Question

Explain how (a) alpha and beta radiation are separated by an electric field. (b) radioactive C-11 can be used as a tracer to study brain disorders. (c) a self-sustaining chain reaction occurs in nuclear fission.

Short answer

Answer: Carbon-11 (C-11), a radioactive isotope of carbon, can be used as a tracer to study brain disorders. It is produced in a cyclotron and tagged to specific molecules that interact with certain brain structures or processes. The C-11 tracer is introduced into the patient's body, and its distribution in the brain is monitored using a positron emission tomography (PET) scanner. By analyzing the accumulation of the tracer in brain regions associated with various disorders, researchers can gain insight into the pathology of the disorder and potentially develop targeted treatments.

Step-by-step solution

Part (a): Separation of Alpha and Beta Radiation by an Electric Field

To separate alpha and beta radiation using an electric field, follow the steps below: Step 1: Understand the types of radiation Alpha radiation consists of helium nuclei (two protons and two neutrons) and has a positive charge. Beta radiation consists of electrons or positrons and has a negative or positive charge, respectively). Step 2: Set up an electric field Alpha and beta particles can be separated by placing a sample of radioactive material between two charged plates (one positive and one negative) to create an electric field. Step 3: Observe the path of the particles in the electric field When the charged particles from the radioactive material enter the electric field, they will experience a force due to the presence of electric field. This force will be in the direction of the electric field for negatively charged particles (like beta) and opposite to the electric field for positively charged particles (like alpha). Step 4: Analyze the force acting on the particles For alpha particles (positively charged), the force due to the electric field will deflect them towards the negative plate. For negatively charged beta particles, the force will cause them to move towards the positive plate. Thus, they will be separated in the electric field.

Part (b): Using Radioactive C-11 to Study Brain Disorders

To understand how the radioactive isotope carbon-11 (C-11) can be used as a tracer to study brain disorders, follow the steps: Step 1: Preparation of C-11 tracer C-11 is a radioactive isotope of carbon with a half-life of about 20 minutes. It can be produced in a cyclotron and used to tag specific molecules that are known to interact with certain brain structures or processes. Step 2: Administer the C-11 tracer to the patient The radioactive C-11 tracer is introduced into the patient's body, either orally or intravenously. Since it behaves similarly to non-radioactive carbon, the tracer will form various compounds and participate in biochemical processes within the body. Step 3: Monitor the distribution of the tracer Using a positron emission tomography (PET) scanner, the distribution of the C-11 tracer in the patient's brain can be monitored. PET detects gamma rays that are emitted when the positrons emitted by the tracer annihilate with electrons in the body's tissue. Step 4: Analyze the PET scan results The PET scan will reveal the distribution of the C-11 tracer, and hence the specific molecules it marks, in the brain. By analyzing the accumulation of these molecules in brain regions associated with various disorders, researchers can gain insight into the pathology of the disorder and potentially develop targeted treatments.

Part (c): Self-sustaining Chain Reaction in Nuclear Fission

To explain how a self-sustaining chain reaction occurs in nuclear fission, follow the steps below: Step 1: Understand nuclear fission Nuclear fission is the process in which a heavy nucleus, like uranium-235, splits into two lighter nuclei by absorbing a slow-moving neutron. This process generates a large amount of energy and releases new neutrons. Step 2: Neutron moderation and absorption To sustain a nuclear fission chain reaction, the neutrons released in each fission event must be slowed down (moderated) and then absorbed by another fissile nucleus to initiate further fission events. This is achieved using substances called moderators (like water or graphite) that slow down the neutrons, and control rods (containing neutron-absorbing materials like boron or cadmium) that regulate the number of neutrons available for further fission. Step 3: Self-sustaining chain reaction When the number of neutrons produced by each fission event is greater than or equal to the number absorbed by fissile nuclei, the chain reaction becomes self-sustaining. As more and more fissile nuclei undergo fission, the energy released increases exponentially, leading to a continuous release of energy. Step 4: Control the reaction In nuclear reactors, the rate of fission is controlled by adjusting control rods, ensuring that the chain reaction remains stable and does not reach a critical state, which could lead to a nuclear explosion. By understanding and controlling these processes, a self-sustaining chain reaction can be maintained safely in nuclear reactors to produce energy.