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

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

Mass separator MASHA

Hot catcher and ECR ion source Ion source scheme. Schematic view of target and hot catcher chamber.

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

SETUP PARAMETERS Mass separator MASHA

Mass resolution and efficiency Mass resolution of Xe isotopes by calibrated leaks into ECR ion source Efficiency (ξ Ion ξ Sep ) by leaks of inert gases (Xe: 84%) Strip numberMass [a.m.u.] Intensity Efficiency [%]

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

Time response – diffusion from graphite Overlapping 40 Ar 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 222 Rn Accumulation of 226 Ra recoils in graphite plate with shape and matrix of catcher (saturation) Measuring alpha decay of 222 Rn implanted to detector with 24 hrs time of implantation (diffusion from catcher) For the same time of implantation Si detector of the same dimensions as plate measured decay of activity implanted into this graphite plate Overall efficiency of mass separator was estimated for isotope 222 Rn was estimated to 13 ± 1,3 % Time [hrs] beginning 24 hours after accumulation Counts

ON-BEAM MODEL REACTIONS Methodology

Experiments on 40 Ar beam Reactions: 284 MeV 40 Ar+ nat Sm→ y Hg+xn (Hg: chem. analogue 112 th element) 255 MeV 40 Ar+ 166 Er→ 206−xn Rn+xn (Rn: α – radioactive noble gas) 2-dimensional mass spectra of isotopes Hg (a) and Rn (b). (a) (b) RnHg

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

40 Ar+ 166 Er→ 206−xn Rn+xn Mass spectrum with decay of daughter nuclei Obr. Mass spectrum of Rn isotopes with beam energy E = 217 MeV (a) and energy spectrum from strips with mass A = 202 (b).

40 Ar+ 166 Er→ 206−xn Rn+xn Measured Rn spectra from A = 199 (E Ar = 231 MeV) to A = 206 (E Ar = 202 MeV). Energy were 3-times (3 measurements) changed by Ti degraders in front of target. E(Ar), МeV 199 Rn 200 Rn 201 Rn 202 Rn 203 Rn 204 Rn 205 Rn 206 Rn Rn yields normed total beam integral on target (with given energy). Tab. Rn isotopes yields.

Assembly testing Confirmed ability of MASHA setup for mass measurement of 112 th and 114 th elements By observation of radon isotopes yields was estimated “speed” of setup as < 5s (mean lifetime of 201 Rn) Measured energies of alpha particles are in perfect accordance with table values. 40 Ar 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 isotopes with mass resolution R = M/ΔM = Ar beam measurements showed transport efficiency 25 ± 20 %. Measurements with 222 Rn provided estimation of total MASHA efficiency to 13 ± 1,3 %. MASHA is ready for experiment 48 Ca U → (283) Cn + 3n.

Spring in Dubna…

CHARACTERISTICS OF SILICON DETECTOR Dead layer problem

Monte carlo simulations in Geant 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 226 Ra (real energies measured by detector) Analysis of alpha registration processes - elimination of peak “tails”

Geometrical efficiency beam F96 beam F1

Geometrical efficiency beam f-96beam1st2nd3rdbeam1st2ndbeam1stbeam jadroABCDBCDCDD focal96,8%56,4%49,6%46,5%97,0%59,0%52,3%97,2%62,8%97,4% U+D9,7%31,8%34,6%35,8%8,9%29,7%32,4%8,0%27,0%7,3% L+R0,3%2,0%2,5%2,7%0,3%1,9%2,3%0,4%1,8%0,4% lost2,5%7,4%4,1%2,5%2,3%7,8%3,9%2,2%8,8%2,2% total106,9%90,2%86,7%85,0%106,2%90,6%87,0%105,6%91,6%105,1% Systematic error ≈ +5 %. beam-f96 ABC focal.[192]44,9%29,8%26,7% bok.[64]40,5%36,0%31,1% kraj.[16]2,7%3,4% total 88,1%69,3%61,3% Tab. Registrácia of alphas in detector planes. Tab. Registration of recoils by 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 implanted 202Rn 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 ≈ m 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