Nuclear Changes Reactions of Unstable or Changeable Nuclei

Usual Reactions not Nuclear u Ordinary reactions involve electron (outer e - ) levels only u Ordinary reactions transfer or alter sharing of outer e - u Ordinary reactions include –acid/base (reorganize sharing of e - with H + ) –redox (transfer of e - ) –others

Ordinary Reactions u May be violent (explosions) u May be dangerous (involve hazardous conditions or chemicals)

Nuclear Changes u May also be hazardous -- usually are! u May involve explosions -- most don’t u Are of several types: –radioactive decay –bombardment transmutation –fission –fusion

Radioactive Decay u Involves atoms with unstable nuclei u Gets part of its name from fact that radiation is produced u Part of name (active) from fact that the production of radiation requires no stimulation or activation -- it always occurs if the unstable atoms are present u Remainder of name (decay) refers to gradual decrease in radiation over time

Types of Radiation from Radioactive Decay (-) (+)  Charged Plates Radioactive source (like Radium)

Types of Radiation from Radioactive Decay (-) (+)  Charged Plates Radioactive source (like Radium) 

Types of Radiation from Radioactive Decay (-) (+)    Charged Plates Radioactive source (like Radium)

Types of Radiation from Radioactive Decay (-) (+)    Charged Plates Radioactive source (like Radium)  is positive  is positive  is negative  is negative  is uncharged  is uncharged

Types of Radiation from Radioactive Decay (-) (+)    Charged Plates Radioactive source (like Radium)  is helium nuclei, He 2+  is helium nuclei, He 2+  is electron beam, e -  is electron beam, e -  is electromagnetic radiation (high-energy light)  is electromagnetic radiation (high-energy light)

Unstable Nuclei u May have too many neutrons u May have too few neutrons u May be too big

Too Few, Too many, Too Big When are Nuclei Stable, Unstable?  Atoms with at. no.  are always unstable (too big) u Smaller atoms have range of neutron numbers which usually allow for stability  For small atoms up to at. no. 20 (Ca), p +  n (protons and neutrons about equal in no.) Ô For bigger atoms, n > p + (more neutrons than protons) if stable

Unstable Nuclei Undergo Radioactive Decay u Alpha, beta, and/or gamma radiation will be formed u Alpha radiation usually part of the radiation if atom is too big: Th He U

Alpha Decay Alpha radiation usually part of the radiation if atom is too big: Th He U Formation of  particles allows very large atoms to become smaller -- mass decreases by 4 units. 4 units of mass

Beta Decay Beta radiation usually part of the radiation if atom has too many neutrons: Xe + 0 e I Formation of  particle allows extra neutron to become proton -- mass is unchanged; atomic no. increases by one.  particle (nuclearly created electron)

Beta Decay Beta radiation usually part of the radiation if atom has too many neutrons: Xe + 0 e I 53 p + 78 n 54 p + 77 n In essence, neutron becomes proton plus beta particle.

Gamma Decay Gamma radiation does not change charge or mass of original particle: Tc  43 99m Tc 43 p + 56n 56 n  may also be written as photon, h  may also be written as photon, h “m” refers to metastable; sometimes called “hot”; indicates nuclide contains extra stored energy

Gamma Decay Gamma radiation seen also seen when atoms with too few neutrons decay u The primary decay mode is –positron emission –electron capture u Both processes result in gamma emission

Positron Emission 6 13 C e 7 13 N 7 p + 6 n 6 p + 7 n A positron or anti-electron In effect, a proton is converted into a neutron plus a positron.

Positron Emission 6 13 C e 7 13 N +1 0 e + 0 e  Ordinary electron -- they’re all around! Observed gamma radiation. (too few neutrons)

Electron Capture Ne Na 11p + 11 n 10 p + 12 n In effect, a proton is converted into a neutron by reacting with an electron + 0 e Captured, or drawn into nucleus from e - region outside

Electron Capture Ne Na 11p + 11 n 10 p + 12 n The captured electron usually comes from the 1st energy level (nearest the nucleus). This leaves a hole or void in the electron level of the daughter. + 0 e Captured, or drawn into nucleus from e - region outside

Electron Capture Ne Na The captured electron usually comes from the 1st energy level (nearest the nucleus). This leaves a hole or void in the electron level of the daughter. + 0 e 2e -, 8e -,... 1e -, 8e -,...

Electron Capture 10p + 12n 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 10p + 12n 2e - 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 u Alpha emission u Beta emission u Positron emission (gamma observed) u Electron capture (gamma observed)

Practice Construct Complete Equations: 7 14 N + 0 e ? Decay mode = ?

Practice Construct Complete Equations: Co + 0 e ? Decay mode = ?

Practice Construct Complete Equations: P S ? Decay mode = ?

Practice Construct Complete Equations: Cu Ni ? Decay mode = ?

Practice Construct Complete Equations: Rn He ? Decay mode = ?

Practice Construct Complete Equations: Pb He ? Decay mode = ?

Practice Construct Complete Equations: Pu + 0 e ? Decay mode = ?

