Calculate the initial mass of the isotope. 10. a) Name the radioactive process displayed above. Give a reason for your answer. b) Suggest one application of t

The total time is 1000 days, and the half-life is 25 days.

The substance undergoes 40 half-lives.

The formula is $N_t = N_0 \left(\frac{1}{2}\right)^n$, where $N_t$ is the final mass, $N_0$ is the initial mass, and $n$ is the number of half-lives.
We are given $N_t = 50 \text{ g}$ and $n = 40$.

The initial mass of the isotope was approximately $5.50 \times 10^{13}$ grams.

The initial mass of the isotope is $\boxed{\text{5.50} \times 10^{13} \text{ g}}$.

10.

a) Name the radioactive process displayed above. Give a reason for your answer.

The process is Nuclear Fission.
Reason: A heavy nucleus ($\frac{235}{92}U$) absorbs a neutron and splits into two lighter nuclei ($\frac{142}{56}Ba$ and $\frac{91}{36}Kr$), releasing energy and additional neutrons.

b) Suggest one application of this process.

One application is electricity generation in nuclear power plants.

11.

a) Complete the nuclear equation below.

This is a beta decay, where a neutron in the nucleus converts into a proton, emitting an electron (beta particle).

b) The half-life of $\frac{131}{53}I$ is 8 days. Determine the mass of $\frac{131}{53}I$ remaining if 50g decayed for 40 days.

The total time is 40 days, and the half-life is 8 days.

The substance undergoes 5 half-lives.

The question states "if 50g decayed for 40 days", implying the initial mass was 50g.
Initial mass ($N_0$) = 50 g.

The mass of $\frac{131}{53}I$ remaining is $\boxed{\text{1.5625 g}}$.

c) Give one harmful effect of radioisotopes.

One harmful effect is causing cancer (e.g., leukemia, thyroid cancer) due to damage to DNA and cells.

12.

a) Identify radiation W.

Radiation W passes through paper and aluminium foil but is stopped by a lead block, and it is undeflected by the electric field. This indicates it is Gamma radiation ($\gamma$).

b) Which of the radiations would cause most danger to human tissues? Explain your answer.

Gamma radiation (W) would cause the most danger.
Explanation: Gamma radiation has very high penetrating power, meaning it can pass through the body and damage internal organs and tissues, leading to widespread cellular damage and increased risk of cancer.

c) Explain why it is not safe to store radioactive substances in containers made of iron sheets.

It is not safe because iron sheets are not dense or thick enough to effectively block all types of radiation, especially gamma rays. Gamma radiation can easily penetrate iron sheets, allowing harmful radiation to escape and pose a health hazard to people nearby.