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Interaction of Charged Particles with Matter., Summaries of Chemistry

The charged particle (alpha or beta particle) exerts just enough force to promote one of the atom's electrons to a higher energy state (shell).

Typology: Summaries

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Interaction of Charged
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Interaction of Charged

Particles With Matter

3/1/

Objectives

QualitativeQuantitative Introduction

GeneralForce of the Interaction

Contents

Force of the InteractionFour Types of Charged Particle Interactions Ionization

GeneralIon PairsDelta Ray

Quantitative Measures of Energy Loss

GeneralW ValueSpecific IonizationStopping Power and Linear Energy TransferMass Stopping Power

Contents

Alpha Particles

GeneralAlpha TracksRangeRange in AirApproximate Data for 5 MeV Alphas

Beta Particles

GeneralRangeRange (as a density thickness)Range and PenetrationBremsstrahlungC

k^

R di ti

Contents

Cerenkov RadiationApproximate Data for 1 MeV Beta Particles Summary

Types of InteractionsAlpha ParticlesBeta Particles References

  • Ionization– Excitation

ObjectivesQualitative

  • Excitation– Bremsstrahlung– Cerenkov radiation

To review the following measures of energy loss:

  • W Value– Specific Ionization

ObjectivesQuantitative

  • Specific Ionization– Stopping Power/Linear Energy Transfer– Mass Stopping Power
•^

“The interaction of charged particles with matter”concerns the transfer of energy from the chargedparticles to the material through which they travel.

-^

The “charged particles” considered here are:

IntroductionGeneral

The

charged particles

considered here are:

  • Alpha particles (+2 charge)- Beta particles (+ or -1 charge) or electrons
•^

Photons and neutrons, which have no charge,interact very differently.

•^

Charged particles passing through matter continuouslyinteract with the electrons and nuclei of the surroundingatoms.

-^

In other words, alpha and beta particles are continually

IntroductionGeneral

slowing down as they travel through matter.

-^

The interactions involve the electromagnetic forces ofattraction or repulsion between the alpha or betaparticles and the surrounding electrons and nuclei.

Things to notice about the equation:

  • The force increases as the charge increases• The force increases as the distance decreases (it

quadruples if the distance is cut in half)

IntroductionForce of the Interaction

q

p^

  • The force can be positive or negative (attractive or

repulsive)

IntroductionFour Types of Charged Particle Interactions • The four types of interactions are:

Ionization (alphas and betas)Excitation (alphas and betas)Bremsstrahlung (primarily betas) Bremsstrahlung (primarily betas)Cerenkov radiation (primarily betas)

  • Ionization is almost always the primary mechanism of

energy loss.

•^

A charged particle (alpha or beta particle) exertssufficient force of attraction or repulsion to completelyremove one or more electrons from an atom.

-^

The energy imparted to the electron must exceed thebi di

f th

l^

t

IonizationGeneral

binding energy of the electron.

-^

Ionization is most likely to involve atoms near thecharged particle's trajectory.

-^

Each ionization event reduces the charged particle'svelocity, i.e., the alpha or beta particles loses kineticenergy.

•^

Ionization turns a neutral atom into an ion pair.

-^

The electron stripped away from the atom is the negativemember of the ion pair.It is known as a secondary electron.

IonizationIon Pairs

y

The secondary electron has some, but not much, kineticenergy - usually less than 100 eV.Sometimes it has enough energy to ionize additionalatoms. Then it is referred to as a delta ray.

-^

The atom , now with a vacancy in one of its electronshells, is the positive member of the ion pair.

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