Radiation Decay 1

Sodium’s atomic number is 11, what is likely decay mode for Na²¹?

positron emission, β⁺… because Z = 11 and N = 10, extra proton removed, returns to Line of Stability

Nearly all emitted radiation from Tc-99m is characterized as what?

Gamma rays… Because Tc-99m is in an excited state, it will undergo Isomeric Transition, emitting a γ-ray

Activity of a radioactive material may be defined as dN/dt, where N is number of atoms, and t is time. T/F.

True

What is true regarding radioactive decay constant?

inversely proportional to half life

Equal to inverse of mean life

Defined as fractional decay in a given time

What is true regarding specific activity?

Defined as activity per unit mass

proportional to decay constant → because A=λN, A_specific is proportional as well

Carbon has an atomic number of 6, what is likely decay mode for C¹⁴?

β^-, because Z=6 and N=8, β^- removes the extra neutron, returning it to line of stability

Pure Ra-226 (T_1/2=1600 yr) is chemically isolated. Its direct progeny, Rn-222 has T_1/2=3.8 days. Immediately after isolation, what equilibrium is present, if any?

NO equilibrium. Key word: IMMEDIATELY. Full equilibrium takes several half lives of daughter

Two isotopes in secular equilibrium both appear to decay with T_{1/2, parent}. T/F

True! Since Progeny is being replaced at a rate equal to parent’s decay, it appears to decay at the same rate

Decay schemes…

yuh

Accompanying all positron emission decays there is also a…? (Neutrino, antineutrino, electron)

Neutrino

Nuclear fission most likely with light nuclei. T/F

False

Which would occur 2 months after placing Ra-226 in a sealed container with its progeny? (Transient, Secular, No equilibrium)

Secular… takes ~ a month

As Z increases, the ratio of Z:N does what?

decreases

Equilibrium between Mo-99 and Tc-99m?

Transient

I-125 is implanted and gives a total dose of 145 Gy. What is the implanted dose rate? (units given at cGy/hr)

2 ways…

1. T_1/2 given on ABR sheet. Calculate Mean Life using T_mean=1.443*T_1/2… follow through with units

2. A_mean = A_o1.443T_1/2, so D_mean = 1.443D_oT_1/2 as well

   So 7 cGy/hr

In a sealed container, parent and progeny achieved secular equilibrium. What is true about decay of progeny? (decays as same rate as parent, reaches steady state value which remains stable)

Reaches steady state value which remains stable

Match decay types with their effect on Z…

Alpha - Z-2

gamma - Z

β^- - Z+1

e^- capture - Z-1

What is released during isomeric decay?

Gamma ray

Ir-192 has activity of 10 Ci. After how many half-lives will it be 2.5 Ci?

2

Which decay type emits characteristic x-ray? (isomeric, internal conversion, alpha)

internal conversion…

not uncommon after isomeric, as emitted gamma can undergo “photoelectric effect” type interaction