Test of internal-conversion theory with a measurement in

We have measured the K-shell and total internal conversion coefficients for the 150.8-keV E3 transition in 111Cd: αK = 1.449(18) and αT = 2.217(26) respectively. The αK value agrees well with Dirac-Fock calculations, in which the effect of the K-shell atomic vacancy is included. It is consistent with our previous precise measurements of αK values, which cover a range of atomic numbers, and extends that range down to Z = 48. The αT measurement, however, disagrees by about two standard deviations from the calculated αT value, whether the atomic vacancy is included or not

Excitation function for the production of 262Bh (Z = 107) in the odd-Z projectile reaction 208Pb(55Mn, n)

The excitation function for production of 262Bh in the odd-Z-projectile reaction 208Pb(55Mn,n) has been measured at three projectile energies using the Berkeley Gas-filled Separator at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron. In total, 33 decay chains originating from 262Bh and 2 decay chains originating from 261Bh were observed. The measured decay properties are in good agreement with previous reports. The maximum cross section of 540 +180 -150 pb is observed at a lab-frame center-of-target energy of 264.0 MeV and is more than fives times larger than that expected based on previously reported results for production of 262Bh in the analogous even-Z-projectile reaction 209Bi(54Cr,n). Our results indicate that the optimum beam energy in one-neutron-out heavy-ion fusion reactions can be estimated simply using the "Optimum Energy Rule" proposed by Swiatecki, Siwek-Wilczynska, and Wilczynski

Development of an odd-Z-projectile reaction for heavy element synthesis: 208Pb(64Ni, n)271Ds and 208Pb(65Cu, n)272111

Seven {sup 271}Ds decay chains were identified in the bombardment of {sup 208}Pb targets with 311.5- and 314.3-MeV {sup 64}Ni projectiles using the Berkeley Gas-filled Separator. These data, combined with previous results, provide an excitation function for this reaction. From these results, an optimum energy of 321 MeV was estimated for the production of {sup 272}111 in the reaction {sup 208}Pb({sup 65}Cu, n). One decay chain was observed, resulting in a cross section of 1.7{sub -1.4}{sup +3.9} pb. This experiment confirms the discovery of element 111 by the Darmstadt group who used the {sup 209}Bi({sup 64}Ni, n){sup 272}111 reaction

New isotope 264Sg and decay properties of 262-264Sg

New isotope, 264Sg, was identified using the 38U(30Si,xn)268-xSg reaction and excitation functions for 262-264Sg were measured. 264Sg decays by spontaneous fission with a half life of 37 +27/-11 ms. The spontaneous fission branch for 0.9-s 263Sg was measured for the first time and found to be (13+-8) percent. 262Sg decays by spontaneous fission with a 15 +5/-3 ms half-life. Spontaneous fission partial half-life systematics are evaluated for even-even Sg isotopes from 258Sg through 266Sg, spanning the transition region between the N=152, Z=100 and N=162, Z=108 deformed shells

The cyro-thermochromatographic separator (CTS): A new detection and separation system for highly volatile osmium and hassium (element 108) tetroxides

We implemented a new concept for heavy element chemistry research using an ion separator to separate the desired products from the beam, transfer products and other undesirable by-products prior to chemical studies. First, a Recoil product Transfer Chamber (RTC) was designed and attached to the Berkeley Gas-filled Separator (BGS) to collect and transfer the recoiling products to the chemical separation system. The RTC consists of a wire-grid-supported thin mylar foil ({le}) 200 {micro}g/cm{sup 2} that separates the BGS detector chamber, at 1.3 mbar pressure, from the chemistry system at different pressures ranging from 480 mbar to 2000 mbar. The overall transport efficiency ranged between 30% and 15%, compared to the activity measured in the focal plane detector of the BGS. The CTS was designed as a separation and {alpha}-decay detection system for the highly volatile tetroxides of osmium and hassium, element 108. The CTS, shown in figure 1, consists of two rows of 32-{alpha} detectors arranged along a negative temperature gradient. The tetroxides adsorb on the surface of one of the silicone photodiodes at a certain deposition temperature, and the nuclide is then identified by the {alpha}-decay. To test the CTS with the expected hassium homologue osmium, different {alpha}-active osmium isotopes were produced using the nuclear reactions {sup 118}Sn({sup 56}Fe, 4,5n) {sup 170,169}Os and {sup 120}Sn({sup 56}Fe, 4,5n) {sup 172,171}Os. After preseparation in the BGS, a mixture of 90% helium and 10% oxygen was used to transport the osmium to a quartz tube heated to 1225 K, where OsO{sub 4} was formed. The negative temperature gradient in the CTS ranged from 248 K to 173 K. Using a flow rate of 500 mL/min, most of the osmium activity was adsorbed at a temperature of about 203 K. From the measured {alpha}-activity distribution, an adsorption enthalpy of 40 {+-} 1 kJ/mol for OsO{sub 4} on the detector surface was calculated using Monte Carlo simulations. The results show that the CTS is working properly and can be used for experiments studying the chemical properties of hassium

Confirmation of production of element 110 by the (208)Pb(64-Ni,n)reaction

We report the experimental confirmation of the production of element110. In the bombardment of a 208Pb target with a 309~;MeV 64Ni beam, we have observed two chains of time- and position-correlated events. Each chain consisted of the implantation of an evaporation residue followed by the emission of alpha-particles. We attribute these two chains to the decay of 271-110 produced with a cross section of 8.3 (+11/-5.3)pb

Attempt to confirm superheavy element production in the 48Ca + 238U reaction

An attempt to confirm production of superheavy elements in the reaction of 48Ca beams with actinide targets has been performed using the 238U(48Ca,3n)283112 reaction. Two 48Ca projectile energies were used, that spanned the energy range where the largest cross sections have been reported for this reaction. No spontaneous fission events were observed. No alpha decay chains consistent with either reported or theoretically predicted element 112 decay properties were observed. The cross section limits reached are significantly smaller than the recently reported cross sections