English: Simulation of many identical atoms undergoing radioactive decay, starting with either four atoms (left) or 400 atoms (right). The number at the top indicates how many half-lives have elapsed. Note the law of large numbers: With more atoms, the overall decay is less random. Image made with Mathematica, I am happy to send the source code if you would like to make this image more beautiful, or for any other reason.
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(* Source code written in Mathematica 6.0, by Steve Byrnes, 2010. I release this code into the public domain. *)
SeedRandom[2]
(*Build list of point coordinates and radii*)
BuildCoordList[SqCenterX_, SqCenterY_, SqSide_, PtsPerRow_] :=
Flatten[Table[{i, j}, {i, SqCenterX - SqSide/2, SqCenterX SqSide/2, SqSide/(PtsPerRow - 1)},
{j, SqCenterY - SqSide/2, SqCenterY SqSide/2, SqSide/(PtsPerRow - 1)}], 1];
coordslist = Join[
BuildCoordList[3.5, 1, 1.8, 20],
BuildCoordList[3.5, 3, 1.8, 20],
BuildCoordList[3.5, 5, 1.8, 20],
BuildCoordList[3.5, 7, 1.8, 20],
BuildCoordList[1, 1, .7, 2],
BuildCoordList[1, 3, .7, 2],
BuildCoordList[1, 5, .7, 2],
BuildCoordList[1, 7, .7, 2]];
NumPts = Length[coordslist];
radiuslist = Join[Table[.03, {i, 1, 4*400}], Table[.1, {i, 1, 4*4}]];
(*Draw borders*)
xlist = {0, 2};
leftx = 0;
rightx = 2;
numx = Length[xlist];
ylist = {0, 2, 4, 6, 8};
topy = 0;
boty = 8;
numy = Length[ylist];
lines = {};
For[i = 1, i <= numy, i ,
lines = Append[lines, Line[{{leftx, ylist[[i]]}, {rightx, ylist[[i]]}}]]];
For[i = 1, i <= numx, i ,
lines = Append[lines, Line[{{xlist[[i]], topy}, {xlist[[i]], boty}}]]];
xlist = {2.5, 4.5};
leftx = 2.5;
rightx = 4.5;
numx = Length[xlist];
ylist = {0, 2, 4, 6, 8};
topy = 0;
boty = 8;
numy = Length[ylist];
For[i = 1, i <= numy, i ,
lines = Append[lines, Line[{{leftx, ylist[[i]]}, {rightx, ylist[[i]]}}]]];
For[i = 1, i <= numx, i ,
lines = Append[lines, Line[{{xlist[[i]], topy}, {xlist[[i]], boty}}]]];
(*Write numbers:
I want to be able to write a number with one decimal place,
including padding with ".0" when it's an integer.*)
WriteNum[num_] := Block[{rounded}, rounded = N[Floor[num, 0.1]];
If[FractionalPart[rounded] == 0, ToString[rounded] <> "0", ToString[rounded]]];
(*Randomly choose decay times:
To get an expontial-decay-distributed random number, we pick a number uniformly between 0 and 1.
Take its negative log to get the time that it blows up, which is between 0 and infinity.
But divide by log 2 so that when the time = 1, there's 50% chance of decaying. *)
BlowTime = Table[-Log[RandomReal[]]/Log[2], {i, 1, NumPts}];
(*Draw graphics*)
GraphicsList = {};
NumFrames = 80;
TimePerFrame = .05;
Video = {};
For[frame = 1, frame <= NumFrames, frame ,
CurrentTime = (frame - 1)*TimePerFrame;
ImageGraphicsList = lines;
ImageGraphicsList =
Append[ImageGraphicsList, Text[WriteNum[CurrentTime], {.8, 8.5}, {-1, 0}]];
ImageGraphicsList =
Append[ImageGraphicsList, Text[WriteNum[CurrentTime], {3.3, 8.5}, {-1, 0}]];
For[pt = 1, pt <= NumPts, pt ,
If[CurrentTime < BlowTime[[pt]],
ImageGraphicsList = Append[ImageGraphicsList, {Blue, Disk[coordslist[[pt]], radiuslist[[pt]]]}]]];
Video = Append[Video, Graphics[ImageGraphicsList, ImageSize -> 100]];];
(*Pause at start*)
Video = Join[Table[Video[[1]], {i, 1, 5}], Video];
(*Export*)
Export["test.gif", Video, "DisplayDurations" -> {10}, "AnimationRepititions" -> Infinity ]
Captions
Add a one-line explanation of what this file represents
Changed top-bottom split to left-right split, with space between; pause at start; 400 atoms in each crowded box instead of 296. (Thanks to Bdb484 for suggestions.)
{{Information |Description={{en|1=Simulation of many identical atoms undergoing radioactive decay. The number at the top indicates how many half-lives have elapsed. Note that after one half-life there are not ''exactly'' one-half of the atoms remaining, o