I.G. Abdullaev

SSNTD and radiochemical studies on the transmutation of nuclei using relativistic ions

Extended targets were irradiated for transmutation studies with relativistic heavy ions. For this, a metal core was surrounded by a paraffin moderator. The metal is either copper or lead and it was irradiated with deuterium, alpha, or carbon beams of 1.5 or 3.7 GeV/u at the SYNCHROPHASOTRON, LHE, JINR, Dubna, Russia. During this irradiation copious amounts of secondary neutrons are produced and studied with SSNTD detectors and radiochemical sensors, for example: 139 La (n,γ) 140 La→ B- . The yield of reaction products allows an estimation of secondary neutron fluxes. The yields of all kinds of reactions produced with deuterium and alpha beams obey to some extent the law of limiting fragmentation, i.e. they show little influence on the energy and the kind of incoming particles. However, one observes with 44 GeV 12 C ions always enhanced nuclear cross-sections induced by secondary particles. This behavior could not be confirmed with theoretical estimations based on the Dubna Cascade Model in its Cascade Evaporation Model version (DCM-CEM). Finally, some results for transmutation studies on 127 I and Cu will be presented.

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.

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.

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.

Neutron production in extended Cu-target irradiated with relativistic 12C-ions at Dubna, as studied with SSNTD and nuclear chemistry

An extended Cu-target was irradiated with 22 and 44 GeV carbon ions, The target was in contact with a (CH2)(n)-block for the moderation of secondary neutrons. Small holes in the moderator were filled with either lanthanium salts or uranium oxide. The reaction La-139 (n,gamma) La-140 -->/(beta) was studied via the decay of La-140 (40 h), and the reaction U-238 (n, gamma) U-239 -->/(beta) Np-239 -->/(beta) was studied via the decay of Np-239 (2.3 d). In addition, a variety of solid state nuclear track detectors (SSNTD) were used. Results will be presented. The yields for the formation of (n, gamma) products agree essentially with other experiments on extended targets carried out at the Synchrophasotron LHE, JINR (Dubna). To a first approximation, the breeding rate of (n, gamma) products, as well as the specific track density, seen with several SSNTDs, doubles when the carbon energy is increased from 22 to 44 GeV. If, however, results at 44 GeV are compared in detail to those at 22 GeV, we observe an excess of (37 +/- 9) % in the experimentally observed Np-239-breeding rate over theoretical estimations. Experiments using solid state nuclear track detectors are giving similar results. We also observed in the past such excess in the yield of other secondary particles in relativistic heavy ion interactions above a total energy of approximately 35-40 GeV.

On Search and Identification of Fossil Tracks dne to Superheavy Cosmic Ray Nuclei (Z ≥ 110) in Meteoritic Crystals

A new method for investigation of the ultra-heavy component of Galactic cosmic-ray nuclei (Z = 50 – 92) has been developed since 1980. It depends on the ability of extraterrestrial silicate crystals (olivine) to register and store during many million years the tracks due to cosmic-ray nuclei with Z ≥ 22. Our approach bases on the partial annealing of both “fossil” tracks and the tracks due to accelerated Kr, Xe, Au, Pb and U ions, and on the chemical etching of total volume track length of the cosmic-ray nuclei in the olivine crystals. The crystals taken from Marjalahti and Eagle Station pallasites (the radiation ages are 180 and 45 million years respectively) were annealed at 703 K during 32 h and etched. The volume tracks due to Z ≥ 50 cosmic-ray nuclei were then measured. The intercomparison of track length spectra of the “fossil” tracks and the tracks due to the accelerated 238U and 208Pb nuclei proves unambiguously that the last two abundant peaks of “fossil” track length spectra (120 – 140 μm and 180 μm, first observed in 1980 in Dubna) are products of the recent nucleosynthesis in our Galaxy due to Pt-Pb and Th-U groups of cosmic-ray nuclei. During 1980 – 1996 more than 1600 Th-U “fossil” tracks were measured and 11 anomalously long tracks (L = 340 – 370 μm) were found. Concerning the origin of the anomalously long tracks we have determined the orientation of these tracks in olivine crystal with the Laue-Roentgen method. We estabilished that five anomalously long “fossil” tracks have an angle ≥ 15° to the main crystal plane (010) and subsequently can not be attributed to any actinide nuclei in meteoritic olivine crystals. Moreover, in the fossil track study of olivines annealed at 703 K during 32 h we found the 250 μm – long track which could not be attributed to Th-U nuclei at any orientation in the crystal lattice. Now we can set an upper limit of Z ≥ 110 (superheavy) nuclei abundance at the level NZ μ 110 / NTh, U ≤ (1÷3) · 10−3. Our goal is to obtain the final, necessary and sufficient proofs of the existence of SHE nuclei in Galactic matter.

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

Experiments with relativistic protons accelerated at the Synchrophasotron LHE, Dubna, with energies of 0.5, 1.0, 1.5, 3.7 and 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 . 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.

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

Experiments with relativistic protons accelerated at the Synchrophasotron LHE, Dubna, with energies of 0.5, 1.0, 1.5, 3.7 and 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 . 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.

Non-Destructive Method of Pu and U Isotope Determination in Specimens

Now it is determined, that plutonium concentration in upper layer of soil (0–30cm) is about 10−13 gram of Pu per gram of soil in Central and Eastern Europe countries.