radioactivity + radioisotopes

nuclear stability

• stability of the nucleus depends on both N and Z

• Z < 20 N=Z N/Z=1

• 20 < Z < 92 N > Z N/Z = 1-1.6

• Z > 92 spontaneous fission

• if N/Z <or> stable ratio, nucleus is radioactive

beta - decay (negatron emission)

its easier to convert a neutron to a proton then expel a neutron from the nucleus

Y decay

• B decay always results in a daughter in an excited state - if this state is long live its called a meta-stable state

• XS energy is lost by expelling a y-ray

B + - decay (positron emission)

easier to convert a proton to neutron than expel a proton from the nucleus

alpha decay

nuclei that are simply too big need to lose both n and p as quickly as possible

a = helium nucleus ^4 2He

2 protons + 2 neutrons

half life

time taken for activity of a radioisotope to each half its value

radioactive - decay equation

At = Are ^-ht

• At - activity at time t

• Ao - activity at time 0 (initial activity)

• h - decay constant (rate constant) and h= 1n2/t1/2

• t - time

• Ln (At) = Ln(A0) - ht straight line graph intercept gradient

biological effects of radiation

• radiation passing through cells of living tissue —> ions and free radicals

• react with compounds in the cell, distributing or altering normal metabolic process

• changes can result in death, cell ability to divide or abnormal cell division, changes in genetic material, increases in rate of ageing

penetrating power of radiation

• different types of radiation have different abilities to penetrate matter

• penetration affects how radiation interacts with tissues and materials

absorbed dose

• measures the amount of energy absorbed by tissue

• unit - grey (Gy)

• 1 Gy = 1Jkg-1

• an absorbed energies can severely disrupt biological processes

dose equivalent

• different radiation types cause different levels of biological damage

• doe equivalent accounts for biological effect not just energy absorbed

• represents damage done to humans

• unit: sievert (sv)