P4 - Radiation For Life Flashcards

Question 1

Q

P4 - Radiation For Life

Which direction do electrons move when a polythene rod is rubbed with a duster?

Answer

A

From duster to rod

Question 2

Q

P4 - Radiation For Life

Which direction do electrons move when an acetate rod is rubbed with a duster?

Answer

A

From rod to duster

Question 3

Q

P4 - Radiation For Life

What is a static charge caused by?

Answer

A

Electrons moving

Question 4

Q

P4 - Radiation For Life

What happens if enough static charge builds up?

Answer

A

It can suddenly move which can cause sparks or shocks that may be dangerous.

Question 5

Q

P4 - Radiation For Life

How can a charged conductor be discharged safely?

Answer

A

By connecting it to earth with a metal strap (earthing).

Question 6

Q

P4 - Radiation For Life

How does earthing work?

Answer

A

Electrons flow down strap to ground if charge is negative and flow up strap from ground if positive.

Question 7

Q

P4 - Radiation For Life

What are ions?

Answer

A

Atoms or molecules with a charge

Question 8

Q

P4 - Radiation For Life

How does static attract dust?

Answer

A

Dust particles are charged and attract opposite charge. Objects in home are insulators (get easily charged) and attract dust.

Question 9

Q

P4 - Radiation For Life

How does static affect clothing?

Answer

A

When synthetic clothes dragged (head or other clothes) electrons scrape off, leaving static charge - two attract. Little sparks/shocks as charges rearrange themselves.

Question 10

Q

P4 - Radiation For Life

What causes shocks from door handles?

Answer

A

Walking on nylon carpet with insulating soles builds up charge. Touching metal door handle/water pipe allows charge to flow via conductor - little shock.

Question 11

Q

P4 - Radiation For Life

How can static on clothing become dangerous?

Answer

A

Charge may become large enough to make a spark - dangerous near inflammable gases or fuel fumes.

Question 12

Q

P4 - Radiation For Life

When can static become dangerous (other than on clothes)?

Answer

A

Fuel flowing out of pipe, paper drags on rollers or grain shoots out of pipe, static builds up. If too big, might spark - explosion in dusty/fumey places (petrol station).

Question 13

Q

P4 - Radiation For Life

What kind of places is static dangerous in?

Answer

A

Areas with inflammable liquids or a high concentration of oxygen (hospital operating theatre)

Question 14

Q

P4 - Radiation For Life

How do anti-static sprays work?

Answer

A

Make surface of a charged object conductive - provides an easy path for charges to move away.

Question 15

Q

P4 - Radiation For Life

How do insulating mats and shoes work?

Answer

A

Prevent static electricity moving through them - stops human getting shocked.

Question 16

Q

P4 - Radiation For Life

How do paint sprayers work?

Answer

A

Spray gun charged and object given opposite to attract. Paint drops repel each other (fine spray).

Question 17

Q

P4 - Radiation For Life

What is the good thing about electrostatic paint sprayers?

Answer

A

Method gives even coat and hardly any paint wasted. No shadows - everywhere covered.

Question 18

Q

P4 - Radiation For Life

How do dust precipitators work?

Answer

A

Smoke particles reach chimney bottom, meet wire grid/rods with high voltage and (-) charge. Dust particles gain electrons (become (-)) Dust particles induce charge on earthed metal plates Dust attracted to metal plates - stick forming larger particles When heavy enough, particles fall off/knocked off with hammer Falls and is removed

Question 19

Q

P4 - Radiation For Life

How does a defibrillator work?

Answer

A

2 paddles to power supply: Paddles firmly on chest (good electrical contact) and charged up Everyone moves away - operator holds insulated handles Charge passes through paddles to patient - heart contracts.

Question 20

Q

P4 - Radiation For Life

If you increase the voltage….

Answer

A

more current will flow

Question 21

Q

P4 - Radiation For Life

If you increase the resistance…

Answer

A

less current will flow (or more voltage is needed to keep same current flowing)

Question 22

Q

P4 - Radiation For Life

Current only flows when?

Answer

A

As long as there is a complete loop - broke circuit means no current.

Question 23

Q

P4 - Radiation For Life

What does the live wire do?

Answer

A

Carries voltage. Alternates between a high + and - voltage of about 230V

Question 24

Q

P4 - Radiation For Life

What colour is the live wire?

