Alpha-Particle Scattering Experiment

Introduction 

A British scientist named Ernest Rutherford conducted several experiments and based on the observations made, the atomic structure of elements was introduced along with the Rutherford Atomic Model. If you’re someone who loves experimenting or reading about it, here’s an interesting article for you. 

Today, in this article on the understanding of the Alpha-particle scattering experiment, you will get detailed information on Rutherford’s alpha scattering experiment, his observations, and other related topics such as the atomic model and more. So, without further ado, let us get started with the Introduction to alpha-particle scattering experiment in the physics study material.

Rutherford’s Alpha Scattering Experiment

Ernest Rutherford experimented with bombarding a thin gold sheet of 100 nm thickness with the alpha particle denoted as α. Later, he conducted a thorough study on the trajectory of these particles once they had interacted with the gold sheet. He passed high energy streams of alpha particles at the gold sheet from a radioactive source during the experiment. 

For studying the deflection faced by the α-particles, a fluorescent zinc sulphide screen was safely placed all around the gold sheet. His observations contradicted Thomson’s atomic model.

A Brief Introduction to Alpha Rays 

The alpha rays are the first to be positively charged particles in the list. The alpha rays are denoted by α. Its particles are also known as helium atoms. These particles are highly energetic and active helium atoms that comprise mainly two protons and neutrons. The alpha particle has the maximum ionisation power, whereas the minimum penetration power. 

If they enter your body due to extremely high ionisation power, they can cause heavy damage to the internal organs. They can ionise several atoms even by a short distance. This happens because radioactive substances, such as alpha, need to be handled only after wearing gloves.

Properties of Alpha Rays

Here is the list of properties of alpha rays –

• Particle’s nature – The alpha rays are positively charged particles that consist of 4He2 nuclei. 
• Charge on the particles – The alpha rays have two positive (+) charge units. This means it is +2e. 
• Mass of the particles – The mass of the alpha particles is 6.6466 × 10–27 kg. 
• Range of the particles – Alpha rays are ~10 cm in air. It can be stopped by 1 mm of aluminium metal sheet. 
• Natural sources of the particles – The alpha rays are naturally radiated through the natural radioisotopes, e.g. 236U92. 

Rutherford’s Alpha Scattering Experiment Observations

According to the Rutherford’s alpha scattering experiment’s observations, he concluded that following points – 

• He recorded that most alpha particles drove towards the thin gold sheet without breakage or deflection. It means that there is no space in an atom. 
• It was recorded that a small number of alpha particles get deflected that too at a very small angle. Therefore, it can be concluded that the positive charge in the atom is not distributed uniformly. 
• The last observation was that a very less number of alpha particles were deflected. It can be concluded that the volume in the atom’s positively charged particles is extremely small compared to the atom’s total volume. 

Rutherford Atomic Model

Depending on the above conclusions and observations, the atomic structure of elements was proposed by Rutherford, which states – 

• Most of the atom’s mass and positively charged particles were present in exceptionally small volumes, referred to as the nucleus. 
• According to the Rutherford atomic model, the negatively charged electrons surround the nucleus. He also believed that electrons surrounding the nucleus were revolving around it at an extremely high speed in a circular motion, called orbits. 
• Nucleus being positively charged; however, electrons being charged positively, both were held together tightly by an electrostatic force of attraction.

Limitations of Rutherford Atomic Model

However, the Rutherford atomic model was a great success; however, there were certain areas that this model failed to explain. Here are the limitations of the Rutherford Atomic Model:

• As mentioned earlier, the electrons surrounding the nucleus revolving around it at an extremely high speed in circular motion were known as orbits. As per Maxwell, the charged particles give rise to electromagnetic radiation; as a result, the electron which is revolving around the nucleus needs to emit electromagnetic radiation. Hence, the Rutherford theory and Maxwell’s theory contradict each other in some significant areas.
• Another major limitation of the Rutherford atomic model was that he did not mention electron’s arrangement in an atom in his entire theory, due to which many believed his theory was not completed.
• Although several atomic models did not meet the expectations when explaining specific experimental results, they were regarded as the base to conduct future research. 

Conclusion 

We studied the alpha-particle scattering experiment in detail. Ernest Rutherford conducted several experiments, and based on the observations made, the atomic structure of elements was introduced along with the Rutherford Atomic Model that we studied in this study material. 

We covered the introduction to Rutherford’s alpha-scattering experiment, where we explored how he decided to bombard a thin gold sheet of 100 nm thickness with the alpha particle denoted as α. We also briefly discussed the alpha rays, along with the observations limitations of the Rutherford atomic model.