Mass Analyzer of SuperHeavy Atoms

1. 2012 Student Practice in JINR Fields of Research 9.oct.2012 Mass Analyzer of SuperHeavy Atoms Some recent results I. Sivacek flerovlab.jinr.ru

2. MASHA scheme Well-shape silicon strip detector: 1 – focal strips (3x64) - width1,1 mm 2, 3 – up & down side strips 2x(2x32) 4 – left & right side strips2x(16)

3. Mass separator MASHA

4. Mass separatorMASHA

5. Mass separator MASHA

6. Hotcatcher andECR ion source Schematic view of target and hot catcher chamber. Ion source scheme.

7. MASHA ion-optical system (a) • 4 dipole magnets(D resp. M) • 3 quadrupole lenses(Q) • 2 sextupoles (S) • 2 focal points– F1 (roughseparation) a F2 (precise mass analysis) Schemes of vertical (a) andhorizontal(b) ion trajectories trough separator(c). (b) (c)

8. Mass separator MASHA Setup parameters

9. Mass resolution and efficiency • Mass resolution of Xe isotopes by calibrated leaks into ECR ion source • Efficiency (ξIonξSep) by leaks of inert gases (Xe: 84%) Intensity Efficiency [%] Strip number Mass [a.m.u.]

10. Time charasteristics • Exponential character of gas extraction from catcher chamber, measured time constants for noble gases Air efficiency air A Efficiency dependence on proton number of gas. Time constants of exponential decrease of pressure in catcher chamber.

11. Time response – diffusion from graphite • Overlapping 40Ar beam by Faraday cup (~ 0,5 s) • By decrease of secondary beam intensity the time constant was estimated Intensity Time

12. Total efficiency of setup by 222Rn • Accumulation of226Ra recoils in graphite plate with shape and matrix of catcher (saturation) • Measuring alpha decay of 222Rn implantedto detector with24 hrstime of implantation(diffusionfrom catcher) • For the same time of implantation Si detector of the same dimensions as plate measureddecay of activity implanted into this graphite plate • Overall efficiency of mass separator was estimated for isotope 222Rn was estimated to 13 ± 1,3 % Counts Time [hrs] beginning 24 hours after accumulation

13. Methodology On-beam Model reactions

14. Experimentson40Ar beam Reactions: 284 MeV40Ar+natSm→yHg+xn(Hg: chem. analogue 112th element) 255 MeV40Ar+166Er→206−xnRn+xn(Rn: α – radioactive noble gas) Hg Rn (b) (a) 2-dimensional mass spectra of isotopesHg (a) andRn (b).

15. 40Ar+natSm→yHg+xn • Registered decays from 180Hg to 186Hg in focal plane Si detector • Decays of daughter nuclei were observed Mass spectrum ofHg isotopes (a), energy spectrum from strips with mass A = 182(b).

16. 40Ar+166Er→206−xnRn+xn • Mass spectrum with decay of daughter nuclei Obr. Mass spectrum of Rn isotopes withbeam energyE = 217 MeV (a) andenergy spectrum from strips with massA = 202 (b).

17. 40Ar+166Er→206−xnRn+xn Rn yields normedtotal beam integral on target (with given energy). • Measured Rn spectra fromA = 199 (EAr = 231 MeV) toA = 206 (EAr = 202 MeV). • Energy were 3-times (3 measurements) changed byTi degraders in front of target. Tab. Rn isotopes yields.

18. Assembly testing • Confirmed ability of MASHA setup for mass measurement of 112th and 114th elements • By observation of radon isotopes yields was estimated “speed” of setupas< 5s(mean lifetime of201Rn) • Measured energies of alpha particles are in perfect accordance with table values. • 40Ar beam and calibrated leaks measurement showed 1,3s and 2,5s time constants for catcher chamber evacuation and evacuation + diffusion from graphite respectively.

19. Conclusions • Off-line measurements showed efficiency of ionization 84 ± 10 % for Xe isotopeswith mass resolutionR = M/ΔM = 1300. • 40Ar beam measurements showed transport efficiency 25 ± 20 %. • Measurements with222Rn provided estimation of totalMASHA efficiency to13 ± 1,3 %. • MASHA is ready for experiment 48Ca + 238U → (283)Cn + 3n.

20. Spring in Dubna… 

21. Dead layer problem Characteristics of silicon detector

22. Monte carlo simulationsinGeant 4 • Geometrical efficiency of Si well-shaped detector • Energy losses of alphas and recoils in detector materials • Angular dependency of alpha particles energy losses in detector (dead layers) • Energy calibration of detector by 226Ra (real energies measured by detector) • Analysis of alpha registration processes - elimination of peak “tails”

23. Geometrical efficiency beam F96 beam F1

24. Geometrical efficiency Tab. Registration of recoils by detector planes. Systematic error ≈ +5 %. Tab. Registráciaof alphas in detector planes.

25. Transport trough dead layer • Depending on source position: • Energy calibration (energy loss from source to sensitive volume of detector) • Depth of implantation (40 keV secondary beam) • Alpha peak “tails” (decay if implanted nuclei)

26. Alpha tails Simulation of decay of implanted202Rn compared to real values.

27. Conclusions • Geometrical efficiency of registering of alpha particles is 92– 95 % depending on beam position and decreases by ~10 % with each decay (100 % alpha decaying isotope) • Depth of implantation into silicon is ≈ 10-9m • Energy calibration of all 352 strips (accordance with table values up to ± 10 keV) • Peak tails are mainly due to inhomogenity of electric field inside silicon crystal