Practice Construct Complete Equations: Decay mode = ?  decay of Ra-226

Practice Construct Complete Equations: Decay mode = ?  decay of Ca-41

Practice Construct Complete Equations: Decay mode = ? electron capture by Pd-100

Practice Construct Complete Equations: Decay mode = ? positron emission from Mn-52

Other Nuclear Changes u Bombardment Transmutation –particles “shot” at nuclei; create new atoms u Fission –large atoms split, forming smaller atoms –neutrons and energy also formed u Fusion –very small atoms fused together –relative large amounts of energy produced

Bombardment Transmutation Np + 0 e U n Note: just as in radioactive decay, mass nos. and charge nos. total the same before and after

Bombardment Transmutation Np + 0 e U n Note: just as in radioactive decay, mass nos. and charge nos. total the same before and after “Bullet” shot at U atom

Bombardment Transmutation P n Al He Note: just as in radioactive decay, mass nos. and charge nos. total the same before and after ?

Practice Tc + 0 e Mo + Remember: just as in radioactive decay, mass nos. and charge nos. must total the same before and after. ? ? ? ? ?

Practice 6 14 C H 0 1 n + Remember: just as in radioactive decay, mass nos. and charge nos. must total the same before and after. ? ? ? ? ?

Practice 7 14 N H 2 4 He + Remember: just as in radioactive decay, mass nos. and charge nos. must total the same before and after. ? ? ? ? ?

Practice 2 4  n Ag + Remember: just as in radioactive decay, mass nos. and charge nos. must total the same before and after. ? ? ? ? ? 2

Fission Sr n U n Note: just as in others, mass nos. and charge nos. total the same before and after Xe + 4 Neutron-induced splitting of large atoms

Fission Ba n Pu n Quite large quantities of energy are given of during fission reactions; the products are radioactive Sr + 3 Neutron-induced splitting of large atoms

Fission Ba n U n Remember: mass numbers must total the same on both sides; similarly, for charge numbers. ? ? ? ? + 4 PRACTICE ?

Fission Ba U n Remember: mass numbers must total the same on both sides; similarly, for charge numbers. ? ? ? ? + PRACTICE ? Kr

Fusion 2 4 He n 1 3 H H Note: just as in others, mass nos. and charge nos. total the same before and after Welding together of very Small Atoms

Fusion 2 4 He n 1 3 H H Note: just as in others, mass nos. and charge nos. total the same before and after Welding together of very Small Atoms Very small atoms

Fusion 2 4 He n 1 3 H H Very large quantities of energy are produced during fusion; products are low in radioactivity Welding together of very Small Atoms

Fusion 2 4 He H Note: just as in others, mass nos. and charge nos. total the same before and after. ? ? ? ? PRACTICE 3 7 Li 2 ?

Fusion 1 1 H He Note: just as in others, mass nos. and charge nos. total the same before and after. ? ? ? ? PRACTICE 2 3 He ? 2

Nuclear Changes Rates of Radioactive Decay

Rates of Decay u Some radioisotopes are very unstable and decay almost as soon as they come into existence –most or all of a sample will decay in a fraction of a second u Some radioisotopes are almost stable and decay very slowly –most of the sample will still be undecayed after millions of years u And others are in between

Rate of Decay u Frequently measured as the radioisotope’s half life –the time required for one-half of the sample of radioisotope to decay –half life depends on the identity of the isotope but not on the original amount  Short half life  rapid decay  Long half life  slow decay

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

Profile of Radioisotope Decay Time % Remaining For this radioisotope, 1/2 of the isotope decays every 2 time units

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

Decay Patterns u Time (hrs) è0 è1 è2 è3 è4 è5 è6 è7 u Amount Remaining (mg) è30.00 è15.00 è7.50 è3.75 è1.86 è0.938 è0.469 è0.234 Here, the half life is one hour.

Decay Patterns u Time (days) è0 è8 è16 è24 è32 è40 è48 è56  Amount Remaining (  g) è10.0 è5.00 è2.50 è1.25 è0.625 è0.313 è0.156 è Here, the half life is 8 days I Xe e-e-e-e- 0

Practice u Time (days) è0  Amount Remaining (  g) è20.0 Here, the half life is 14 days P e-e-e-e- 0 ?

Radiation Intensity The Inverse Square Law

Radiation Intensity and Distance u Intensity drops as distance from source increases u Intensity is an inverse function of the square of the distance from source –Double then distance  intensity cut to 1/4 th –Triple the distance  intensity cut to 1/9 th –10 X the distance  intensity cut to 1/100 th

Inverse Square Law A B C D Distance At double distance the radiation is “diluted” over four times the area. A

Inverse Square Law A B C D Distance At double distance the radiation is “diluted” over four times the area. A

Inverse-Square Law IxIx IyIy = dydy dxdx 2 2 or, after “crossmultiplying:” IxIx dxdx 2 = IyIy dydy 2

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 u May convert critical molecules of heredity (DNA, eg) to altered forms -- primary effect –if the cells with these altered molecules reproduce, foreign growth may form u May create foreign substances out of more common molecues, eg, H 2 O -- secondary effect –These foreign substances may react chemically with DNA, altering its structure –if the cells with these altered molecules reproduce, foreign growth may form

Radiation’s Effect on H 2 O H O H radiation H + + OH - Ordinary ions; present in all cells. Radiation has been safely absorbed.

Radiation’s Effect on H 2 O H O H radiation H + OH “Free radicals”; uncharged and highly reactive; dangerous to cellular molecules like DNA.

Radiation’s Effect on H 2 O H O H radiation H - + OH + Foreign ions; charged and highly reactive; dangerous to cellular molecules like DNA.

Radiation’s Effect on H 2 O H O H radiation Foreign species; charged and highly reactive; dangerous to cellular molecules like DNA. H O H + + e -