Search

Data is presented on the radioactive decay of isotopes 256Rf and 249, 250No synthesized in complete fusion reactions 50Ti + 208Pb, and 48Ca + 204Pb, with subsequent evaporation of neutrons from the excited state of the composite nucleus. Experiments use high-intensity beams of accelerated heavy ions 48Ca and 50Ti from the U-400 cyclotron at the Flerov Nuclear Reactions Laboratory of the Joint Institute for Nuclear Research and the SHELS kinematic separator.

International audience; GABRIELA (Gamma Alpha Beta Recoil Investigations with the Electromagnetic Analyzer) is a detection system installed at the focal plane of the SHELS (Separator for Heavy Elements Spectroscopy) recoil separator for gamma and internal conversion electron spectroscopy of heavy and superheavy nuclei. GABRIELA has recently been upgraded. The characteristics of the new setup are presented using the Geant4 Monte Carlo simulation toolkit and validated against experimental results. The impact of summing on the gamma-ray and electron detection efficiencies is discussed.

International audience; The neutron yield from the spontaneous fission of the short-lived neutron-deficient$^{254}$Rf nucleus produced in the complete fusion reaction with the beam of multiply charged ions from the U400 accelerator at the Flerov Laboratory of Nuclear Reactions (FLNR), Joint Institute for Nuclear Research (JINR), is measured using the combined detection system of the SHELS velocity filter. The half-life and the branching ratio of$^{254}$Rf are also measured. The data on the multiplicity of prompt neutrons from spontaneous fission of$^{256}$Rf ($\bar {\nu }$ = 3.87 ± 0.34) are presented for the first time.

The analysis of fission events following the implantation of evaporation residues produced in the fusion reaction of 50Ti and 209Bi at different bombarding energies has revealed 5 millisecond decays, which are attributed to the spontaneous fission of proton-evaporation channels. The average cross sections for proton evaporation are found to be ∼100 and 10 times smaller than the largest neutron-evaporation channel cross section at the same excitation energy. These results suggest that the proton evaporation channel, albeit weak, may represent a realistic alternative to synthesize new, more neutron rich super heavy nuclei. Keywords: Fusion-evaporation reaction, Proton evaporation, Super heavy nuclei, Cross section

International audience; Experiments aimed at synthesizing and investigating the features of radioactive decay of isotopes of superheavy elements (Z ≥ 110) have been conducted in the Flerov Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research. Complete fusion reactions of an accelerated beam of$^{48}$Ca ions with transactinide targets with the subsequent evaporation of several neutrons from excited compound nucleus are typically used in these experiments. “Exotic” reaction channels with the evaporation of protons and several neutrons may be used to produce more neutron-rich isotopes of superheavy elements. The production cross sections were measured in experiments at the SHELS separator for Db and Rf isotopes produced in xn and pxn channels of the$^{50}$Ti +$^{209}$Bi →$^{259}$Db* reaction. The ratio of cross sections σ(xn)/σ(pxn) was on the order of 100.

The problem of studying the spontaneous fission of nuclei from the exotic region of short-lived neutron-deficient isotopes with Z ≥ 100 is considered. A combined detecting system is created in the focal plane of the VASSILISSA separator. The main part of this system is a neutron detector that allows us to measure the yields of spontaneous fission neutrons from nuclei produced in a total fusion reaction with heavy ion beams in the on-line mode. This procedure is used for the first time to acquire data on the emission of spontaneous fission neutrons from short-lived 244,246Fm isotopes. Data gathered earlier for 252No isotopes are refined in the scope of this work.

