Nuclear

Question 1

why a radiation need an evacuated chamber

Answer 1

a paricle has short range in air

Question 2

why the lead box has a narrow slit

Answer 2

obtain a narrow beam of a particle

Question 3

background radiation source

Answer 3

1. cosmic rays form the atmosphere

2. radon gas in rocks

Question 4

a particle in a cloud chamber

Answer 4

thick,straight,short

Question 5

half-life definition

Answer 5

time is taken for half of the nuclei present in the source to decay

Question 6

b decay mass change?

Answer 6

b particle has negligible mass

so original substance mass remain unchanged

Question 7

why b is used in thickness gauge

Answer 7

a particle cant pass-through

gamma’s activity won’t decrease

Question 8

why long half-life in thickness gauge

Answer 8

activity remains stable

Question 9

why the smoke detector is not dangerous

Answer 9

radiation dose is small (Sv)

Question 10

which should be used to kill cancer cell ( beta or gamma)

Answer 10

beta

the ionizing power is higher

Question 11

what is the change of energy in nuclear fusion

Answer 11

energy change to electric potential energy

Question 12

what is the condition for fission occurs

Answer 12

more neutrons are produced for triggering further fission, ie neutron no. >1

Question 13

b particle in a cloud chamber

Answer 13

thin and twisted.

Question 14

precaution of dealing with radioactive substances

Answer 14

keep distance with the sample
use gloves
wash hands after experiment

Question 15

state an necessary condition for chain reaction of fission to occur.

Answer 15

More neutrons are produced in each fission for triggering further fissions, ie neutron>1

Question 16

why b particles are also emitted even though the source is primarily an a emitter

Answer 16

Some of the daughter products are also radioactive and emit b particles

Question 17

why the photoelectric current become saturated after V reaches a certain value

Answer 17

All photoelectrons emitted from (X) can reach (Y)

Question 18

what is order of magnitude

Answer 18

9 XXXXXX

10^9 correct

Question 19

how can nuclear radiation be detected

Answer 19

spark counter
ionisation chamber
diffusion cloud chamber
GM counter
photographic film

Question 20

what can stop b particle

Answer 20

5mm aluminium

Question 21

what can half gamma ray

Answer 21

25mm lead

Question 22

average background count rate in s-1 in HK is of the order of

Answer 22

10^0

Question 23

what is activity

Answer 23

number of disintegrations per second

unit:Bq becquerels

Question 24

how to find the accurate value for the activity of the excavated wood?

Answer 24

take a count over as long a period of time as possible

tale a second count without the presence of the excavated wood

Question 25

reaction of forming carbon 14

Answer 25

14,7N + 1,0n to 14,6C + 1,1H

Question 26

what is critical mass

Answer 26

the minimum amount of fissionable substance requried for a sustained chain reaction

Question 27

is gamma source suitable for checking the thickness of the lead plates

Answer 27

yes

scl mock

Question 28

in the nucleus, th electrostatic repulsion between two protons is overcome by the nuclear force between them
T/F

Answer 28

T

Question 29

what is the application of radioactive isotopes in industry

Answer 29

thickness gauge.

smoke detector

Question 30

what is the application of radioactive isotopes in medicine

Answer 30

radiotherapy

killing cancer cells

Question 31

why is an opague plastic bag used to wrap the photographic film

Answer 31

it prevents light entering the badge to expose the film inside

Question 32

hazard of exposure to ionizing rdiations

Answer 32

lead to cancer

destroy or damage living cells