How can I accurately plot the Bragg curve for alpha particles?

[Bob S]

A good comprehensive review of charged particle energy loss in matter is given by the LBL Particle Data Group:

http://www.google.com/url?sa=t&sour...tp://www.phy.bris.ac.uk/people/cussans_dg/phy

See especially Eqn(27.3) and text. The Bethe Bloch ionization energy loss theory is based on the fact that the major energy loss is collisions with atomic electrons and not with nuclei. Incident charged particles elestically scatter on nuclei with very little energy loss.

Here in attachment is my code for a 5.3 MeV alpha particle (Polonium alpha) in air, including a plot of the Bragg curve. It is surprisingly accurate. Note that the log on line 350 of my code is the natural log and not base 10.

I don't know of a simple discussion of the derivation of these equations.

Bob S

 

[ekosulistya]

Thank you very much Bob. You've been very helpful. I don't have Truebasic, so I write your code in Excel worksheet. I've tried write your code in Python, but this program also new to me, I can't figure out how to do the condition in the loop part. I attach the picture from Excel worksheet, and part of the worksheet. I can't open the page that you suggested. Anyway, thanks again.

 

[ekosulistya]

Hi Bob,

Is it okay if use TZ for air with (0.8*14+0.2*16) and TA with (0.8*28+0.2*32)? The graph is't change much. And if I change the alpha energy to 5.49 MeV, the graph shows that the projected range is 3,83 cm.

Eko

 

[ekosulistya]

Thank you. :-D

Eko S

 

[naiveBen]

hi .( I`m not used to using english.)

I have a question.

There isn`t any clue on distance with the Beth-Bloch Formular

I mean this formula is independent on the distance except for β
(I hope it makes sense)


so Bob sugested to insert dx

but It seems to me that there is no way we could find out

real amount of dx

it`s a differential distance, isn`t it

but how on Earth we just use dx without any real value??
(if i use it with some kind of coding program. there`s no problem?)

so my queation is

what is the value of dx? and when it comes to deciding the value of dx, is there any reasonable reason

 

[naiveBen]

it`s needless to say that dx is supposed to be really small amount.

but i need some reasonable clue.. let me know why it has to be 0.01 or something..

T^T

 

[spenmurphy]

Thank you very much Bob. You've been very helpful. I don't have Truebasic, so I write your code in Excel worksheet.

What did this code look like? I'm just learning how to use Excel VBA.

Thanks!

 

[ekosulistya]

naiveBen,
did you mean that it has to do with the free path length of the ion? I think, dx in the equation is a small step the ion make, whatever the interaction that has happened to the ion, and in any direction. it's computational step, the smaller step we choose, the graph is more smooth.

spenmurphy,
I wasn't using VBA Excel, but worksheet formula only. You can see the snapshot of part of the worksheet in my previous message. I rewritten the code from Bob in worksheet cell, step by step, copy all the way down, and the result is a data set, from which we can choose the value of x and dE/dx, and plot it with Excel scatter chart

 

[Moho]

In case anybody is still around, I have a question about the Bragg curve for alpha particles. I was able to follow Bob S's code above (albeit in Excel) and I get a good result, but I notice that energy (E, not dE/dX) never goes to 0. The alpha particle still seems to have a lot of energy (~0.18 MeV) even after it has traversed its stopping distance. Does this make physical sense? What could be wrong? I'm a PhD geology student but my physics is at undergraduate level so I'm a bit confused.