series of experiments performed in 2014–2015 using the SHELS separator and a beam of multicharged ions from the U-400 accelerator at the Flerov Laboratory of Nuclear Reactions (Joint Institute for Nuclear Research) in Dubna is described. In preparation for a large program of experiments with a beam of highly charged ions of 50Ti, an experiment is performed to study the spontaneous fissioning (SF) of short-lived neutron-deficient isotope 256Rf formed in complete fusion reaction50Ti + 208Pb = 256Rf + 2n. The half-life of 256Rf is measured along with the probability of its SF decay. The average number of neutrons per one event of 256Rf SF ( $$\bar v$$ = 4.47 ± 0.09) is obtained for the first time. The results from experiments to study the SF of short-lived neutron-deficient isotopes synthesized in complete fusion reaction 48Ca + 204Pb → 252No* are presented as well. Two short-lived activities attributed to the SF of the ground and isomeric states of 250No are revealed. The half-life, total kinetic energies of fission fragments, and neutron multiplicities are measured for the obtained short-lived nuclei. The average numbers of neutrons per one SF event are $$\bar v$$ = 4.38 ± 0.13 and $$\bar v$$ = 3.90 ± 0.20, respectively, for SF activity with t1/2 = 5.1 ± 0.3 and t1/2 = 36 ± 3 μs.

A high intensity ion beam of 50Ti ions was obtained using the ECR ion source on the U400 cyclotron. The experimental tests using accelerated 50Ti ions were performed with a modernized VASSILISSA separator (SHELS). Data has been obtained on the transmission coefficients of recoil nuclei synthesized in complete fusion reactions. Estimates from ion optical calculations performed in the design phase of the project of modernizing the separator are completely confirmed.

International audience; Spontaneous fission properties of the short-lived neutron-deficient 256Rf nucleus produced in thecomplete fusion reaction with a beam of multiply charged heavy 50Ti ions from the U-400 cyclotron (FLNR,JINR) are experimentally investigated. Its half-life and decay branching ratio are measured. The averagenumber of neutrons per spontaneous fission of 256Rf ( = 4.47 ± 0.09) is determined for the first time.

The neutron-deficient isotope 246Fm , produced in the complete fusion reaction 40Ar$ + $208Pb , was investigated. The main goal of the experiment was to determine the neutron multiplicity at spontaneous fission of this isotope. For experiments aimed at the study of spontaneous fission of transfermium nuclei improvements in the focal plane detector system of recoil separator VASSILISSA have been made. A neutron detector consisting of 54 3He -filled counters has been mounted around the focal-plane detector chamber. From the experimental data the average number of neutrons per spontaneous fission of 246Fm was determined ( $ \bar{{\nu}}$ = 3.55±0.5) .

The upgraded separator VASSILISSA was used to confirm results of previous experiments on the synthesis of the heavy isotopes of the element 112 obtained in complete-fusion reactions of 48Ca and 238U. An additional reason was the non-observation of any events in the same reaction studied with the BGS separator at Berkeley. Limits of $280 \leq A \leq 286$ for the atomic mass number of the observed spontaneously fissioning isotope were measured. The obtained results on the decay mode, half-life and production cross-section are in agreement with those obtained in our first experiment.

Within the past 15 years, the recoil separator VASSILISSA has been used for the investigations of evaporation residues produced in complete fusion reactions induced by heavy ions. The study of decay properties and formation of cross-sections of the isotopes of elements 110, 112 and 114 was performed using high-intensity 48 Ca beams and 232 Th , 238 U , 242 Pu targets. For further experiments aimed at the synthesis of the superheavy element isotopes ( Z ⩾110) with the use of intense 48 Ca extracted beams, improvements in the ion optical system of the separator and the focal plane detector system have been made. The results from the test reactions and new results for the isotope 283 112 are presented.

