Background Model

[Shoram444]

LIST OF BACKGROUND SOURCES

INTERNAL FOIL

• [x] Bi214
  • [X] source_foil_bulk (from contamination): $\varepsilon = 0.163$%, 1e8 events

• [x] Tl208

  • [X] source_foil_bulk (from contamination): $\varepsilon = 0.099$%, 1e8 events

• [X] Pa234m

• Decay chain: U238 $\rightarrow$ 234Th (decays beta <300keV) $\rightarrow$ 234mPa (beta decays $Q_\beta$ 2.2MeV)

  • [X] source_foil_bulk (from contamination): $\varepsilon = 0.169$%, 1e8 events

• [X] K40
  • [X] source_foil_bulk (from contamination): $\varepsilon = 0.040$%, 1e8 events

INTERNAL DETECTOR

RADON

• [x] Bi214

  • [x] PMT - $\varepsilon =$ 0.000034% 1e7 events
    • Interactions in PMT (likely) is as follows: Tl beta decays with subsequent 1-3 gammas $\rightarrow$ beta dies in PMT, gammas can potentially get all the way to the surface of scintilator $\rightarrow$ at the surface we get compton from gamma which creates electron inside detector $\rightarrow$ electron travels through entire detector, crosses foil $\rightarrow$ hits OM at the other side. Needs to be checked in simulation!
  • [ ] detector_steel_frame - Didn't find this option in falaise, maybe in newer version?
  • [x] source_foil_surface (from 222Radon in detector, background is replenished, Rn - Bi - Po): $\varepsilon = 0.038$%, 1e7 events
  • [X] anode_wire_surface : $\varepsilon = 0.018$%, 1e7 events
  • [X] anode_wire_bulk : $\varepsilon = 0.022$%, 1e7 events

• [ ] Pb214

• Pb214 decays via beta (Qb = 1MeV, 26.8min), excited daughter Bi214 via gammas with most prominent gammas being 260keV and 351keV...probably not so problematic here?

  • [ ] anode_wire_surface
  • [ ] anode_wire_bulk
  • [ ] foil surface

• [ ] Pb210

• I guess here shouldn't be a problem, decays beta (Qb = 63keV, 22yr); only 1 46keV gamma transition if excited daughter

  • [ ] anode_wire_surface
  • [ ] anode_wire_bulk
  • [ ] foil surface

• [ ] Tl208

  • [x] PMT: $\varepsilon = 0.00093$%; 1e8 events simulated
  • [ ] detector_steel_frame - this option ain't in flsimulate-configure?!
  • [x] source_foil_surface (from 220Radon in detector, background is replenished, Rn - Bi - Po): $\varepsilon = 0.031$%, 117e6 events simulated
  • [ ] anode_wire_surface (from Radon ^^)
  • [ ] anode_wire_bulk (from Radon ^^)

• [x] Pa234m

  • [x] PMT: $\varepsilon = 0.0$%,1e8 events simulated; could it be Q value? Pa234m decays by beta stright into ground state of 234U so generally no gammas.
  • [ ] detector_steel_frame

• [x] K40

  • [x] PMT : 0.000054% efficiency, 1e8 events simulated. K40 either decays straight by beta to stable Ca40 (so no gammas) or via intermediate excited Ar40* and then with 1.4MeV gamma deexcites - this channel can contribute to background from PMT
  • [ ] scintilator plastic - gammas may be problematic
  • [ ] detector_steel_frame

• [ ] Bi212

• Part of 232Th decay chain: from 220Rn $\rightarrow$ 216Po $\rightarrow$ 212Pb (beta decays, low Qb = 0.5MeV) $\rightarrow$ 212Bi

• 212Bi Decays via beta, $Q_\beta=2.2MeV$, 60min hl; 212Pb decays either to excited or ground state of 212Bi; gamma transitions

  • [ ] I guess simulate same places as Tl208

• [ ] Bi210

  • BiPo series, Qb = 1.1MeV, hl = 5d, different delay time from Bi214
  • [x] PMT: $\varepsilon = 0$ - need more sim?, 10e6 events simulated. There's no gammas in the transition, Bi210 decays straight to stable Po210, so no chance of escaping?
  • [ ] detector_steel_frame - this option ain't in flsimulate-configure?!
  • [x] source_foil_surface: $\varepsilon = 0.0024$%, 10e6 events simulated
  • [X] anode_wire_surface: $\varepsilon = 0.0011$%, 10e6 events simulated
  • [X] anode_wire_bulk: $\varepsilon = 0.0012$%, 10e6 events simulated

OTHER

• [ ] Co60

• Decays by 3MeV beta to excited state 60Ni, then >1MeV gammas (potentially pair production/ cmopton + moller/ 2compton)

  • [ ] detector_steel_frame
  • [ ] shielding_steel_frame (samples measured on Jasmin detector -> only 40K (1460 keV), 226Ra (352 keV), 232Th/228Th (238 keV) seen - activities were acceptable)
  • [ ] scintilator gammas may be a problem

• [ ] Ac228

• Part of 232Th decay chain: 232Th (alpha decays, long t12) $\rightarrow$ 228Ra (low beta decay long hl) $\rightarrow$ 228Ac

• 228Ac Decays via beta, $Q_\beta=2.2MeV$, 6.15h hl; low probability of gammas, at most 1.9MeV

  • [ ] I guess simulate same places as 208Tl

• [ ] Cu (pins are made from CuBe material, what are the problematic isotopes?)

