Ru in the target. A detection limit of 6-10 μBq for water and environmental samples has been reported [192,194]. In TIMS, the separated TcO 4 -is transferred to filament and reduced to TcO 2 using HI, the iodine is removed by pre-heating to 930 °C and the Tc is then measured using magnetic sector thermal ionization mass spectrometers equipped with ion counter.…”

Determination of technetium-99 in environmental samples: A review

“…99 Tc can also be produced by cosmic ray reactions with Mo, Ru and Nb in the earth crust. It has been estimated that these two types of processes have produced about 60 PBq (6×10 16 Bq) of 99 Tc. This 99 Tc is mainly distributed in the crust.…”

“…Up to now, a huge amount of 99 Tc has been produced during the operation of the nuclear power plants. It has been estimated that [16][17][18][19] PBq ((1.6∼1.9)×10 16 Bq) of 99 Tc had been produced worldwide up to the mid 1980's [29]. It was calculated that the production rate of 99 Tc in nuclear power plants is about 5.8 TBq (GW(th)y) -1 [30].…”

“…The long halflife, and therefore low specific activity, of 99 Tc (0.64 Bq ng -1 ) makes mass spectrometry (MS) a potentially sensitive method for measurement of 99 Tc. Accelerator mass spectrometry (AMS) [14][15][16], thermal ionization mass spectrometry (TIMS) [17] and inductively coupled plasma mass spectrometry (ICP-MS) [18][19][20][21] have been applied for 99 Tc measurement. Among these MS techniques, ICP-MS is the most widely and frequently used mass spectrometric method for measurement of 99 Tc in many types of environmental samples, due to its low cost and easy accessibility.…”