Summary We present results of the second experiment on the chemical identification of element 112. Similar to the first test in 2000, we aimed at the production of the spontaneously fissioning 283112 nuclei with T 1/2≈3min. A natU3O8 (with some Nd) target, 2mg of U/cm2 thick, was bombarded with 233-MeV 48Ca ions (the energy in the middle of the target layer). The nuclei recoiling from the target were thermalized in flowing helium. The target chamber was connected through a 25m long capillary to detectors of α-particles and fission fragments. All the equipment and detectors were kept at ambient temperature. According to the test experiments, of all the heavy elements produced in the bombardment, only Hg, Rn and At could be transported to the detectors. The first detecting device was similar to that used earlier – an assembly of 8 pairs of PIPS detectors coated with gold. Here one would observe the decay of element 112 atoms if they like Hg adsorbed on gold. The atoms which were not retained and freely passed through the PIPS detectors entered a new, flow-through ionization chamber, 5000 cm3 in volume, optimized for detecting fission fragments. The PIPS detectors and the ionization chamber were placed inside a large assembly of 3He – filled neutron counters to detect prompt neutrons from the fission events. In 22.5 days, a beam dose of 2.8×1018 ions was accumulated. More than 95 of the simultaneously produced α-active 185Hg (T 1/2=49 s) were found deposited already on the first pair of PIPS detectors; meanwhile, all the PIPSs did not detect any fission event. In the ionization chamber, eight fission events were observed in coincidence with neutron counts while the expected background was insignificant. Hence, the spontaneous fissions of the volatile activity can be conclusively attributed to the decay of element 112 produced in the fusion reaction 48Ca+ 238U, and formerly observed in Dubna physical experiments. Evaluation of the experimental data in terms of the adsorption enthalpies indicates much weaker interaction of element 112 with Au than that of Hg. One can conclude that in the given chemical environment, element 112 behaves like Rn rather than like Hg. The formation cross section of 283112 estimated from the data amounts to several pb. The experiments were carried out at the Flerov Laboratory of Nuclear Reactions at JINR in November–December 2001.

Within the past twelve years, the recoil separator VASSILISSA has been used for the investigations of evaporation residues produced in heavy-ion-induced complete fusion reactions. In the course of the experimental work, fourteen new isotopes have been identified by the parent-daughter correlations in the region of elements with 92≤Z≤94. The study of the decay properties and formation cross sections of the isotopes of elements 110, 112, and 114 was performed using high-intensity 48Ca beams and 232Th, 238U, and 242Pu targets. At the beam energies corresponding to the calculated cross-section maxima of the 3n evaporation channels, the isotopes 277110, 283112, and 287114 were produced and identified. For further experiments aimed at the synthesis of the superheavy element isotopes (Z≥110) with the use of intensive 48Ca extracted beams, improvements in the ion optical system of the separator and the focal plane detector system have been made.

Heavy-ion fusion reactions 48Ca + 204Pb and 44Ca + 208Pb leading to the same compound nucleus 252No* were run in attempts to produce new neutron-deficient spontaneous-fission isotopes of 249,250No using the electrostatic separator VASSILISSA. Production cross-sections for the spontaneous-fission activities with the half-lives 5.6 and 54 μs observed in these reactions are compared with the measured ones for the well-known isotopes of 251 - 255No formed in the heavy-ion fusion reactions 48Ca + 206Pb and 48Ca + 208Pb. The obtained excitation functions for the reaction products formed after the evaporation of 1-4 neutrons from the corresponding compound No nuclei have been compared with similar data obtained earlier and results of statistical model calculations.

International audience; Investigations of complete fusion reactions leading to the synthesis of heavy and superheavy nuclei have been an important part of the experimental program at the Flerov Laboratory of Nuclear Reactions (JINR, Dubna). For synthesis and decay studies of heavy nuclei, a project of modernization of the existing experimental set up VASSILISSA is now underway. The results of the first experimental tests with the modernized VASSILISSA separator are presented, in particular the experimentally measured transmission coefficients for recoil nuclei synthesized in asymmetric reactions with a Ne-22 beam. These results completely confirm the ion optical calculations performed during the design stage of the modernization.

