Question:
In neutron method used to measure soil moisture, the source of fast neutrons is a mixture
In neutron method used to measure soil moisture, the source of fast neutrons is a mixture
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In any neutron moisture meter, Beryllium is always the target element used to release neutrons when bombarded by alpha particles from a heavy emitter (like Radium or Americium).
This makes the presence of Beryllium key to identifying the correct answer.
This makes the presence of Beryllium key to identifying the correct answer.
Updated On: Jul 6, 2026
- Radium -- beryllium
- Silicon-beryllium
- Silicon-sodium
- Sodium and americium
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Verified By Collegedunia
The Correct Option is A
Solution and Explanation
Step 1: Understanding the Concept:
The neutron probe method is a rapid, non-destructive technique used to measure soil volumetric water content in the field.
It relies on the physical principle that fast neutrons are slowed down (thermalized) primarily when they collide with hydrogen atoms, which are found almost exclusively in soil water.
Step 3: Detailed Explanation:
The instrument consists of a probe containing a source of fast (high-energy) neutrons and a detector for slow (thermalized) neutrons.
The fast-neutron source is a radioactive mixture.
Historically, a mixture of Radium-226 and Beryllium (Ra-Be) was the standard source.
In modern equipment, a mixture of Americium-241 and Beryllium (Am-Be) is also used.
In both cases, alpha particles emitted by the radioactive element (Radium or Americium) collide with Beryllium nuclei, releasing fast neutrons.
Silicon-based and sodium-based mixtures do not function as fast neutron sources.
Step 4: Final Answer:
The radioactive source mixture is Radium-beryllium, which corresponds to option (A).
The neutron probe method is a rapid, non-destructive technique used to measure soil volumetric water content in the field.
It relies on the physical principle that fast neutrons are slowed down (thermalized) primarily when they collide with hydrogen atoms, which are found almost exclusively in soil water.
Step 3: Detailed Explanation:
The instrument consists of a probe containing a source of fast (high-energy) neutrons and a detector for slow (thermalized) neutrons.
The fast-neutron source is a radioactive mixture.
Historically, a mixture of Radium-226 and Beryllium (Ra-Be) was the standard source.
In modern equipment, a mixture of Americium-241 and Beryllium (Am-Be) is also used.
In both cases, alpha particles emitted by the radioactive element (Radium or Americium) collide with Beryllium nuclei, releasing fast neutrons.
Silicon-based and sodium-based mixtures do not function as fast neutron sources.
Step 4: Final Answer:
The radioactive source mixture is Radium-beryllium, which corresponds to option (A).
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