Space-radiation environment and dosimetry: galactic cosmic rays, solar modulation, trapped particle belts (Van Allen), particle energy-loss physics (Bethe–Bloch stopping power, linear energy transfer), radiation quality factors, and the…
radiation-physics
Galactic cosmic rays (GCRs)
Isotropic, nearly constant-in-time flux of high-energy (≳100 MeV/n) ionised nuclei (≈87% H, 12% He, 1% HZE, + electrons) originating…
Solar modulation of GCR flux
The heliospheric magnetic field and solar wind convectively and diffusively attenuate low-energy GCRs, with 11-year anti-correlation to…
Van Allen radiation belts
Regions of geomagnetically-trapped energetic particles around Earth: inner belt (~1000–6000 km, protons up to ~100s MeV) and outer belt…
Bethe–Bloch stopping power
Mean energy-loss rate for a charged particle in matter: −⟨dE/dx⟩ = K·z²·(Z/A)/β² · [½·ln(2mₑc²β²γ²T_max/I²) − β² − δ/2]. Inputs: particle…
Linear energy transfer (LET)
Energy deposited per unit path length by ionising radiation in matter, L = dE/dx, restricted to energy delivered locally (i.e. excluding…
Radiation quality factor Q(L)
ICRP 60 / NCRP quality factor mapping LET to biological effectiveness: Q(L) = 1 for L ≤ 10 keV/μm, Q(L) = 0.32·L − 2.2 for 10 < L < 100…
Ambient dose equivalent H*(10)
Operational dosimetric quantity used for area monitoring: the dose equivalent at a 10 mm depth in the ICRU sphere under an expanded,…
Cherenkov radiation
Electromagnetic radiation emitted when a charged particle traverses a dielectric medium faster than the phase velocity of light in that…
Dose equivalent (Sv)
H = Σ wR × D with radiation weighting factor wR (1 for β/γ, 20 for α). Linked to stochastic health risk. ICRP recommendations (1 mSv/y…
Bragg peak & proton therapy
Charged-particle dE/dx rises sharply near stopping; localized dose deposition. Proton/heavy-ion therapy spares healthy tissue vs photon…
Photon-matter interactions
Photoelectric (∝Z⁴/E³), Compton scattering (∝Z), pair production (>1.022 MeV). Total attenuation µ/ρ tabulated by NIST.
Photoelectric absorption cross-section
σ_PE ∝ Z^n/E^(7/2) (n≈4-5); K-edge discontinuity; dominant <100 keV in high-Z; imaging contrast mechanism.
Klein–Nishina Compton cross-section
QED result for photon-electron scattering; reduces to Thomson at ω ≪ m_e c²; asymmetric at high E.
Electron-positron pair production
γ + nucleus → e⁺e⁻ above 1.022 MeV; σ ~ αZ²r_e²/E at high E; dominates above 10 MeV; basis of PET isotopes.
Bethe–Bloch stopping power
-dE/dx = K(Z/A)(z²/β²)[ln(2m_ec²β²γ²T_max/I²) - 2β² + ...]; ionization energy loss; Bragg peak for hadron therapy.
Dosimetry: Gy, Sv, dose-response
Absorbed dose D (J/kg = Gy); equivalent H = w_R D (Sv); effective E = Σ w_T H_T; LNT vs threshold vs hormesis debates.
Radiation-induced DNA damage
Direct (ionization) + indirect (·OH radicals); DSB repair by NHEJ/HR; oxygen-enhancement factor ~3 for X-rays.
Scintillation detectors (NaI, LaBr, plastic)
Inorganic crystals with activator dopants emit visible light after γ absorption; organic scintillators faster but lower Z.
Semiconductor radiation detectors (HPGe, Si)
Reverse-biased p-n junction; e-h pairs drift in field; HPGe FWHM ~2 keV at 1.3 MeV; silicon vertex detectors in LHC.
Gaseous detectors (MWPC, TPC, GEM)
Charpak MWPC (1968 Nobel); Time-projection chambers give 3D tracks; GEM/Micromegas modern micro-pattern.
Mass attenuation coefficient μ/ρ
I(x) = I₀ e^(-μx); μ/ρ tabulated NIST XCOM; half-value layer HVL = ln2/μ; build-up factor for broad beams.
Time-of-flight techniques
ToF used in mass spec, neutron spectroscopy, PET scanners; timing resolution <100 ps in modern TOF-PET.
Čerenkov radiation detectors
RICH, DIRC identify particle species via cone angle; IceCube, SuperK use H₂O/ice; threshold detectors separate π/K.
GEANT4 radiation transport
Monte Carlo simulation of particles interacting with matter; CERN developed; used in medical physics, HEP, space dosimetry.
Klein–Nishina angular distribution as a random variable (radiation-physics)
Radiation-physics application of L0 random-variable and expectation-operator theory. In Compton scattering, the outgoing photon angle θ is…
Photon-counting detector Poisson statistics (radiation-physics)
Radiation-physics application of L0 Poisson-process and moment-generating-function theory. A photon-counting detector exposed to a weak…