Rotating Wheel Apparatus Research Articles

Production of Bh266 in the Cm248(Na23,5n)Bh266 reaction and its decay properties

The nuclide Bh266 was produced in the Cm248(Na23,5n)Bh266 reaction at beam energies of 125.9, 130.6, and 135.3 MeV. Decay properties of Bh266 were investigated with a rotating wheel apparatus for α and spontaneous fission (SF) spectrometry under low background conditions attained by a gas-jet transport system coupled to the RIKEN gas-filled recoil ion separator. Based on genetically correlated α−α and α-SF decay chains, a total of 23 chains were assigned to Bh266 and its daughter nuclide Db262 and granddaughter Lr258. The half-life of Bh266 was measured to be T1/122=10.0−1.7+2.6s which is an order of magnitude longer than the literature data. The α-particle energies of Bh266 disperse widely in the range of Eα=8.62–9.40MeV. The maximum production cross section for the Cm248(Na23,5n)Bh266 reaction was determined to be σ=57±14 pb at 130.6 MeV, whereas the upper limit for the Cm248(Na23,4n)Bh267 reaction was σ≤14 pb at 121.2 MeV. These cross sections are discussed by comparing with the literature data as well as the theoretical calculations.1 MoreReceived 11 June 2020Accepted 30 July 2020DOI:https://doi.org/10.1103/PhysRevC.102.024625©2020 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAlpha decayFissionLow & intermediate energy heavy-ion reactionsNuclear fusionNuclear reactionsPropertiesA ≥ 220Nuclear Physics

Superheavy element chemistry at GARIS

A gas-jet transport system has been installed to the RIKEN GAs-filled Recoil Ion Separator, GARIS to start up SuperHeavy Element (SHE) chemistry. This system is a promising approach for exploring new frontiers in SHE chemistry: background radioactivities from unwanted by-products are suppressed, a high gas-jet transport yield is achieved, and new chemical reactions can be investigated. Useful radioisotopes of 261 Rfa ,b , 262 Db, and 265 Sga ,b for chemical studies were produced in the reactions of 248 Cm(18 O,5n )261 Rfa ,b , 248 Cm(19 F,5n )262 Db, and 248 Cm(22 Ne,5n )265 Sga ,b , respectively. They were successfully extracted to a chemistry laboratory by the gas-jet method. Production and decay properties of 261 Rfa ,b , 262 Db, and 265 Sga ,b were investigated in detail with the rotating wheel apparatus for α- and spontaneous fission spectrometry. Present status and perspectives of the SHE chemistry at GARIS are also briefly presented.

Production ofDb262in theCm248(F19,5n)Db262reaction and decay properties ofDb262andLr258

The nuclide $^{262}\mathrm{Db}$ was produced in the $^{248}\mathrm{Cm}$($^{19}\mathrm{F}$,5$n$)$^{262}\mathrm{Db}$ reaction at beam energies of 103.1 and 97.4 MeV. Decay properties of $^{262}\mathrm{Db}$ were investigated with a rotating wheel apparatus for \ensuremath{\alpha} and spontaneous fission (SF) spectrometry under low background conditions attained by a gas-jet transport system coupled to the RIKEN gas-filled recoil ion separator. Based on genetically correlated \ensuremath{\alpha}-\ensuremath{\alpha} and \ensuremath{\alpha}-SF decay chains, a total of 76 chains were assigned to $^{262}\mathrm{Db}$ and its \ensuremath{\alpha}-decay daughter nuclide $^{258}\mathrm{Lr}$. No correlated decay chain was observed for Db produced in the $^{248}\mathrm{Cm}$($^{19}\mathrm{F}$,4$n$)Db reaction and its daughter Lr. The half-lives of $^{262}\mathrm{Db}$ and $^{258}\mathrm{Lr}$ were measured to be ${T}_{1/\phantom{\rule{0.0pt}{0ex}}2}=33.{8}_{\ensuremath{-}3.5}^{+4.4}$ and $3.{54}_{\ensuremath{-}0.36}^{+0.46}\mathrm{s}$, respectively, and they confirmed the literature data. The \ensuremath{\alpha}-particle energy $({E}_{\ensuremath{\alpha}})$ and intensity (${I}_{\ensuremath{\alpha}}$) of $^{262}\mathrm{Db}$ were revised to ${E}_{\ensuremath{\alpha}}$ = 8.46 \ifmmode\pm\else\textpm\fi{} 0.04 MeV (${I}_{\ensuremath{\alpha}}$ = 70 \ifmmode\pm\else\textpm\fi{} 5%) and ${E}_{\ensuremath{\alpha}}$ = 8.68 \ifmmode\pm\else\textpm\fi{} 0.03 MeV (${I}_{\ensuremath{\alpha}}$ = 30 \ifmmode\pm\else\textpm\fi{} 5%). The SF activity with ${T}_{1/2}$ = 30.2 \ifmmode\pm\else\textpm\fi{} 6.1 s was assigned to $^{262}\mathrm{Db}$, and the SF branch of $^{262}\mathrm{Db}$ was determined to be ${b}_{\mathrm{SF}}$ = 52 \ifmmode\pm\else\textpm\fi{} 4%. From an observation of two SF decays which correlated to the \ensuremath{\alpha} decay of $^{262}\mathrm{Db}$, an electron capture (EC) decay with ${b}_{\mathrm{EC}}$ = 2.6 \ifmmode\pm\else\textpm\fi{} 1.8% was suggested in $^{258}\mathrm{Lr}$. The production cross sections for the $^{248}\mathrm{Cm}$($^{19}\mathrm{F}$,5$n$)$^{262}\mathrm{Db}$ reaction were determined to be 2.1 \ifmmode\pm\else\textpm\fi{} 0.7 nb at 103.1 MeV and $0.{23}_{\ensuremath{-}0.11}^{+0.18}\mathrm{nb}$ at 97.4 MeV, whereas, those for the $^{248}\mathrm{Cm}$($^{19}\mathrm{F}$,4$n$)Db reaction were the upper limits of \ensuremath{\le}0.064 nb at 103.1 MeV and \ensuremath{\le}0.13 nb at 97.4 MeV. These cross sections are discussed by comparing with the literature data as well as the theoretical prediction.

