Help I'm radioactive! How chain reactions power the world - CBS talk 2019

Public summary: 

CBS! 2019 talk about radioactivity. Find out how chain reactions power the world with flaming demos of chain reactions, a real Geiger counter and balloons!

Useful information
Kit List: 

Nuclear fission balloon demo:
- Lots of modelling balloons (will need 1 per audience member + spares)
- Safety scissors (ideally 1 pair per audience member. More likely to have 2 pairs per row for example)
Chain reaction demo with matches:
- Two boards, each containing an array of matches
- Lighter or box of matches to start the fire
- Large heat mat (or multiple heat mats)
Geiger counter and radiation suit:
- Geiger counter
- Radiation suit

Packing Away: 

Collect in scissors (assistant to stand at door and collect).
Clear away balloon pieces before the start of the next talk.
Wait for anything which was previously on fire from the match demo to cool to room temperature. Dispose of anything which has been spent.
Pack away radiation suit/Geiger counter.


A series of demos to illustrate different principles of nuclear physics.

Nuclear fission balloon demo:
Nuclear fission is when a single large atom decays into 2 smaller atoms, and both move apart with a non-zero kinetic energy.
This can be demonstrated using modelling balloons.
1. Ask everyone to blow up their balloon.
2. Everyone should twist their balloon at the centre.
3. Get a partner to cut the balloon along the central twist.
4. The two balloon fragments will fly off in opposite directions.
This demonstrates the conservation of momentum in nuclear fission reactions.

Uncontrolled chain reactions match demo:
This should be performed on a heat mat, and any flammable objects (e.g. paper) must be cleared from the vicinity of the demonstration. No audience members should approach the demonstration.
There are two boards containing arrays of matches. The matches should be fixed horizontally so that the flame extends in the vertical direction, ideally upwards. When separate, the matches on one of the boards are too far apart for the flame to spread across from one match to the next. However, bringing the second array in proximity of the first allows an uncontrolled chain reaction to occur, as the spacing between nearest-neighbour match heads is now smaller (the two arrays should be designed such that the matches are interdigitated once brought together).
1. With the arrays separate, light a single match at the bottom of one of the arrays and watch how it burns out without the fire spreading (hopefully. Would suck if this demonstration failed).
2. Bring the second array in close proximity with the first. Make sure the audience can see the whole setup side-on to get the full effect.
3. Light a single match at the bottom of one of the arrays, and watch as a chain reaction takes place and the the matches catch fire in sequence!

Geiger counter and radiation suit:
Presenter or (more likely) volunteer to wear the radiation suit to illustrate to children that radiation can be harmful. Ask why you might need to wear a suit like this and what they think it does.
Use the Geiger counter to test whether things are radioactive or not and to show that there's a background level of radiation that doesn't harm us - ask where it might be from and generally cement the concept of radiation in the audience's minds!

Risk Assessment
Date risk assesment last checked: 
Thu, 07/02/2019
Risk assesment checked by: 
Grace Exley
Date risk assesment double checked: 
Thu, 07/02/2019
Risk assesment double-checked by: 
Risk Assessment: 
Demo Hazard Risk Likelihood Severity Overall Mitigation Likelihood Severity Overall
Nuclear Fission of Balloons Demo Scissors People may cut themselves accidentally. Possible that children may run/play with scissors and injure themselves or others. 3 4 12 Use safety scissors (ideally plastic). Only give out scissors to adults. Instruct everyone to let the adults do the cutting. Make sure all scissors have been collected before people leave the lecture theatre. Will require an assistant to do this. 2 3 3
Balloons Balloons fly off with high velocity and there may be some elastic recoil. Could hit another member of the audience. 4 2 8 Ask people to be careful when they release fission products. Try to encourage them to do this above the level of children’s faces/out of the way of other spectators. Possibly stagger the cutting of balloons. 2 2 4
Balloons (ingested) Balloons pose a choking hazard if ingested. 2 4 8 Only had out balloons to adults, potentially pre-inflated to reduce the ease of ingestion. Instruct adults to keep balloons away from small children. In case of ingestion, call a first aider. 1 3 3
Uncontrolled Chain Reactions Match Demo Pre-set boards of matches It is possible (though very unlikely) that the demo could ignite before the talk with the right conditions – i.e. exposure to a flame. 2 3 6 Try to keep covered using a non-flammable sheet before the demonstration begins. This prevents temptation of setting it on fire, and also prevents the entire thing going up in flames. This talk is also the first of the day, so the time left out is minimised. No potential sources of ignition to be permitted in lecture theatre. 1 3 3
Lit demonstration Flames from the demonstration may spread. 2 5 10 Ensure no flammable material is in the vicinity of the demonstration. There will be at least one assistant on standby with a fire extinguisher or fire blanket who will act at the first sign of fire spreading from the demo; presenter to step back immediately if this occurs. Perform the demo on a heat-proof mat and protect floor appropriately. In case of fire, audience to evacuate via the fire exits for the lecture theatre. Do not place the demonstration close to the fire exit. 1 4 4
Lighting the demonstration There is the possibility of a larger-than-expected flame from the demonstration, which may result in burns for the presenter and possible shock (but no serious injury to) audience members. 3 4 12 Trial the exact demonstration setup in advance of the demo. Ensure there is sufficient clearance between the demo and ceiling of the lecture theatre so nothing can catch fire. Position screen between the presenter/audience and the setup and the audience. Ensure the demo is not very close to the front row of the lecture theatre. Use a long lighter/splint to ignite the first match. Ensure easy access to a fire blanket and fire extinguisher, and ensure presenter/assistant is trained and confident to use in case of emergency. 1 3 3
Geiger Counter and Radiation Suit Geiger counter Possible sharp edges/finger trap risks if not carefully handled. May also be dropped on feet etc. 2 2 4 Only presenter to handle counter. If particularly enthusiastic children want to see the counter after the talk, encourage very careful handling and the presenter/parent should hold the counter to avoid dropping it. In case of accident, call a first aider. 1 2 2
Suit appearance The suit is quite scary looking for small children – they may panic/be distressed when they see it worn. 3 1 3 Warn parents that they will see somebody dressed in a radiation suit and allow them to take their children out of the theatre if they are upset. 2 1 2