Question 25

Q

P4 - Radiation For Life

What does the earth wire do?

Answer

A

Works together with fuse for safety

Question 26

Q

P4 - Radiation For Life

What does the neutral wire do?

Answer

A

Completes tcircuit - electricity flows out through neutral - always at 0V.

Question 27

Q

P4 - Radiation For Life

What colour is the neutral wire?

Question 28

Q

P4 - Radiation For Life

What colour is the earth wire?

Answer

A

Green and yellow

Question 29

Q

P4 - Radiation For Life

What must all appliances with metal cases be?

Question 30

Q

P4 - Radiation For Life

What does double insulated mean?

Answer

A

If appliance has casing that is non-conductive (e.g. plastic) - doesn’t need earthing (never live)

Question 31

Q

P4 - Radiation For Life

What happens is a fault develops where the live wire touches the metal case?

Answer

A

A big current flows through live wire. Surge blows fuse and causes wire inside to melt. Cuts off live supply by breaking circuit.

Question 32

Q

P4 - Radiation For Life

When the fuse blows, what does this prevent?

Answer

A

Electric shocks by isolating appliance. Stops flex overheating which may cause fire. Prevent further damage to appliance.

Question 33

Q

P4 - Radiation For Life

What is a circuit breaker?

Answer

A

Works like a fuse but can be reset and used again.

Question 34

Q

P4 - Radiation For Life

How should fuses be rated?

Answer

A

As near as possible but just higher than normal operating current.

Question 35

Q

P4 - Radiation For Life

What are the fixed fuse ratings?

Answer

A

3A, 5A and 13A

Question 36

Q

P4 - Radiation For Life

What is a variable resistor?

Answer

A

Rheostat - resistor whose resistance can be changed by turning a knob.

Question 37

Q

P4 - Radiation For Life

What are variable resistors good for?

Answer

A

Alternating the current flowing through a circuit. Turn up resistance, current drops (vice versa).

Question 38

Q

P4 - Radiation For Life

Why do thinner wires increase resistance?

Answer

A

Electric charge has less space to move through.

Question 39

Q

P4 - Radiation For Life

What is the resistance of a fixed resistor like?

Answer

A

Steady - at a constant temperature

Question 40

Q

P4 - Radiation For Life

How is resistance calculated?

Answer

A

Voltage / current

Question 41

Q

P4 - Radiation For Life

How is the ammeter set up in a circuit to measure resistance?

Answer

A

In series with other components

Question 42

Q

P4 - Radiation For Life

How is the voltmeter placed in a circuit to measure resistance?

Answer

A

In parallel around component being tested.

Question 43

Q

P4 - Radiation For Life

What is the official name for voltage around a test circuit?

Answer

A

Potential difference

Question 44

Q

P4 - Radiation For Life

What are compressions?

Answer

A

Parts of a wave under high pressure (lots of particles)

Question 45

Q

P4 - Radiation For Life

What are rarefactions in a wave?

Answer

A

Parts under low pressure (fewer particles)

Question 46

Q

P4 - Radiation For Life

What is wavelength?

Answer

A

A full cycle of a wave from crest to crest/compression to compression

Question 47

Q

P4 - Radiation For Life

What is frequency?

Answer

A

How many complete waves there are per second passing a certain point. Measured in hertz. Sound - high frequency=high pitch

Question 48

Q

P4 - Radiation For Life

What is amplitude?

Answer

A

Measured from rest position to crest. Tells you how much energy wave is carrying, or how loud it is.

Question 49

Q

P4 - Radiation For Life

How does a longitudinal wave move?

Answer

A

Vibrations are along same direction as wave is travelling

Question 50

Q

P4 - Radiation For Life

How does a transverse wave move?

Answer

A

Vibrations are at 90 degrees to direction of travel of the wave

Question 51

Q

P4 - Radiation For Life

What is ultrasound?

Answer

A

Electric devices can be made which produce electrical oscillations of any frequency. Easily converted into mechanical vibrations to produce longitudinal waves beyond range of human hearing.

Question 52

Q

P4 - Radiation For Life

How does ultrasound work when breaking down accumulation in the body?

Answer

A

Removing kidney stones. High energy of ultrasound at stone turns it into sand like particles. Particles pass out of body in urine. Doesn’t need surgery and painless.

