Solid State Detectors

Solid State Detectors Physics

Refers to types of crystalline substances that exhibit measurable effects when exposed to radiation.

Solid State Detectors Physics

Crystals have valence band (bound electrons) and conduction band (free electrons).

valence band; conduction band

Solid State Detectors Physics Crystals have _____ (bound electrons) and ____ (free electrons).

electron-hole pairs (EHPs)

Solid State Detectors Physics

Radiation creates___

electric field sweeps charges

Solid State Detectors Physics

Applied____ to electrodes →current pulse proportional to deposited energy.

Solid State Detectors Physics

More pairs created than in gases (≈3 eV per pair vs ~30 eV in gas).

Solid State Detectors Physics

Advantages: excellent energy resolution, compact, high intrinsic efficiency for certain energies.

Conductivity detectors

s a semiconductor device that measures radiation by detecting changes in electrical conductivity of the material.

excites electrons

Conductivity detectors

When ionizing radiation enters the crystal:

• It ____ from the valence band → conduction band.

electron–hole pairs (EHPs)

Conductivity detectors

When ionizing radiation enters the crystal:

This creates __.

drift to electrodes

Conductivity detectors

When ionizing radiation enters the crystal:

An applied electric field causes these charges to ____

proportional

Conductivity detectors

When ionizing radiation enters the crystal:

The collected charge is _____ to the energy deposited by the radiation

Direct conversion

Conductivity detectors

Key Characteristics

____ of radiation → electrical signal (no scintillation step).

High energy resolution

Conductivity detectors

Key Characteristics

(much better than NaI)

crystal purity; cooling

Conductivity detectors

Key Characteristics

Requires ___ and often _____ to reduce electronic noise

spectroscopy

Conductivity detectors

Key Characteristics

Used mainly in _____, less in clinical gamma imaging.

HPGe (High Purity Germanium)

Best energy resolution for gamma spectrometry (excellent for isotope identification)

HPGe (High Purity Germanium)

Require cryogenic cooling (liquid nitrogen or mechanical coolers) to reduce thermal noise.

thermal excitations

produce electron-hole pairs and raise noise

leakage current; improves resolution

HPGe (High Purity Germanium)

cooling reduces the ___ and _____

HPGe (High Purity Germanium

Typical uses: environmental monitoring, radionuclide identification, high-precision energy spectrum work.

HPGe (High Purity Germanium

Care: hygroscopic or sensitive to thermal cycles; require careful handling and spectrum calibration (energy & efficiency)

HPGe (High Purity Germanium)

gold standard for spectroscopy but not used for routine imaging.

Si(Li) Detector (Silicon Lithium Detector)

are semiconductor detectors madefrom siliconwith a lithium-drifted layer.

Si(Li) Detector (Silicon Lithium Detector)

They are commonly used for X-ray spectroscopy and are sensitive to X-rays and gamma rays

Si(Li) Detector (Silicon Lithium Detector)

can be operated at room temperature, making them more convenient to use compared to HPGe detectors, which require cryogenic cooling

Si(Li) Detector (Silicon Lithium Detector)

They are often used in applications like X-ray fluorescence (XRF) analysis and energy-dispersive X-ray spectroscopy (EDS) in materials science and geology

CZT (Cadmium Zinc Telluride)

A semi conductor detector that directly converts gamma photons into an electrical signal.

CZT (Cadmium Zinc Telluride)

Made of Cadmium, Zinc, and Tellurium(CdZnTe or CZT).

CZT (Cadmium Zinc Telluride)

Works at room temperature (unlike HPGe, which requires liquid nitrogen).

Gamma photon;CZT crystal; electron–hole pairs (EHPs)

electrodes

Collected charge pulse; photon energy

Pixelated anodes

CZT (Cadmium Zinc Telluride)

Step-by-step process:

____ interacts in ____ → creates____.

Electric field across the crystal sweeps charges to ___

____ is proportional to ___

____allow 2D position information (x,y), giving both energy and spatial localization

LiF (Lithium Fluoride) Detector

are typically used as Thermoluminescent dosimeters (TLDs) to measure ionizing radiation doses.

LiF (Lithium Fluoride) Detector

These detectors contain lithium fluoride crystals that can trap energy from ionizing radiation when exposed

visible light; radiation dose received

LiF (Lithium Fluoride) Detector

After exposure, the crystals can be heated, causing them to release the stored energy in the form of ____, which can be measured to determine the ____.

Scintillation detectors

Consists of phosphor, photocathode, photomultiplier tube (PMT) and charge collector

𝛾-or X-ray; light pulses

Scintillation detectors

_____ radiation causes ionization, the phosphor converts ionization into ____

photocathode; photoelectrons

Scintillation detectors

Light strikes ____ and emits ____.

Scintillation detectors

PMT accelerates and multiplies photo electrons

Luminescence Detectors

Uses electron trapping process

Luminescence Detectors

The electron are trapped when exposed to radiation and are stable at normal temperatures

Luminescence Detectors

If heated or subject to light, trapped electron returns to valence band and emits light

Thermoluminescent dosimeters (TLD)

Materials: LiF (Lithium Fluoride), CaF₂ (Calcium Fluoride), CaSO₄ (Calcium Sulfate), Li₂B₄O₇ (Lithium Borate), etc. Most common: LiF (TLD-100)

Thermoluminescent dosimeters (TLD)

Mechanism: radiation → trapped electrons in crystal defects; heating releases electrons → recombination emits light → light intensity is proportional to the dose

Thermoluminescent dosimeters (TLD)

Readout: heat is required to release trapped charge. heating in TLD reader produces glow curve; integrated light gives dose

Thermoluminescent dosimeters (TLD)

Pros: small, tissue-equivalent (LiF), reusable (after annealing), wide dose range.

Thermoluminescent dosimeters (TLD)

Cons: destructive readout (erases dose), requires calibrated reader, potential fading over time.

Thermoluminescent dosimeters (TLD).

OSL dosimeters (Optically Stimulated Luminescence)

Material: commonly Al₂O₃:C (aluminum oxide doped with carbon) —usedinmanymodernbadges

OSL dosimeters (Optically Stimulated Luminescence)

Mechanism: radiation traps electrons in metastable traps; stimulation with light (usually green laser/LED) releases electrons → emits luminescence measured by a photomultiplier or photodiode.

OSL dosimeters (Optically Stimulated Luminescence)

Pros vs TLD: high sensitivity, can be read multiple times (partial reads possible) without full erasure in some systems, lower fading, stable signal

OSL dosimeters (Optically Stimulated Luminescence)

Cons: readout equipment needed, small energy dependence at low photon energies.

OSL dosimeters (Optically Stimulated Luminescence).