Context Navigation

← Previous Revision
Latest Revision
Next Revision →
Blame
Revision Log

material.html @ 1287

Last change on this file since 1287 was 1208, checked in by garnier, 15 years ago
CVS update
File size: 16.5 KB

Line
1	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
2	<HTML>
3	<HEAD>
4	<META NAME="GENERATOR" CONTENT="Mozilla/3.0Gold (X11; I; OSF1 V4.0 alpha) [Netscape]">
5	</HEAD>
6	<BODY>
7
8	<!-- Changed by: Katsuya Amako, 14-Jul-1998 -->
9	<!-- Proof read by: Joe Chuma, 29-Jun-1999 -->
10
11	<TABLE WIDTH="100%" >
12	<TR>
13	<TD>
14	</A>
15	<A HREF="index.html">
16	<IMG SRC="../../../../resources/html/IconsGIF/Contents.gif" ALT="Contents" HEIGHT=16 WIDTH=59></A>
17	<A HREF="geometry.html">
18	<IMG SRC="../../../../resources/html/IconsGIF/Previous.gif" ALT="Previous" HEIGHT=16 WIDTH=59></A>
19	<A HREF="electroMagneticField.html">
20	<IMG SRC="../../../../resources/html/IconsGIF/Next.gif" ALT="Next" HEIGHT=16 WIDTH=59></A>
21	</TD>
22
23	<TD ALIGN="Right"><FONT COLOR="#238E23"><FONT SIZE=-1>
24	<B>Geant4 User's Guide</B> <BR>
25	<B>For Application Developers</B> <BR>
26	<B>Detector Definition and Response</B> </FONT></FONT> </TD>
27	</TR>
28	</TABLE>
29	<P><BR>
30
31	<CENTER><FONT COLOR="#238E23"><FONT SIZE=+3>
32	<B>4.2 Material</B> </FONT></FONT>
33	</CENTER>
34	<BR>
35	<BR>
36
37	<HR ALIGN="Center" SIZE="7%">
38	<p>
39
40	<a name="4.2.1">
41	<H2>4.2.1 General considerations</H2></a>
42
43	In nature, materials (chemical compounds, mixtures) are made of elements,
44	and elements are made of isotopes. Geant4 has three main classes
45	designed to reflect this organization. Each of these classes has a table,
46	which is a static data member, used to keep track of the instances of the
47	respective classes created.
48	<p>
49	<dl><dl>
50	<dt><i>G4Isotope</i>
51	<dd>This class describes the properties of atoms: atomic number, number of
52	nucleons, mass per mole, etc.
53	</p>
54	<p>
55	<dt><i>G4Element</i>
56	<dd>This class describes the properties of elements: effective atomic number,
57	effective number of nucleons, effective mass per mole, number of isotopes,
58	shell energy, and quantities like cross section per atom, etc.
59	</p>
60	<p>
61	<dt><i>G4Material</i>
62	<dd>This class describes the macroscopic properties of matter:
63	density, state, temperature, pressure, and macroscopic quantities like
64	radiation length, mean free path, dE/dx, etc.
65	</p>
66	</dl></dl>
67	<p>
68	Only the <i>G4Material</i> class is visible to the rest of the toolkit and
69	used by the tracking, the geometry and the physics. It contains all the
70	information relevant to its constituent elements and isotopes, while at
71	the same time hiding their implementation details.
72	</p>
73
74	<hr>
75	<a name="4.2.2">
76	<h2>4.2.2 Introduction to the Classes</h2></a>
77
78	<b><i>G4Isotope</i></b>
79	<p>
80	A <i>G4Isotope</i> object has a name, atomic number, number of nucleons, mass
81	per mole, and an index in the table. The constructor automatically stores
82	"this" isotope in the isotopes table, which will assign it an index number.
