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Negative Beta (-) Decay :Negative Beta (-) Decay
Negative Beta (-) Decay :n p + e + extra neutron proton beta antineutrino Negative Beta (-) Decay Unstable nuclei which have too many neutrons (i.e., neutron-rich nuclei) tend to decay by the emission of negative beta particles.
The negative beta particle, also known as a negatron, is an electron formed in an unstable nucleus through the following nuclear conversion:
Negative Beta (-) Decay :Negative Beta (-) Decay This nuclear transformation results in the loss of a neutron and the addition of a proton to the nucleus, thereby altering the neutron to proton ratio.
The nuclear electron (-) and the antineutrino () are ejected from the unstable nucleus.
Slide 4:What Is Negative Beta Particle? e- = nuclear electron = - Particle A beta particle (negatron) is an electron ejected from a radioactive nucleus which is neutron-rich.
Properties of Negative Betas :Properties of Negative Betas Charge: - 1 (i.e., - 1.6 x 10-19 coul)
Mass: me (i.e., one electron mass)
LET and SI: relatively low (compared to alphas)
Range in Air: ~ 12 feet/MeV
Energy: polyenergetic
betas are emitted with energies ranging from 0 to Emax
energies given in tables for beta particles represent Emax
Slide 6:Energy Spectrum of 32P - A Pure Beta Emitter Number Of Betas Energy (MeV) EAV 0.7 MeV Emax =1.71 MeV 1.5 2.0 0.5
Properties of Negative Betas : Properties of Negative Betas Paths in Matter: usually long and torturous due to their small mass
For these particles, path length does not equal range.
Slide 8:Typical Path of a Beta Particle Through Matter ions origin end Range
Properties of Betas (Con’t) :Properties of Betas (Con’t) Penetrating Ability: more penetrating than alphas but dependent upon energy
Best Shielding: low Z-number materials (e.g., plastic, cardboard, plexiglas, wood, etc.)
Remember :Remember Do not use high Z-number shielding materials (i.e., Pb, W, or depleted uranium, etc.) with high energy beta emitters!!
Doing so will result in the production of bremsstrahlung (braking radiation)…. otherwise known as x-rays!!
Slide 11:Recall that x-ray tubes produce x-rays by accelerating electrons into tungsten (W) targets Fast Moving Electrons Cathode (-) Target Anode (+) X-rays Filtration
Slide 12:Negative Beta Decay Equation: X A Z Y + + A Z+1 0 -1 0 parent daughter beta antineutrino Example: S 35 16 Cl 35 17 + + 0 0 -1 0 0
Commonly Used - Emitters in Medical Research and Therapy :Commonly Used - Emitters in Medical Research and Therapy
Commonly Used - Emitters :Commonly Used - Emitters