Fission: conserve charge and nucleons, account for energy
Đã giới thiệu| English | Ý nghĩa |
|---|---|
| chain reaction/tʃeɪn rɪˈækʃn/ | phản ứng dây chuyền |
| fission/ˈfɪʃn/ | phân hạch |
What would explain this observation?
- A neutron can trigger a heavy nucleus to split, releasing energy and further neutrons. Whether the process becomes a chain reaction 链式反应 depends on what happens to those neutrons.
Build the model
- In nuclear fission 核裂变 a heavy nucleus splits into lighter nuclei.
- Proton number and nucleon number balance in a nuclear equation.
- The total rest mass can decrease; the difference corresponds to released energy through E = Δmc².
- fission: Splitting of a heavy nucleus into lighter nuclei.
- chain reaction: A sequence in which products initiate further events.
What permits a continuing fission chain reaction?
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Each fission releases two or three neutrons, and if at least one triggers another fission the reaction sustains itself. Escaped neutrons break the chain, and charge conservation is never suspended.
Match each technical term to its precise meaning.
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Separate conservation of nucleon number from conservation of total energy.
- Released neutrons may initiate further fissions, escape or be absorbed.
- A controlled reactor and an uncontrolled chain reaction have different neutron-management conditions.
In the lab: Balance a supplied nuclear equation, use the specified mass data and identify the system. Analyse models or published reactor data; this is not a school attempt to produce fission or handle reactor materials.
Which two habits make the investigation or model in this case more defensible?
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: U-235 absorbs one neutron, forming Ba-141, Kr-92 and three neutrons.
- Nucleon balance: 235+1 = 141+92+3 = 236.
- Proton balance: 92 = 56+36.
- A mass decrease of 2.0×10⁻²⁸ kg corresponds to 1.8×10⁻¹¹ J using c=3.0×10⁸ m/s.
Your turn: A U-235 nucleus plus one neutron produces fragments with mass numbers 141 and 92. How many neutrons balance the equation?
A U-235 nucleus plus one neutron produces fragments with mass numbers 141 and 92. How many neutrons balance the equation?
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
The result is 3 neutrons. Known: U-235 plus one neutron gives fragments 141 and 92. Nucleon balance: 235 + 1 = 141 + 92 + n, so n = 236 - 233 = 3 neutrons. Proton numbers must balance separately (92 = 56 + 36 for barium and krypton).
Check the conclusion and its limits
- Mass number is not a precise mass in kilograms.
- Balanced integer labels alone do not calculate the released energy.
- Radioactive decay and neutron-induced fission are not interchangeable descriptions.
Not true: A balanced nucleon-number equation alone gives the energy release in joules. Integer mass and charge labels only check conservation; they say nothing about energy. The released energy comes from the small decrease in actual MASS via E = mc^2, which needs measured masses, not mass numbers.
- In nuclear fission a heavy nucleus splits into lighter nuclei.
- Separate conservation of nucleon number from conservation of total energy.
- Watch for: mass number is not a precise mass in kilograms.
Write from 2 balancing neutrons
- A U-235 nucleus plus one neutron produces fragments with mass numbers 140 and 94.
- Find how many neutrons balance the nucleon number. That count is not the energy release in joules.
A balanced nucleon-number equation alone gives the energy release in joules.
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Integer mass and charge labels only check conservation; they say nothing about energy. The released energy comes from the small decrease in actual MASS via E = mc^2, which needs measured masses, not mass numbers.
Splitting of a heavy nucleus into lighter nuclei: write the technical term.
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
fission means Splitting of a heavy nucleus into lighter nuclei.
A U-235 nucleus plus one neutron produces fragments with mass numbers 140 and 94. How many neutrons balance the nucleon number, and why does that balanced equation not give the energy release in joules?
Nucleon number is conserved. Energy accounting needs the mass change, which the integer labels do not state.
How many neutrons balance the nucleon number?
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
236 minus 234 is 2, so two neutrons balance the equation. Other options — 3 (the lesson fragments 141 and 92); 236 (the nucleon number of the left side).