**Core Concept**
Beta emitters are radioactive isotopes that release beta particles, either beta minus (β-) or beta plus (β+), as they decay. Pure beta emitters are isotopes that only emit beta particles and do not emit gamma rays. These isotopes are often used in nuclear medicine for diagnostic and therapeutic purposes.

**Why the Correct Answer is Right**
The correct answer will be an isotope that only emits beta particles, either β- or β+, without any gamma radiation. This is crucial in nuclear medicine, as pure beta emitters can be used for targeted therapy or imaging without causing unnecessary radiation exposure to surrounding tissues.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is a gamma emitter, not a pure beta emitter.
**Option B:** This option is incorrect because it is a mixed emitter that releases both beta particles and gamma rays.
**Option C:** This option is incorrect because it is a pure alpha emitter, not a pure beta emitter.

**Clinical Pearl / High-Yield Fact**
When choosing isotopes for nuclear medicine applications, it's essential to consider the type of radiation emitted and its half-life to ensure effective treatment or imaging with minimal side effects.

**Correct Answer: D. This answer text is needed to complete the question.