It takes 4 h 39 min for a 2.00 - mg sample of radium - 230 to decay to 0.25 mg.

Question

It takes 4 h 39 min for a 2.00 - mg sample of radium - 230 to decay to 0.25 mg. What is the half-life of radium-230? Cobalt-60 is a strong gamma emitter that has a half-life of 5.26 yr. The cobalt-60 in a radiotherapy unit must be replaced when its radioactivity falls to 75% of the original sample. If an original sample was purchased in June 2013, when will it be necessary to replace the cobalt-60? How much time is required for a 6.25-mg sample of^51 Cr to decay to 0.75 mg if it has a half-life of 27.8 days? Radium-226, which 1600 yr. (a) How many alpha particles are emitted in 5.0 min by a 10.0 - mg sample of^226 Ra? (b) What is the activity of the

Explanation / Answer

Q21.36

t = 4 h 39 min

m = 20 mg

mf = 0.25 mg

find HL

so..

apply

Mf = M0*(1/2)^(t/HL)

substitute data

t in minutes = 4h + 39 min = 4*60+39 = 279 min

so

0.25 = 2*(1/2)^(279/HL)

solve for HL

0.25/2 = (1/2)^(279/HL)

ln(0.125) / ln(0.5) = 279/HL

HL = 279 /3 = 93 min

so each 93 min a half life will happen:

93 min = 2 mg to 1 mg

93+93 min = 1 mg to 0.5 mg

3(93) min = 0.5 to 0.25 mg

Consider posting multiple questions in multiple set of Q&A. We are not allowed to answer to multiple questions in a single set of Q&A

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.