83	</p>
84	<br>
85
86	<b><i>G4Element</i></b>
87	<p>
88	A <i>G4Element</i> object has a name, symbol, effective atomic number,
89	effective number of nucleons, effective mass of a mole, an index in the
90	elements table, the number of isotopes, a vector of pointers to such isotopes,
91	and a vector of relative abundances referring to such isotopes (where relative
92	abundance means the number of atoms per volume). In addition, the class has
93	methods to add, one by one, the isotopes which are to form the element.
94	</p>
95	<p>
96	A <i>G4Element</i> object can be constructed by directly providing the
97	effective atomic number, effective number of nucleons, and effective mass of
98	a mole, if the user explicitly wants to do so. Alternatively, a
99	<i>G4Element</i> object can be constructed by declaring the number of
100	isotopes of which it will be composed. The constructor will "new" a vector
101	of pointers to <i>G4Isotopes</i> and a vector of doubles to store their
102	relative abundances. Finally, the method to add an isotope must be invoked
103	for each of the desired (pre-existing) isotope objects, providing their
104	addresses and relative abundances. At the last isotope entry, the system will
105	automatically compute the effective atomic number, effective number of
106	nucleons and effective mass of a mole, and will store "this" element in the
107	elements table.
108	</p>
109	<p>
110	A few quantities, with physical meaning or not, which are constant in
111	a given element, are computed and stored here as "derived data members".
112	</p>
113	<p>
114	Using the internal Geant4 database, a G4Element can be accessed by atomic
115	number or by atomic symbol ("Al", "Fe", "Pb"...). In that case
116	G4Element will be found from the list of existing elements or
117	will be constructed using data from the Geant4 database, which is derived
118	from the NIST database of elements and isotope compositions
119	(http://physics.nist.gov/PhysRefData/Compositions/index.html). Thus,
120	the natural isotope composition can be built by default. The same element
121	can be created as using the NIST database with natural composition of isotopes
122	and from scratch in user code with user defined isotope composition.
123	</p>
124	<br>
125
126	<b><i>G4Material</i></b>
127	<p>
128	A <i>G4Material</i> object has a name, density, physical state, temperature
129	and pressure (by default the standard conditions), the number of elements and
130	a vector of pointers to such elements, a vector of the fraction of mass for
131	each element, a vector of the atoms (or molecules) numbers of each element,
132	and an index in the materials table. In addition, the class has methods to
133	add, one by one, the elements which will comprise the material.
134	</p>
135	<p>
136	A <i>G4Material</i> object can be constructed by directly providing the
137	resulting effective numbers, if the user explicitly wants to do so (an
138	underlying element will be created with these numbers). Alternatively, a
139	<i>G4Material</i> object can be constructed by declaring the number of
140	elements of which it will be composed. The constructor will "new" a vector
141	of pointers to <i>G4Element</i> and a vector of doubles to store their
142	fraction of mass. Finally, the method to add an element must be invoked
143	for each of the desired (pre-existing) element objects, providing their
144	addresses and mass fractions. At the last element entry, the system will
145	automatically compute the vector of the number of atoms of each element per
146	volume, the total number of electrons per volume, and will store "this"
147	material in the materials table. In the same way, a material can be
148	constructed as a mixture of other materials and elements.
149	</p>
150	<p>
151	It should be noted that if the user provides the number of atoms (or
152	molecules) for each element comprising the chemical compound, the system
153	automatically computes the mass fraction. A few quantities, with physical
154	meaning or not, which are constant in a given material, are computed and
155	stored here as "derived data members".
156	</p>
157	<p>
158	Some materials are included in the internal Geant4 database, which
159	were derived from the NIST database of material properties
160	(http://physics.nist.gov/PhysRefData/Star/Text/method.html).
161	Additionally a number of materials frequently used in HEP is included
162	in the database.
163	Materials are interrogated or constructed by their <a href="materialNames.html">
164	<i>names</a></i>. There are UI
165	commands for the material category, which provide an interactive
166	access to the database. If material is created using the NIST database it will
167	consist of elements with natural composition of isotopes.