Question 53

Q

P4 - Radiation For Life

How does ultrasound work in body scanning?

Answer

A

Waves pass through body but are reflected back when they meet a boundary between two different media. Echoes are processed by computer to produce video image.

Question 54

Q

P4 - Radiation For Life

What advantages does ultrasound have?

Answer

A

Ultrasound is great for imaging soft tissue. Safer doesn’t damage cells.

Question 55

Q

P4 - Radiation For Life

What do X-rays do compared to ultrasound?

Answer

A

Better for viewing bone. Can damage living cells by being ionising radiation, causing cancer at high doses.

Question 56

Q

P4 - Radiation For Life

What are radioactive materials made up of?

Answer

A

Atoms with unstable nuclei that naturally decay at random

Question 57

Q

P4 - Radiation For Life

What happens as radioactive material decays?

Answer

A

Give out alpha, beta and gamma. Nucleus often changes into new element.

Question 58

Q

P4 - Radiation For Life

What is the relative atomic mass number?

Answer

A

Top number = number of protons and neutrons (AKA mass number)

Question 59

Q

P4 - Radiation For Life

What is the atomic number?

Answer

A

Number of protons

Question 60

Q

P4 - Radiation For Life

What is an isotope?

Answer

A

Atoms of same element with different mass numbers

Question 61

Q

P4 - Radiation For Life

When does gamma radiation happen in decay?

Answer

A

After alpha and beta, if nucleus has extra energy to get rid of. Emits gamma ray that has no mass or charge - atomic and mass number don’t change.

Question 62

Q

P4 - Radiation For Life

What is an alpha particle?

Answer

A

Helium nucleus of two protons and two neutrons

Question 63

Q

P4 - Radiation For Life

What charge does an alpha particle have?

Question 64

Q

P4 - Radiation For Life

What mass does an alpha particle have?

Answer 60

A

Decreases by 4 because it loses 2 protons and 2 neutrons

Answer 61

A

Decreases by 2 because it has 2 less protons

Answer 62

A

Fast moving electron

Answer 63

A

Doesn’t change - lost a neutron but gained a proton

Answer 64

A

Increases by 1 - has 1 more proton

Answer 65

A

Radioactivity of the source as whole decreases - older a resource, less radiation emitted.

Answer 66

A

Activity never reaches 0

Answer 67

A

Time taken for half of the radioactive nuclei now present to decay.

Answer 68

A

Activity falls quickly because lots of nuclei decay in a short time.

Answer 69

A

Activity falls slowly, because most of nuclei doesn’t decay for a long time.

Answer 70

A

When some materials absorb ionising radiation - can enter living cells and interact with molecules.

Answer 71

A

Charged particles called ions

Answer 72

A

Ionising radiation

Answer 73

A

Transfer energy to electrons. Electrons then have enough energy to escape from atom, ionising it and leaving it positively charged.

Answer 74

A

Remove electrons from atom/molecule leaving them positively charged.

Answer 75

A

Ionises it making it negatively charged.

Answer 76

A

Remove electrons, making atom positive.

Answer 77

A

Relatively large - easy to collide with atoms or molecules 2. Highly charged - easily remove electrons from atoms they pass or collide with.

Answer 78

A

Minor damage without killing cells. Can give rise to mutant cells which divide uncontrollably - cancer.

Answer 79

A

Kill cells completely, which causes radiation sickness if a lot of cells all get blasted at once.

Answer 80

A

Beta and gamma - can still get to delicate organs (pass through skin)

Answer 81

A

It can’t penetrate the skin

Answer 82

A

Alpha - do all their damage in a localised area, highly ionising.

Answer 83

A

Beta and gamma - less ionising, often pass straight out with very little damage

Answer 84

A

High frequency

Answer 85

A

Short wavelength electromagnetic waves

Answer 86

A

Released from some unstable atomic nuclei when they decay. No way to control when they are released.

Answer 87

A

By firing high speed electrons at a heavy metal like tungsten. Much easier to control production of than gamma.

Answer 88

A

Thicker and denser material like bone or metal.

Answer 89

A

Varying amount of radiation that’s absorbed (denser materials absorb more X-rays)

Answer 90

A

*Gamma focused on tumour using wide beam. *Beam rotated round patient - tumour at centre. *Minimises exposure of normal cells to radiation, reducing risk of damage to rest of body.

