Radioactivity

Question 1

what does the term radioactive mean

Answer 1

a nuclide whose nucleus is unstable. In these nuclei the forces disrupting the nucleus are stronger than the forces which hold it together.

Question 2

the nucleus therefore seeks to become stable by ejecting energy in the form of

Answer 2

• a particle with kinetic energy
  OR
  a photon of energy

Question 3

each time the nucleus ejects this energy it is called

Answer 3

a nuclear disintegration and it is used as the basis for quantifying how much radioactivity is present

Question 4

the activity (radioactivity) of a radionuclide is defined as

Answer 4

the number of nuclear disintegration’s per second

Question 5

what is the SI unit of activity

Answer 5

the becquerel (Bq) where 1 Bq= 1 disintegration per second

Question 6

the nucleus undergoing the radioactive decay is

Answer 6

the parent

Question 7

the new nucleus after the decay is

Answer 7

the daughter

Question 8

the decay of a radionuclide is an

Answer 8

exponential process

Question 9

the Activity (At) at any elapsed time is given by

Answer 9

At = Ao e^-nt
n- the decay constant of the radionuclide
t-elapsed time

Question 10

what is the decay constant (n)

Answer 10

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

Question 11

if n is large

Answer 11

theradionuclide ecays more rapidly than if n is small

Question 12

what is half-life

Answer 12

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

Question 13

5 types of radioactive decay

Answer 13

• alpha
• Beta (B-)
• Positron (B+)
• electron capture
• Gamma (y)

Question 14

in what types of radioactive decay is the mass number of the daughter the same as the parent

Answer 14

• alpha
• beta (B-)
• Positron (B+)
• electron capture

Question 15

in what type of radioactive decay does the atomic number and mass number remain the same

Answer 15

-gamma (y)

Question 16

for the spontaneous emission of an alpha particle from a nucleus

Answer 16

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

Question 17

what is anm alpha particle

Answer 17

4- atomic mass number
a
2- atomic number

Question 18

B- particles are emitted from the nuclei which

Answer 18

have too many neutrons for nuclear stability

Question 19

a neutron transforms into

Answer 19

a proton and an electron

n–> p + e-

Question 20

what happens to the proton and the electron

Answer 20

the proton stats within the nucleus and the negative electron is ejected with kinetic energy. The electron is now termed a beta minus particle

Question 21

B+ particles are emitted from nuclei which

Answer 21

have insufficient number of neutrons for nuclear stability

Question 22

a proton transforms into a

Answer 22

neutron and a positive electron

P+ –> n + B+

Question 23

what happens to the neutron and the positive electron

Answer 23

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

Question 24

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

Answer 24

electron capture (usually from the K or L shells)

Question 25

During electron capture a proton is converted

Answer 25

to a neutron and a neutrino v, which is emitted by the nucleus:
p+ + e- –> n + v

Question 26

during electron capture, as the electron vacancy is filled

Answer 26

characteristic radiation is emitted

Question 27

what is isomeric transition (gamma decay)

Answer 27

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

Question 28

a metastable nucleus is

Answer 28

when the daughter nucleus is in an excited state for a measurable length of time

Question 29

in radioactive decay, X and y energies range from

Answer 29

approximately 0.01 to 3.0 MeV

Question 30

low energy X an gamma rays are attenuated by

Answer 30

a few mm of lead

Question 31

higher energy gamme rays may require

Answer 31

lead in excess of 0.5cm

Question 32

how do you calculate a radioisotopes activity after n half lives

Answer 32

new activity = (original activity) / 2^n