Since the past 10 years, the recoil separator VASSILISSA has been used for the investigations of evaporation residues produced in heavy-ion-induced complete fusion reactions. In the course of experimental work in the region of the elements with 92⩽Z⩽94 , 14 new isotopes have been identified by the parent–daughter correlations. For further experiments aimed at the synthesis of the superheavy element isotopes ( Z⩾110 ) with intensive 48 Ca extracted beams, improvements in the focal plane detector system have been made. As a result, energy and position resolutions of the detectors have been significantly improved, the detection efficiency for the α -particles, emitted from the implanted into the focal plane detector recoil nuclei, has been increased to 85%. The decay properties of the new isotope of element 112 and the isotope of the new element 114 with mass 287 have been measured in two-nuclei decays.

The reaction 48Ca+238U was investigated at the recoil separator VASSILISSA at the Flerov Laboratory of Nuclear Reactions, JINR Dubna, in attempts to synthesize new isotopes of element 112. The experiments were performed at two beam energies resulting in excitation energies of the compound nucleus of 33 and 39 MeV. The collected beam dose was 3.5 × 1018 and 2.2 × 1018, respectively. Two spontaneous fission events were observed at the lower beam energy, which tentatively were assigned to the new neutron rich isotope 283112 produced in the reaction 238U(48Ca,3n)283112. The measured cross-section is (5.0+6.3−3.2) pb and the half–life is (81+147−32) s. No event was observed at the higher beam energy resulting in the upper cross–section limit of 7.3 pb.

224U nuclei were populated in fusion-evaporation reactions using a 206Pb target and an intense 22Ne beam. Fusion-evaporation residues were separated by the new separator SHELS at the FLNR, Dubna and implanted into a large-area double-sided silicon strip detector. Position- and time-correlated alpha decays were used to identify evaporation residues. A new $ \alpha$ -decay line at 8095(11) keV was observed in this work and assigned as the decay from 224U to the first excited 2+ in the daughter nucleus 220Th. Coincident photons were also observed allowing to unambiguously determine the excitation energy of the first excited 2+ state in 220Th to be 386.5(1) keV and not 373.3(1)keV as previously reported. The half-life of 224U was measured to be 396(17)μs.

Within the past seven years the electrostatic separator VASSILISSA [A.V. Yeremin et al., Nucl. Instr. and Meth. A 274 (1989) 528; A 350 (1994) 608] has been used for the investigations of evaporation residues (ER) produced in heavy-ion induced complete fusion reactions. Two types of such studies were of specific interest to us. These are the synthesis of heavy (Z ≥ 100) nuclides and investigations of heavy-ion fusion reactions leading to formation of neutron-deficient nuclei with Z ≥ 82 and high excitation energy ( 60 MeV ≤ E ∗ ≤ 200 MeV ). In the course of the experimental work the optimization of the ion-optical and other systems of the separator including the improvements in the focal plane detector system has been made. As a result, the separation efficiency values ranging from 3 to 30% were achieved for ER's produced in the reactions with heavy ions from 12C to 48Ti. The suppression factors > 1019 for the full energy beam particles and > 104 for multinucleon transfer reaction products were achieved. The results of the performed experiments illuminating the separator performance and future plans of the separator upgrade are briefly presented.

For experiments aimed at the study of spontaneous fission of transfermium nuclei improvements in the focal plane detector system of recoil separator VASSILISSA have been made. A neutron detector consisting of 54 3He-filled counters has been mounted around the focal-plane detector chamber. The reaction 48Ca + 206Pb = 2n + 252No is used for tuning the separator settings and calibrating the detector system with the spontaneous fission of the 252No. The average neutron number per 252No spontaneous fission event is as large as ν̅ = 4.06 ± 0.12. The short-lived heavy isotopes 244,246Fm, produced in the complete fusion reactions 40Ar + 206,208Pb, are investigated. The average number of neutrons per spontaneous fission of 244,246Fm from the experimental data were (ν̅ = 3.3 ± 0.3) and (ν̅ = 3.55 ± 0.50), respectively. Both values are determined for the first time.

