Radioactivity Flashcards
what does the term radioactive mean
a nuclide whose nucleus is unstable. In these nuclei the forces disrupting the nucleus are stronger than the forces which hold it together.
the nucleus therefore seeks to become stable by ejecting energy in the form of
- a particle with kinetic energy
OR
a photon of energy
each time the nucleus ejects this energy it is called
a nuclear disintegration and it is used as the basis for quantifying how much radioactivity is present
the activity (radioactivity) of a radionuclide is defined as
the number of nuclear disintegration’s per second
what is the SI unit of activity
the becquerel (Bq) where 1 Bq= 1 disintegration per second
the nucleus undergoing the radioactive decay is
the parent
the new nucleus after the decay is
the daughter
the decay of a radionuclide is an
exponential process
the Activity (At) at any elapsed time is given by
At = Ao e^-nt
n- the decay constant of the radionuclide
t-elapsed time
what is the decay constant (n)
the fractional reduction in the activity of a radionuclide per unit time.
An indicator of the probability of each atom of the radionuclide disintegrating per unit time
if n is large
theradionuclide ecays more rapidly than if n is small
what is half-life
the activity of a sample of radioactive material decreases with time. each radionuclide has a unique physical half-life (T1/2) which is a measure of the time taken for the activity of a given sample to fall to half its initial value
5 types of radioactive decay
- alpha
- Beta (B-)
- Positron (B+)
- electron capture
- Gamma (y)
in what types of radioactive decay is the mass number of the daughter the same as the parent
- alpha
- beta (B-)
- Positron (B+)
- electron capture
in what type of radioactive decay does the atomic number and mass number remain the same
-gamma (y)
for the spontaneous emission of an alpha particle from a nucleus
the nucleotide must have an atomic mass number greater than 150. The nucleus must also have insufficient neutrons for the number of protons present. A proportion of the excess energy in the nucleus is given to the alpha particle in the form of kinetic energy
what is anm alpha particle
4- atomic mass number
a
2- atomic number
B- particles are emitted from the nuclei which
have too many neutrons for nuclear stability
a neutron transforms into
a proton and an electron
n–> p + e-
what happens to the proton and the electron
the proton stats within the nucleus and the negative electron is ejected with kinetic energy. The electron is now termed a beta minus particle
B+ particles are emitted from nuclei which
have insufficient number of neutrons for nuclear stability
a proton transforms into a
neutron and a positive electron
P+ –> n + B+
what happens to the neutron and the positive electron
the neutron stays within the nucleus an the positive electron (positron) is ejected with kinetic energy. the positron is now termed a beta plus particle
if a nucleus of low mass number has too few neutrons for stability but has insufficient excess energy to eject a positron it can lose enrgy by
electron capture (usually from the K or L shells)
During electron capture a proton is converted
to a neutron and a neutrino v, which is emitted by the nucleus:
p+ + e- –> n + v
during electron capture, as the electron vacancy is filled
characteristic radiation is emitted
what is isomeric transition (gamma decay)
when both alpha and beta decay can leave the daughter nucleus in an excited state. in order to achieve stability energy can be emitted as gamma rays
a metastable nucleus is
when the daughter nucleus is in an excited state for a measurable length of time
in radioactive decay, X and y energies range from
approximately 0.01 to 3.0 MeV
low energy X an gamma rays are attenuated by
a few mm of lead
higher energy gamme rays may require
lead in excess of 0.5cm
how do you calculate a radioisotopes activity after n half lives
new activity = (original activity) / 2^n
