<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body>
<div class="" style="word-wrap:break-word; line-break:after-white-space">
<div class=""><font face="Verdana" size="2" class="">(Sent by Peter Willendrup on behalf of </font><span class="" style="font-family:Verdana; font-size:small">Thierry Bigault, ILL who originally sent the mail to the now defunct
<a href="mailto:mcstas-support@mcstas.org" class="">mcstas-support@mcstas.org</a> address)</span></div>
<div class=""><font size="-1" class=""><font face="Verdana" class=""><br class="">
</font></font></div>
<div class=""><font size="-1" class=""><font face="Verdana" class=""><br class="">
</font></font></div>
<div class=""><font size="-1" class=""><font face="Verdana" class="">Dear McStas programmers,<br class="">
<br class="">
As I try to get advantage of these special conditions to try and use McStas, I have a beginner's question:<br class="">
<br class="">
One of my aims is to be sure to have correct orders of magnitude for absolute flux.<br class="">
<br class="">
I started to use the components Source_simple and Source_gen.<br class="">
I assume that for the simplest case, the parameters "flux" in Source_simple and "I1" in Source_gen play the same role.<br class="">
My expectation is that the flux measured by a monitor at a certain distance from the source follows Equation 3.1 in the "McStas 2.6 Component Manual of 24/01/2020", which links the source brilliance with source area, solid angle and wavelength interval.<br class="">
<br class="">
This is the case with both sources if I set the parameter to 1: with 1 Ang bins, I get a flux on my monitor which scales according to this equation.<br class="">
Following the component help, this behaviour should be observed by setting the parameter to 0. This in not the case, with 0 as input the calculation gives different flux values, which I am not able to link to anything physical.<br class="">
The documentation is a bit misleading, because it recommends to put the value to 0 and the default is 1.<br class="">
<br class="">
in Source_simple:<br class="">
name: flux <br class="">
unit: 1/(s*cm**2*st*energy unit) <br class="">
description: flux per energy unit, Angs or meV if flux=0, the source emits 1 in 4*PI whole space.
<br class="">
default: 1<br class="">
<br class="">
in Source_gen:<br class="">
name: I1<br class="">
unit: 1/(cm**2*sr)<br class="">
descrption: Source flux per solid angle, area and Angstrom if I1=0, the source emits 1 in 4*PI whole space.<br class="">
</font></font><font size="-1" class=""><font face="Verdana" class=""><font size="-1" class=""><font face="Verdana" class="">default: 1<br class="">
<br class="">
My feeling is that:<br class="">
- the unit should be in both case as in Source_simple,<br class="">
- the same sentences would work with "flux=1" and "I1=1", which would be consistent with the default values. I have no idea if the 0 value is useful for some case.<br class="">
<br class="">
But maybe I completely missed something...<br class="">
I attached the very simple instrument file which I used. <br class="">
<br class="">
Thierry<br class="">
<br class="">
<br class="">
<br class="">
</font></font></font></font></div>
</div>
<div style="word-wrap:break-word; line-break:after-white-space"><br class="">
<br class="">
<div class="">
<div style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none">
<br class="">
Peter Kjær Willendrup<br class="">
Forskningsingeniør, Specialkonsulent<br class="">
Næstformand for DTU Fysik LSU<br class="">
<br class="">
DTU Physics<br class="">
<br class="">
</div>
<span style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none"><br class="x_Apple-interchange-newline">
<span></span></span></div>
</div>
<div><img src="cid:6b49ff07-bbc6-4db3-820c-5307f51551b2@win.dtu.dk"> </div>
<div style="word-wrap:break-word; line-break:after-white-space">
<div id="x_AppleMailSignature"><span class="x_Apple-string-attachment" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none"><span></span><br class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none">
<br class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none">
<br class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none">
<span class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none; float:none; display:inline!important">Technical
University of Denmark</span><br class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none">
<br class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none">
<br class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none">
<span style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none"><span></span></span></span></div>
</div>
<div><img src="cid:0cea8b1e-d480-46b2-bcd4-98dec8674d3c@win.dtu.dk"> </div>
<div class="" style="word-wrap:break-word; line-break:after-white-space">
<div class=""><span style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none"><span style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none"><span></span><br class="x_Apple-interchange-newline">
<br class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none">
<br class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none">
<br class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none">
<span class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none; display:inline!important; float:none">Department
of Physics</span><br class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none">
<span class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none; display:inline!important; float:none">Fysikvej</span><br class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none">
<span class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none; display:inline!important; float:none">Building
307</span><br class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none">
<span class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none; display:inline!important; float:none">DK-2800
Kongens Lyngby</span><br class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none">
<span class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none; display:inline!important; float:none">Direct
+45 2125 4612</span><br class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none">
<span class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none; display:inline!important; float:none">Mobil
+45 2125 4612</span><br class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none">
<span class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none; display:inline!important; float:none">Fax
+45 4593 2399</span><br class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none">
<span class="" style="color:rgb(0,0,0); font-family:Helvetica; font-size:12px; font-style:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px; text-decoration:none; display:inline!important; float:none"><a href="mailto:pkwi@fysik.dtu.dk" class="">pkwi@fysik.dtu.dk</a></span>
</span></span></div>
<br class="">
</div>
</body>
</html>