168	</p>
169	<br>
170
171	<b>Final Considerations</b>
172
173	The classes will automatically decide if the total of the mass fractions
174	is correct, and perform the necessary checks. The main reason why a fixed
175	index is kept as a data member is that many cross section and energy tables
176	will be built in the physics processes "by rows of materials (or elements,
177	or even isotopes)". The tracking gives the physics process the address of
178	a material object (the material of the current volume).
179	If the material has an index according to which the cross section table
180	has been built, then direct access is available when a number in such a
181	table must be accessed. We get directly to the correct row, and the energy
182	of the particle will tell us the column. Without such an index, every access
183	to the cross section or energy tables would imply a search to get to the
184	correct material's row. More details will be given in the section on
185	processes.
186	</p>
187	<br>
188
189	<hr>
190	<a name="4.2.3">
191	<h2>4.2.3 Recipes for Building Elements and Materials</h2></a>
192
193	Source listing 4.2.1 illustrates the different ways to define materials.
194	<p>
195	<center>
196	<table border=2 cellpadding=10>
197	<tr>
198	<td>
199	<PRE>
200	#include "G4Isotope.hh"
201	#include "G4Element.hh"
202	#include "G4Material.hh"
203	#include "G4UnitsTable.hh"
204
205	int main() {
206
207	G4String name, symbol; // a=mass of a mole;
208	G4double a, z, density; // z=mean number of protons;
209	G4int iz, n; //iz=nb of protons in an isotope;
210	// n=nb of nucleons in an isotope;
211
212	G4int ncomponents, natoms;
213	G4double abundance, fractionmass;
214	G4double temperature, pressure;
215
216	G4UnitDefinition::BuildUnitsTable();
217
218	//
219	// define Elements
220	//
221
222	a = 1.01*g/mole;
223	G4Element* elH = new G4Element(name="Hydrogen",symbol="H" , z= 1., a);
224
225	a = 12.01*g/mole;
226	G4Element* elC = new G4Element(name="Carbon" ,symbol="C" , z= 6., a);
227
228	a = 14.01*g/mole;
229	G4Element* elN = new G4Element(name="Nitrogen",symbol="N" , z= 7., a);
230
231	a = 16.00*g/mole;
232	G4Element* elO = new G4Element(name="Oxygen" ,symbol="O" , z= 8., a);
233
234	a = 28.09*g/mole;
235	G4Element* elSi = new G4Element(name="Silicon", symbol="Si", z=14., a);
236
237	a = 55.85*g/mole;
238	G4Element* elFe = new G4Element(name="Iron" ,symbol="Fe", z=26., a);
239
240	a = 183.84*g/mole;
241	G4Element* elW = new G4Element(name="Tungsten" ,symbol="W", z=74., a);
242
243	a = 207.20*g/mole;
244	G4Element* elPb = new G4Element(name="Lead" ,symbol="Pb", z=82., a);
245
246	//
247	// define an Element from isotopes, by relative abundance
248	//
249
250	G4Isotope* U5 = new G4Isotope(name="U235", iz=92, n=235, a=235.01*g/mole);
251	G4Isotope* U8 = new G4Isotope(name="U238", iz=92, n=238, a=238.03*g/mole);
252
253	G4Element* elU = new G4Element(name="enriched Uranium", symbol="U", ncomponents=2);
254	elU->AddIsotope(U5, abundance= 90.*perCent);
255	elU->AddIsotope(U8, abundance= 10.*perCent);
256
257
258	cout << *(G4Isotope::GetIsotopeTable()) << endl;
259
260	cout << *(G4Element::GetElementTable()) << endl;
261
262	//
263	// define simple materials
264	//
265
266	density = 2.700*g/cm3;
267	a = 26.98*g/mole;
268	G4Material* Al = new G4Material(name="Aluminum", z=13., a, density);
269
270	density = 1.390*g/cm3;
271	a = 39.95*g/mole;
272	G4Material* lAr = new G4Material(name="liquidArgon", z=18., a, density);
