nuclear changes reactions of unstable or changeable nuclei

Nuclear Changes

Reactions of Unstable or Changeable NucleiReactions of Unstable or Changeable Nuclei

Usual Reactions not Nuclear

Ordinary reactions involve electron (outer eOrdinary reactions involve electron (outer e --) ) levels onlylevels only

Ordinary reactions Ordinary reactions transfertransfer or or alter sharingalter sharing of outer eof outer e--

Ordinary reactions includeOrdinary reactions include– acid/base (reorganize sharing of eacid/base (reorganize sharing of e-- with H with H++))– redox (transfer of eredox (transfer of e--))– othersothers

Ordinary Reactions

May be violent (explosions)May be violent (explosions) May be dangerous (involve hazardous May be dangerous (involve hazardous

conditions or chemicals)conditions or chemicals)

Nuclear Changes

May also be hazardous -- usually May also be hazardous -- usually areare!! May involve explosions -- most don’tMay involve explosions -- most don’t Are of several types:Are of several types:

– radioactive decayradioactive decay– bombardment transmutationbombardment transmutation– fissionfission– fusionfusion

Radioactive Decay

Involves atoms with Involves atoms with unstable nuclei unstable nuclei Gets part of its name from fact that Gets part of its name from fact that

radiationradiation is produced is produced Part of name (active) from fact that the Part of name (active) from fact that the

production of radiation requires no production of radiation requires no stimulation or activation -- it always occurs stimulation or activation -- it always occurs if the unstable atoms are presentif the unstable atoms are present

Remainder of name (decay) refers to Remainder of name (decay) refers to gradual decrease in radiation over time gradual decrease in radiation over time

Types of Radiation from Radioactive Decay

(-)(-)

(+)(+)

Charged PlatesCharged Plates

Radioactive sourceRadioactive source(like Radium)(like Radium)

(-)(-)

(+)(+)

(-)(-)

(+)(+)

(-)(-)

(+)(+)

• is positiveis positive

• is negativeis negative

• is unchargedis uncharged

(-)(-)

(+)(+)

• is helium nuclei, Heis helium nuclei, He2+2+

• is electron beam, eis electron beam, e--

• is electromagnetic radiation (high-energy light)is electromagnetic radiation (high-energy light)

Unstable Nuclei

May have May have too many neutronstoo many neutrons May have May have too few neutronstoo few neutrons May be May be too bigtoo big

Too Few, Too many, Too BigWhen are Nuclei Stable, Unstable?When are Nuclei Stable, Unstable?

Atoms with at. no. Atoms with at. no. are always unstable are always unstable (too big)(too big)

Smaller atoms have range of neutron numbers Smaller atoms have range of neutron numbers which usually allow for stabilitywhich usually allow for stability For small atoms up to at. no. 20 (Ca), pFor small atoms up to at. no. 20 (Ca), p+ + n n

(protons and neutrons about equal in no.)(protons and neutrons about equal in no.) For bigger atoms, n > pFor bigger atoms, n > p+ + (more neutrons than (more neutrons than

protons) if stableprotons) if stable

Unstable Nuclei Undergo Radioactive Decay

Alpha, beta, and/or gamma radiation will Alpha, beta, and/or gamma radiation will be formedbe formed

Alpha radiation usually part of the Alpha radiation usually part of the radiation if atom is radiation if atom is too bigtoo big::

90234 Th ++ 2

Alpha DecayAlpha radiation usually part of the radiation Alpha radiation usually part of the radiation

if atom is if atom is too bigtoo big::

90234 Th ++ 2

Formation of Formation of particles allows particles allows very large atoms to become very large atoms to become smaller -- mass decreases by 4 smaller -- mass decreases by 4 units.units.

4 units of mass4 units of mass

Beta DecayBeta radiation usually part of the radiation if Beta radiation usually part of the radiation if

atom has atom has too many neutronstoo many neutrons::

54131 Xe + -1

Formation of Formation of particle allows particle allows extra neutron to become proton -- extra neutron to become proton -- mass is unchanged; atomic no. mass is unchanged; atomic no. increases by one.increases by one.

particle particle (nuclearly created (nuclearly created electron)electron)

Beta DecayBeta radiation usually part of the radiation if Beta radiation usually part of the radiation if

atom has atom has too many neutronstoo many neutrons::

54131 Xe + -1

53 p53 p++

78 n78 n54 p54 p++

77 n77 n

In essence, neutron becomes proton plus beta particle.In essence, neutron becomes proton plus beta particle.

