Radiation occurs in nature…the earth is ‘bathed’ in radiation from a variety of sources. Humans have evolved with these levels of radiation in the environment. Naturally Occurring Radioactive Materials These include Uranium-238, which has radioactive half-life of 4.47 billion years. 238 U decays via a series of alpha and beta decays (some of which also emit gamma rays). These create radionuclides including: Radium-226 Radon-222 Polonium-210 (all of which are  emitters). Other NORM includes 40 K (in bones!)

Q   210 Po) = 5.41 MeV E  = 5.30 MeV E( 206 Pb) = 0.11 MeV T 1/2 = 138 days. ‘ 218 Po =Radium A’ ‘ 218 At =Radium B’ C D E 210 Po =Radium ‘F’ Radon =‘Emanation’ ‘Radium’ C’ C’’ The Natural Decay Chain for 238 U

Alpha decay can also leave daughter in excited states which can then decay by (characteristic) gamma emission.

Other nuclides in the ‘background’ Man-made radionuclides in the environment. – Nuclear weapons tests / Chernobyl / Fukushima Fission fragment daughters such as 137 Cs, 90 Sr, 131 I, & 111 Ag (recent NPL work) 236 Np, 237 Np, 239 Pu, 240 Pu, 241 Am, 242 Am etc. (from neutron capture reactions and decay on 235,8 U in fuel) or residues from weapons tests.

Fukushima…

UK press response….

neutron Uranium-235 nucleus Uranium-235 nucleus plus a neutron = Uranium-236 splits, releasing energy. 2 primary, fission fragment nuclei. A~135 and A~90 plus fast neutrons. Neutron-induced Nuclear fission. e.g., 235 U + n → 236 U* → 137 Xe + 97 Sr + 2 neutrons + approx 200 MeV of energy. 137 Xe and 97 Sr are both radioactive…subsequently also decay, e.g., 137 Xe, T 1/2 = 4 mins → 137 Cs, T 1/2 =30 years → 137 Ba (stable)

~ 200 MeV of energy released per fission event in a reactor. ~ MeV of energy in the form of ‘decay heat’. Reactor fuel still generates some heat after the fission stops….

Beta (  - ) decay changes a neutron into a proton This keeps A constant but increases Z by 1 ( Z → Z+1 ). For each A value, there is a preferred, most stable (N,Z) combination. – 131 Xe (Z=54, N=77, A=131) stable. – 131 I (Z=53, N=78, A=131) unstable and  - decays 131 Xe. Radioactive nuclei can emit characteristic gamma rays which can be used to identify each nuclear species. The number of radioactive nuclei decreases over time. The time for radioactivity to reduce by x2 = the half-life (T 1/2 ). Half-lives are radionuclide specific, range from fractions of seconds to millions of years (‘physics’ dependent). Number of radioactive nuclei present / decaying decreases with time. For a single radionuclide this is given by the law of radioactive decay. N(t) = N 0 exp ( * time / T 1/2 ) Nuclear Physics 101 (lecture 2)

See Line of ‘constant A = N+Z Isobars, e.g., 131 Te, 131 I, 131 Xe NEUTRON NUMBER, N → PROTON NUMBER, Z →

Nucleus T 1/2 (    Daughter E  (keV) 131 I8 days 131 Xe I2 hours 132 Xe668, I21 hours 133 Xe I53 mins 134 Xe847, I7 hours 135 Xe1260, I83 seconds 136 Xe1313, I25 seconds 137 Xe1218, 601

Nucleus T 1/2 (    Daughter E  (keV) 133 CsSTABLE 134 Cs2 years 134 Ba605, Cs2 Myears 135 Ba- 136 Cs13 days 136 Ba819, Cs30 years 137 Ba Cs33 minutes 138 Ba1436, Cs1.4 hours 139 Ba1283, Cs1 minute 140 Ba Cs25 seconds 141 Ba190, Cs2 seconds 142 Ba360, Cs2 seconds 143 Ba195, 233

Nucleus T 1/2 (    Daughter E  (keV) 137 Ba STABLE 137 Cs30 years 137 Ba Xe4 minutes 137 Cs456 13I XeSTABLE 131 I8 days 131 Xe Te25 seconds 131 I190, 304

Look for signature gamma ray of 131 I decay (365 keV) in various samples.... such as Vancouver rainwater. Obvious effect of 8 day half-life of this particular activity as the 131 I decays to form the (stable) 131 Xe.

134 Cs…a smoking gun of a reactor fuel leak…

X 134 Cs (T 1/2 ~2 years) can not be created by  - decay of heavier A=134 fission fragments since 134 Xe is stable. Presence of 134 Cs is evidence for nuclear reactor waste. 134 Cs is made in reactors via (n,  ) capture on stable 133 Cs. 134 Cs is not present in nuclear weapons fallout.

(courtesy, Dr.Pieter Doornenbal, RIKEN, Japan)

131 I (t 1/2 = 8 days) 95 Nb (t 1/2 = 64 days) 134 Cs (t 1/2 = 2 years) 137 Cs (t 1/2 = 30 years)

100 mL samples in U8 container, net weight 81 gram/sample Brown rice grown in Fukushima after the nuclear accident; measured in radioactivity department at NPL using low-background HPGe dets Jun Saegusa, Fukushima Environmental Safety Center, Japan Atomic Energy Agency & Visiting Scientist at NPL

Radioactivity in Fukushima Rice? Japanese AEA inspected 10 million bags of rice at 160 Inspection centres last year. 71 bags showed radiocesium values which exceeded the reference level. (i.e % were below this). Rice above reference level not shipped out. Source: Jun Saegusa, Fukushima Environmental Safety Center, Japan Atomic Energy Agency & Visiting Scientist at NPL

604 keV: 5702 counts, 661 keV ( 137 Cs): counts, 795 keV: 3987 counts, 1461 keV (from 40K): 602 counts. 80,000 sec measurements on 05 Sep Evaluations underway From Jun Saegusa, Fukushima Environmental Safety Center, Japan Atomic Energy Agency & Visiting Scientist at NPL, Teddington.

Summary Radioactive material surrounds us from NORMS (U, Th decay series; 40 K) and nuclear weapons fallout ( 137 Cs, 90 Sr). It’s part of our daily lives. By measuring characteristic energy  and  decays we can identify what and how much radioactive materials is present. Understanding the quantum nature of the nucleus allows us to interpret these decays via nuclear energy level schemes. We can utilize novel detection technologies developed for fundamental nuclear structure physics research and apply them to ‘routine’ industrial metrological / medical measurements of radioactivity.