Nuclear 1

Question 1

What 3 observations were there from the alpha/Rutherford scattering experiment?

Answer 1

• vast majority of alpha particles go straight through
• a few alpha particles are deflected less than 90°
• very few alpha particles deflect more than 90°

Question 2

What does the fact that the vast majority of alpha particles went straight through the gold leaf tell us about the atom?

Answer 2

most of the atom is empty space, the nucleus is very small

Question 3

What does the the fact a few alpha particles were deflected less than 90° tell us about the atom?

Answer 3

the nucleus is positively charged

Question 4

How did the Rutherford scattering show the nucleus is positively charged?

Answer 4

there was a shadow behind the nucleus

Question 5

What does the fact that very few alpha particles deflect more than 90° tell us about the atom?

Answer 5

the nucleus is massive (almost all the atom’s mass)

Question 6

What is a typical atom diameter?

Answer 6

approx 10^-10 m

Question 7

What is a typical nuclear diameter?

Answer 7

approx 10^-14 / 10^-15 m

Question 8

For the Rutherford scattering, why was it essential for there to be a vacuum in the chamber?

Answer 8

• to prevent the alpha particles being absorbed or scattered

- by air molecules

Question 9

How can we use alpha particles to calculate/estimate nuclear radii?

Answer 9

• project alpha particle towards the nucleus
• at the point where the alpha particle is closest to the nucleus, KE = 0
• if the KE of the particle at the beginning is known, this can be used to calculate r (by equating the loss in KE to the gain in EPE)

Question 10

How can we use electrons to calculate/estimate nuclear or atomic radii?

Answer 10

• an electron will diffract the maximum amount when its wavelength is approximately equal to the diameter of the nucleus or atom
• the wavelength of the electron can be changed by changing its energy (changing its velocity)

Question 11

Why is it that the detector reading doesn’t fall to zero when electrons are diffracted by atoms or nuclei?

Answer 11

• negatively charged electrons are scattered by positively charged nuclei - electrostatic attraction

Question 12

Why is using electrons considered better for determining nuclear radii, compared to alpha particles?

Answer 12

• alpha particles are hadrons, so are affected by the SNF, may fuse with the nucleus
• electrons are leptons, so are unaffected by the SNF, so can get close to the nucleus and not fuse

Question 13

What’s a disadvantage of using alpha particles to determine nuclear radii?

Answer 13

• only gives an upper limit

- as it gets close but doesn’t touch the nucleus

Question 14

What’s an advantage of using alpha particles to determine nuclear radii?

Answer 14

KE of alpha particles is all the same as they are monoenergetic

Question 15

What does the fact that nuclear volume is proportional to mass number tell us?

Answer 15

all nuclei are made of the same material (density is constant)

Question 16

What radiation is used to diagnose in medicine, and why?

Answer 16

• gamma
• it is penetrating
• lower dose for the patient
• can be detected outside the body

Question 17

What radiation is usually used to treat in medicine, and why?

Answer 17

• alpha
• more ionising
• destroys damaged cells

Question 18

Define count rate

Answer 18

the number of counts per unit time detected by the GM tube

Question 19

What are the possible units for count rate?

Answer 19

• cpm

- cps

Question 20

Define activity

Answer 20

the number of decays per second for a radioactive sample

Question 21

What is the unit for activity?

Answer 21

Bq

Question 22

Define background radiation

Answer 22

low level radiation that surrounds us from natural and artificial sources

Question 23

Name 3 natural sources that contribute to background radiation

Answer 23

• radon gas
• cosmic rays
• food

Question 24

Name 3 artificial sources that contribute to background radiation

Answer 24

• nuclear fallout/leaks
• air travel
• medical uses

Question 25

How do you get a corrected count rate from a reading?

Answer 25

subtract the background radiation

Question 26

What is the 4 key characteristic of exponential decay?

Answer 26

• the same fractional decrease occurs over the same time interval, anywhere on the curve (constant ratio test)
• variable power
• y-intercept and x asymptope
• dy/dx is proportional to y

Question 27

What two words are used to describe radioactivity, and what do they mean?

Answer 27

• random: don’t know which nuclei will decay next

- spontaneous: don’t know when the next nuclei will decay

Question 28

Define the decay constant

Answer 28

the probability of a given nucleus decaying in the next second

Question 29

What is one mole defined as?

Answer 29

• the number of atoms/particles in 12g of Carbon-12

- 6.02 x 10^23 particles/molecules