Answer 91

A

Radioactive isotopes that emit gamma (short half life - few hours)

Answer 92

A

Injected, drunk, eaten or ingested.

Answer 93

A

Progress followed by radiation detector outside body.

Answer 94

A

Iodine-123 absorbed by thyroid gland and shows if thyroid is taking all iodine it should.

Answer 95

A

Can penetrate tissue so are detectable outside. Can pass out easily.

Answer 96

A

Exposing them to high dose of gamma radiation.

Answer 97

A

It kills microbes

Answer 98

A

Doesn’t involve high temperatures. Plastic instruments can be sterilised without damaging them.

Answer 99

A

Tracks movement of waste material to find route underground of pipes or detect leaks/blockages

Answer 100

A

If detection of radioactivity stops/reduces must be a blockage/leak.

Answer 101

A

Gamma emitters so it can be detected through metal/pipe. Needs short half life.

Answer 102

A

So it doesn’t cause a hazard if it collects somewhere. Doesn’t pollute water.

Answer 103

A

A weak alpha source close to two electrodes.

Answer 104

A

In a fire, smoke particles are hit by alpha particles (less ionising of air) so current reduces, alarm sounds.

Answer 105

A

All around us. In air, food, building materials and rocks. Large proportion of background radiation comes from natural sources.

Answer 106

A

Known as cosmic rays. Come mostly from sun.

Answer 107

A

E.g. Fallout from nuclear explosions, waste from industry and hospitals. Represents a small proportion of total.

Answer 108

A

Depending on where you are or job you have.

Answer 109

A

Naturally occurring unstable isotopes. Space. Human activity.

Answer 110

A

Measuring amount of radioactive isotope left in sample, and knowing its half life.

Answer 111

A

1/10,000,000 (one ten-millionth)

Answer 112

A

5730 years.

Answer 113

A

Stop exchanging gas with air outside atmosphere and is trapped inside. Gradually decays.

Answer 114

A

Very long. Decay via series of short lived particles to produce stable isotopes of lead.

Answer 115

A

50% uranium 50% lead

Answer 116

A

25% uranium 75% lead

Answer 117

A

Nuclear reactors

Answer 118

A

Controlled chain reaction takes place - nuclear fission.

Answer 119

A

Uranium/plutonium atoms split up - releasing energy as heat.

Answer 120

A

Heat from fission is used to produce steam. Steam turns turbines which drive generator, producing electricity.

Answer 121

A

Uranium-235

Answer 122

A

Quite stable

Answer 123

A

When they absorb extra neutrons.

Answer 124

A

By firing slow moving neutrons at the U-235 atom.

Answer 125

A

Neutron joins, making it U-236 which is unstable.

Answer 126

A

Splits into 2 smaller nuclei, releasing energy and producing radioactive waste.

Answer 127

A

2 or 3 fast moving neutrons which go on to produce a chain reaction.

Answer 128

A

They are used to hit other U-235 atoms

Answer 129

A

Chain reactions that are out of control.

Answer 130

A

Using control rods

Answer 131

A

Limit the rate of fission by absorbing excess neutrons.

Answer 132

A

Two light nuclei combine to create a larger nucleus.

Answer 133

A

Fusion at extremely high temperatures and pressures.

Answer 134

A

Doesn’t leave behind much radioactive waste and there is plenty of hydrogen available.

Answer 135

A

Only happens at really high pressures and temperatures (about 10,000,000 degrees C). No material can withstand that, so reactors are difficult to build. Safety issues.

Answer 136

A

JET (Joint European Torus)

Answer 137

A

It takes more power to get up to temperature than reactor can produce.

Answer 138

A

To share cost, expertise, experience and benefits (when problem solved)

Answer 139

A

(AKA H-Bomb) Fission reaction creates high temperatures needed for fusion reaction which follows.

Answer 140

A

Validation Process

Answer 141

A

Nuclear fusion which occurs at room temperature.

Answer 142

A

Data was shared so experiments could be repeated. Very few managed to reproduce results reliably - not realistic method of energy production.

Answer 143

A

Which direction do electrons move when a polythene rod is rubbed with a duster?

Answer 144

A

Which direction do electrons move when an acetate rod is rubbed with a duster?

Answer 145

A

What is a static charge caused by?

Answer 146

A

What happens if enough static charge builds up?

