Difference between revisions of "LSC Principles"
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| − | {| cellspacing="1" cellpadding="1" border="1" style=" | + | {| width="490" cellspacing="1" cellpadding="1" border="1" style="" |
| + | |+ Tsble 1: Typical radionuclodes for LSC counting | ||
|- | |- | ||
| + | | <br> | ||
| + | | <br> | ||
| + | | <br> | ||
| + | | colspan="2" | β energy<br> | ||
| + | | <br> | ||
| <br> | | <br> | ||
| + | |- | ||
| + | | <br> | ||
| Half-Life | | Half-Life | ||
| Decay | | Decay | ||
| Line 12: | Line 20: | ||
| 60 days | | 60 days | ||
| <span class="texhtml">γ</span> | | <span class="texhtml">γ</span> | ||
| − | | Auger electrons<br> | + | | Auger electrons<br> |
| − | | 0.035 MeV<br> | + | | 0.035 MeV<br> |
| − | | < | + | | <span class="texhtml">γ</span>-probe<br> |
| 2167 Ci/mA<br> | | 2167 Ci/mA<br> | ||
|- | |- | ||
| Line 20: | Line 28: | ||
| 12.3 years | | 12.3 years | ||
| β | | β | ||
| − | | 0.019 MeV<br> | + | | 0.019 MeV<br> |
| − | | 0.035 MeV<br> | + | | 0.035 MeV<br> |
| − | | Swabs<br> | + | | Swabs<br> |
| 28.8 Ci/mA<br> | | 28.8 Ci/mA<br> | ||
|- | |- | ||
| Line 29: | Line 37: | ||
| β | | β | ||
| 0.156 MeV | | 0.156 MeV | ||
| − | | 0.006 MeV<br> | + | | 0.006 MeV<br> |
| − | | < | + | | <span class="texhtml">β</span> Counter<br> |
| 62.4 Ci/mA<br> | | 62.4 Ci/mA<br> | ||
|- | |- | ||
| Line 36: | Line 44: | ||
| 87.4 days | | 87.4 days | ||
| β | | β | ||
| − | | 0.167 MeV <br> | + | | 0.167 MeV <br> |
| − | | 0.049<br> | + | | 0.049 MeV<br> |
| − | | < | + | | <span class="texhtml">β</span> Counter<br> |
| 1494 Ci/mA<br> | | 1494 Ci/mA<br> | ||
|- | |- | ||
| Line 44: | Line 52: | ||
| 14.3 days | | 14.3 days | ||
| β | | β | ||
| − | | 1.709<br> | + | | 1.709 MeV<br> |
| − | | 0 | + | | 0.69 MeV<br> |
| − | | < | + | | <span class="texhtml">β</span> Counter<br> |
| 9311 Ci/mA<br> | | 9311 Ci/mA<br> | ||
|} | |} | ||
| + | <br> | ||
| + | uantitative measurements of beta-radiation, alpha-radiation and low-energy gamma-radiation with traditional gas or solid state detectors may be difficult due to the self-absorption of the radiation in the sample itself and further absorption in the counter window. Therefore, low-energy radiation is, in many cases, best detected and measured with liquid scintillation counting where absorption loss is absent. Here, the sample and the detector (the liquid scintillator) is intimately mixed in a homogeneous solution. In addition, this leads to nearly 100% counting geometry (only the liquid surfaces against the container wall and the air above the liquid account for a small loss in counting geometry). | ||
| + | <br> | ||
| + | A liquid scintillator consists of a solvent and a primary scintillant. In some cases a secondary scintillant is also added. The function of these substances is described below. | ||
| + | The solvent: The primary function of the solvent is to solubilize the radioactive sample, preferentially into a homogeneous solution. An equally important function is to absorb and transfer the energy deposited by the radioactive decay event to the primary scintillant. The process is as follows: | ||
| + | <br> | ||
| + | The -particles from the radioactive substance ionize and excite molecules in the solution, - first and foremost the solvent molecules because of its high concentration. The excitation energy is transferred from one solvent molecule X to another. Some of these excitation transfer chain reactions result in the encounter with a molecule of the primary scintillant Y. The excitation is transferred to this molecule: | ||
| + | <br> | ||
| + | <br> | ||
| + | <math>\beta+X_{1}\rightarrow X_{1}*+X_{2}\rightarrow X_{2}*+X_{3}\rightarrow X_{3}*...\rightarrow X_{n}* + Y \rightarrow Y*</math> | ||
Revision as of 14:17, 19 June 2012
| |
|
|
β energy |
|
| |
| |
Half-Life | Decay | Emax | Emin | Monitor | Specific Activity |
| 125I | 60 days | γ | Auger electrons |
0.035 MeV |
γ-probe |
2167 Ci/mA |
| 3H | 12.3 years | β | 0.019 MeV |
0.035 MeV |
Swabs |
28.8 Ci/mA |
| 14C | 5730 years | β | 0.156 MeV | 0.006 MeV |
β Counter |
62.4 Ci/mA |
| 25S | 87.4 days | β | 0.167 MeV |
0.049 MeV |
β Counter |
1494 Ci/mA |
| 32P | 14.3 days | β | 1.709 MeV |
0.69 MeV |
β Counter |
9311 Ci/mA |
uantitative measurements of beta-radiation, alpha-radiation and low-energy gamma-radiation with traditional gas or solid state detectors may be difficult due to the self-absorption of the radiation in the sample itself and further absorption in the counter window. Therefore, low-energy radiation is, in many cases, best detected and measured with liquid scintillation counting where absorption loss is absent. Here, the sample and the detector (the liquid scintillator) is intimately mixed in a homogeneous solution. In addition, this leads to nearly 100% counting geometry (only the liquid surfaces against the container wall and the air above the liquid account for a small loss in counting geometry).
A liquid scintillator consists of a solvent and a primary scintillant. In some cases a secondary scintillant is also added. The function of these substances is described below.
The solvent: The primary function of the solvent is to solubilize the radioactive sample, preferentially into a homogeneous solution. An equally important function is to absorb and transfer the energy deposited by the radioactive decay event to the primary scintillant. The process is as follows:
The -particles from the radioactive substance ionize and excite molecules in the solution, - first and foremost the solvent molecules because of its high concentration. The excitation energy is transferred from one solvent molecule X to another. Some of these excitation transfer chain reactions result in the encounter with a molecule of the primary scintillant Y. The excitation is transferred to this molecule:
