Beta and Gamma Decay
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Beta and Gamma Decay Contents: Beta What it is and the Neutrino Hypothesis Reverse decay: electron capture Enrico Fermi, Wolfgang Pauli, and the “little neutral one” Gamma What it is Being Discrete Whiteboards. b. g. Beta Decay:. 60 27 Co 60 28 Ni + - +  e.

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  • Beta and Gamma Decay

  • Contents:

  • Beta

    • What it is and the Neutrino Hypothesis

    • Reverse decay: electron capture

    • Enrico Fermi, Wolfgang Pauli, and the “little neutral one”

  • Gamma

    • What it is

    • Being Discrete

    • Whiteboards

b

g


Beta Decay:

6027Co 6028Ni + - + e

137N 136C + + + e

  • Conservation of charge

  • Beta minus - electron

    • “As if” neutron -> proton + electron

  • Beta plus - positron

    • “As if” proton -> neutron + positron

  • Particles are “of the nucleus” (not orbital)

  • - Neutrino, (anti neutrino) – fudge (Conserve lepton number)

    Energy is continuous (i.e. neutrino gets random share)

TOC


Pauli, Fermi, and the little neutral one

Wolfgang Pauli

1900-1958

Enrico Fermi

1901-1954

Beta decay products were missing energy

Pauli proposes a particle is carrying away energy

Fermi names it Neutrino - “Little neutral one” - It.

Neutrinos confirmed in 1956, no surprise

TOC


ne

e


Gamma Decay:

23994Pu 23994Pu + 

Nucleus has energy levels

Energy of transition emitted as a high energy photon ( ≈ 5 - .05 nm)

Usually after a beta or alpha decay

Many energies possible

Stopped by meters of lead

Used for food irradiation

TOC


Example: Tl-208 emits a 0.6210 MeV gamma and the neutral (un -excited) atom has a mass of 207.9820047 u. What was the mass before the gamma was emitted?

Gamma ray energies associated with alpha and beta decays – so Alpha and Gamma energies are discrete. (Like spectral lines we saw)


Example: Tl-208 emits a 0.6210 MeV gamma and the neutral atom has a mass of 207.9820047 u. What was the mass before the gamma was emitted?

Well, 0.6210 MeV has a mass of

(0.6210 MeV)/(931.5 MeV) = 0.000666667 u

So the parent is this much more massive:

207.9820047 + 0.000666667 = 207.9826714 u


Whiteboards: atom has a mass of 207.9820047 u. What was the mass before the gamma was emitted?

Gamma Decay

1 | 2

TOC


239 atom has a mass of 207.9820047 u. What was the mass before the gamma was emitted?94Pu --> 23994Pu + 

239.052464 --> 239.052157

What is the energy of the gamma emitted?

Parent mass = 239.052464 u

Product mass = 239.052157 u

Mass defect = parent - products = 0.000307 u

Energy of radiation = (0.000307 u)(931.5 MeV/u)

= 0.2860 MeV

W

0.2860 MeV


245 atom has a mass of 207.9820047 u. What was the mass before the gamma was emitted?96Cm --> 24596Cm + 

???.?????? --> 245.065486

What is the excited mass of the parent, if a 0.2957 MeV gamma photon is emitted?

Mass of 0.2957 MeV = (0.2957 MeV)/(931.5 MeV/u)

= 0.000317445 u

Excited parent is more massive than this by that amount

Parent mass = 245.065484 + 0.000317445 u = 245.0658034 u

W

245.0658034 u


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