Excitation functions are measured for the fusion reactions 27 Al+ 175 Lu and 31 P+ 169 Tm leading to the isotopes 192–198 Po. A comparison to the data for the reactions 100 Mo + 92–100 Mo shows that characteristics of the compound nucleus evaporation do not depend on the bombarding ion mass in the whole range of the entrance channel asymmetry up to the fully symmetrical systems. It is also shown that a satisfactory description of the experimental data is possible in the frame of the statistical deexcitation model only at an assumption involving, in comparison to theory predictions, a considerable reduction of macroscopic fission barriers for neutron-deficient isotopes of Bi.

The neutron detector with 3He -filled counters placed in the focal plane of the VASSILISSA separator is used for measuring the average number and determining the multiplicity distribution of prompt neutrons from the spontaneous fission of heavy short-lived isotopes. The test reaction $\ensuremath \mathrm{{}^{48}Ca}+\mathrm{{}^{206}Pb}=2{\rm n}+\mathrm{{}^{252}No}$ is used for tuning the separator settings and calibrating the detector system with the spontaneous fission of the 252No . The average neutron number per 252No spontaneous fission event is as large as $\ensuremath \bar{\nu}=4.06 \pm 0.12$ . The short-lived heavy isotope 244Fm , produced in the complete fusion reaction 40Ar + 206Pb , is investigated. The average number of neutrons per spontaneous fission of 244Fm from the experimental data ( $\ensuremath \bar{\nu}=3.3 \pm 0.3$ is determined for the first time.

Within the last five years the kinematic separator VASSILISSA [A.V. Yeremin et al., Nucl. Instr. and Meth. A 274 (1989) 528; and A.V. Yeremin et al., Preprint JINR E15-90-347, Dubna 1990] has been used for investigations of neutron deficient evaporation residues (ER) produced in heavy ion fusion reactions. In the course of this work optimization of the ion-optical and other systems of the separator including improvements of the focal plane detector system have been made. As a result, the separation efficiency values ranging from 3 to 30% were achieved for ERs produced in the reactions with heavy ions ranging from 16O to 40Ar. The suppression factors >1019 for the full energy beam particles and >104 for multinucleon transfer reaction products were achieved. The results of the performed experiments illuminating the separator performance are briefly presented.

Construction and properties of a double ionization chamber (DIC) are described. Heavy ion fusion-evaporation reaction products obtained at the focal plane of the kinematic separator VASSILISSA enter the DIC volume through a thin plastic window. After their thermalization in the gas, they drift in the electric field to the DIC cathode. Their α-decay and/or spontaneous fission are detected in 4π-geometry in two ionization chambers, divided by the common cathode. Using DIC the α-decay of Bi and Pb isotopes produced in the fusion reactions 40 Ar + 159 Tb and 40 Ca + 153 Eu were detected. A new isomer, 189m Bi was observed.

The deformed doubly magic nucleus (270)Hs has so far only been observed as the four-neutron (4n) evaporation residue of the reaction Mg-26+Cm-248, where a maximum cross section of 3 pb was measured. Theoretical studies on the formation of (270)Hs in the 4n evaporation channel of fusion reactions with different entrance channel asymmetry in the framework of a two-parameter Smoluchowski equation predict that the reactions Ca-48+Ra-226 and S-36+U-238 result in higher cross sections due to lower reaction Q values, in contrast to simple arguments based on the reaction asymmetry, which predict opposite trends. Calculations using HIVAP predict cross sections for the reaction S-36+U-238 that are similar to those of the Mg-26+Cm-248 reaction. Here, we report on the first measurement of evaporation residues formed in the complete nuclear fusion reaction S-36+U-238 and the observation of (270)Hs, which is produced in the 4n evaporation channel, with a measured cross section of 0.8(-0.7)(+2.6) pb at 51-MeV excitation energy. The one-event cross-section limits (68% confidence level) for the 3n, 4n, and 5n evaporation channels at 39-MeV excitation energy are 2.9 pb, while the cross-section limits of the 3n and 5n channel at 51 MeV are 1.5 pb. This is significantly lower than the 5n cross section of the Mg-26+Cm-248 reaction at similar excitation energy.

