Durability of targets and foils in experiments on synthesis of superheavy nuclei

Durability of targets and window foils irradiated by intense heavy ion (HI) beams in the experiments on synthesis of superheavy nuclei (SHN), which are carried out in Dubna with a Gas-Filled Recoil Separator (DGFRS), has been considered. High fluxes of HIs and heat generated within relatively small areas and thicknesses of the target and foils are inherent in such long-term experiments. The ability of these elements to withstand radiation damages, sputtering and evaporation of atoms becomes questionable. All the processes are influenced by the target (foil) temperature and none of them is independent of the others, but they can be considered separately. Thus, sputtering yields were approximated on the grounds of available models and experimental data and compared to the results of measurements carried out to verify the estimates. The temperature of the target (foil), in turn, was estimated in the conditions of pulse heating followed by subsequent cooling with a radiation emitted from their surfaces. These conditions correspond to the rotating target and window irradiated by a continuous HI beam in the DGFRS experiments. Estimates show that radiative cooling might be the most effective way of heat removal at the temperature of few hundred Celsius degrees

Charge distributions of Ra recoil ions produced in 12C+Pb fusion-evaporation reactions

Charge state distributions of the Ra recoil ions produced in the 12C+Pb fusion-evaporation reactions have been obtained by measuring their yields as a function of the high voltage applied to an electrostatic deflector. Well-defined two-humped yield curves for evaporation residues (ERs) were observed. Such observations can be explained by the different sets of charge states inherent in Ra recoil ions. These charge sets correspond to the equilibrated and nonequilibrated components, as earlier observed for evaporation residues produced in different reactions. The main parameters of the distributions (mean charge values, widths, and relative intensities) for both components have been estimated using Monte Carlo simulations of the transmission of the Ra recoil ions through the deflector. For the equilibrated component the values of the mean charge and width are close to those given by different empirical systematics. For the nonequilibrated component these parameters have been obtained for the first time. The additional nonequilibrated ionization is presumably due to the formation of inner shell vacancies produced by the internal conversion of nuclear isomeric transitions of ERs. Nonequilibrated charge parameters obtained for Ra recoil ions are compared to similar available experimental data and some theoretical predictions

Investigation of the quasifission process by theoretical analysis of experimental data of fissionlike reaction products

The fusion excitation function is the important quantity in planning experiments for the synthesis of superheavy elements. Its values seem to be determined by the experimental study of the hindrance to complete fusion by the observation of mass, angular and energy distributions of the fissionlike fragments. There is ambiguity in establishment of the reaction mechanism leading to the observed binary fissionlike fragments. The fissionlike fragments can be produced in the quasifission, fast fission, and fusion-fission processes which have overlapping in the mass (angular, kinetic energy) distributions of fragments. The branching ratio between quasifission and complete fusion strongly depends on the characteristics of the entrance channel. In this paper we consider a wide set of reactions (with different mass asymmetry and mass symmetry parameters) with the aim to explain the role played by many quantities on the reaction mechanisms. We also present the results of study of the $^{48}$Ca+$^{249}$Bk reaction used to synthesize superheavy nuclei with Z = 117 by the determination of the evaporation residue cross sections and the effective fission barriers $$ of excited nuclei formed along the de-excitation cascade of the compound nucleus.Comment: 21 pages, 15 figures, 2 table

Competition of fusion and quasi-fission in the reactions leading to production of the superheavy elements

The mechanism of fusion hindrance, an effect observed in the reactions of cold, warm and hot fusion leading to production of the superheavy elements, is investigated. A systematics of transfermium production cross sections is used to determine fusion probabilities. Mechanism of fusion hindrance is described as a competition of fusion and quasi-fission. Available evaporation residue cross sections in the superheavy region are reproduced satisfactorily. Analysis of the measured capture cross sections is performed and a sudden disappearance of the capture cross sections is observed at low fusion probabilities. A dependence of the fusion hindrance on the asymmetry of the projectile-target system is investigated using the available data. The most promising pathways for further experiments are suggested.Comment: 8 pages, 7 figures, talk presented at 7th International School-Seminar on Heavy-Ion Physics, May 27 - June 1, 2002, Dubna, Russi

The use of {99m}Tc-Al[2]O[3] for detection of sentinel lymph nodes in cervical cancer patients

The purpose of the study was to evaluate the feasibility of using {99m}Tc-Al[2]O[3]- based radiopharmaceutical, a novel molecular imaging agent for sentinel lymph node detection in patients with invasive cervical cancer. The study included 23 cervical cancer patients (TlaNxMx- T[2]bNxMx) treated at the Tomsk Cancer Research Institute. At 18 hours before surgery, 80 MBq of the {99m}Tc-Al[2]O[3] were injected peritumorally, followed by single-photon emission computed tomography (SPECT) of the pelvis and intraoperative SLN identification. Twenty-seven SLNs were detected by SPECT, and 34 SLNs were identified by intraoperative gamma probe. The total number of identified SLNs per patient ranged from 1 to 3(the mean number of SLNs was 1.4 per patient). The most common site for SLN detection was the external iliac region (57.2%), followed by the internal iliac, obturator, presacral and retrosacral regions (they amounted to 14%, respectively),and the parametrial region (1%). Sensitivity in detecting SLNs was 100% for intraoperative SLN identification and 79% for SPECT image