  • [ ] feedthrough_pins
  • [ ] magnetic coil - several hundreds of kg!

• [ ] Polystyrene (Sample measured with HPGe detector OBELIX at LSM. Sample was produced by NUVIA

Mass [g]	Time [h]	40K [mBq/kg]	238U [mBq/kg]	214Bi [mBq/kg]	228Th [mBq/kg]
4500	325	20.6 $\pm$ 2.2	1.8 $\pm$ 0.7	<0.14	< 0.09

• [ ] Polyethylene C0 (Sample measured with HPGe detector OBELIX at LSM. Sample was produced by Ekomor)

Mass [g]	Time [h]	40K [mBq/kg]	235U [mBq/kg]	226Ra [mBq/kg]	228Th [mBq/kg]	60Co [mBq/kg]
3900	672	<1	<0.13	0.65 $\pm$ 0.08	0.30 $\pm$ 0.07	<0.06

EXTERNAL NEUTRONS

• [ ] Neutrons (Read Veronika's thesis..)
  • From Muons: Produced by the high energy muon interactions in the rock or detector $\rightarrow$ spallation creates neutrons $\rightarrow$ neutrons are absorbed and create $\gamma$'s:
    1. pair production - missinterpreting positron as electron
    2. 2 compton scatterings
    3. compton and subsequent moller
  • Ambient neutrons from $(\alpha, n)$: Produced from alphas stemming from the U and Th decay chains. $\alpha$ from decay is captured on detector material $\rightarrow$ neutron out $\rightarrow$ thermalization $\rightarrow$ capture and subsequent $\gamma$ emission within detector
  • Spontaneous fission: Uranium in rock and materials fissions releasing neutrons
  • [ ] neutron spectrum from outside $\rightarrow$ captures on shielding
  • [ ] Simulate neutron capture on H
  • [ ] Check whether there are relevant beta transitions from deexcitations of compound nuclei (Fe, Cu) after capturing neutron...Veronika only checked gammas from deexcitation

EXTERNAL HE GAMMA

• [ ] from muon bremstrahlung
• [ ] from (n, gamma) reactions
• [ ] gamma deexcitations from contaminants in PMT
  • [ ] 226Ra - this was studied in NEMO-3 bkg paper, but from what I found Ra226 decays alpha, daugter deexcites with at most 600keV gamma?
  • [ ] 228Ra - this was studied in NEMO-3 bkg paper, but from what I found 228Ra decays beta (Qb = 50keV), daughter is 228Ac which decays beta (Qb = 2MeV) and if excited gammas can go up to 2MeV, this maybe problem? 6h T12
  • [ ] 40K - decays beta (Qb = 1.3MeV)

LITERATURE TO READ

• [x] Veronika's thesis
• [x] Miro's thesis Ch. 5
• [x] https://arxiv.org/abs/1806.05553
• [x] http://dx.doi.org/10.1103/PhysRevD.94.072003
• [x] http://dx.doi.org/10.1103/PhysRevC.80.032501
• [x] http://dx.doi.org/10.1016/j.nima.2009.04.011
• [X] External Bkg Analysis for SuperNEMO - Presentation includes activities and processes, it finds that bkg from PMT is dominant (?!)

DISCUSSION

with Veronika:

• External background from neutrons has been simulated for neutron capture and $(\alpha, n)$ reaction on isotopes of Fe and Cu. These are relevant for $0\nu\beta\beta$, in addition for $2\nu\beta\beta$ neutron capture on H needs to be simulated.
• With Francois, we need to communicate when shielding will be added to Falaise
• Veronika thinks external Tl, Bi, Pa, K will be most relevant regardless
• Veronika will provide what is on CC

Cheryl's work

0nu: efficiencies with background isotopes

• [x] Tl208 in foil
• [x] Bi214 in foil
• [x] Bi214 on foil surface (mylar)
• [x] Tl208 on foil surface (mylar)
• [x] Bi214 on wires (from radon in tracker)

NEMO3 analysis

From NEMO3: code for fitting histograms? There's a lot of bkg options, prolly not all needed

Miro

Here I (Miro) suggest this:

• [x] Learn more about materials from Laurent - thesis of Cloé, but also Steven Calvez and Fang who worked with Randon background. Learn which event generators are right to use. Is it ok to use only Bi214 from foils and anode wires? Do we need to do more?

  • 17

• [x] Once you learn something about this, add everything which needs to be added concerning radon into the background model.

[Shoram444]

BACKUP External background from Veronika:

/sps/nemo/scratch/vpalusov/CCLyon_back_up tu je cesta k variant profiles, conf suborom, nejake scripty na analyzu a pomocne subory ktore som pouzivala na simulacie

DICEBOX folder ma vsetky gamma kaskady z n captures

a je tam README file co vysvetluje vacsinu veci

[Shoram444]

When I simulated vertices from PMT_bulk I should probably have split it into 5'' and 8'' PMTs and simulate separately?

[Shoram444]

Spectra using SDBDRC: