R.I. Petrova

Nuclear track radiography of “Hot” aerosol particles

Abstract Nuclear track radiography was applied to identify aerosol “hot” particles which contain elements of nuclear fuel and fallout after Chernobyl NPP accident. For the determination of the content of transuranium elements in radioactive aerosols the measurement of the α-activity of “hot” particles by SSNTD was used in this work, as well as radiography of fission fragments formed as a result of the reactions (n,f) and (γ,f) in the irradiation of aerosol filters by thermal neutrons and high energy gamma quanta. The technique allowed the sizes and alpha-activity of “hot” particles to be determined without extracting them from the filter, as well as the determination of the uranium content and its enrichment by 235 U, 239 Pu and 241 Pu isotopes. Sensitivity of determination of alpha activity by fission method is 5×10 −6 Bq per particle. The software for the system of image analysis was created. It ensured the identification of track clusters on an optical image of the SSNTD surface obtained through a video camera and the determination of size and activity of “hot” particles.

On the determination of and content in human tissues

Abstract The growing concentration of man-made Pu in natural environment—water, soil, plants and food can provide the serious danger for all kind of animals and especially for mankind. Actually, as it has been established recently, Pu is accumulated during the whole life and the dangerous concentrations are estimated to be 10 −12 – 10 −13 g of Pu/g of human tissues. We warn that now the average concentration of Pu in human body is not less that 10 −14 g/g and much higher for some “hot” regions in Europe and Asia. Here we present the data on 239 Pu and also 241 Am in human hair (Semipalatinsk region area) and in human gall stones of some samples from more “quiet” regions—Minsk (Belarus) and Krakow (Poland). At the measurements of 239 Pu concentration in human hair and gall stones it has been found that it varies from 10 −13 up to 3×10 −12 g/g for south part of heavily damaged Semipalatinsk nuclear bomb test site region. Further possible improvement of neutron–gamma activation analysis—up to the level of 10 −15 g/g of Pu in human tissues, based on application of ultra clean chemicals and track detectors and on selective extraction of U out of electroplated Pu layers in flow of chlorides at high temperatures are discussed. Such upgrading the method can allow one to use the specimens of human tissues as small, as 0.1– 0.2 g in the routine Pu analysis.

Fission of Pb nuclei induced by 0.5, 1.0, 1.5, 3.7 and 7.4 GeV protons in the volume of massive U/Pb and Pb targets

Abstract Experiments with relativistic protons accelerated at the Synchrophasotron LHE, Dubna, with energies of 0.5, 1.0, 1.5, 3.7 and 7.5 GeV hitting massive targets of (nat. U)/Pb and Pb were carried out using SSNTD during the years 1996–1999. The beam profiles and intensities of both primary particles and fast secondary neutrons were measured inside the massive cylinder blocks of Pb and U by counting fission fragment tracks due to the induced fission of Pb nuclei. The beam diameter typically increases by 20–30% at the depth 10 and 20 cm . With increasing the energy of protons the number of secondary neutrons increases with the depth of the target. Further studies on beam profile measurements inside the massive heavy metal targets are discussed.

On problem of ultrasensitive determination of man-made plutonium in living species

Abstract To improve the sensitivity of the method of Pu determination in specimens we applied two additional steps of chemical separation of Pu from U. After the usual chemical separation of Pu we used second step with ion-exchange column, where the ions of U 4+ were absorbed by sorbent and Pu 3+ ions remains in solution. For converting Plutonium to Pu 3+ state the electrochemical procedure has been used. After the electrochemical separation procedure the solution was deposited onto quartz glass. Then the quartz glass plates were inserted into the gas mixture flow (SOCL 2 +air) at the temperature 650°C. Such a procedure extracts ≥90% U from Pu layer. Now we provide the chemical separation of Pu from U by a factor ≥10 7 . It means that now we are able to perform the routine Pu analysis at the level of sensitivity 10 −14 –10 −15 g/g. By using combined n-γ activation technique we can determine the Pu content in the small fragments of tissues of living species with the weight as small as 0,05-0,1 gram. The new technique could be used in routine analysis of Pu in population of heavily Pu damaged regions (Chernobyl, Ural Region, Semipalatinsk).

On determination of Th concentration in specimens by means of gamma rays and alpha particles

Abstract Experiments on improving the track technique for the determination of Th content in natural samples have been performed. For Th concentration measurements, γ-rays with energies of 18 and 20 MeV were used. For γ-rays in the energy range 6–23.5 MeV, the ratio of fission fragment track densities NU/NTh of these elements for thick targets has been obtained. The ratio ranges from 1.7 to 3.2 with the maximum at a γ-ray energy of 15 MeV. The determined Th concentrations in the calibrated Th standards and iron manganese nodules agree, within experimental error, with the known values. For 9.1 MeV/n α-particles, the track density ratio NTh/NU has been found to be equal to (1.06 ± 0.07), but the Th content was lowered, possibly due to the vertical inhomogeneity of the α-particle beam and also due to partial thermal fading of the tracks in mica. The investigation was performed at the Laboratory of Nuclear Reactions, JINR.

