Radioactivity Part 2Nuclear Chemistry

Three types

Alpha Radiation• Polonium-210 is an alpha emitter. During radioactive decay, it

loses two protons, and becomes a lead-206 atom, which is stable (i.e., nonradioactive).

Uses• Radium-226 to treat cancer• Polonium-210 eliminates static in paper mills by alpha

particles attracting loose electrons• Americium-241 in smoke detectors to help create electrical

current (smoke will interrupt the current and set off the alarm)

Found in Nature• Radium-226 & Uranium-238 are present in all rocks, soil,

water• Mining tends to increase exposure in humans & the

environment

Effects• Lack energy to penetrate skin (must be inhaled, ingested,

absorbed)• Greatest hazard to lung tissue (inhaled)• Inside us it’s the most dangerous (Causes cancer)

Human Exposure to Radioactivity

• Radon (Radioactive Gas) is part of the radioactive decay chain of naturally occurring uranium in soil. You can’t see, smell or taste radon.

• Health effect = lung cancer • Test every 2 years 

Above 4.0 pCi/L of radan in the air should be dealt with. 

• important for the management/disposal of radioactive materials• During decay – Radon-222 is commonly produced.

• It’s a gas and seeps up through the soil into the air. It can accumulate into high concentrations in basements.

• Gives off alpha particles • Its short half life means it emits alpha particles at a high rate.

Beta RadiationUses•Iodine-131 to treat cancer•Strontium-90 is a tracer in medical & agricultural fields•Tritium used for luminous exit signs, dials and watches•Carbon-14 for dating organic matter

Found in Nature•Carbon-14 & Potassium-40 found in our bodies

Effects•Lack energy to penetrate solid material•Direct exposure can redden or burn the skin•Kills cells

• Iodine-131 accumulates in the thyroid gland• Strontium-90 accumulates in bone and teeth

Gamma RadiationUses•Cesium-137 cancer treatment, measurements (soil density, packaging, oil wells)•Cobalt-60 sterilize medical equipment, treats cancer, pasteurizes foods and spices, measures thickness of metals•Technetium-99 used for medical imaging (xrays)•Can inspect welds and metal parts for leaks and defects

Found in Nature•Potassium-40 found in soil and water, meats and foods high in potassium like bananas

Effects•Can improve durability of wood and plastics•Radiation sickness

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Your annual Radiation Dose

Average annual radiation dose in US is 360 mrem.

The normal permissible limit is 5,000 mrem for those who work around radiation.

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Radiation DetectionApproximate amounts of radiation can be detected by the following devices:

•Film badge•Geiger-Muller counter•Scintillation counter

Half-life • Half-life – time required for half of the

original sample of radioactive nuclides to decay

• Half of the radioactive parent atoms decay after one half-life. Half of the remainder decay after another half-life and so on……..

Half lifeThe decay of radioisotopes can be used to measure the material’s age.

At start there are 16

radioisotopes

After 1 half life half have

decayed (that’s 8)

After 3 half lives another 2 have decayed

(14 altogether)

After 2 half lives another

half have decayed (12 altogether)

= radioisotope = new atom formed

Decay Curveshows the decay of radioactive atoms and the remaining radioactive sample.

A very important point here is that we cannot predict when aparticular entity will decay. We do know though, that if we had a large sample of a radioactive substance, some number will decay after a given amount of time. Some radioactive substances have a very high “rate of decay”,while others have a very low decay rate.

Application of Half Life

Radioactive dating a process used to determine the approximate age of an object.

Ex. Carbon -14, a radioactive isotope is in all living things. When organisms die Carbon-14 decreases and can estimate how long something has been dead.

Video http://www.youtube.com/watch?v=phZeE7Att_s

Application of Half Life• Iodine-131, a radioactive isotope, is injected into the

body to treat thyroid cancer.

• It’s half life is 8 days – this tells us the rest will disappear in 80 days

• Good because it will be active long enough for a cancer treatment, but should be short enough not to do more damage to healthy cells and organs.

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Videos

• http://www.youtube.com/watch?v=27qSAqafQ6o

• Alpha, Beta, Gamma http://youtu.be/5oUagoF_viQ

• Alpha http://www.youtube.com/watch?v=j5TJRtJxVfs

• Beta http://www.youtube.com/watch?v=rW0A5FZTxt0

• ½ life - http://youtu.be/tzM6aK5QbSU

• http://www.youtube.com/watch?v=xhOtKurHayo

• Carbon dating