33:
273:
In the case of sound waves, HVL is the distance that it takes for the intensity of a sound wave to be reduced to one-half of its original value. The HVL of sound waves is determined by both the medium through which it travels, and the frequency of the beam. A "thin" half-value layer (or a quick drop
168:
Half-value layer refers to the first half-value layer, where subsequent (i.e. second) half-value layers refer to the amount of specified material that will reduce the air kerma rate by one-half after material has been inserted into the beam that is equal to the sum of all previous half-value layers.
152:
rate (AKR), rather than intensity: the half-value layer is the thickness of specified material that, "attenuates the beam of radiation to an extent such that the AKR is reduced to one-half of its original value. In this definition the contribution of all scattered radiation, other than any present
172:
Quarter-value layer is the amount of specified material that reduces the air kerma rate (or exposure rate, exposure, air kerma, etc...) to one fourth of the value obtained without any test filters. The quarter-value layer is equal to the sum of the first and second half-value layers.
266:, however the mean free path is the average distance a unit of radiation can travel in the material before being absorbed, whereas HVL is the average amount of material needed to absorb 50% of all radiation (i.e., to reduce the
281:
A similar concept is the tenth-value layer or TVL. The TVL is the average amount of material needed to absorb 90% of all radiation, i.e., to reduce it to a tenth of the original intensity. 1 TVL is greater than or equal to
258:
The HF for a narrow beam will always be less than or equal to one (it is only equal to one in the case of a monoenergetic beam). In case of a narrow polychromatic beam, the HF is less than one because of beam hardening.
254:
339:
409:
382:
116:
50:
97:
69:
54:
289:
Here are example approximate half-value layers for a variety of materials against a source of gamma rays (Iridium-192):
76:
181:
353:
83:
43:
65:
315:
320:
162:
158:
414:
267:
141:
90:
153:
initially in the beam concerned, is deemed to be excluded." Rather than AKR, measurements of
176:
The homogeneity factor (HF) describes the polychromatic nature of the beam and is given by:
154:
149:
274:
of -3 dB) results from a high frequency sound wave and a medium with a high rate of
263:
165:
can be used to determine half value layer, as long as it is given in the description.
403:
286:(10) or approximately 3.32 HVLs, with equality achieved for a monoenergetic beam.
275:
32:
372:
Edelman, Sidney Ph.D. Understanding
Ultrasound Physics. 3rd ed. Copyright 2007.
17:
145:
148:
entering it is reduced by one half. HVL can also be expressed in terms of
354:"Sec. 1020.30 Diagnostic x-ray systems and their major components"
26:
184:
278:, such as bone. HVL is measured in units of length.
57:. Unsourced material may be challenged and removed.
248:
249:{\displaystyle HF={\frac {1^{st}HVL}{2^{nd}HVL}}}
140:, is the thickness of the material at which the
8:
225:
201:
194:
183:
117:Learn how and when to remove this message
332:
7:
270:of the incident radiation by half).
55:adding citations to reliable sources
129:
25:
31:
42:needs additional citations for
1:
431:
410:Radiation health effects
316:Attenuation coefficient
293:Concrete: 44.5 mm
250:
134:half-value layer (HVL)
385:. NDT Resource Center
302:Tungsten: 3.3 mm
251:
340:Half value thickness
321:Radiation protection
305:Uranium: 2.8 mm
182:
138:half-value thickness
51:improve this article
296:Steel: 12.7 mm
383:"Half-Value Layer"
262:HVL is related to
246:
66:"Half-value layer"
299:Lead: 4.8 mm
244:
127:
126:
119:
101:
16:(Redirected from
422:
394:
393:
391:
390:
379:
373:
370:
364:
363:
361:
360:
349:
343:
337:
255:
253:
252:
247:
245:
243:
233:
232:
219:
209:
208:
195:
131:
122:
115:
111:
108:
102:
100:
59:
35:
27:
21:
430:
429:
425:
424:
423:
421:
420:
419:
400:
399:
398:
397:
388:
386:
381:
380:
376:
371:
367:
358:
356:
351:
350:
346:
342:euronuclear.org
338:
334:
329:
312:
285:
221:
220:
197:
196:
180:
179:
123:
112:
106:
103:
60:
58:
48:
36:
23:
22:
15:
12:
11:
5:
428:
426:
418:
417:
412:
402:
401:
396:
395:
374:
365:
344:
331:
330:
328:
325:
324:
323:
318:
311:
308:
307:
306:
303:
300:
297:
294:
283:
264:Mean free path
242:
239:
236:
231:
228:
224:
218:
215:
212:
207:
204:
200:
193:
190:
187:
125:
124:
39:
37:
30:
24:
18:Half thickness
14:
13:
10:
9:
6:
4:
3:
2:
427:
416:
413:
411:
408:
407:
405:
384:
378:
375:
369:
366:
355:
348:
345:
341:
336:
333:
326:
322:
319:
317:
314:
313:
309:
304:
301:
298:
295:
292:
291:
290:
287:
279:
277:
271:
269:
265:
260:
256:
240:
237:
234:
229:
226:
222:
216:
213:
210:
205:
202:
198:
191:
188:
185:
177:
174:
170:
166:
164:
163:exposure rate
160:
156:
151:
147:
143:
139:
135:
121:
118:
110:
107:November 2023
99:
96:
92:
89:
85:
82:
78:
75:
71:
68: –
67:
63:
62:Find sources:
56:
52:
46:
45:
40:This article
38:
34:
29:
28:
19:
387:. Retrieved
377:
368:
357:. Retrieved
347:
335:
288:
280:
272:
261:
257:
178:
175:
171:
167:
137:
133:
128:
113:
104:
94:
87:
80:
73:
61:
49:Please help
44:verification
41:
276:attenuation
132:material's
415:Radiometry
404:Categories
389:2016-12-29
359:2007-12-05
327:References
77:newspapers
268:intensity
155:air kerma
150:air kerma
146:radiation
142:intensity
310:See also
159:exposure
91:scholar
93:
86:
79:
72:
64:
352:FDA.
161:, or
136:, or
98:JSTOR
84:books
70:news
282:log
144:of
53:by
406::
157:,
392:.
362:.
284:2
241:L
238:V
235:H
230:d
227:n
223:2
217:L
214:V
211:H
206:t
203:s
199:1
192:=
189:F
186:H
130:A
120:)
114:(
109:)
105:(
95:·
88:·
81:·
74:·
47:.
20:)
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
