Radioactivity

Question 0

Alpha scattering- very few alpha particles are deflected. What can be concluded from this?

Answer 0

The nucleus is small

Question 1

Alpha scattering- most particles passed through the atom. What can be concluded from this?

Answer 1

Atom is mostly empty space

Question 2

Alpha scattering- alpha are repelled. What conclusions can be drawn from this?

Answer 2

Nucleus is positively charged

Question 3

Estimating the closest approach of a scattered particle. What two energies must be equal?

Answer 3

Initial kinetic energy and the electrical force between the two particles at the closest distance.

Question 4

Why is electron scattering more accurate than alpha scattering?

Answer 4

Electrons are leptons. They do not interact via the strong nuclear force.

Question 5

How do you find nuclear radius using electron diffraction?

Answer 5

First order maxima appears when
Sin theta = 1.22 lambda / d

From this equation the spacing and size can be worked out

Question 6

What is Ro in the nuclear radius equation?

Answer 6

1.4x10^-15 m

Constant

Question 7

Why do atoms have similar densities?

Answer 7

Because neutrons and protons have nearly the same mass.

Question 8

Nuclear density is significantly bigger than atomic density. What three things does this suggest?

Answer 8

1) most of mass is in nucleus
2) nucleus is much smaller than atom
3) atom is mostly empty space

Question 9

Why are some atoms unstable?

Answer 9

Too many or not enough neutrons

Or just too much energy.

Question 10

What is decay?

Answer 10

Am atom releases energy or particles until it is stable

Question 11

Alpha particle- absorption?

Answer 11

Absorbed by paper or a few cm of air

Question 12

Alpha particle- ionisation?

Answer 12

Strong. 10,000 ionisations per particle

Question 13

Beta particle- absorption?

Answer 13

Absorbed by roughly 3mm of aluminium.

Question 14

Beta particle- ionisation?

Answer 14

Weakly. 100 ionisations per b particle.

Question 15

Gamma- absorption?

Answer 15

Absorbed by many cm of lead or several m of concrete

Question 16

Gamma- ionisation?

Answer 16

Very weakly

Question 17

Beta minus- why does it have relatively no ionisation or absorption?

Answer 17

Annihilated by electron so virtually zero range.

Question 18

Applications of an alpha particle?

Answer 18

Smoke alarms

Question 19

Application of gamma ?

Answer 19

Diagnostic techniques in medicine

Question 20

What direction does gamma travel in?

Answer 20

All directions- radiates from source. (Follows inverse square law)

Question 21

Where does background radiation come from? (List three and give details)

Answer 21

1) Air- radon gas released from rocks
2) ground and buildings- all rocks contain radioactive isotopes
3) cosmic radiation- high energy protons from space collide with particles in the upper atmosphere and produces radiation.

Question 22

What is Activity? [A]

Answer 22

The number of atoms that decay each second.

[A]= Bq

Question 23

Define the decay constant

[lambda]

Answer 23

The probability than an atom of an isotope will decay at that moment.

[ ] = s^-1

Question 24

Define half life

Answer 24

The half life of an isotope is the average time that it takes for the number of non-decayed atoms to halve.

Question 25

Give two uses for radioactive isotopes:

Answer 25

1) radioactive dating- Carbon 14 content falls after death with a fixed half life. 2) medical diagnosis- substances that are used to show tissue or organ function.