Radioactivity Flashcards
What is radioactive decay?
The breakdown of the nucleus of an atom.
What is natural radioactivity?
The decay of nuclei in atoms, releasing particles and energy.
What is an isotope?
Atoms of an element that have the same number of protons but not electrons.
Give a reason why an atom might be radioactive.
Unstable Nuclei:
- Maybe the nucleus is too big or there are too many neutrons.
What is radiation measure with?
A Geiger Counter.
What is Background Radiation.
Radiation that is random and natural and occurs all around us.
Name the 3 types of radiation:
Alpha(α)
Beta(β)
Gamma(γ)
Identify the structure of Alpha Radiation:
- Equivalent to a helium nucleus
- Is a particle
- 2 protons 2 neutrons
- Positively charged
- Mass of 4au
- Relatively slow
- Occurs if a nucleus is too big
Identify the structure of Beta Radiation:
- High Speed
- Negatively Charged
- Negligible mass.
Occurs if an atom has too neutrons! - One neutron transforms into a proton and an electron, then the electron is emitted from nucleus as Beta decay.
Identify the structure of Gamma Radiation:
- NOT a particle
- Electro-magnetic wave
- Travels at the speed of light
- Has no mass and no charge
- NO CHANGE OCCURS WHEN RELEASED FROM NUCLEUS!
- emitted after beta and gamma.
What is the chemical representation of alpha decay:
-4 off atomic mass and -2 off atomic number to get product of an element after alpha decay. (2 protons, 2 neutrons)
What is the chemical representation of beta decay:
Take nothing off atomic mass and add one to the atomic number. Beta decay is represented as B with a 0 at the top and a -1 at the bottom.
What is the chemical representation of Gamma decay:
Just the symbol don’t change the numbers at all.
+ (γ)
Order Beta, Alpha and Gamma in there ability to penetrate. Then say Why:
- Gamma (Best and Penetrating)
- Worst at ionising (longest time to lose energy)
- Stopped by lead or concrete. - Beta (Mid Penetrating power)
- Medium ionising power (Loses energy fairly quickly)
- Stopped by aluminium - Alpha (Worst Penetrating Power)
- Good at ionising (Loses energy very fast)
- Stopped by a piece of paper or even air
Between 2 plates charged positively and the other negatively where would the particle/radiations go?
The Beta (overall - charge) would go to the positively charged plate quickly.
The Gamma (neutral charge) would go straight through not leaning towards either plate
The Alpha (overall + charge) would lean towards the negatively charge plate but take longer to get there than Beta.
What is ionising Radiation?
Particles or waves that cause atoms to lose or gain electrons and become charged.
What is the half-life?
Average time taken for half a sample of radioactive substance to decay (or for the activity to halve)
What does “the activity” mean?
The number of decays per second.
{Carbon dating is a process used to determine the age of dead organic materials.} -C14 has a half life of 6000 years.
Scientists are studying a mammoth found frozen in ice. They find a sample of carbon from the remains that has a count rate of 200Bq. The scientists work out that when the mammoth died the count rate was 800Bq. Use this information to calculate how long ago the mammoth died.
800Bq 🡢 400Bg 🡢 200Bq
- 2 half lives
2 × 6000 = 12000 years ago.
What happens to a radioactive source the older it gets?
The activity decreases = less radiation emits.
(how quickly the activity decreases is DIFFERENT for each isotope)
Describe the Ionising power of Alpha:
- Turning a neutral atom into a charged ion
- Alpha ionises the easiest (It has the biggest charge) 2+
- Alpha can attract nearby electrons from further away.
Describe the Ionising power of Gamma
- Worst at ionising
- No charge
- Needs to come in direct contact with an electron to cause ionisation (very rare).
Describe the Ionising power of Beta:
- Less easily than alpha (more easily than gamma as it has charge) (smaller charge) 1-
- Beta will repel an electron from a nearby atom to ionise it.
What is countrate?
The number of ionizing events detected by a radiation detector per unit of time.
What does Bq Stand for? What are they?
Becquerels
- A unit that measures radioactivity.
Name the Eight uses of Radioactivity:
1) Automatic Thickness Monitoring
2) Medical tracers
3) Uranium Dating
4) Carbon Dating
5) Killing cells
6) Smoke Detectors
7) Fault Tracers
Explain Automatic Thickness Monitoring:
- Used in factories to control the thickness of materials
- If materials too thick = more radiation absorbed = less reaches detector
- If material is too thin = less radiation absorbed= more reaches detector.
- Detector sends signal to adjust rollers accordingly.
Explain Medical Tracers:
- Trace a flow of substance through a system.
-e.g. see if patients kidneys are blocked. - Patient drinks radioactive substance.
- Detector is placed on the outside of the patients body to monitor flow.
- Radioactive substance must be emitters of Beta or Gamma because:
- Short half life wont stay in body too long and cause harm.
- Alpha particles cannot penetrate skin.
Explain Uranium Dating:
- Finds age of rocks
- Uranium decays into lead
- Half life of Uranium = 4.5 billion years.
-Ratio of uranium to lead helps to estimate age.
Explain Carbon Dating:
- Carbon 14 is an isotope that decays into Carbon 12 (stable)
-When an organism dies it stops taking in Carbon 14 so it begins to decay into Carbon 12 - Time since organism died can be worked out by measuring the amount of C14 left vs Starting amount.
Explain Killing Cells:
- Gamma radiation used
. High energy + High frequency causes cells to die - kills cancer cells, sterilise medical equipment, kill food bacteria.
- When radiation enters a living cell 2 things can happen:
-high does =kill cell
-low doses =cause cancer
Explain Smoke Detectors:
- Within smoke detectors there is = Americium (Alpha radiation source)
- Since Alpha particles are charged it ionises the air causing a current to flow between 2 charged plates.
- Smoke particles absorb alpha particles and neutralize the ions decreasing the current
- This decrease causes alarm to sound.
ALPHA used because will not escape and harm people.
Explain Fault Tracers
- Radioisotopes used for tracking substances
- Finds leaks or blockages underground in pipes
- Gamma often used because it can pass through many substances.
To find the blockage/leak: - Radioactive material put into one end of the pipe
- Radiation detector above ground tracks its process.
- Leak/Blockage detected where radiation changes.
Places there’s a leak = Higher count Rate.
Outline Ernst Rutherford’s Gold foil experiment:
-Alpha particles shot at gold foil in experiment from a radioactive source
-There was a detector surrounding an experiment that detected that some alpha particles went straight through whilst some bounced back and some deflected slightly.
Ernst Rutherford observed that some alpha particles travelled through undeflected. What did he infer from this?
- The atom is mainly empty space.
Ernst Rutherford observed that some alpha particles were deflected by small angles. What did he infer from this?
- The nucleus is positively charged and as is the alpha particle.
Ernst Rutherford observed that some alpha particles travelled straight back from foil. What did he infer from this?
- The nucleus carries most of the atom’s mass. (The nucleus has mass)