International audience; An IN2P3-JINR collaboration has launched a project called GABRIELA at the Flerov Laboratory for Nuclear Reactions (FLNR) within the Joint Institute for Nuclear Research (JINR) in Dubna (Russia). The goal of the project is to perform gamma-ray and internal conversion electron spectroscopy of heavy nuclei produced in fusion-evaporation reactions and transported to the focal plane of the recoil separator VASSILISSA. During five experimental campaigns of GABRIELA, the detection system has gained in sensitivity and new spectroscopic information has been obtained for 249Fm, 251Fm, 253No and 255Lr.

The new neutron deficient isotope 217U was produced in the bombardment of the 182W target with 40Ar ions and identified using a recoil-α-α correlation method. The α-decay energy and the half-life of 217U were determined to be 8005 ± 20 keV and 15.6 −5.7 +21.3 ms, respectively.

International audience; An IN2P3‐JINR collaboration has launched a project called GABRIELA at the Flerov Laboratory for Nuclear Reactions (FLNR) within the Joint Institute for Nuclear Research (JINR) in Dubna (Russia). The goal of the project is to perform gamma‐ray and internal conversion electron spectroscopy of heavy nuclei produced in fusion‐evaporation reactions and transported to the focal plane of the recoil separator VASSILISSA. During five experimental campaigns of GABRIELA, the detection system has gained in sensitivity and new spectroscopic information has been obtained for 249Fm, 251Fm, 253No and 255Lr. In this contribution new results for 253No will be discussed. © 2010 American Institute of Physics

The production of 283112 in 48Ca induced nuclear reactions was investigated using physical and chemical separation techniques. In the reaction 48Ca on 238U, four events were registered at the SHIP velocity filter. The mean atomic mass of the evaporation residues (EVR)

In continuation of our work on investigation of the neutron-deficient plutonium isotopes [1] we carried out the experiments aimed to produce new isotopes228,229Pu. The isotope228Pu has been produced in the bombardment of the208Pb target with a beam of24Mg and the isotope229Pu — in the reactions of207,208Pb targets with26Mg projectiles. The isotopes were identified after in-flight separation from the beam and target-like particles by the VASSILISSA electrostatic separator [2] and implantation into silicon strip detectors. The assignment of unknown α-decays was made by establishing their genetic position and time correlations with those belonging to known α-decay chains. The α-decay energies of228,229Pu were measured to be (7810±20) keV and (7460±30) keV, respectively.

In continuation of our experimental program on investigation of evaporation residues (ER's) in the region close to N=126 [1, 2], the new neutron-deficient isotope219U has been produced in the irradiations of an197Au target with a beam of27A1 ions. The identification of219U was made establishing genetic position and time correlations between the implanted ER's with their subsequentα-decays. Theα-decay energy and half-life were measured to be (9680±40) keV and (42−13+34)μs, respectively. To separate the evaporation residues in-flight the kinematic separator VASSILISSA [3] was used.

The neutron-deficient isotopes 257,258105 were produced in the reaction 27Al+236U in 6n and 5n evaporation channels, respectively. The evaporation residues emerging from the target were separated in-flight from the projectiles and from products of different nuclear reactions by the electrostatic separator VASSILISSA [1]. The isotopes were then implanted into position-sensitive silicon detectors and identified using the α-α-correlation method. The measured production cross-section is σ(5n)=(0.45±0.20)nb at E P =154 MeV and σ(6n)=(0.075±0.055) nb at E P =163 MeV. These cross-sections are compared with data measured for the same isotopes in the more symmetrical reaction 50Ti+209Bi.

