Proton andαradioactivity below theZ=82shell closure

Abstract

Ground and isomeric proton and alpha decay branches are reported for the new isotope 177 Tl, produced by bombarding a 102 Pd target with a 370 MeV beam of 78 Kr ions. The ground state is assigned as a s 1/2 configuration and the high spin isomer is assigned as a (h 11/2 ) Ϫ1 configuration. The ground-state proton decay of 171 Au has been identified for the first time, produced by bombarding a 96 Ru target with 78 Kr ions. The 171 Au ground state is also assigned as a s 1/2 configuration. Spectroscopic factors, masses, and proton separation energies are derived using these new proton decay measurements. New ground-state ␣ decays for 169 Ir and 173 Au are also reported. ͓S0556-2813͑99͒50206-9͔ PACS number͑s͒: 23.50.ϩz, 23.60.ϩe, 21.10.Pc, 27.70.ϩq Proton radioactivity measurements in the region of the drip-line from Zϭ69-79 ͓1͔ have revealed detailed information on the positions of single-particle levels, proton binding, and proton decay rates. In all cases protons have been identified as originating from approximately degenerate s 1/2 , d 3/2 , or h 11/2 orbitals. A proton decay spectroscopic factor S l j derived from a low seniority shell model calculation assuming degenerate single particle states reproduces the systematic variation in proton decay rates very well ͓1͔, as does a more sophisticated approach ͓2͔. It is of interest to extend these measurements to Tl nuclei since they reside immediately below the Zϭ82 shell closure. The most neutrondeficient Tl isotope identified to date is 179 Tl ͓3,4͔, which has ␣-decay branches from a low and a high spin state. Nearer to stability it has been shown that odd-A Tl isotopes are characterized as having a s 1/2 ground state with an isomeric h 9/2 intruder state configuration that involves the promotion of a proton from the s 1/2 orbital across the Z ϭ82 shell closure ͓5͔. It is known that these intruder states reach a minimum excitation energy of 281 keV for 189 Tl, which approximately corresponds to the neutron mid-shell. On either side of this minimum there is predicted to be a parabolic increase in excitation energy of the intruder due to the reduced interaction strength between the valence neutrons and the proton hole ͓6͔. This behavior is closely followed nearer to stability, but the information on neutrondeficient isotopes is somewhat limited, with 183 Tl being the lightest isotope for which the intruder state has been clearly identified ͑at an excitation energy of 625 keV ͓7͔͒. It is clearly of great interest to identify proton radioactivity from Tl isotopes both to obtain insight into the variation in proton decay rates in this region, and to study the low energy structure at the extreme limit of stability. The present paper describes a successful search for proton radioactivity from 177 Tl. A 4 pnA beam of 370 MeV 78 Kr ions from the Argonne ATLAS accelerator facility was used to bombard a 1 mg/cm 2 78% enriched 102 Pd target for a period of 65 hours in order to produce 177 Tl nuclei via the 1 p2n fusionevaporation channel. The Argonne Fragment Mass Analyz...

Characterizing the atomic mass surface beyond the proton drip line viaα-decay measurements of theπs1/2ground state ofThornthwaite1, O’Donnell2, Page3 et al. 2012Phys. Rev. C9010View full textAdd to dashboardCite

“…The half-life of this decay was measured using a similar method to the 173 Au m activity except in this case the difference in time between the 173 Au m and 169 Ir m α decays were recorded. A least-squares fit to this distribution yielded a half-life of 280(1) ms which is in good agreement with previous studies [1]. A branching ratio of 78(6) % was measured for the α decay of this state which agrees well with the value of 84(8) % reported by Poli et al [1].…”

“…A least-squares fit to this distribution yielded a half-life of 280(1) ms which is in good agreement with previous studies [1]. A branching ratio of 78(6) % was measured for the α decay of this state which agrees well with the value of 84(8) % reported by Poli et al [1]. In addition to the main peak, a further two, relatively weak, peaks can be seen in Fig.…”

“…The 173 Au g α decays have been measured to have an energy of 6688 (14) keV and using the least-squares method the half-life of the activity was found to be 26.3(12) ms. Both the energy and half-life values measured here agree well with previous measurements [1]. Fig.…”

“…As the masses of both 148 Dy [2] and 149 Ho [3] have been measured, this study not only provides a cross check of the mass excesses deduced in Ref. [1] based state to be deduced.…”

“…A representative example of direct relevance to the present study is the work of Poli et al [1], who measured proton and α-particle emission from the πs 1/2 ground state and πh 11/2 isomeric state in 177 Tl. As illustrated in Fig.…”