Continuation of discussion: High energy backscattering at 1.4GeV beam

From: Helmut Vincke <>
Date: Wed, 15 Dec 2010 11:31:51 +0000

Dear colleagues

Short problem description: backscattering of high-energy protons (having
energies close to initial beam energy) on a massive iron target.

After some discussion and some time spent on this topic we found some answers.
We extracted two backscattered high-energy particles from 3E6 particles
started and looked at them with SimpleGeo+Pipsicad (reading out USERDUMP):
The backscattered particles with such high energies turned out to originate
from two double elastic scattering events, changing each of which the angle
of the incoming proton by about 90 degree or less.

I attach a file showing these events. Moreover, we put a detector to score
backwards scattered particle upstream the impact point as a function of energy.
Persons interested in this topic please have a look otherwise ignore my message.
On the first glance the high-energy shape of the spectrum looked a bit odd to me
because I did not expect a dip in the range of 600 MeV to 1 GeV followed by a
fluence increase when coming to closer initial beam energy.
If you have a dedicated clear opinion on the creation of this dip feel
free to send me your opinion.

Best regards

From: Helmut Vincke
Sent: 07 December 2010 11:42
Cc: Chris Theis
Subject: High energy backscattering at 1.4GeV beam

Dear colleagues

In my simulation I am sending a 1.4 GeV proton beam on a thick iron target
(l=1.55m, r=50 cm). When looking at the result I see backscattered
protons between 1.2 GeV and 1.4 GeV. Within 6E6 protons sent on the targets
I found 3 protons with more than 1.2 GeV going backwards. I separated these
three tracks in a separate run introducing a proton threshold of 1.2 GeV
(see the picture in the attachment). Looks almost like elastic scattering but
I did not expect it at that energy with such a large scattering angle.
Although it concerns only a very minor fraction of the final fluence, I would
like to understand its reason. I would be grateful for an explanation
concerning the physics behind such an event.

Thanks in advance


Received on Wed Dec 15 2010 - 15:45:22 CET

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