Answer 147

A

How can a charged conductor be discharged safely?

Answer 148

A

How does earthing work?

Answer 149

A

What are ions?

Answer 150

A

How does static attract dust?

Answer 151

A

How does static affect clothing?

Answer 152

A

What causes shocks from door handles?

Answer 153

A

How can static on clothing become dangerous?

Answer 154

A

When can static become dangerous (other than on clothes)?

Answer 155

A

What kind of places is static dangerous in?

Answer 156

A

How do anti-static sprays work?

Answer 157

A

How do insulating mats and shoes work?

Answer 158

A

How do paint sprayers work?

Answer 159

A

What is the good thing about electrostatic paint sprayers?

Answer 160

A

How do dust precipitators work?

Answer 161

A

How does a defibrillator work?

Answer 162

A

If you increase the voltage….

Answer 163

A

If you increase the resistance…

Answer 164

A

Current only flows when?

Answer 165

A

What does the live wire do?

Answer 166

A

What colour is the live wire?

Answer 167

A

What does the earth wire do?

Answer 168

A

What does the neutral wire do?

Answer 169

A

What colour is the neutral wire?

Answer 170

A

What colour is the earth wire?

Answer 171

A

What must all appliances with metal cases be?

Answer 172

A

What does double insulated mean?

Answer 173

A

What happens is a fault develops where the live wire touches the metal case?

Answer 174

A

When the fuse blows, what does this prevent?

Answer 175

A

What is a circuit breaker?

Answer 176

A

How should fuses be rated?

Answer 177

A

What are the fixed fuse ratings?

Answer 178

A

What is a variable resistor?

Answer 179

A

What are variable resistors good for?

Answer 180

A

Why do thinner wires increase resistance?

Answer 181

A

What is the resistance of a fixed resistor like?

Answer 182

A

How is resistance calculated?

Answer 183

A

How is the ammeter set up in a circuit to measure resistance?

Answer 184

A

How is the voltmeter placed in a circuit to measure resistance?

Answer 185

A

What is the official name for voltage around a test circuit?

Answer 186

A

What are compressions?

Answer 187

A

What are rarefactions in a wave?

Answer 188

A

What is wavelength?

Answer 189

A

What is frequency?

Answer 190

A

What is amplitude?

Answer 191

A

How does a longitudinal wave move?

Answer 192

A

How does a transverse wave move?

Answer 193

A

What is ultrasound?

Answer 194

A

How does ultrasound work when breaking down accumulation in the body?

Answer 195

A

How does ultrasound work in body scanning?

Answer 196

A

What advantages does ultrasound have?

Answer 197

A

What do X-rays do compared to ultrasound?

Answer 198

A

What are radioactive materials made up of?

Answer 199

A

What happens as radioactive material decays?

Answer 200

A

What is the relative atomic mass number?

Answer 201

A

What is the atomic number?

Answer 202

A

What is an isotope?

Answer 203

A

When does gamma radiation happen in decay?

Answer 204

A

What is an alpha particle?

Answer 205

A

What charge does an alpha particle have?

Answer 206

A

What mass does an alpha particle have?

Answer 207

A

What happens to the mass number when a nucleus emits an alpha particle?

Answer 208

A

What happens to the atomic number when the nucleus emits an alpha particle?

Answer 209

A

What is a beta particle?

Answer 210

A

What charge does a beta particle have?

Answer 211

A

What mass does a beta particle have?

Answer 212

A

What happens to the mass number when a nucleus emits a beta particle?

Answer 213

A

What happens to the atomic number when a nucleus emits a beta particle?

Answer 214

A

What happens as more unstable nuclei decay?

Answer 215

A

What is the problem with trying to measure how quickly radioactive material decays?

Answer 216

A

What is the definition of half life?

Answer 217

A

What does a short half life mean?

Answer 218

A

What does a long half life mean?

Answer 219

A

What causes ionisation?

Answer 220

A

What does ionisation produce?

Answer 221

A

What is nuclear radiation and X-rays types of?

Answer 222

A

What can X-rays and gamma rays do to electrons?

Answer 223

A

What can beta particles do to electrons?

Answer 224

A

What happens if a beta particle sticks to an atom?

Answer 225

A

What can alpha particles do to electrons in an atom?

Answer 226

A

Why are alpha particles good ionisers?

