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2012 Student Practice in JINR Fields of Research 9.oct.2012. Mass Analyzer of SuperHeavy Atoms. Some recent results. I. Sivacek flerovlab.jinr.ru. MASHA scheme. Well-shape silicon strip detector :. 1 – focal strips (3x64 ) - width 1,1 mm
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2012 Student Practice in JINR Fields of Research 9.oct.2012 Mass Analyzer of SuperHeavy Atoms Some recent results I. Sivacek flerovlab.jinr.ru
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)
Hotcatcher andECR ion source Schematic view of target and hot catcher chamber. Ion source scheme.
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)
Mass separator MASHA Setup parameters
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.]
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.
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
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
Methodology On-beam Model reactions
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).
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).
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).
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.
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.
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.
Dead layer problem Characteristics of silicon detector
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”
Geometrical efficiency beam F96 beam F1
Geometrical efficiency Tab. Registration of recoils by detector planes. Systematic error ≈ +5 %. Tab. Registráciaof alphas in detector planes.
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)
Alpha tails Simulation of decay of implanted202Rn compared to real values.
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