273
274	density = 8.960*g/cm3;
275	a = 63.55*g/mole;
276	G4Material* Cu = new G4Material(name="Copper" , z=29., a, density);
277
278	//
279	// define a material from elements. case 1: chemical molecule
280	//
281
282	density = 1.000*g/cm3;
283	G4Material* H2O = new G4Material(name="Water", density, ncomponents=2);
284	H2O->AddElement(elH, natoms=2);
285	H2O->AddElement(elO, natoms=1);
286
287	density = 1.032*g/cm3;
288	G4Material* Sci = new G4Material(name="Scintillator", density, ncomponents=2);
289	Sci->AddElement(elC, natoms=9);
290	Sci->AddElement(elH, natoms=10);
291
292	density = 2.200*g/cm3;
293	G4Material* SiO2 = new G4Material(name="quartz", density, ncomponents=2);
294	SiO2->AddElement(elSi, natoms=1);
295	SiO2->AddElement(elO , natoms=2);
296
297	density = 8.280*g/cm3;
298	G4Material* PbWO4= new G4Material(name="PbWO4", density, ncomponents=3);
299	PbWO4->AddElement(elO , natoms=4);
300	PbWO4->AddElement(elW , natoms=1);
301	PbWO4->AddElement(elPb, natoms=1);
302
303	//
304	// define a material from elements. case 2: mixture by fractional mass
305	//
306
307	density = 1.290*mg/cm3;
308	G4Material* Air = new G4Material(name="Air " , density, ncomponents=2);
309	Air->AddElement(elN, fractionmass=0.7);
310	Air->AddElement(elO, fractionmass=0.3);
311
312	//
313	// define a material from elements and/or others materials (mixture of mixtures)
314	//
315
316	density = 0.200*g/cm3;
317	G4Material* Aerog = new G4Material(name="Aerogel", density, ncomponents=3);
318	Aerog->AddMaterial(SiO2, fractionmass=62.5*perCent);
319	Aerog->AddMaterial(H2O , fractionmass=37.4*perCent);
320	Aerog->AddElement (elC , fractionmass= 0.1*perCent);
321
322	//
323	// examples of gas in non STP conditions
324	//
325
326	density = 27.*mg/cm3;
327	pressure = 50.*atmosphere;
328	temperature = 325.*kelvin;
329	G4Material* CO2 = new G4Material(name="Carbonic gas", density, ncomponents=2,
330	kStateGas,temperature,pressure);
331	CO2->AddElement(elC, natoms=1);
332	CO2->AddElement(elO, natoms=2);
333
334	density = 0.3*mg/cm3;
335	pressure = 2.*atmosphere;
336	temperature = 500.*kelvin;
337	G4Material* steam = new G4Material(name="Water steam ", density, ncomponents=1,
338	kStateGas,temperature,pressure);
339	steam->AddMaterial(H2O, fractionmass=1.);
340
341	//
342	// What about vacuum ? Vacuum is an ordinary gas with very low density
343	//
344
345	density = universe_mean_density; //from PhysicalConstants.h
346	pressure = 1.e-19*pascal;
347	temperature = 0.1*kelvin;
348	new G4Material(name="Galactic", z=1., a=1.01*g/mole, density,
349	kStateGas,temperature,pressure);
350
351	density = 1.e-5*g/cm3;
352	pressure = 2.e-2*bar;
353	temperature = STP_Temperature; //from PhysicalConstants.h
354	G4Material* beam = new G4Material(name="Beam ", density, ncomponents=1,
355	kStateGas,temperature,pressure);
356	beam->AddMaterial(Air, fractionmass=1.);
357
358	//
359	// print the table of materials
360	//
361
362	G4cout << *(G4Material::GetMaterialTable()) << endl;
363
364	return EXIT_SUCCESS;
365	}
366	</PRE>
367	</td>
368	</tr>
369	<tr>
370	<td align=center>
371	Source listing 4.2.1<BR>
372	A program which illustrates the different ways to define materials.
373	</td>
374	</tr>
375	</table></center>
376	<p>
377	As can be seen in the later examples, a material has a state: solid (the
378	default), liquid, or gas. The constructor checks the density and
379	automatically sets the state to gas below a given threshold (10 mg/cm3).
