P7-Radioactivity Flashcards
Atoms are very small , what is the radius of an atoms .
1*10to the power of negative 10
What is the radius of a nucleus ?
-Less than 1/10,000 of the atom .
Where is most of the mass of an atom
-concentrated in the nucleus .
What does the nucleus contain , so what is its charge ?
Protons postive charge , ad neutrons no charge so overall charge of nucles is positive .
Electrons
negatievly charged found at fixed energy levels form the nucleus .
Energy levels that are further form the nucleus …
are at a higher energy than those which are close to the nucleus .
If an atom absorbs electromagnetic radiation-light-…
an electron can move from a lower energy level to a higher energy level .
-An atom can now emit electromagnetic radiation , returns to the lower energy level .
What is the mass number?
number of protons and neutrons
What is the atomic number ?
protons - all atoms of an elemnt have same protons or it isn’t that elemnt .
What is the charge of an atom ?
No charge
-As the numbero f electons are = to the nuumber of protons .
(The negative charges on the electrons cancel out positive charged on the protons )
How do you work out the number of neutrons ?
Mass Number - Atomic Number .
What are Isotopes ?
-Atoms of the same elemnt thata have different number of neutrons .
What are ions
electrically charged particles formed when atoms gain or loose elctrons .
-Atoms can loose electrons from their out energy elvels .
Atoms loose an electron…
Atoms gains an electron
1+charge
1- charge
What did the ancient Greeks believe everything was made of ?
- Evertyhing is made of atoms .
- Thought atoms were tiny spheres which cannot be divided .
What did scientists discover in 1897 ?
- Atoms contain tiny negative particles . They are called electrons .
- This showed atoms are not spherres that cannot be divided , atoms have an internal structure .
Plum pudding model :
draw ad explain .
-An atom is as a ball of positive charge with negative elctrons embedded in it . Check sheet .
Why was the Alpha Scattering experiment done ?
To see if the plum pudding model was correct .
What is the first step of the alpha scattering experiment .
Take a place of gold foil.
Why was gold foil used ?
-Gold foil was used s it can be hammered down into very thin foil , just a few atoms thick .
What is the second step of the alpha scattering experiment ?
Then they fired tiny alpha particles at the gold foil .
What was the first observation of the alpha particle experiment ?
-Most of the alpha particles passed straight through the foil without changing direction .
What was the second observation of the alpha particle experiment ?
-Sometimes an alpha particle was deflected .
What was the third observation of the alpha particle experiment ?
-Sometimes an alpha particles bounced straight back off the goild foil .
What does the first observation suggest ?
-Atoms are mainly empty spacce .
What does the second observation suggest ?
-The center of the atoms must hve had a posiitve charge that repelled the alpha particles .
What does the third observation suggest ?
-The mass of the atom must be the concentrated center , we now call this paert of an atom the nucleus .
what was the final conclusion to the plum pudding model ?
-replaced with the nuclear model .
Tiny positive nucleus
Mostly empty space
negative lectron around the edge .
What did Niels Bohr do ?
- Electrons orbit the nucleus at speicifc disances , his work agreed with other sicenitsts
- We now call the “Orbits” energy levels or shells .
Wha did James Chadwick do ?
- several years later , positive chargge in nuncleus so called protons .
- years after nuclar model , James Chadwick discovered neutrons , said they have no charge , are neutral .
Some isotopes have an unstbale nucleus , what do they do to become stable , and what is this called ?
- To become stable , the nucleus gives out radiation , this is known as radiactive decay .
- Radioactive decay is a random process .
What is the activity ?
The activity is the rate at which a source of unstable nuclei decay .
What is activity measrued in ?
In Becquerel (Bq) 1Bq is = s decay per second .
What is the countrate ?
Is the number of deays recorded each second by a detector .
What are alpha particles ?
-Consist of two protons and two neutrons same as a helium nucleus .
What are Beta particles ?
-A beta particle is an electorn ejected from the nucleus at a very high speed.
How is an electrons ejected form the cenetr whne htere is no electrons in the center ?
- Beta particle formed inside the nucleus when a neutron changes into a proton and an electron . This is now ejected rom thhe nueclues and is called a beta particle .
What is Gamma radiation ?
-Gamma rays are a type of electromagentic radiaition from the nucleus .
What is the last time of radiaition sometimes given out by the nucleus ?
A neutron
What is the range of alpha particles ?
-Alpha particles are large , They can travel around 5 cm in air before they collide with air particles and sotp .
What is the range of Beta particles ?
-Can travel further than alpha particles as they smaller than em too . Can reach 15cm before stopping .
What is the range of Gamma radiation ?
-Travels severeal metres in air before stopping , longest range .
Penetrating power of alpha .
-stopped by a single sheet of paper .
Penetrating power of Beta .
-stopped by a few milimetries of aluminium .
Penetraitng power of Gamma radiation ?
-Even harde rto stop , stopped bys everal cm lead or concrete .
WHat is ionsiing power of radiation ?
-When radiaition collides with atoms , causes atoms to lose electrons to form ions .
Ionsising power of alpha
Very strongly ionsing
Ionsiing power of Beta
Quiet strongly ionsing
Ionising power of Gamma
Weakly ionising
What is half life ?
-half life of a radiactive isotope is the time it takes for the number of nuclei in the isotope of a sample to halve .
half life
short hlf lfie -fast decay to half
Lon half life - slow decay to half .
What is the second definiton of half life?
Half life is also the time it takes for the countrate (or activity) of a sample containing the isotope to half its inital level .
A radioactive isotope has a half life of 15 days and an initial countrate of 200 days per second . What is its countrate in 45 days , show full working out /
25 counts/s
Why is ionising radiation dangerous ?
-Ionsing radiaiton can increase hte irsk of cancer in humans .
What is irradiation ?
- Exposing an object to nuclear radiation (alpha , beta , gamma or neutrons ) e,g for sterilisation.
- Most sterilistion can be done by heating but for substances that can’t be heated use gamma radiation .
How do you sterilise a syringe ?
- Object neededing to be sterilised is placed in a plastic wrapper stopping bacteria from enetering .
2.Place object near radioactive isotope tgar emits gamma radiaitoin .
Lead shield protects workers .
4.Withdrawing the lead shield allows gamma radiation irradiate the object , the gamma radiaition kills any bacteria .
How does the obeject during sterilisation not become radioactive ?
As the object itself is not in contact with the radioactive isotope only the radiation emited from it .
What precautions do you have to take for each radioactvite sustances ?
*-Alpha , not very penetrating , so gloves .
Beta and Gamma - more penetrative , lead apron can stop .
High levels of radiation - lead walls , lead glass windows .
What is another way to reudce exposure to radiation ?
By monitoring radiation with a raidiation monitor , we can measure how much radiation has been recieved , cannot sotp though .
What is radioacitve contamination ?
- When unwated radiactive isotopes end up on other materials .
- This is hazardous as radioactive toms decay and emit ionisng rdiation .
How hazardous is alpha radiation ?
-Alpha is strongly ionsing , easily stopped by skin as it is not very penetrative , HOwever can be dangerous if inhaled or swallowed .
How hazardous is Beta radiation ?
-Quet ionisng , easily penetrate skin and inot the body damage the cell and DNA .
How hazardous is Gamma radiation ?
Least damaging as it is weakly ionsing , can penetate the body , but is likely to pass straight thorgh you .
Peer review on the effects of radiation ?
- Scientists have explored the effects of radiation on human .
- Studies have to be published and shared with other scientists allowing findings to be checked.
What is Background radiation ?
Radiaion all around us all the time .
Give one natural source of background radiation ?
-Rradioactive rockk - certain rocks are radiactive granite .
Give another natural source of background radiation ?
Cosmic rays from space - Cosmic rays are very high energy particles which travel through space and crsh into the Earth’s atmospehre .
Give one source of manmade background radiation ?
Nuclear weapon testing - has released radiactive isotopes into the environment for decades.
Give another source of manmade background radiation ?
Nuclear accidents - Radioactive isotopes are released by accdients at nuclear power stations .
What is your exposure to background radiation influenced by ?
-Your locatin (Cornwall -rocks) and Occupation (Cabin crew , cosmic trays )
What is radiation dose measured in
Sievert (Sv)
-One millisievert (mSv) is 1/1000 of a Sievert .
What is the first use of nuclear radiation in medicine ?
-Exploring internal organs using a radioactive source to check whether an organ is funcitioning normally or if a cancer has developed .
What does radioacitve iodine do ?
- Radioactive iodine is a type of gamma radiatio , passes out the body , can be detected .
- If the scan shows the thyroid has absorbed tooo much or too little iodine , doctors can use this to dianose pateints condtiions .
What is the first requirement of a radioactive tracer ?
1.The tracer must emit radiaition that can pass out the body and be detected (gamma or beta radiation ).
What is the second requirement of a radioactive tracer ?
2.The tracer must not be strongly ionisng , to minimise damage ot body tissues .
What is the third requirement of a radioactive tracer ?
-The tracer must not decay into another radioctive isotope .
What is the fourth requirement of a radioactive tracer ?
-The tracer must have a short-half lfie , so it is not present in the body for a long period .
Cancer cells ?
-Certain cancer cells can be destroyed using ionisng radiation - radiotherapy .
How does radiotherapy work ?
Rays pass into the body and destroy the tumour
Probelm with radiation on the outside ?
Healthy tissue may also be damaged as radiaition passes throguh the body .
Advanatge of radiation in the inside ?
Radiation is targeted very precisiely to the tumour , less damage to healthy tissue .
What is nuclear fission ?
- Some elements have large and unstable nucelueses .
- In nuclear fission , the nuceus of these element split , due to absorbtion of NEUTRON .
- Stage of nuclear fission ?
-When uranium absorbs a neutron , this triggers the nucleus to undergo fission (split).
- Stage of nuclear fission ?
- When the nucleus splits , it forms two smaler nuclei roughly euqal in size (daughter nuclei ).
- Also emit two or three neutrons and gamma radiaition .
3.What is also released from nuclear fission .
- Energy is also released during fission , fission products have kinetic energy .
- These neutrons can be absorbed by more uranium nuclei and trigger ufsion again known as a CHAIN REACTION .
Example of a controlled chain reaction .
-Used to release energy in a nuclear reactor .
Example of an uncontrolled chain reaction ?
The explosion of a nuclear weapon .
What is nuclear fusion ?
- Two light nuclei are joined to form a hevaier nucleus .
- Some of the mass of the nuclei can be converted into energy which is released as radiation . Not A CHAIN REACTION .
What is a nuclear reactor label parts of it
-where controlled fissionr eactions occur .
-Control rods - control the number of neeutrons gthat start new fisisn reactions .
-Fuel rolds ontin thematerial that relese energy during fisison .
-eacotr is where fission occurs , releses energy to het up th emoderator for electriciy generation .
-Moderator - slowd down the netrons for new fision rwactions .
