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Register a new userRepolarization of Negative Muons by Polarized $^{209}$Bi Nuclei
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A large $mu^-$ polarization was achieved in muonic Bi atoms with the help of the strong hyperfine field in a polarized nuclear target. Using $^{209}$Bi nuclei polarized to ($59pm9$)% in ferromagnetic BiMn, we observed a $mu$-$e$ decay asymmetry of ($13.1pm3.9$)%, which gives $mu^-$ polarization per nuclear polarization equal to $-1.07pm 0.35$. This value is almost consistent with $-0.792$ calculated for nuclei with spin $I= frac{9}{2}$ and a positive magnetic moment under the assumption that the hyperfine interaction becomes effective in the lowest muonic states.
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The capture cross section of $^{209}$Bi(n,$gamma$)$^{210g}$Bi was measured at different astrophysically energies including thermal capture cross section (25 meV), resonance integral, and the Maxwellian averaged cross section at a thermal energy of $kT$ = 30 keV. The partial capture cross section ($sigma_g$) was determined using the activation technique and by measuring the $^{210}$Po activity. The newly developed and tested NICE detector setup was used to measure the $alpha$-activity of the $^{210}$Po. Using this setup the thermal and resonance integral cross sections were determined to be $16.2;pm;0.97$~mb and $89.81;pm;8.0$~mb, respectively. And the Maxwellian average cross section was measured to be $2.01;pm;0.38$~mb.
A search for an exotic natural radioactivity of lead nuclei, using nuclear emulsion sheets as detector, is described. We discuss the experimental set-up of a test performed at the Gran Sasso National Laboratory (Italy), the event simulation, data analysis and preliminary results.
We present the first measurement of the energy spectrum up to 70 MeV of electrons from the decay of negative muons after they become bound in $^{27}$Al atoms. The data were taken with the TWIST apparatus at TRIUMF. We find a muon lifetime of (864.6 $pm$ 1.2) ns, in agreement with earlier measurements. The asymmetry of the decay spectrum is consistent with zero, indicating that the atomic capture has completely depolarised the muons. The measured momentum spectrum is in reasonable agreement with theoretical predictions at the higher energies, but differences around the peak of the spectrum indicate the need for oalpha radiative corrections to the calculations. The present measurement is the most precise measurement of the decay spectrum of muons bound to any nucleus.
$^{209}$Bi alpha decay to the ground and to the first excited state have been contemporary observed for the first time with a large BGO scintillating bolometer. The half-life of $^{209}$Bi is determined to be $tau_{1/2}$=(2.01$pm$0.08)$cdot10^{19}$ years while the branching ratio for the ground-state to ground-state transition is (98.8$pm$0.3)%.
The high spin states in $^{195}$Bi has been studied by $gamma$-ray spectroscopic method using the $^{181}$Ta($^{20}$Ne, 6n) fusion evaporation reaction at 130 MeV. The $gammagamma$ coincidence data were taken using an array of 8 clover HPGe detectors. The spin and parity assignments of the excited states have been made from the measured directional correlation from oriented states (DCO) ratios and integrated polarization asymmetry (IPDCO) ratios. The results show, for the first time, the evidence of a rotational like band based on a 13/2$^+$ band head in this nucleus, indicating the onset of deformation at neutron number $N = 112$ for the Bismuth isotopes. The results obtained were found to be consistent with the prediction of the total Routhian surface calculations using Woods Saxon potential. The same calculations also predict a change in shape from oblate to triaxial in $^{195}$Bi at high rotational frequency.
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