Опыт применения стереотаксической лучевой терапии при олигометастазах колоректального рака в печени

Introduction: The problem of treating patients with unresectable liver metastases of colon cancer is currently far f rom being solved. One possible approach is the use of stereotactic body radiotherapy.The purpose of this study was to evaluate the immediate and long-term results of stereotactic radiotherapy in patients with colorectal cancer and oligometastatic liver metastases.Methods: This study was designed as a retro-prospective, open-label, controlled, non-randomized clinical trial. We assessed one-year local control, one-year overall survival, progression-free survival, and toxicity in 60 patients with oligometastatic liver disease from colorectal cancer who underwent stereotactic body radiotherapy, with median dose of 54 Gy.Results: The median follow-up was 20,1 months. One-year local control (LC) was 73,7 % (95 % CI = 62,7–86,6 %). Oneyear overall survival (OS) was 92,8 % (95 % CI = 86,3–99,9 %), one-year progression-free survival (PFS) was 31,3 % (95 % CI = 21,1–46,4 %) with a median of 8,1 months. Grade ≥ 3 toxicity was not noted. No cases of radiation-induced liver failure were observed. Radiation dose (HR = 0.88, 95 % CI = 0.81–0.95, p = 0.00087), metastasis size (HR = 1.51, 95 % CI = 1.07–2.12, p = 0.01858) and their number (HR = 1.8, 95 % CI = 1.01–3.22, p = 0.04669) are significant risk factors for LC. Metastasis size > 3 cm is a significant risk factor for LC (HR = 5.5, 95 % CI = 1.7–17.9, p = 0.005) and OS (HR = 3.8, 95 % CI = 1.3–11.7, p = 0.02).Conclusion: Stereotactic body radiotherapy is an effective and safe method of providing local control of oligometastatic liver metastases in colorectal cancer as part of a combined treatment approach. Further studies are required to individualize the indications for this treatment method.Обоснование: Проблема лечения больных с нерезектабельными метастазами рака толстой кишки в печени в настоящее время далека от решения. Один из возможных подходов – применение стереотаксической лучевой терапии.Цель исследования: Оценка непосредственных и отдаленных результатов стереотаксической лучевой терапии в рамках комбинированного лечения рака толстой кишки с олигометастатическим поражением печени.Методы: Данное исследование проведено как ретроспективное открытое контролируемое нерандомизированное клиническое исследование. Одногодичный локальный контроль, одногодичная общая выживаемость, выживаемость без прогрессирования и токсичность были оценены у 60 больных с олигометастатическим поражением печени на фоне колоректального рака, которым проводилась стереотаксическая лучевая терапия, медиана суммарной очаговой дозы 54 Гр.Результаты: Медиана наблюдения составила 20,1 мес. Одногодичный локальный контроль (ЛК) достиг 73,7 % (95 %ДИ = 62,7–86,6 %). Одногодичная общая выживаемость (ОВ) составила 92,8 % (95 % ДИ = 86,3–99,9 %), одногодичная выживаемость без прогрессирования (ВБП) – 31,3 % (95 %ДИ = 21,1–46,4 %) с медианой 8,1 мес. Токсичности 3 степени и выше не отмечено. Случаев радиационно индуцированной печеночной недостаточности не наблюдалось. Было установлено, что доза облучения (HR = 0,88, 95 % ДИ = 0,81–0,95, p = 0,00087), размер метастазов (HR = 1,51, 95 % ДИ = 1,07–2,12, р = 0,01858) и их число (HR = 1,8 95 % ДИ = 1,01–3,22, р = 0,04669) являются значимыми факторами риска для ЛК. Размер метастазов > 3 см является значимым фактором риска по снижению показателя локального контроля (HR = 5.5, 95 % ДИ = 1.7–17.9, p = 0.005) и ОВ (HR = 3.8, 95 % ДИ = 1.3–11.7, p = 0.02).Заключение: Стереотаксическая лучевая терапия – эффективный и безопасный метод обеспечения локального контроля над олигометастатическим поражением печени при колоректальном раке в рамках комбинированного подхода к лечению. Требуется проведение дальнейших исследований для индивидуализации показаний к проведению данного метода лечения и оптимизации его методологии.

Attempt to produce element 120 in the 244 Pu + 58 Fe reaction

An experiment aimed at the synthesis of isotopes of element 120 has been performed using the 244 Pu( 58 Fe,xn) 302−x 120 reaction. No decay chains consistent with fusion-evaporation reaction products were observed during an irradiation with a beam dose of 7.1 × 10 18 330-MeV 58 Fe projectiles. The sensitivity of the experiment corresponds to a cross section of 0.4 pb for the detection of one decay