R. J. Irvine

Proton radioactivity from highly deformed nuclei.

Proton emission half-lives are calculated within the DWBA formalism for {sup 131}Eu and {sup 141}Ho assuming permanent quadruple deformation. The decay rates are consistent with a decay from either [411 3/2] or [413 5/2] Nilsson states for {sup 131}Eu and [523 7/2] Nilsson state for {sup 141}Ho.

Different aspects of nuclear structure and reaction mechanisms in the collision 13N+11B

The reaction N-13 + B-11 has been investigated at two 13N beam energies: 29.5 and 45 MeV, Charged particles and gamma rays emitted in the reactions have been detected using a large array of silicon strip detectors and BaF2 scintillators, respectively. Several reaction channels have been analysed with different aims. The proton transfer reaction B-11(N-13, C-12)C-12 to various excited states of C-12 has been studied to obtain information on the N-13(g.s.) structure. The excitation energy of the Mg-24 compound nucleus was in the region where several resonances occur in the C-12 + C-12 system. The six-alpha decay of the Mg-24 intermediate system has been studied. Some of these events have been identified as coming from the break-up of two C-12* in the 3(1)(-)-3(1)(-) and 3(1)(-)-0(2)(+) states. The total fusion cross section has also been extracted from the data. In order to extract information on the isospin purity/mixing in Mg-24 at high excitation energy (E-x similar to 47 MeV), the GDR gamma emission from this self-conjugate nucleus has been studied. A comparison of gamma spectra has been undertaken for the reactions N-13 + B-11 and N-14 + B-10

Masses and proton separation energies obtained from Q and Q measurements

For many nuclei beyond the proton drip line in the Z>72, N>82 region, both proton and α emission are energetically allowed. In the case of some proton emitters, there are α-decay chains emanating from both parent and daughter nuclei. This means that if the mass excess of one member of an α-decay chain is known, then the mass excesses for all members of both chains can be obtained. In addition, proton separation energies may be derived for nuclei in the α-decay chain of the proton emitter. The method of time- and space-correlations also allows the identification of isomeric states in these nuclei. As an example, a large number of mass excesses and proton separation energies for ground and metastable states have been derived from Qα and Qp values obtained from the proton emitters 165,166,167Ir, 171Au, 177Tl, and their daughters.

Behavior of intruder based states in light Bi and Tl isotopes: the study of 187Bi α decay

Intruder state excitation energies in odd-mass nuclei just outside a closed proton shell plotted versus neutron number generally exhibit parabola-shaped curves with minima near neutron mid-shells. The Bi isotopes, however, do not seem to follow this trend. Recent experiments performed at Argonne National Laboratory have identified the previously unobserved {sup 187}Bi ground state (h{sub 9/2}) to {sup 183}TI ground state s{sub 1/2} {alpha} transition. Its energy when combined with those of two earlier known transitions, namely {sup 187}Bi (h{sub 9/2}) {yields} {sup 183m}Tl (h{sub 9/2}) and {sup 187m}Bi (s{sub 1/2}) {yields} {sup 183}Tl(s{sub 1/2}), establishes the excitation energies of the {sup 183m}Tl and {sup 187m}Bi to be 620(20) keV and 110(20) keV, respectively. This value for {sup 187m}Bi is 80 keV lower than the excitation energy of the same intruder level in {sup 189}Bi. Implications of this result with respect to intruder-state systematics are discussed.

Investigation of short-lived PT and PB α emitters near the proton drip line

In a series of experiments at the Argonne ATLAS Accelerator Facility, several α emitters near the proton drip line were produced with fusion evaporation reactions, separated from the beam and dispersed in M/Q with a recoil mass spectrometer, and implanted and studied in a double-sided silicon strip detector. In 78Kr bombardments of 92Mo and 96Ru, the new isotopes 166Pt and 167Pt were identified via their α-decay properties and more accurate half-lives were measured for 168Pt and 170Pt. The light isotopes of lead, 180Pb, 182Pb, and 184Pb were produced in Mo bombardments of Zr target nuclei. The α-decay energies and half-lives of the new isotopes are as follows: 1) 166Pt, Eα=7110(15) keV, T1/2=0.3(1) ms; and 2) 167Pt, Eα=6988(10) keV, T1/2=0.7(2) ms. Also, the half-life of 168Pt, which was previously unknown, was determined to be 2.0(4) ms and that of 170Pt was observed to be 14.7(5) ms. The tentative α-decay energies and half-lives of the even Pb isotopes are: 1) 184Pb, Eα=6625(10) keV, T1/2=500(25) ms; 2)...