Electromagnetic Rates

Size: px

Start display at page:

Download "Electromagnetic Rates"

Kory Hodge
5 years ago
Views:

1 Electromagnetic Rates B(λ;J i ζ J f ξ) = J f M f ζ O λµ J i M i ξ A µm f O λµ (Eλ) = e(i) r λ i Y λµ (Ω i ) i=1 A # O λµ (Mλ) = g s (i) s! i g l (i) 2! l & % i (! i # $ r λ i Y λµ (Ω i )& ' $ λ 1' i=1 2 = 1 2J i 1 J fζ O λµ J i ξ 2! ji =! s i! l i gyromagnetic factors W (λ 1) W (λ) Selection Rules ~ (kr) 2 large reduction in probability with increasing multipolarity order! J f J i λ J f J i PO λµ (Eλ)P -1 = ( 1) λ O λµ (Eλ), PO λµ (Mλ)P -1 = ( 1) λ1 O λµ (Mλ) π i π f = ( 1) λ π i π f = ( 1) λ1

2 Magnetic transitions are weaker than electric transitions of the same multipolarity 6 E2, (M3, E4, ) 4 5 M1, E2, (M3, E4, ) mixed M1E2 transition 4 A decay scheme: E1, E2 and M1 transitions 140 Gd

3 HW: What is the radiative width corresponding to: a) 1 fs b) 1ps c) 1ns gamma decays? Find the radiative widths of the lowest 0, 2, 4, and 6 states of 166 Er. What are the corresponding recoil energies?

$Atomic electrons, especially those in the inner orbits, such as K- and L-orbits, spend a large frac,on of their,me in the vicinity of the nucleus, the source of the EM field.$

4 Internal conversion An atomic electron is ejected instead of gamma-ray (atomic Auger effect). Atomic electrons, especially those in the inner orbits, such as K- and L-orbits, spend a large frac,on of their,me in the vicinity of the nucleus, the source of the EM field. T e Electron kinetic energy = ( E i E f ) B n Electron binding energy nucleonic wave functions electron wave functions Virtual photon exchange. This process can occur between I=0 states! Electron spectrum: internal conversion beta-decay background Important for heavy nuclei (large Z): it goes as Z 3!!!

5 No X-Rays 6 -> 4 8 -> > > > > No Energy [kev] Fig. 20. A singles γ-ray spectrum (upper) from the 48 Ca 208 Pb reactions gated with fusion-evaporation residues. The same γ-ray spectrum but in addition, tagged with the 254 No α decays (lower)

6 Internal pair production An electron-positron pair is emibed in the place of gamma-ray. This can happen if the energy of the decay E γ > 2m e c 2 =1.02MeV electron scattering pair creation Usually, this process is several orders of magnitude retarded compared to allowed gamma-ray decays. The pair produc,on rate is largest where the internal conversion rate is smallest. That is in the region of low atomic number and high transi,on energies. E0 (ICe e _ )

7 2-gamma decay Nucl. Phys. A474, 412 (1987) γγ = 2E12M1 M1 and E1 transitions are similar in strength! Best candidates: 16 O, 40 Ca, 90 Zr Provides important structural informa,on about nuclear electric polarizability and diamagne,c suscep,bility.

8 137 Cs is formed as one of the more common fission products by the nuclear fission of 235 U. About 95% decays by beta emission to a metastable 137m Ba. It has a number of prac,cal uses M4E m In 16 O, 40 Ca, 90 Zr, γγ = E1 E1M1 M1 In 137 Ba, γγ = E2 M2E1 M3M1 E3 Just measured: Waltz et al., Nature 526, 406 (2015) hbp:// hbp:// hbp://phys.org/news/ compe,,ve-double-gamma-nuclear.html

γ-ray laser? hbp://physics.aps.org/synopsis-for/10.1103/physreva.84.053429 Hafnium-178m has a long half-life of 31 years and a high excita,on energy of 2.4 MeV.

9 γ-ray laser? hbp://physics.aps.org/synopsis-for/ /physreva Hafnium-178m has a long half-life of 31 years and a high excita,on energy of 2.4 MeV. As a result, 1 kilogram of pure 178m Hf contains approximately J of energy. Some es,mates suggest that, with accelerated decay, 1 gram of 100-percent isomeric 178m Hf could release more energy than the detona,on of 200 kilograms of TNT. 178 Hf 2008 LLNL report: Our conclusion is that the u,liza,on of nuclear isomers for energy storage is imprac,cal from the points of view of nuclear structure, nuclear reac,ons, and of prospects for controlled energy release. We note that the cost of producing the nuclear isomer is likely to be extraordinarily high, and that the technologies that would be required to perform the task are beyond anything done before and are difficult to cost at this,me. hbps://str.llnl.gov/str/julaug05/becker.html hbps:// hbp:// hbp://journals.aps.org/prc/abstract/ /physrevc

Nuclear Chemistry. Decay Reactions The most common form of nuclear decay reactions are the following:

Nuclear Chemistry. Decay Reactions The most common form of nuclear decay reactions are the following: Nuclear Chemistry Nuclear reactions are transmutation of the one element into another. We can describe nuclear reactions in a similar manner as regular chemical reactions using ideas of stoichiometry,