Gamma DecayGamma radiation does not change charge or Gamma radiation does not change charge or

mass of original particle:mass of original particle:

99Tc + 0

43 p43 p++

56n56n43 p43 p++

56 n56 n may also be may also be written as written as photonphoton, h, h““mm” refers to ” refers to metastablemetastable; sometimes called; sometimes called

““hothot”; indicates nuclide contains extra stored ”; indicates nuclide contains extra stored energyenergy

Gamma DecayGamma radiation seen also seen when atoms Gamma radiation seen also seen when atoms

with with too few neutrons too few neutrons decaydecay

The primary decay mode isThe primary decay mode is– positron emissionpositron emission– electron captureelectron capture

Both processes result in gamma emissionBoth processes result in gamma emission

Positron Emission

6 13 C + +1

7 p7 p++

6 n6 n

6 p6 p++

7 n7 n

A positron or A positron or anti-electronanti-electron

In effect, a proton is converted into a In effect, a proton is converted into a neutron plus a positron. neutron plus a positron.

Positron Emission

6 13 C + +1

Ordinary electron -- they’re all around!

Observed gamma radiation.

(too few neutrons)

Electron Capture

22Ne 11

11p11p++

11 n11 n

10 p10 p++

12 n12 n

In effect, a proton is converted into a In effect, a proton is converted into a neutron by reacting with an electronneutron by reacting with an electron

CapturedCaptured, or drawn , or drawn into nucleus from einto nucleus from e-- region outsideregion outside

Electron Capture

22Ne 11

11p11p++

11 n11 n

10 p10 p++

12 n12 n

The captured electron usually comes from the 1st The captured electron usually comes from the 1st energy level (nearest the nucleus). This leaves a energy level (nearest the nucleus). This leaves a hole or void in the electron level of the daughter.hole or void in the electron level of the daughter.

CapturedCaptured, or drawn , or drawn into nucleus from einto nucleus from e-- region outsideregion outside

Electron Capture

22Ne 11

The captured electron usually comes from the 1st The captured electron usually comes from the 1st energy level (nearest the nucleus). This leaves a energy level (nearest the nucleus). This leaves a holehole or void in the electron level of the daughter. or void in the electron level of the daughter.

2e2e--, 8e, 8e--, ..., ... 1e1e--, 8e, 8e--, ..., ...

Electron Capture

1e- 7 other e- (not shown)·· the 8th e-

A large release of energy occurs as the electron makes transition from level 2 to level 1. This release occurs as gamma radiation.

Electron Capture

12n2e-

7 other e- (not shown)·

A large release of energy occurs as the electron makes transition from level 2 to level 1. This release occurs as gamma radiation.

Four Decay Modes

Alpha emissionAlpha emission Beta emissionBeta emission Positron emission (gamma observed)Positron emission (gamma observed) Electron capture (gamma observed)Electron capture (gamma observed)

PracticeConstruct Complete Equations:Construct Complete Equations:

7 14 N + -1

Decay mode = ?

27 60 Co + -1

Decay mode = ?

15 32 P + 16

Decay mode = ?

29 59 Cu + 28

Decay mode = ?

86 224 Rn + 2

Decay mode = ?

82 208 Pb + 2

Decay mode = ?

94 239 Pu + -1

Decay mode = ?

decay of Ra-226

Decay mode = ?

decay of Ca-41

Decay mode = ?

electron capture by Pd-100

Decay mode = ?

positron emission from Mn-52

Other Nuclear Changes Bombardment TransmutationBombardment Transmutation

– particles “shot” at nuclei; create new atomsparticles “shot” at nuclei; create new atoms FissionFission

– large atoms split, forming smaller atomslarge atoms split, forming smaller atoms– neutrons and energy also formedneutrons and energy also formed

FusionFusion– very small atoms fused togethervery small atoms fused together– relative large amounts of energy producedrelative large amounts of energy produced

Bombardment Transmutation

93239 Np ++ -1

0 e92238 U ++ 0

Note: just as in radioactive decay, mass nos. and charge nos. total the same before and after.

239239

93239 Np ++ -1

0 e92238 U ++ 0

239239

“Bullet” shot at U atom

1530 P ++ 0

1n1327

Al ++24He

Practice

4399 Tc ++ -1

0e4298Mo ++

Remember: just as in radioactive decay, mass nos. and charge nos. must total the same before and after.

Practice

614 C ++ 1

1H0 1n ++

Practice

14N ++ 1

1H2 4He ++

Practice

4 ++ 0

1n47 109

Fission

90Sr ++

01 n92

235 U ++ 0

Note: just as in others, mass nos. and charge nos. total the same before and after.

236236

54142 Xe ++ 4

Neutron-induced splitting of large atoms

Fission

142Ba ++

01 n94

239 Pu++ 0

Quite large quantities of energy are given of during fission reactions; the products are radioactive.

240240

Sr ++ 3

Neutron-induced splitting of large atoms

Fission

140Ba ++

01 n92

235 U ++ 0

Remember: mass numbers must total the same on both sides; similarly, for charge numbers.

PRACTICE

Fission

143Ba ++92

235 U ++ 0

Remember: mass numbers must total the same on both sides; similarly, for charge numbers.

PRACTICE

Fusion

He ++ 01 n1

3H ++ 1

Welding together of very Small Atoms

Fusion

He ++ 01 n1

3H ++ 1

Very small atoms

Fusion

He ++ 01 n1

3H ++ 1

Very large quantities of energy are produced during fusion; products are low in radioactivity.

