Proton decay study ofLu150andLum

Abstract

150 Lu was produced via the 1p3n fusion-evaporation channel by bombarding a 96 Rn target with a 297-MeV 58 Ni beam, evaporation residues were analyzed using the fragment mass analyzer at Argonne National Laboratory. A new delay-line amplification system was used to make a new more precise measurement of proton decay from the isomeric state in 150 Lu [E p =1.286͑6͒ MeV, t 1/2 =52.5 −8.7+13 s]. In addition the half-life of the proton emitting ground state was measured to be 43(5) ms. Proton decay partial half-lives for both transitions are compared with theory. The isomeric transition is found to have a significantly smaller spectroscopic factor than the h 11/2 ground state transition.While great progress has been made in understanding the decay rates of spherical [1,2] and deformed odd-A proton emitters the situation for odd-odd proton emitters is not so clear [3]. Accurate information is needed on transitions in odd-odd nuclei to provide stringent tests of new theoretical calculations of proton decay rates from odd-odd nuclei [3]. In many cases of proton decay from odd-odd nuclei, the ␤-decay branches are unknown, but are expected to be comparable in size to the proton branch. This causes a large uncertainty in the proton decay rate, making comparison with theory difficult. In the case of 150 Lu the ground state has a proton decay branch which is relatively long lived (E p =1.216͑4͒ MeV, t 1/2 =35͑10͒ ms [4] and t 1/2 =49͑5͒ ms [5]), which limits the precision of the derived proton decay partial half-life. A new short-lived isomeric state was reported, however it has large uncertainties in the energy and the half-life. The present paper describes new measurements for the proton decays from the ground and isomeric states in 150 Lu. In particular, a new delay-line amplification system has been employed to improve the energy and the time response to short-lived proton decays in order to provide a more precise comparison of the proton decay rates with theoretical models.The standard proton decay setup for use at the Argonne fragment mass analyzer (FMA) has been described elsewhere [1]. In the present experiment a new design 60-m thick, 80ϫ80 double sided strip detector (DSSD) with a strip pitch of 400 m, was situated behind the focal plane of the FMA [6]. As usual the DSSD was instrumented with semiGaussian shaping amplifiers and charge-sensitive preamplifiers [7]. However, the observation of proton emission on a microsecond time scale is problematic. Following an evaporation residue implant signal the shaping amplifiers have an initial dead time period of 0-7 s. If a decay proton event occurs in the following overload recovery period ͑7-25 s͒ the energy measured for the proton will include the tail of the overload pulse. Thus short-lived decays with half-lives in the microsecond range will have energies depending on the time of decay. This latter effect can be reduced but not entirely eliminated by the insertion of degrader foils in front of the DSSD to lower the energy of the implanted ion. This behavior is illustr...

Spectroscopic factor and proton formation probability for the d3/2 proton emitter 151Lu

“…This leads to the presence of low-spin and high-spin states in close proximity. Systematic analysis of the experimental data [5][6][7][8], shows good agreement of the theoretical spectroscopic factors with the experimental ones for h 11/2 and s 1/2 emitters. In contrast, for d 3/2 states the observed spectroscopic factors are systematically lower than those predicted by, e.g., a low-seniority spherical shell model calculation [5] or BCS calculations [6].…”

“…One can assert that the way one extracts the experimental spectroscopic factor is an effective theory since one has to introduce an effective single-proton potential to mimic the motion of the decaying proton inside the nucleus. The calculated penetration probability and the extracted experimental spectroscopic factor are sensitive to that potential, as already indicated in various calculations [5][6][7][8][9][10][11][12][13][14].…”

“…[20]) would interpret the quadrupole deformation β 2 as around -0.07. Furthermore, a slightly reduced half-life of the 3/2 + isomeric state (from 16.5 (7) µs to 15.4(8) µs), will also give a smaller β 2 value (see Fig. 7 in Ref.…”

Recent developments in radioactive charged-particle emissions and related phenomena

“…As expected, the decaying single-particle orbitals that have been observed so far from proton-rich neutron between Z = 53 and 83 involve in particular d 5/2,3/2 , s 1/2 , g 9/2 as well as h 11/2 and f 7/2 . The decay from the d 3/2 orbital was expected to be slower than those from the neighbouring s 1/2 and h 11/2 orbitals (i.e., with smaller formation probability) [35,36,37]. However, recent more precise measurement tend to suggest no such strong hindrance [21,38].…”

β-delayedγ-ray spectroscopy of203,204Au and

“…Other data are taken from Refs. [2,7,9,[13][14][15][16][17][18][19][20]. The inset shows the decay paths originating from the πh 11/2 state in 159 Re.…”