Preparation of Thick Americium Targets and Synthesis of 259Db

A new isotope of Db has been produced via the reaction Am(Ne, 4n) at Elab = 118 MeV, and its half-life of 0.51± 0.16 s and α-decay energy of 9.47 MeV were determined in this work. The americium targets with thickness ranged from 0.7 to 1.0 mg/cm were prepared by molecular plating method through a single electrodeposition cycle. The reaction products were transported and collected using a helium-jet technique and a rotating wheel apparatus. The α decays of both the products and their daughter nuclides were detected by a series of Si(Au) surface barrier detectors arranged ingeniously. The identification of Db was performed based on the genetic relationship between the new activity and the known Lr established by α-recoiled milking measurement. The Qα value of Db derived from the present experiment is in good agreement with theoretical prediction.

A new alpha-particle-emitting isotope 259Db

An isotope of the element 105 with mass number 259 has been produced via the reaction 241Am(22Ne, 4n)259Db at Elab = 118 MeV. The reaction products were transported and collected using the helium-jet technique and the rotating wheel apparatus. The α-decays of the products and their daughter nuclides were detected by a set of Si(Au) detectors arranged ingeniously. The Z and A of the nuclide have been unambiguously identified by the genetic relationship between the new activity and the known nuclide 255Lr established by α-recoiled milking measurement. The new nuclide 259Db has a half-life of 0.51±0.16 s and decays by alpha-particle emission of Eα = 9.47 MeV. Furthermore, the nuclide 258Db and its daughter 254Lr have also been clearly observed using the same projectile-target combination. Their half-lives and α-particle energies determined in this work are in agreement with previous known data, thus also proving the reliability of our assignment of 259Db.

XPS and electrochemical characterization of tarnish films on dental alloys

Three gold resin casting alloys ranging in nobility between 30 and 74 wt.% have been analysed by XPS, SEM plus energy-dispersive spectroscopy (EDS) as well as by L * a * b * colorimetry before and after in vitro tarnishing in 0.1 M Na 2 S solution with a rotating wheel apparatus. The lower the nobility of the alloy, the higher the tarnishing tendency: the alloys appear darker with increased redness and yellowness, as determined by colorimetric analysis. On the three alloys, corrosion products of almost the same chemical composition are detected in different amounts. The products are mainly Cu (53-57 wt.%), S (23-29 wt.%) and Ag (∼4 wt.%), as determined by EDS. X-ray photoelectron spectroscopy analysis carried out in the first tarnishing steps indicates more sulphur enrichment on the surfaces of the alloys with the lower nobility. Auger maps of the tarnished surfaces show evidence of the onset of a selective reaction of sulphur with Cu and Ag in the first steps. The electrochemical results are in accordance with the previously exposed data: the polarization curves recorded on alloys with increasing Ag and Cu amounts show higher current density values indicating a worse performance.

Rhythmic theta-like unit activity of the hippocampal formation during acquisition and performance of avoidance behavior in rabbits

Neuronal activity was recorded from the hippocampal formation during instrumental conditioning of avoidance behavior in rabbits. The conditional stimuli (CSs) were pure tones, the unconditional stimulus (UCS) was a constant-current footshock, and the response was locomotion in a rotating wheel apparatus. Prior to conditioning the rabbits received pretraining, involving noncontingent presentations of the CSs and the UCS. The specific focus of this report is on neuronal records which displayed rhythmic bursts of action potentials similar to the theta rhythm of the EEG. Early in training, rhythmic theta-like neuronal bursts occurred throughout the CS-UCS interval on trials manifesting the initialmost behavioral conditioned responses (CRs). Late in training during asymptotic CR performance there was a build-up in the frequency and rhythmicity of neuronal bursts prior to the CR. The maximum frequency of bursting (9–10 Hz) always occurred just prior to the CR. Relatively little theta-like activity occurred in the early portions of the CS-UCS interval, in the late stage of training. During pretraining ample preresponse theta-like activity occurred in some subjects but not in others. However, no subject manifested a systematic build-up in bursting prior to behavioral responses in pretraining.

An overtraining-reversal effect with differential avoidance conditioning in rabbits

Two groups were formed from a large sample of rabbits used as subjects in ongoing studies of the neural correlates of discriminative avoidance conditioning and reversal. The members of one group (N = 9) received conditioning to criterion, whereas members of the second group (N = 9) received conditioning to criterion followed by three sessions of overtraining. All subjects received 5 days of reversal training. The groups were matched for mean number of sessions to the acquisition criterion. The CS+ and CS− were pure tones which differed in frequency, and the UCS was shock delivered through the grid floor of a rotating wheel apparatus. The response was locomotion within the wheel. The overtrained group showed a significantly greater discrimination appropriate to the reversal problem than did the nonovertrained group on Day 5 of reversal training. This result indicates that an overtraining reversal effect (ORE) occurs in the context of acoustically cued, aversively motivated discriminative avoidance behavior of rabbits.