Johann Wolfgang Hammer

The3He(α,γ)7Be reaction and the solar neutrino problem

The capture reaction3He(α,γ)7Be has been investigated in the energy range ofEc.m. =107 to 1,266 keV. The4He or3He beams of up to 300 μA particle current were incident on3He or4He gas targets, respectively. The gas target systems were all of the windowless and recirculating type. Excitation functions have been obtained with the use of an extended-static gas target, while the measurements ofγ-ray angular distributions involved a quasi-point supersonic jet system. The determination of absolute cross sections has been carried out with both types of gas target systems. Theγ-ray yields in the3He(α,γ)7Be reaction were detected using 80 cm3 Ge(Li) detectors. The data lead to a zero-energy intercept of the astrophysicalS(E) factor ofS(0)=0.30±0.03 keV-b. This result reduces the calculated solar neutrino rate by a factor of 1.76.

Experimentelle Untersuchungen am Elektroneneinfang des 85Strontium und 88Yttrium

The electron capture decay of85Sr and55Y has been investigated using NaI(Tl)-detectors. Spectroscopic-coincidence techniques have been employed to examine theK-electron capture rates. The experimental results arePKωK(Sr)=.5959 ± 0.0035 andPKωK(Y)=0.6340± 0.0032. Using theK-capture probabilities, derived from the capture ratios ofBrysk andRose with the exchange correction ofBahcall:PK(Sr)=0.880± 0.008 andPK(Y)=0.883 ± 0.008, one can derive from these results the fluorescence yieldsωK(Rb)=0.677± 0.009 andωK(Sr)=0.712± 0.010. Functions ofωK(Z) were fitted to recent experimental data and tabulated forZ=5–90. In addition to these results the half life of the 514 keV state of85Rb and the branching ratios and the positron rate of the88Y-decay have been measured with the same techniques. The data obtained partly disagree from measurements of other authors.

Experimentelle Untersuchungen am Elektroneneinfang des Mangan 54 und Zink 65

The electron capture decay of Mn 54 and Zn 65 was investigated using Na I(Tl)-detectors. Spectroscopic-coincidence techniques were employed to examine theK-electron capture rates of Mn 54 and Zn 65, the branching ratio and positron rate of Zn 65.The experimental results are:Pkωk(Mn)=0.2492±0.0017,Pkωk(Zn)=0.3927±0.0026,EC*/EC0(Zn)=53.2±1.0/46.8±1.0,γ/β+=35.1±1.7,K0/β+=27.7±1.5. Thus electron capture to the excited state of Cu 65 occurs to the extent of 52.4±1.0% while electron capture and positron decay to the ground state were found to be associated with 46.1±1.0% and 1.49±0.05% of the disintegrations. These data partly disagree significantly from measurements of other authors.Using the fluorescence yieldsωk(Cr)=0.279 andωk(Cu)=0.4425, deduced from other measurements, values ofL+M/K of electron capture to the excited state could be derived:L+M/K(Mn 54)=0.120±0.015 andL+M/K(Zn 65)=0.127±0.015. These ratios agree with the calculations ofBahcall.The half-lives of Mn 54 and Zn 65 have been determined to beT1/2(Mn 54)=312±5d,T1/2(Zn 65)=243±4d The energy of the Zn 65-γ-rays was measured with a Ge(Li)-counter:Eγ=1115.5±0.5 keV.

DieK-Fluoreszenzausbeute von Titan und der Zerfall des48Vanadium

TheK-fluorescence yieldΩK of Titanium has been measured using the coincidence method and investigating the electron capture decay of48V. The detectors used have been a Si(Li)- and a Ge(Li)-detector for the X- andγ-rays. The experimental results arePKΩK=0.2005 ±0.0030 andΩK(Ti)=0.224±0.003 usingPK=0.896. For the branching ratios of the decay of48V we obtainedEC (3.239) 7.9±0.6%EC (3.224) 2.9±0.4%EC (2.295) 35.6±2.0% Β+ (2.295) 52±1.0% all others 1.6%. Additionally someγ-ray-energies of the decay of48V and the half-life,T1 2=(16.23 ±0.03)d, have been measured.