aa r X i v : . [ nu c l - e x ] O c t ICP-SFMS search for long-lived naturally-occurring heavy, superheavy andsuperactinide nuclei compared to AMS experiments
A. Marinov, ∗ A. Pape, Y. Kashiv, D. Kolb, L. Halicz, I. Segal, and R. Brandt Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel IPHC-UMR7178, IN2P3-CNRS/ULP, BP 28, F-67037 Strasbourg cedex 2, France Department of Physics, University GH Kassel, 34109 Kassel, Germany Geological Survey of Israel, 30 Malkhei Israel St., Jerusalem 95501, Israel Kernchemie, Philipps University, 35041 Marburg, Germany (Dated: September 22, 2011)Negative results obtained in AMS searches by Dellinger et al. on mostly unrefined ores haveled them to conclude that the very heavy long-lived species found in chemically processed sampleswith ICP-SFMS by Marinov et al. are artifacts. We argue that it may not be surprising thatresults obtained from small random samplings of inhomogeneous natural minerals would contrastwith concentrations found in homogeneous materials extracted from large quantities of ore. We alsopoint out that it is possible that the groups of counts at masses 296 and 294 seen by Dellinger etal. could be, within experimental uncertainties, due to
Rg and eka-Bi in long-lived isomericstates. In such case, the experiments of Dellinger et al. lend support to the experiments of Marinovet al.
PACS numbers: 21.10.Dr, 21.10.Tg, 27.90.+b
In a recent paper entitled ”Ultrasensitive search forlong-lived superheavy nuclides in the mass range A =288 to A = 300 in natural Pt, Pb, and Bi”, Dellingeret al. [1] searched for superheavy elements, mainly innative samples of Pt, Pb, and Bi, using the AMS tech-nique. Negative results were claimed in this and in theirprevious investigations on Th [2] and Au [3], with upperlimits of relative abundances in the range of 5x10 − to10 − g/g. The authors then concluded that the obser-vation of long-lived isomeric states, by measuring accu-rate masses using ICP-SFMS, in various heavy, super-heavy and superactinide nuclei are artifacts. Such iso-meric states have been reported in the neutron-deficient , , , Th isotopes (abundance (1-10)x10 − rela-tive to Th) [4], in the superheavy nuclei , Rg(abundance of (1-10)x10 − relative to Au) [5, 6] , andin the superactinide nucleus eka-Th (abundance of (1-10)x10 − relative to Th) [7].An important difference between our works [4–7] andthose of Dellinger et al. [1–3] is that we used processedAu and Th starting materials, and Dellinger et al., ex-cept for a few cases, used raw minerals. It may not besurprising that results obtained with random samplingsof a few mg would contrast with concentrations found inprocessed homogeneous starting materials which probe alarge amount of natural ore. This factor could be moreimportant than presumably very little differences in sep-aration factors between an eka-element and its lower ho-mologue that might occur during the purification of thelower homologue from the ore. The cases where Dellinger ∗ Electronic address: [email protected]; Fax: +972-2-6586347. In [6] an enrichment of Rg relative to Au of three to four ordersof magnitude has been achieved. et al. studied processed samples were ThO [2], Pt, PbS(galena) and Bi [1]. The latter three are irrelevant forcomparison with our results since we did not measurethese elements. (However see below.) As for ThO , wedo not think, that based on a single measurement usinga very complicated system, one can conclude that all ourmeasurements [4–7] done with the relatively straightfor-ward ICP-SFMS system are artifacts. It would be moreconvincing to point out a weakness in our measurements,which neither we nor Dellinger et al. [1–3] have been ableto find.It is claimed [2] that they checked the efficiency of theirAMS system by measuring the ratio of Th/
Th. For
Th in equilibrium with its daughters this ratio shouldbe equal to the ratio of the corresponding half-lives whichis 1.4x10 − . However, when one measures the mass 228with AMS (or with ICP-SFMS) one measures, togetherwith Th, also
Ra, which belongs to the same ra-dioactive chain. Its half-life is 3.0 times longer than thatof
