1. Estimation of Source Range and Graphene Response (C-Chips) Edward Cazalas 8/21/12

2. C-Chip and Source Geometry Substrate (Si)500 um Disk Source (active region) 0.6 cm Not to scale ~0.3 cm Graphene (~10 x 10 um) Both alpha and beta sources have same active area. Due to comparatively large size of source and distance from graphene/substrate, both sources can be approximated as beam sources. ~ 0.6 cmSurrounded by Air

3. Alpha: Am-241 (half-life = 433 yr, 20 uCi, E = 5.486 MeV) dated 5/2/84, decay not considered Beta: Tl-204 (half-life = 3.78 yr, 100 uCi, E avg = 0.7634 MeV) dated 6/12, decay not considered Estimated source activity: where A 0 = Source activity as listed, Area I = Active of graphene/substrate, Area S = Area of source. Alpha source A 0 = 20 uCi Beta source A 0 = 10 uCi ALPHA: For graphene Area I = 100 um 2 = 1E-6 cm 2  A = 1.3 alphas/s For substrate Area I = Area S = 0.2826 cm 2  A = 3.7E5 alphas/s BETA: For graphene Area I  A = 0.65 e-/s For substrate Area I =  A = 1.8E5 e-/s

4. Estimated Energy Deposition: -If we consider full energy deposition of both the alpha and e-, the amount of energy deposited within the chip is by alpha vs. e- is comparable. -For full energy deposition the range of the particle must be ≤ the substrate thickness. This is true of alphas but not for e-. -Use GEANT4 to visually verify range for alpha vs. e-. -Use GEANT4 to obtain energy deposition for alpha vs. e-.

5. Tl-204 Electrons: Graphene accounts for 1/10 of beam size (beam of 100 e-). Many electrons escape or leave effective volume. Energy deposited into substrate = 0.377 MeV/e- (~44% of original energy) Considering source strength, total deposited energy = 6.78E4 MeV/s in entire substrate. 0.245 MeV/s under graphene area.

6. Am-241 Alphas: Graphene accounts for 1/10 of beam size (beam of 100 alphas). Short range and heavy ionization along alpha path. Range ~= 45 um Energy deposited into substrate = 5.16 MeV/alpha (~94% of original energy) Considering source strength, total deposited energy = 1.9E6 MeV/s in entire substrate. 6.7 MeV/s under graphene area.

7. Is the Tl-204 Source Detectable in DARK? From the plot or resistance change, noise is estimated as ~20 ohms. Change due to alphas ~140 ohms. Beta source should deposit 3.5% of alpha energy and, in theory, result in 3.5% of the change of resistance if we assume a linear relation. Thus, a change of 5 ohms due to betas would result, which is not observable over noise in dark.

8. Is the Tl-204 Source Detectable with LIGHT? From the plot or resistance change, noise is estimated as ~50 ohms. Change due to alphas ~1500 ohms. Beta source should deposit 3.5% of alpha energy and, in theory, result in 3.5% of the change of resistance if we assume a linear relation. Thus, a change of 53 ohms due to betas would result, which is just barely observable over noise with light.