Chemistry 988 Part 1

Transcription

1 Chmisry 988 Par 1 Radiaion Dcion & Masurmn Dp. of Chmisry --- Michigan Sa Univ. aional Suprconducing Cycloron Lab DJMorrissy Spring/2oo9 Cours informaion can b found on h wbsi: hp://

2 Chap. 1 Radiaion Sourcs.. Wha? Ionizing Radiaion: a ypical Ionizaion Ponial for a molcul (or work funcion for a mal) is a fw V.. Thus, w will b concrnd wih sourcs ha produc radiaions wih significanly mor nrgy han his (lar w will s ha h imporan paramr for dcors is an ffciv ionizaion ponial somwha largr han h minimum). Radiaion yps: sor by mass & charg Gamma rays Elcrons +/- urons uclar Chargd Paricls Rquird Informaion: nuclid (, radiaions), amoun ( 0 ) d d d d , manlif ln2 T 12, half lif uxiliary informaion: puriy Spcificciviy mass MM Spcificciviy mass (if pur) MM ( ) (if pur)

3 Radiaion Sourcs.. Growh Sourcs: wih a vry fw xcpions h radioaciv sourcs ha w us hav o b producd in nuclar racions. Th producion can b dirc such as in a nuron capur procss (n,γ) or indircly by h dcay of anohr nuclid. Growh: a nuclar racion of h sor x +, whr will b our sourc marial d d d d ( ProducionRa) ( DcayRa) 0 σ x Φ x Limi: If is sabl, 0 0 x x ( σ Φ )( 1 ) 0 x x Producion up o 1, subsqun dcay 2 1

4 τ τ < >τ τ τ τ >> τ τ >> >> τ τ Radiaion Sourcs.. Growh & Dcay Growh & Dcay: ofn a sourc may consis of a dcay chain: C ( ) ( ) ( ) bu d d d d ) (... ) ( ) ( ) ( Dcay Ra Producion Ra Som xampls for various cass of τ viz. τ.. h curvs ar h aciviis.

5 Radiaion Sourcs.. Elcrons 1 a Dcay: n p ν + Q.g., 14 C ν + Q Q M( 14 0 ) - M( 14 C) and (p + n ν + Q ).g., C ν + Q C ν + Q Thr-bodis in final sa givs coninuous nrgy disribuion bu hr ar housands of radioaciviis o choos from. o limis: 0 < Kinic Enrgy < Q Q M( 13 C 0 ) + 2 m o c 2 -M( 14 C) Phas spac or Frmi Funcions hav Coulomb shifs 64 Cu 64 i ν + Q β MV 64 Cu 64 Zn ν + Q β MV lso lcron capur: 64 Cu 64 i + ν + Q β MV Typical nrgy scal

6 Radiaion Sourcs.. Elcrons 2 Inrnal convrsion: Z* Z + + -, whr h lcron was a bound aomic lcron. 207 i (38 yr) 207 Pb * + ν + Q c Two-bodis in final sa givs a discr nrgy disribuion of lcrons bu hr ar rlaivly fw xampls of sourcs (compard o ba-dcay). 207 Pb (KEΔE aomic.e. ) K: 88 kv, L: 16 kv (n1, 1s) (n2, 2s,2p) Typical nrgy scal 9/2-207 i 7% 83% 10% 7/ MV M1 ΔE / MV, 0.81 s M4 ΔE / MV, 131 ps E2 ΔE Pb 1/2- g.s.

7 Radiaion Sourcs.. Chargd Paricls 1 lpha Dcay: Z -4 (Z-2) H 2+ +Q α.g., 238 U 234 Th H 2+ + Q α Q α M[ -4 (Z-2) 0 ] +M[ 4 H 0 ] M[ Z] ucli havir han ~ 150 ar hrmodynamically unsabl agains alpha dcay bu bcaus h nrgy of dcay is much lowr han h Coulomb barrir i is a quanum mchanical unnling procss ha is xrmly snsiiv o h Q-valu of h procss. Thus, alpha dcay is only imporan for h havis nucli and i rarly fds xcid sas. Th paricls ar qui nrgic 4-9 MV bu inrac vry fficinly wih lcrons in marials and sop wihin ~100 microns in solids. Two-body final sa givs a discr nrgy disribuion mus accoun for rcoil nrgy. E.g., h 4n naural dcay chain: Th 10 Ra c α,10 yr β β 228 Th 228 Th α,1.9 yr 224 Ra α,4d 220 Rn α,56s 216 Po α,0.2s 212 Pb 212 Pb β,11hr 212 i β,61m α E α 6.05, 6.09 MV Po Tl α,0.3μs β,3 m Pb Pb* E α 8.78 MV E γ 2.61 MV

8 Radiaion Sourcs.. Chargd Paricls 2 Sponanous Fission: Z -x (Z-y)* + x y* + Q f.g., 252 Cf (~3% SF) TKE 185 MV Sponanous fission is anohr quanum mchanical unnling procss similar o alpha-dcay ha is rar in h ligh acinid nucli and incrass in imporanc wih Z and limis h sabiliy of nucli wih Z>98. ll fission procsss produc a saisical disribuion of radioaciv producs, fas nurons and γ s. Two-body final sa givs a discr nrgy disribuion for ach fission vn bu hr ar many mass-splis and nuron vaporaion from h xcid fragmns. Ths fragmns go on o β- dcay vnually raching sabiliy. From: Schmi & Plasonon, IM 40 (1966) 204

9 Radiaion Sourcs.. γ rays Gamma rays ar mid by nuclar xcid sas, hir lifims ar gnrally oo shor o provid usful sourcs (xcp for som spcial cass calld isomric sas). a-dlayd: (Z+/-1) Z* Z + γ h gamma dcay is for many purposs promp, bu ofn h lifims of h xcid sas ar significan and hir xponnial dcay can b masurd. Two-bodis in final sa givs a yr discr nrgy disribuion 60 Co 100% β- E2 ΔE E2 ΔE i MV, 1.1ps MV, 0.71 ps 0+ g.s. Thr will b an angular corrlaion among h ba and wo gammas.. nnihilaion: 1/2-13 C 100% β+ 1/ m 13 rmssrahlung: from lcron bams, coninuous nrgy spcrum primarily usd for irradiaions

10 Radiaion Sourcs.. nurons urons hav o b producd in nuclar racions, h nrgy spcrum will dpnd on h racion.. Sponanous Fission: 252 Cf h nurons ar primarily mid wih a hrmal nrgy spcrum in h rs fram of h moving fragmns (KE ~ 1 MV/u). Pu & m: inimaly mixd mals Phoonuclar Racions: I E 1/ 2 E / T 238 Pu 234 U H 2+ + Q α MV, KE α < 5.14 MV 4 H C 2+ * 12 C 2+ + n + Q gg MV 12 C 2+ * + n + Q γ n + Q gg MV 124 Sb 124 T* (firs xcid sa) 124 T + γ MV, n Q n MV cclraor Racions: p+ 7 Li 7 + n + Q gg MV d n + Q gg MV [MdCyc] d + d n + 3 H + Q gg MV d + n + 4 H + Q gg MV [fusion racion]