P7: Radioactivity

Question 1

alpha decay

Answer 1

nucleus loses two protons and two neutrons. higest ionising power. travels a few centimeters in are.stopped by a sheet of paper

Question 2

beta decay

Answer 2

a neutron changes into a proton and an electron. high ionising power.travels 1m in air. stopped by a few millimeters of aluminium

Question 3

gamma decay

Answer 3

some energy is transferred away from the nucleus. low ionising power.virtually unlimited range in air. stopped by several centimeters of thick lead or meters of concrete

Question 4

half life

Answer 4

time for half the number of unstable nuclei in a sapmle to decay. the half life of a source can be found from a graph of its count rate or activity against time

Question 5

how to find the reduction in activity after a number of given half lives

Answer 5

1)calculate the activity after each half life
2)subtract the final activity from the original activity

Question 6

ionising radiation

Answer 6

living cells cann be damaged or killed by ionising radiationThe risk depends on the half‐life of the source and the type of radiation.
Alpha radiation is very dangerous inside the body
because it affects all the surrounding tissue.
Outside the body it only aff ects the skin and eyes
because it cannot penetrate further.
Beta and gamma radiation are dangerous
outside and inside the body because they can
penetrate into tissues.

Question 7

irradiation

Answer 7

when an object is exposed to nuclear radiation cause harm through ionisation prevented by shielding removing or moving away the source of radiation

Question 8

contamination

Answer 8

when atoms of a radioactive material are on or in an object cause harm through ionisation object remains exposed to radiation as long as it is contaminated contamination can be very difficult to remove

Question 9

nuclear fission

Answer 9

Nuclear fission is when a large unstable nucleus
absorbs an extra neutron and splits into two smaller nuclei of roughly equal size. during nuclear fission: gamma radiation is emitted and energy is released two or three neutrons are emitted that can go on to cause a chain reaction On rare occasions an unstable nucleus splits apart without absorbing a neutron. This is called spontaneous fission.

Question 10

nuclear fusion

Answer 10

Nuclear fusion is when two light nuclei join to
make a heavier one. Some of the mass is converted to energy and transferred as radiation.