SSNTD studies of lead nuclei fission induced by relativistic p, d, He and 12C projectiles inside massive Pb and U targets

Abstract A series of experiments was carried out with relativistic protons, deuterons, helium and carbon-12 projectiles accelerated at SYNCHOPHASOTRON LHE, Dubna which hit massive Pb and U targets. The beam profiles and intensities of both primary particles and secondary fast neutrons were measured using plastic SSNTD inside the massive cylinder blocks of Cu, Pb and U by counting of fission fragment tracks due to the induced fission of Pb nuclei. The beam diameter increases typically by 20–30% at the depth 10 and 20 cm. With increasing the energy of projectiles the number of secondary neutrons rises with the depth for protons, deutrons and helium ions. Nevertheless, for 12 C ions beams with changing the energy from 18 GeV to 44 GeV we first observe the effect of significant increase both the yield of secondary fast neutrons and the half-width of the beam. The observed enhanced yield of secondary fast neutrons confirms unusual behavior of nuclear interaction cross section of 44 GeV 12 C ions observed earlier in our studies with massive blocks of Cu, Pb and U.

Uranium and thorium content determination in solids using thermal neutron and double gamma irradiation methods

Abstract Two different methods for simultaneous determination of the uranium (U) and thorium (Th) content in diverse solid construction materials, soil samples and natural minerals were applied. The first method consists in the double irradiation of diverse powdered solid, packed in Mylar envelops used as fission fragment track detectors, with 23 MeV gamma rays and then after remounting, with thermal neutron at the JINR microtron MT- 25. The second method consists in the double irradiation of the same specimens mounted as layers, also in contact with Mylar, with high fluence (up to 10 19 cm −2 ) of 23 and 15 MeV gamma rays. In both cases well-calibrated U nat etalon layers were used to check gamma ray and thermal neutron fluence. The data obtained display the reliable correspondence of both methods in the interval of 10 −6 – 10 −8 g / g of U and Th content in diverse solid samples.

Fossil track studies of the Omolon pallasite crystals

Abstract The olivine and stanfildite crystals from Omolon pallasite meteorite were selected from some residue and from locations of an about 150 g fragment of that meteorite in the Meteoritic Committee, Moscow, Russia. The radiation age of Amnion pallasite was determined to be about 78 MY The Olivine crystals were mounted in epoxy resin, polished and etched in Krishnaswami solution, modified by adding 30 g per liter oxalic acid. The etching of the olivine crystals was performed in hermetically closed vessels during 36–72 hours at T = 100 ° C. The measured Fe- group track density varies from 3 × 10 4 up to 2.6 × 10 5 track. cm −2 . The measure in 12 Fe-group track rich olivine 43 track due to VVH nuclei were found. It means that the depth of ablation of Omolon meteorite does not exceed (8.2 ± 2.1) cm out of preatmospheric surface for the most favourable locations.

Determination of the track age of some terrestrial and meteoritic minerals

Abstract The track age measurements of a number of crystal minerals and natural glasses were performed. The effects of partial annealing of “fossil” fission fragment (f.f.) tracks were taken into account - either by comparison of “ fossil” and “fresh” f.f. track length spectra or by intercomparison of f.f. track diameters for natural glasses.

On search and identification of tracks due to short-lived SHE nuclei in extraterrestrial crystals

Abstract The unique approach for search and unambiguous identification of short-lived (T1/2=103–107 years) superheavy nuclei in cosmic-ray products of the recent nucleosynthesis in our Galaxy are discussed. It is based on: (a) the ability of non-conducting crystals to register and to store for many million years the tracks due to fast nuclei with atomic number Z⩾20 (“fossil” tracks); (b) calibrations of the said crystals with accelerated heavy ions (20⩽Z⩽92) and on revealing the volume etchable track length (VETL) of the fast nuclei coming to rest inside crystals—both of fossil and “fresh” tracks—to determine the charge distribution of cosmic-ray nuclei tracks and (c) the so-called “four-zone” model of tracks in crystals (and also glasses) which provides not only the VETL track length dependence for 20⩽Z⩽92 nuclei but also demonstrates the regular annealing behavior of VETL of 20⩽Z⩽92 nuclei in a broad temperature interval. This approach was first applied in the early 1980s to investigate the “fossil” tracks due to 22⩽Z⩽92 cosmic-ray nuclei in olivine crystals from meteorites-pallasite Marjalahti and Eagle Station. The discovery of Th–U cosmic-ray nuclei tracks in 1980 was unambiguously confirmed by calibrations of the same crystals with 238 U , 197 Au and 208 Pb accelerated ions in the late 1980s. More than 1600 tracks due to cosmic-ray actinide nuclei were measured during the last two decades of the 20th century. Also, 11 anomalously long tracks (track length exceeds by a factor (1.6±0.1) the track length due to Th–U nuclei were measured. The detailed analysis shows that at least 5 of these tracks could not be attributed to the Th–U nuclei. It means that now we have a preliminary proof on the existence Z⩾110 nuclei in cosmic-rays. The abundance is Z⩾110/Th–U=(1–3)×10−3 in Z⩾110 freshly formed cosmic-rays (time interval 103–107 years). The method proposed can provide the necessary and sufficient conditions for the discovery of Z⩾110 nuclei in nature.