The new neutron-deficient isotope218U was produced in the bombardment of197Au target with27Al ions and identified using theα-α correlation method. The α-decay energy and the half-life of218U were determined to be 8625±25 keV and 1.5−0.7+7.3 ms, respectively. Evaporation residues recoiling from the target were separated in-flight from the projectiles and from the products of other nuclear reactions by the electrostatic separator VASSILISSA [1].

In the heavy-ion complete fusion reaction208Pb+20Ne the new isotopes223,224U were produced. These nuclei were identified after in-flight separation with the kinematic separator VASSILISSA, followed by their implantation into a passivated ion implanted silicon detector and the observation of the genetic relationships of subsequent α-decays.223U was found to decay withEα=(8780±40) keV and T1/2=18 −5 +10 μs. For224U the α-line atEα=(8470±15) keV and T1/2=0.7 −0.2 +0.5 ms was observed.

In the heavy-ion complete fusion reaction208Pb+26Mg at a beam energy of 135 MeV the new nuclide230Pu was produced. The measuredα-decay energy was found to be Eα=7050±15 keV. The new isotope was identified after in-flight separation with the kinematic separator VASSILISSA, followed by its implantation into a silicon surface-barrier detector and the observation of the genetic relationships of subsequentα-decays. The half-life of226U was measured more accurately.

Experiments have been performed to synthesize isotopes of elements 114–116 in fusion reactions between 48Ca ions and 246, 248Cm, 243Am and 242Pu target nuclei. The detection of reaction products by recording spontaneous fission and α-decay events allowed us to set upper limits of 5 × 10−35 cm2 and ≈ 2 × 10 −34 cm2 on the production cross sections for superheavy elements with 2 h ≦ Tsf ≦ 1 y and 2 h ≦ Tα ≦ 10 d, respectively.

The Vassilissa facility is described. The main component is an electrostatic separator of complete-fusion reaction products from the ion beam. The facility is capable of transmitting recoil nuclei emitted by the target in the beam direction within a solid angle of 10 −2 sr and has a ± 10% spread in energy and ionic charge. The time required to transport the nuclei to the detectors is 3 × 10 −6 s The separation of scattered ions is performed using a system of three electrostatic condensers. Separation factors obtained for Ar, P and Ne are equal to 10 10 , 10 11 and 10 12 , respectively.

This report describes a series of experiments aimed on investigating characteristics of spontaneous fission of nuclei in the exotic region of short-lived neutron-deficient isotopes with Z ≥ 100. Unique data on the decay properties of neutron-deficient isotopes 244,246Fm, 250No, 252No, 254Rf and 256Rf produced in the complete fusion reactions with accelerated heavy ions 40Ar + 206,208Pb → 246,248Fm*, 48Ca + 204,206Pb → 252,254No*, 50Ti + 206,208Pb →256,258Rf* were obtained in experiments at the VASSILISSA (SHELS) separator combined with a neutron detector. This report describes a series of experiments aimed on investigating characteristics of spontaneous fission of nuclei in the exotic region of short-lived neutron-deficient isotopes with Z ≥ 100. Unique data on the decay properties of neutron-deficient isotopes 244,246Fm, 250No, 252No, 254Rf and 256Rf produced in the complete fusion reactions with accelerated heavy ions 40Ar + 206,208Pb → 246,248Fm*, 48Ca + 204,206Pb → 252,254No*, 50Ti + 206,208Pb →256,258Rf* were obtained in experiments at the VASSILISSA (SHELS) separator combined with a neutron detector. ispartof: 27TH INTERNATIONAL NUCLEAR PHYSICS CONFERENCE (INPC2019) vol:1643 ispartof: 27th International Nuclear Physics Conference (INPC) location:SCOTLAND, Glasgow date:29 Jul - 2 Aug 2019 status: published