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Quenching factor and electronic LET in gas at low energy

3rd Symp. on LargeTPCs for Low Energy Rare Event Detection Carre des Sciences, Paris, 11-12 December 2006. Quenching factor and electronic LET in gas at low energy. Akira Hitachi 　 （ Kochi Med. School ）. Quenching factors for rare gases Bragg-like curves for gas TPC Treatment for Z 1 ≠ Z 2.

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Quenching factor and electronic LET in gas at low energy

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  1. 3rd Symp. on LargeTPCs for Low Energy Rare Event Detection Carre des Sciences, Paris, 11-12 December 2006 Quenching factor and electronic LET in gas at low energy Akira Hitachi　 （Kochi Med. School） Quenching factors for rare gases Bragg-like curves for gas TPC Treatment for Z1≠ Z2

  2. Stopping Power Low energy v < v0 =e2/ħ Lindhard Th. for all Z1,Z2 Nuclear S.P. a screened Rutherford scatter. Electronic S.P. Se = ke1/2Thomas-Fermi e: energy e > 0.01 k = 0.133Z2/3A-1/2 k = 0.1~0.2 Nuclear Sn and electronic Se stopping powers as a fn. of energy ε for k=0.15.

  3. Energy shearing in low energy For slow ions, v < v0 = e2/ħ, Se and Sn are similar in magnitude. The secondaries, recoil atoms and electrons, may again go to the collision process and transfer the energy to new particles and so on. After this cascade process complete, the energy of the incident particle E is given to atomic motion ν and electronic excitation η. atomic, υ⇒ heat T Bolometer E electronic, η charge Q SSD,gas TPC LXe scinti. S Scintillator Electronic energy Nuclear quenching factor qnc = ————————— = η /E Ion energy

  4. Quenching factor in rare gases Z1 =Z2 Lindhard factor qnc Numerical Calc. k =0.1, 0.15, 0.2 Asymptotic form k = 0.1~0.2 e > 0.01 Xe > 10 keV, He & Ne satisfies e > 0.01 large W-values ⇒ small Ni change in the energy balance W = Ei+ (Nex/Ni)Eex + ε RN/g ratio in gas qnc≈RN/g Energy dependence in Wg Dashed curves are not reliable

  5. Quenching factor in condensed media The total quenching factor in liquid and solid scintillators qT = qnc × qel qel: the electronic q. factor Additional electronic quenching due to high ionization density qel≈ 0.68 for LXe 0.6 for LAr RN/g = qT/SgSg : g scint. eff. Fig. Quenching factor and RN/g ratio in LXe. Expt.: DAMA, ICARUS, ZEPPLIN, XENON, Coimbra. RN/g ratio axis on the right. Hitachi, Astropart. Phys. 24, 247 (2005).

  6. Recoil/γ ratio in CsI(Tl) Park, NIMA 491, 460 (2002)Pécourt, Astropt. Phys. 11, 457 (1999) Fig. 4 The recoil ion to g ratio in CsI(T) as a function of recoil ion energy. The broken lines are present estimates. The solid line is fitting to the Birks-Lindhard model by Pecourt. qnc is the same as LXe.

  7. Linear Energy Transfer (LET) LET: The energy deposited per unit length LET ≡ -dE/dx for fast ions ST≈ Se The electronic LET LETel = -dη/dxST= Se + Sn should be introduced for slow ions The ionization density The quenching calc., S/T ratio etc. given by LETel[not by the electronic SP (dE/dx)el ] The Bragg-like curve for TPCThe direction of recoil ions Easy to obtain if qnc is known.

  8. Electronic Linear Energy Transfer (LETel) LETel≡ -dh/dR = -Dh/DRR: the range Quenching calc. etc. The range R is given by the total stopping power RT = ∫(dE/dx) total -1 dE The Bragg-like curve for TPC The projected range, RPRJ, may be used (depth) E2 E1 h2 h1 R1 R2 • = qnc × E RT > RPRJ RPRJ

  9. Stopping Power and LET Fig. 1 The stopping power and the electronic LET as a function of the recoil energy for Xe in Xe. HMI & Lindhard

  10. Bragg-like curve ions -dη/dRT Fig. 6 Bragg-like curves for recoil ions in rare gases. The ions enter from the right hand side. Points are plotted at every 5 keV The area below the curve shows the number of ions produced.

  11. Stopping Power and Bragg-like curve for He/He For TPC LETel = -dη/dRPRJ For quenching calc. LETel = -dη/dRT

  12. Treatment for Z1≠ Z2 Recoil ions in a-decay: Pb in Ar, 100 < E <150 keV Lindhard: A power law approximation at lowest energy range (E < E1C, E2C ) h = AE3/2, A = 3/2 {E1C-1/2 +½ g1/2 E2C-1/2} h = 0.019E3/2 E < 660 keV qnc = h/E Ling & Knipp [P.R. 80, 106 (1950)] v << 0.4v0 qnc = [2/3a + (16a’/21]v = (Wa/15.4)v/v0, Wa=26.4eV

  13. Quenching factor in Ar Experimental results for N, O and Ar; Phipps et al [1964] Pb; Madsen [1945], Jesse & Sadauskis [1956]

  14. Quenching factor in Ar – light ions Empirical formula in Ar Z1 < Z2, v0/v > 2.5 WRN (eV) = 6.1(v0/v) + 15.3 qnc = Wα / WRN = 26.4/[6.1 (v0/v) +15.3]

  15. Summary A) Lindhard factor (qnc) for 1-50 keV He, Ne, Ar and Xe have been presented. Restrictions are: Heavy elements ε > 0.01 Light elements W-values – small Ni B) The electronic linear energy transfer (LETel = -dη/dRPRJ) and the Bragg-like curve were introduced. The curve may be used for detecting the direction of low energy recoil ions in μTPC. C) Treatment for Z1≠ Z2 light ions W – (v0/v) plot heavy ions the power law approximation by Lindhard

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