Th. In addition, it is possible that the formationof negative ions of RaO is higher, perhaps much higher,than for ThO . According to the ”Negative-Ion Cook-book” of Middleton [8], the production of negative ThO ions is quite poor, and the maximum current measuredby him was 50 nA. It is not clear how Dellinger et al.obtained an average current of about 320 nA of negativeThO ions (table 2 of [2]).Another comment we would like to make is related tothe conclusion of Dellinger et al. that based on theirresults, there are no naturally-occurring SHEs. In addi-tion to what was mentioned above [4–7] and also in [9], itseems to us that even their results could indicate the con-trary. We refer in particular to Fig. 4(b) in [3] on Rgand Fig. 11(b) in [1] on eka-Bi. Both spectra are clean,without pile-up. In the first one there is a group of fiveevents and in the second one there is a group of six events,both very close to the estimated positions of
Rg and eka-Bi, respectively. These groups were ignored by theauthors on the basis of their measured residual energies.In the first case the peak appears at a residual energyof about 10.5 MeV, where according to the authors, itscenter should appear at 12.0 MeV. In the second case of eka-Bi this peak appears at 11.8 MeV, where its calcu-lated position should be at 13.0 MeV. Such differences of1.5 and 1.2 MeV out of predicted energy loss in the detec-tor window of 12 and 10.5 MeV (about half of the initialenergies of the ions of 24.0 and 23.5 MeV, respectively)could be due to experimental and theoretical uncertain-ties. Besides in window thickness and energy calibrationof the AMS detector, there could be uncertainties in theenergy loss and range when extrapolated to unstudiedheavy species like Rg and eka-Bi. In addition, the appre-ciable scatter of these ions in the detector window, dueto their large energy loss, decreases the residual energyof the ions in the detector. In conclusion, a residual en-ergy of 10.5 MeV instead of 12 MeV in the case of
Rg,and 11.8 MeV instead of 13.0 MeV in the case of eka-Bi, when the total energy loss in the window is about 12MeV, could be within the uncertainties inherent in theexperiments.If
Rg and eka-Bi have been observed in these ex- periments, then it is a very important result. With Z =111 and N = 185 for
Rg, Z = 115 and N = 179 for eka-Bi, they are in the center of the island of stabilitypredicted for nuclei in their normal g.s. Since if found innatural materials, their half-lives should be ≥ y, orotherwise they would have decayed away. However, thepredicted half-lives for Rg and eka-Bi in their nor-mal g.s. are 4.5x10 and 1.0x10 s, respectively [10]. Aconsistent interpretation is that, like in , , , Th[4], , Rg [5, 6] and eka-Th [7], long-lived isomericstates exist in
Rg and eka-Bi.In summary, we have pointed out that the article ofDellinger et al. [1] does not show that the observationof long-lived isomeric states in neutron-deficient Th iso-topes [4], in superheavy , Rg nuclei [5, 6], and in thesuperactinide nucleus eka-Th [7], are artifacts. It isalso pointed out that long-lived
Rg and eka-Bi mayhave been observed by them. If so, based on lifetimes, itis argued that these species would not be in their normalground state, but rather in long-lived isomeric states ashave been reported earlier [4–7]. These results may addcredibility to the original discovery of long-lived isomericstates in naturally-occurring heavy, superheavy and su-peractinide nuclei. [1] F. Dellinger, O. Forstner, R. Golser, A. Priller, P. Steier,A. Wallner, G. Winkler, and W. Kutschera, Phys. Rev.C , 065806 (2011).[2] F. Dellinger, O. Forstner, R. Golser, W. Kutschera, A.Priller, P. Steier, A. Wallner, and G. Winkler, Nucl. In-strum. Meth. B , 1287 (2010).[3] F. Dellinger, W. Kutschera, O. Forstner, R. Golser, A.Priller, P. Steier, A. Wallner, and G. Winkler, Phys. Rev.C , 015801 (2011).[4] A. Marinov, I. Rodushkin, Y. Kashiv, L. Halicz, I. Segal,A. Pape, R.V. Gentry, H.W. Miller, D. Kolb, and R.Brandt, Phys. Rev. C , 021303(R) (2007).[5] A. Marinov, I. Rodushkin, A. Pape, Y. Kashiv, D. Kolb,R. Brandt, R.V. Gentry, H.W. Miller, L. Halicz, and I.Segal, Int. J. Mod. Phys. E , 621 (2009). [6] A. Marinov, A. Pape, D. Kolb, L. Halicz, I. Segal, N.Tepliakov, and R. Brandt, arXiv:1011.6510, and to bepublished.[7] A. Marinov, I. Rodushkin, D. Kolb, A. Pape, Y. Kashiv,R. Brandt, R.V. Gentry, and H.W. Miller, Int. J. Mod.Phys. E , 131 (2010).[8] R. Middleton, A Negative-Ion Cookbook,
Department ofPhysics, University of Pennsylvania, Philadelphia, PA19104. October 1989 (Revised February 1990).[9] A. Marinov, S. Gelber, D. Kolb, R. Brandt, and A. Pape,Int. J. Mod. Phys. E , 661 (203).[10] P. M¨oller, J.R. Nix, and K.-L. Kratz, At. Data Nucl.Data Tables66