Answer 227

A

What do lower doses of ionising radiation tend to cause?

Answer 228

A

What can high doses of ionising radiation tend to do?

Answer 229

A

Which types of radiation are most dangerous outside the body?

Answer 230

A

Why is alpha not dangerous outside the body?

Answer 231

A

Which source of radiation is most dangerous inside the body?

Answer 232

A

What sources of radiation are les dangerous inside the body?

Answer 233

A

What level of frequency do X-rays and gamma rays have?

Answer 234

A

What distance wavelength do X-rays and gamma rays have?

Answer 235

A

How are gamma rays made?

Answer 236

A

How are X-rays produced?

Answer 237

A

What can X-rays pass easily through?

Answer 238

A

What can X-rays not pass easily through?

Answer 239

A

What makes an X-ray image?

Answer 240

A

How is gamma used to treat cancer?

Answer 241

A

What radiation can be used as medical tracers?

Answer 242

A

How can a patient be given a medical tracer?

Answer 243

A

How are medical tracers monitored?

Answer 244

A

What is an example of a medical tracer?

Answer 245

A

Why must all isotopes in the body be beta or gamma?

Answer 246

A

How can medical instruments be sterilised?

Answer 247

A

Why does gamma radiation sterilise equipment?

Answer 248

A

What is the advantage of using radiation instead of water to sterilise equipment?

Answer 249

A

How can radiation be used as tracers in industry?

Answer 250

A

How is a leak detected using a radioactive tracer?

Answer 251

A

What must the isotope be for industrial tracers?

Answer 252

A

Why does the industrial tracer need a short half life?

Answer 253

A

What source is used in a smoke detector?

Answer 254

A

How does a smoke alarm work?

Answer 255

A

How does background radiation come from radioactivity of naturally occurring unstable isotopes?

Answer 256

A

How does background radiation come from space?

Answer 257

A

How does background radiation come from human activity?

Answer 258

A

How can the amount of background radiation vary?

Answer 259

A

What 3 ways do we receive background radiation?

Answer 260

A

How can you work out the age of something using radioactive dating?

Answer 261

A

What fraction of the carbon in the air does carbon-14 make up?

Answer 262

A

What is the half life of carbon-14?

Answer 263

A

What happens when carbon-14 isotopes die?

Answer 264

A

How does uranium have a different half life?

Answer 265

A

What is produced after 1 half life of uranium?

Answer 266

A

What is produced after 2 half lives of uranium?

Answer 267

A

What is the ratio of uranium to lead after 2 half lives?

Answer 268

A

What is the ratio of uranium to lead after 1 half life?

Answer 269

A

What is the ratio of uranium to lead before a half life?

Answer 270

A

What are nuclear power stations powered by?

Answer 271

A

What happens in a nuclear reactor?

Answer 272

A

What is nuclear fission?

Answer 273

A

What happens after a nuclear reactor?

Answer 274

A

What isotope is used in some nuclear reactors and bombs?

Answer 275

A

What is uranium-235 like?

Answer 276

A

How do materials become radioactive?

Answer 277

A

How is uranium-235 made radioactive?

Answer 278

A

What does uranium-235 become to make it unstable?

Answer 279

A

What happens to the U-236?

Answer 280

A

What does the split nucleus of U-236 also release?

Answer 281

A

What happens to neutrons from previous fission reactions of U-235?

Answer 282

A

What is a nuclear bomb?

Answer 283

A

How is the chain reaction controlled in nuclear reactors?

Answer 284

A

What are control rods usually made of?

Answer 285

A

What do control rods do?

Answer 286

A

What is nuclear fusion?

Answer 287

A

What is the equation for two hydrogen isotopes combining to form helium?

Answer 288

A

Where does all the energy released from stars come from?

Answer 289

A

What is good about nuclear fusion?

Answer 290

A

What is the big problem with nuclear fusion?

Answer 291

A

Name an experimental fusion reactor…

Answer 292

A

Why are no fusion reactors producing electricity yet?

Answer 293

A

Why is research into fusion being undertaken by international groups?

Answer 294

A

What happens in a fusion bomb?

Answer 295

A

What does a new scientific theory have to go through before being accepted?

Answer 296

A

What is ‘cold fusion’?

Answer 297

A

Why is cold fusion not accepted?

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P4 - Radiation For Life Flashcards

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