Fusion

2 4He ++++ 1

PRACTICE

7Li 2 ?

Fusion

1 1H ++++ 2

PRACTICE

3He ?2

Nuclear Changes

Rates of Radioactive DecayRates of Radioactive Decay

Rates of Decay Some radioisotopes are very unstable and decay Some radioisotopes are very unstable and decay

almost as soon as they come into existencealmost as soon as they come into existence– most or all of a sample will decay in a fraction of a most or all of a sample will decay in a fraction of a

secondsecond Some radioisotopes are almost stable and decay Some radioisotopes are almost stable and decay

very slowlyvery slowly– most of the sample will still be undecayed after most of the sample will still be undecayed after

millions of yearsmillions of years And others are in betweenAnd others are in between

Rate of Decay

Frequently measured as the radioisotope’s Frequently measured as the radioisotope’s half lifehalf life– the time required for one-half of the sample of the time required for one-half of the sample of

radioisotope to decayradioisotope to decay– half life depends on the identity of the isotope half life depends on the identity of the isotope

but but notnot on the original amount on the original amount Short half life Short half life rapid decayrapid decay Long half life Long half life slow decayslow decay

Profile of Radioisotope Decay

0102030405060708090

0 2 4 6 8 10Time

0102030405060708090

0 2 4 6 8 10Time

For this radioisotope, 1/2 For this radioisotope, 1/2 of the isotope decays of the isotope decays every 2 time units every 2 time units

0102030405060708090

0 2 4 6 8 10Time

For this radioisotope, 1/2 For this radioisotope, 1/2 of the isotope decays of the isotope decays every 2 time units every 2 time units

0102030405060708090

0 2 4 6 8 10Time

For For anyany given time period, given time period, the same fraction of decay the same fraction of decay occurs occurs

0102030405060708090

0 2 4 6 8 10Time

For For anyany given time given time period, the same fraction period, the same fraction of decay occurs of decay occurs

Decay Patterns

Time (hrs)Time (hrs)0011223344556677

Amount Remaining (mg)Amount Remaining (mg)30.0030.0015.0015.007.507.503.753.751.861.860.9380.9380.4690.4690.2340.234

Here, the half life is one hour.Here, the half life is one hour.

Decay Patterns

Time (days)Time (days)0088161624243232404048485656

Amount Remaining (Amount Remaining (g)g)10.010.05.005.002.502.501.251.250.6250.6250.3130.3130.1560.1560.07810.0781

Here, the half life is 8 daysHere, the half life is 8 days

II5353131131

XeXe5454131131

++ ee---1-1

Practice

Time (days)Time (days)00

Amount Remaining (Amount Remaining (g)g)20.020.0

Here, the half life is Here, the half life is 14 days14 days

PP1515 3232

++ ee---1-1

Radiation Intensity

The Inverse Square LawThe Inverse Square Law

Radiation Intensity and Distance

Intensity drops as distance from source Intensity drops as distance from source increasesincreases

Intensity is an Intensity is an inverseinverse function of the function of the square of the distance from sourcesquare of the distance from source– Double then distance Double then distance intensity cut to 1/4 thintensity cut to 1/4 th– Triple the distance Triple the distance intensity cut to 1/9 thintensity cut to 1/9 th– 10 X the distance 10 X the distance intensity cut to 1/100 thintensity cut to 1/100 th

Inverse Square Law

1 20 Distance

At double distance the radiation is “diluted” over four times the area.

Inverse Square Law

1 20 Distance

At double distance the radiation is “diluted” over four times the area.

Inverse-Square Law

or, after “crossmultiplying:”

2= Iy dy

Practice

What will be the intensity of radiation at 20 ft if radiation from the same source at 10 ft is 75 mrem?

Practice

What will be the intensity of radiation at 20 ft if radiation from the same source at 100 ft is 25 mrem?

Effects of Ionizing Radiation May convert critical molecules of heredity (DNA, May convert critical molecules of heredity (DNA,

egeg) to altered forms -- primary effect) to altered forms -- primary effect– if the cells with these altered molecules reproduce, if the cells with these altered molecules reproduce,

foreign growth may formforeign growth may form May create foreign substances out of more May create foreign substances out of more

common molecues, common molecues, egeg, H, H22O -- secondary effectO -- secondary effect

– These foreign substances may react chemically with These foreign substances may react chemically with DNA, altering its structureDNA, altering its structure

– if the cells with these altered molecules reproduce, if the cells with these altered molecules reproduce, foreign growth may formforeign growth may form

Radiation’s Effect on H2O

H+ + OH-

Ordinary ions; present in all cells. Radiation has been safely absorbed.

H + OH

“Free radicals”; uncharged and highly reactive; dangerous to cellular molecules like DNA.

H - + OH+

Foreign ions; charged and highly reactive; dangerous to cellular molecules like DNA.

n Foreign species; charged and highly reactive; dangerous to cellular molecules like DNA.

nuclear changes reactions of unstable or changeable nuclei

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