Unit 2: The AtomUnit 2: The Atom

Nuclear DecayNuclear Decay

Band Of StabilityBand Of Stability Atoms that lie Atoms that lie

outside outside the band of the band of stability are unstablestability are unstable

Atoms 1-20 nAtoms 1-20 n00/p/p++ ratio ratio must be must be 1:11:1

Atoms 21-83 nAtoms 21-83 n00/p/p++ ratio is ~ ratio is ~ 1.5 : 11.5 : 1

Atoms 84 and up are Atoms 84 and up are ALL ALL unstableunstable

Unstable atoms will lose pieces of itself until it becomes stable. – This is Nuclear Decay

3 Types of Decay3 Types of DecayRegion A:Region A: Atoms have Atoms have

too many too many neutronsneutrons; ; Beta DecayBeta Decay

Region B:Region B: Atoms have Atoms have too many too many protonsprotons;; Positron emission and Positron emission and ee- - capturecapture

Region C:Region C: Elements Elements have too many have too many neutrons and protonsneutrons and protons; ; Alpha DecayAlpha Decay

Alpha DecayAlpha Decay I am an isotope that have too many neutrons I am an isotope that have too many neutrons

and protons… What to do?and protons… What to do? Alpha decay!!!Alpha decay!!! Atoms that undergo alpha decay lose Atoms that undergo alpha decay lose 2 2

protons and 2 neutronsprotons and 2 neutrons

αα (alpha particles) (alpha particles)are are simply the nucleus of simply the nucleus of a a He atom with no He atom with no electrons!!)electrons!!)

The result is an atom The result is an atom with with lowerlower atomic atomic number number andand mass mass

He42

Alpha DecayAlpha Decay•Alpha decay is how elements greater than atomic #83 try to become stable.•They will emit an alpha particle (2 neutrons and 2 protons) to try to become stable.•Alpha reactions will always have He on the right side!•To balance: write the upper and lower equations!

210 = 206 + 4

84 = 82 + 2

Beta DecayBeta Decay I am an isotope with I am an isotope with too many too many neutronsneutrons… what to do?… what to do?

Get rid of a neutron by Beta Decay!Get rid of a neutron by Beta Decay!

During Beta decay, a During Beta decay, a neutronneutron is is converted into a proton and econverted into a proton and e--

(which is ejected from the (which is ejected from the nucleus)nucleus)Neutron = proton + electronNeutron = proton + electron

Beta particles are known as Beta particles are known as high high

energy electronsenergy electrons

The extra proton creates an The extra proton creates an atom with a atom with a higher higher atomic atomic numbernumber

e

B01

01

There are 2 ways to write a Beta

particle!

Beta DecayBeta Decay

•Beta decay is how elements who have too many neutrons try to become stable (on top of the band)•Beta reactions will always have ß or e- on the right side!

14 = 14 + 0

6 = 7 + -1

Gamma DecayGamma Decay Gamma decayGamma decay never never happens alone! (it happens alone! (it

usually usually accompanies accompanies alpha or beta alpha or beta decay)decay)

It represents a It represents a photon of energy or photon of energy or lightlight

Gamma decay alone involves Gamma decay alone involves no no transformation or changetransformation or change of an atom’s of an atom’s nucleusnucleus

00

Gamma DecayGamma Decay

0042

22991

23393 * HePaNp

The * represents extra energy that will be lost.

93 = 91 + 2 + 0

233 = 229 + 4 + 0

PracticePracticeFor each of the following, fill in the missing parts of the For each of the following, fill in the missing parts of the

equation:equation:

015413153 XeI 131

He42

0042

23592 HeU Th231

90

XeRa 22286

22688 Rn

Nuclear Decay SeriesNuclear Decay Series•Radioactive atoms will continue to decay until they reach a stable nucleus.

•For large atoms with atomic number greater than 83, the stable element will be lead.

Nuclear Decay SeriesNuclear Decay Series

Detecting RadiationDetecting Radiation

Radioactive particles can be detected by a Radioactive particles can be detected by a Geiger Counter which gives a clicking Geiger Counter which gives a clicking sound for each particle detected.sound for each particle detected.

Different types of radiation required Different types of radiation required different types of different types of protection.protection.

The greater the The greater the distancedistance from a from a radioactive source will give better radioactive source will give better protection.protection.

Radiation SafetyRadiation Safety

Alpha ParticlesAlpha Particles Cannot penetrate very far into matter.Cannot penetrate very far into matter. Cannot penetrate a sheet of Cannot penetrate a sheet of paperpaper.. Cannot penetrate your skin.Cannot penetrate your skin. Only dangerous to humans if eaten or Only dangerous to humans if eaten or

inhaled.inhaled.

Beta ParticlesBeta Particles

Can penetrate a bit more deeplyCan penetrate a bit more deeply Can be stopped by a sheet of Can be stopped by a sheet of

aluminum foilaluminum foil or or plexiglass.plexiglass. Only dangerous to people if eaten or Only dangerous to people if eaten or

inhaled.inhaled.

Gamma ParticlesGamma Particles

The The mostmost penetrating (have the most penetrating (have the most energy).energy).

They will penetrate the body through They will penetrate the body through the skin and do damage.the skin and do damage.

Have Have moremore energy than an x-ray energy than an x-ray Can only be stopped by thick pieces Can only be stopped by thick pieces

of of leadlead

Radiation SafetyRadiation Safety