380	</p>
381	<p>
382	In the case of a gas, one may specify the temperature and pressure. The
383	defaults are STP conditions defined in <tt>PhysicalConstants.hh</tt>.
384	</p>
385	<p>
386	An element must have the number of nucleons >= number of protons >= 1.
387	</p>
388	<p>
389	A material must have non-zero values of density, temperature and pressure.
390	</p>
391	<p>
392	Materials can also be defined using the internal Geant4 database.
393	Source listing 4.2.2 illustrates how to do this for the same materials
394	used in 4.2.1. There are also UI commands which allow the database to
395	be accessed. <a href="materialNames.html">
396	<i>The list of currently available material names</a></i> is extended permanently.
397	</p>
398	<p>
399	<center>
400	<table border=2 cellpadding=10>
401	<tr>
402	<td>
403	<PRE>
404	#include "globals.hh"
405	#include "G4Material.hh"
406	#include "G4NistManager.hh"
407
408	int main() {
409
410	G4NistManager* man = G4NistManager::Instance();
411	man->SetVerbose(1);
412
413	//
414	// define elements
415	//
416
417	G4Element* C = man->FindOrBuildElement("C");
418	G4Element* Pb = man->FindOrBuildMaterial("Pb");
419
420	//
421	// define pure NIST materials
422	//
423
424	G4Material* Al = man->FindOrBuildMaterial("G4_Al");
425	G4Material* Cu = man->FindOrBuildMaterial("G4_Cu");
426
427	//
428	// define NIST materials
429	//
430
431	G4Material* H2O = man->FindOrBuildMaterial("G4_WATER");
432	G4Material* Sci = man->FindOrBuildMaterial("G4_PLASTIC_SC_VINYLTOLUENE");
433	G4Material* SiO2 = man->FindOrBuildMaterial("G4_SILICON_DIOXIDE");
434	G4Material* Air = man->FindOrBuildMaterial("G4_AIR");
435
436	//
437	// HEP materials
438	//
439
440	G4Material* PbWO4 = man->FindOrBuildMaterial("G4_PbWO4");
441	G4Material* lAr = man->FindOrBuildMaterial("G4_lAr");
442	G4Material* vac = man->FindOrBuildMaterial("G4_Galactic");
443
444	//
445	// define gas material at non STP conditions (T = 120K, P=0.5atm)
446	//
447
448	G4Material* coldAr = man->ConstructNewGasdMaterial("ColdAr","G4_Ar",120.kelvin,0.5atmosphere);
449
450	//
451	// print the table of materials
452	//
453
454	G4cout << *(G4Material::GetMaterialTable()) << endl;
455
456	return EXIT_SUCCESS;
457	}
458	</PRE>
459	</td>
460	</tr>
461	<tr>
462	<td align=center>
463	Source listing 4.2.2<BR>
464	A program which shows how to define materials from the internal database.
465	</td>
466	</tr>
467	</table></center>
468
469	<hr>
470	<a name="4.2.4">
471	<h2>4.2.4 The Tables</h2></a>
472
473	<b>Print a constituent</b>
474	<p>
475	The following shows how to print a constituent:
476
477	<PRE>
478	G4cout << elU << endl;
479	G4cout << Air << endl;
480	</PRE>
481	<p>
482	<b>Print the table of materials</b>
483	<p>
484	The following shows how to print the table of materials:
485
486	<PRE>
487	G4cout << *(G4Material::GetMaterialTable()) << endl;
488	</PRE>
489	<br>
490	<br>
491
492	<hr><a href="../../../../Authors/html/subjectsToAuthors.html">
493	<i>About the authors</a></i>
494	</p>
495
496	</BODY>
497	</HTML>

Note: See TracBrowser for help on using the repository browser.

Context Navigation

source: trunk/documents/UserDoc/UsersGuides/ForApplicationDeveloper/html/Detector/material.html @ 1287

Download in other formats: